{"id":39025,"date":"2015-07-01T12:25:06","date_gmt":"2015-07-01T16:25:06","guid":{"rendered":"http:\/\/www.gunsamerica.com\/blog\/?p=39025"},"modified":"2015-07-01T12:25:06","modified_gmt":"2023-08-18T20:12:50","slug":"build-an-ar-15-ar-calibers","status":"publish","type":"post","link":"https:\/\/gunsamerica.com\/digest\/build-an-ar-15-ar-calibers\/","title":{"rendered":"Build an AR-15: AR Calibers"},"content":{"rendered":"<div id=\"attachment_39035\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/Rock-River-Arms-LAR-68-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39035\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39035\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/Rock-River-Arms-LAR-68-1-1024x683.jpg\" alt=\"The AR platform can be adapted to dozens of different calibers, like this Rock River Arms LAR-6.8 chambered in 6.8 Remington SPC.\" width=\"1024\" height=\"683\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Rock-River-Arms-LAR-68-1-1024x683.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Rock-River-Arms-LAR-68-1-150x100.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Rock-River-Arms-LAR-68-1-400x267.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Rock-River-Arms-LAR-68-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39035\" class=\"wp-caption-text\">The AR platform can be adapted to dozens of different calibers, like this Rock River Arms LAR-6.8 chambered in 6.8 Remington SPC.<\/p><\/div>\n<h2>THE SERIES<\/h2>\n<ul>\n<li><strong>Part 1:<\/strong> <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-15-step-by-step-series-introduction\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: The Series Introduction<\/a><\/li>\n<li><strong>Part 2:<\/strong> <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-15-ar-calibers\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: AR Calibers<\/a><\/li>\n<li><strong>Part 3:<\/strong> <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-direct-impingement-or-piston-operation\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: Direct Impingement or Piston Operation<\/a><\/li>\n<li><strong>Part 4:<\/strong> <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-15-tools-and-materials\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: Tools and Materials<\/a><\/li>\n<li><strong>Part 5<\/strong>: <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-15-the-lowdown-on-lowers\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: The Lowdown on Lowers<\/a><\/li>\n<li><strong>Part 6<\/strong>: <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar15-intro-to-uppers\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: Intro to Uppers<\/a><\/li>\n<li><strong>Part 7<\/strong>: <a class=\"clickTracking\" href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-choosing-and-installing-the-barrel\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Build an AR-15: Barrels<\/a><\/li>\n<li><strong>Part 8: <\/strong><a href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-15-choosing-the-right-butt-stock\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\">Build an AR-15: Choose The Right Buttstock\u00a0<\/a><\/li>\n<li><strong>Part 9: <\/strong><a href=\"https:\/\/www.gunsamerica.com\/blog\/build-an-ar-15-choosing-the-right-optic\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\">Build an AR-15: Choosing the Right Optic<\/a><\/li>\n<\/ul>\n<p>In these troubled times where everyone wants to stir up trouble and hate over our differences in appearance, I want it to go on record that I don\u2019t just tolerate diversity, I embrace it.<\/p>\n<p>In my safe right this moment, I have AR-type rifles chambered in .223\/5.56mm, 6.8 SPC, 300 Blackout, and .308 Winchester. Of course, .308 is admittedly related to the Armalite AR-10, not AR-15 family. When it comes to diversity, I put my money where my mouth is. As we speak, I\u2019m Jonesing for something in 6.5mm. Not only that, I\u2019ve been begging the folks at Smith &amp; Wesson to come out with an M&amp;P 338, chambered in, you guessed it, .338 Lapua. Why? Because diversity is fun.<\/p>\n<div id=\"attachment_39032\" style=\"width: 410px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/ar-magazine-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39032\" title=\"Build an AR-15: AR Calibers\" class=\"size-medium wp-image-39032\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/ar-magazine-1-400x267.jpg\" alt=\"One of the limitations for caliber swaps is the length of the standard magazine and magazine well. \" width=\"400\" height=\"267\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/ar-magazine-1-400x267.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/ar-magazine-1-150x100.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/ar-magazine-1-1024x683.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/ar-magazine-1.jpg 1200w\" sizes=\"(max-width: 400px) 100vw, 400px\" \/><\/a><p id=\"caption-attachment-39032\" class=\"wp-caption-text\">One of the limitations for caliber swaps is the length of the standard magazine and magazine well.<\/p><\/div>\n<p>The neatest and spiffiest thing about AR-type rifles is that they\u2019re not really\u00a0just a single rifle type. They\u2019re a platform, or set of common design specifications on which you can build a whole lot of differrent, but related, guns.<\/p>\n<p>The split receiver design of AR-type rifles lends itself to using a standard lower receiver with stock, grip, magazine well, and fire control system containing trigger, hammer, sear and safety mechanisms. Then, in theory, and for the most part practicality, you can mount different upper receivers that house the chamber, barrel, bolt carrier, bolt and hand guard. Of course, you can\u2019t just put any caliber upper on a standard lower. The primary reason for this is that the magazine well is part of the lower receiver, and that creates some limitations on cartridge size. For example, one of the big differences between AR-15 and AR-10 type rifles is the larger magazine well on the AR-10 to accommodate .308 Winchester. Everything is bit larger owing to the need to handle bigger cartridges.<\/p>\n<h2>.223 Remington \/ 5.56x45mm<\/h2>\n<p>What\u2019s not to love about the \u201coriginal?\u201d Well, more or less the original. Back in the <a href=\"https:\/\/armalite.com\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">ArmaLite<\/a> days when the AR direct impingement rifle was being developed, the original plan was to make it a .308 \/ 7.62mm rifle, but the military folks liked the smaller caliber option. The thinking was that the average soldier could hump a lot more cartridges if they were smaller and lighter.<\/p>\n<p>The debate over terminal effectiveness will outlast all of us, so I\u2019ll stick to the theoretical performance idea. A very small and very light bullet, moving insanely fast, should fragment, tumble, and wreak all sorts of havoc on organic targets. There\u2019s plenty of evidence that it does. There\u2019s also plenty of evidence that it\u2019s not a magic one-shot stopper like the old 7.62 and .30-06 ammo fired from M-14s and M1 Garands. More suppressive firepower weighed against better terminal effectiveness per hit? You make your call as to your personal preference.<\/p>\n<p>One thing that has become interesting is the standard caliber AR platform\u2019s suitability for home defense. That same theory that says a light and fast bullet will fragment and tumble also helps with potential over-penetration in the home. If you want to perform a fun science experiment, take a bunch of wallboard to the range, separate it to create artificial walls, and shoot it with 55 grain .223 ammo and some normal handgun hollow-points. You might be surprised at which one penetrates the most interior walls.<\/p>\n<h2>.300 AAC Blackout \/ .300 Whisper<\/h2>\n<p>I love this caliber in an AR platform. Before the hate mail starts, I\u2019m not claiming it\u2019s \u201cbetter\u201d than any other AR cartridge, I just really enjoy it, mainly because I love to reload ammunition. The 300 AAC Blackout allows for a near-infinite variety of bullet weight and velocity combinations.<\/p>\n<div id=\"attachment_39034\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/300-Blackout-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39034\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39034\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/300-Blackout-1-1024x768.jpg\" alt=\"The huge 300 AAC Blackout subsonic projectiles are stuffed into cut down .5.56mm cartridge cases.\" width=\"1024\" height=\"768\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/300-Blackout-1-1024x768.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/300-Blackout-1-150x113.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/300-Blackout-1-400x300.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/300-Blackout-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39034\" class=\"wp-caption-text\">The huge 300 AAC Blackout subsonic projectiles are stuffed into cut down .5.56mm cartridge cases.<\/p><\/div>\n<p>You can launch a 245-grain hunk of pure lead downrange at 1,000 feet per second. This flying brick approach yields 544 foot-pounds of energy. Using a suppressor, this is a freakishly quiet combination sure to elicit very un-macho giggles from anyone present at the range.<\/p>\n<p>You can also go supersonic and zing an 110-grain bullet at 2,500 feet per second. This .30 caliber projectile cranks out 1,527 foot-pounds of energy. That\u2019s about 50% more kinetic energy than a standard .223\/5.56mm 55-grain bullet moving at 3,000 feet per second. It\u2019ll stay supersonic out past 600 yards or so depending on local conditions.<\/p>\n<p>As an AR-type rifle cartridge, I love that it fits in standard .223 \/ 5.56mm magazines. That\u2019s because it uses cut down cartridge cases from .223 \/ 5.56mm. I don\u2019t mean vaguely similar, I mean it\u2019s literally the exact same case, trimmed down and reshaped with a lower and less aggressive shoulder to accommodate a .30 caliber bullet. There are some 300 Blackout specific magazines that do a better job of handling odd-shaped bullets, but, for the most part, compatibility is excellent. It even uses the same bolt carrier and bolt as the 5.56mm.<\/p>\n<div id=\"attachment_39028\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/CMMG-pistol-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39028\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39028\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/CMMG-pistol-1-1024x643.jpg\" alt=\"Use of shorter barrel ARs prompted development of alternate calibers like this 300 Blackout to gain improved terminal performance.\" width=\"1024\" height=\"643\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/CMMG-pistol-1-1024x643.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/CMMG-pistol-1-150x94.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/CMMG-pistol-1-400x251.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/CMMG-pistol-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39028\" class=\"wp-caption-text\">Use of shorter barrel ARs prompted development of alternate calibers like this 300 Blackout to gain improved terminal performance.<\/p><\/div>\n<h2>6.5 Grendel<\/h2>\n<p>While the AR-type rifle in traditional calibers is assumed to be a 400 yards or less cartridge, some enterprising folks have turned a variant into a pretty nifty longer range performer. Bill Alexander and Janne Pohjoisp\u00e4\u00e4 developed this round as a way to make a standard AR rifle reach out to 800 (and more) yards. It\u2019s designed to fit in a standard AR magazine size, so it gains its extra oomph by using a larger diameter case to launch a long and thin bullet.<\/p>\n<p>Most 6.5 Grendel bullets weigh between 90 and 140 grains, with a common one landing at 123 grains and moving at over 2,500 feet per second. The low-drag projectiles maintain supersonic velocity past 1,000 yards. It also carries over 1,000 foot-pounds of kinetic energy to nearly 450 yards.<\/p>\n<p>Bolt action 6.5 calibers can outperform it, but only because they\u2019re not limited by the same overall length restriction due to the magazine well. You\u2019ll want a longer barrel to take full advantage of this one, and, due to the larger case diameter, you\u2019ll need a new bolt. Even though the cartridges are larger, you can still stuff about 26 of them into a standard size magazine.<\/p>\n<h2>6.8 Remington SPC<\/h2>\n<p>Here\u2019s another one I really like, although I can\u2019t exactly say why. If \u201cjust because\u201d is a good enough reason to like an AR variant, then I\u2019m sticking with that reason.<\/p>\n<p>The 6.8 Remington SPC was developed by some special forces guys, some other folks from the Army Marksmanship Unit, along with some engineers from Remington. The idea was to provide better terminal performance than the 55 and 62 grain 5.56mm NATO ammo being used overseas, especially from short-barreled rifles. Tired of evil d00dz not falling down when shot; they wanted a heavier and larger diameter projectile that could still work in the AR platform and maintain reasonably high-capacity magazines.<\/p>\n<div id=\"attachment_39037\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/68-SPC-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39037\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39037\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/68-SPC-1-1024x683.jpg\" alt=\"The 6.8 Remington SPC cartridge is based off the .30 Remington.\" width=\"1024\" height=\"683\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/68-SPC-1-1024x683.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/68-SPC-1-150x100.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/68-SPC-1-400x267.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/68-SPC-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39037\" class=\"wp-caption-text\">The 6.8 Remington SPC cartridge is based off the .30 Remington.<\/p><\/div>\n<p>While the overall length is the same as 5.56mm, so it fits in existing magazine wells, you\u2019ll probably need 6.8 SPC specific magazines for best reliability. That\u2019s what I&#8217;ve found anyway. The cartridge case is not based on the 5.56mm, but rather a .30 Remington, so to convert a standard AR, we\u2019re talking about replacing bolt, barrel and, magazine.<\/p>\n<p>While 6.8mm sounds cool and metric, it\u2019s really just a .270 caliber bullet, which actually measures .277 inches in diameter. Because we gun people like to make things confusing, I guess. If you&#8217;re a hand loader, .270 bullets are plentiful, even in these times of limited reloading supplies availability.<\/p>\n<p>The \u201caverage\u201d 6.8 SPC load contains a 115-grain projectile moving at 2,640 feet per second. Of course, you can load lighter or heaver bullets too. The average load translates to 1,785 foot-pounds of kinetic energy. Our average bullet will stay supersonic out past 850 yards, and bullet drop is still manageable at that distance by many magnified optics, so it has more \u201creach out and touch\u201d capability than the lighter weight 5.56mm rounds.<\/p>\n<h2>5.7x28mm<\/h2>\n<div id=\"attachment_39038\" style=\"width: 211px\" class=\"wp-caption alignright\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/SWAT-SHOT-w-copyright.jpg800x2000.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39038\" title=\"Build an AR-15: AR Calibers\" class=\"size-medium wp-image-39038\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/SWAT-SHOT-w-copyright.jpg800x2000-201x300.jpg\" alt=\"The AR57 upper receiver actually uses the top-mounted FN PS90 magazine and ejects through the lower receiver magazine well.\" width=\"201\" height=\"300\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/SWAT-SHOT-w-copyright.jpg800x2000-201x300.jpg 201w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/SWAT-SHOT-w-copyright.jpg800x2000-100x150.jpg 100w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/SWAT-SHOT-w-copyright.jpg800x2000-686x1024.jpg 686w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/SWAT-SHOT-w-copyright.jpg800x2000.jpg 800w\" sizes=\"(max-width: 201px) 100vw, 201px\" \/><\/a><p id=\"caption-attachment-39038\" class=\"wp-caption-text\">The <a href=\"https:\/\/www.57center.com\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">AR57 <\/a>upper receiver actually uses the top-mounted FN PS90 magazine and ejects through the lower receiver magazine well.<\/p><\/div>\n<p>There\u2019s only a little bit of cheating happening with inclusion of this one on the AR variants list. Yes, you can use a standard AR-type lower receiver with the AR57 upper to fire the tiny little FN 5.7x28mm cartridges.<\/p>\n<p>However, it\u2019ll look somewhat non-traditional. The FN magazines for this cartridge, used by the PS90 carbine, store cartridges sideways and rest on top of the upper receiver. The magazine well on the AR lower is actually the ejection port. By the way, this unusual magazine holds 50 rounds.<\/p>\n<p>Ou example cartridge is the <a href=\"https:\/\/www.fnhusa.com\/l\/products\/ammunition\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">SS195LF<\/a>. This little 28 grain bullet hums along at 2,350 feet per second and delivers 344 foot-pounds of energy.<\/p>\n<h2>7.62x39mm<\/h2>\n<p>If you\u2019re looking for the ultimate in AR diversity, how about one that accepts it\u2019s traditional \u201cenemy\u2019s\u201d ammo? The 7.62x39mm cartridge has been used in at least 319 trillion AK-47 type rifles worldwide for over 2,000 years. Ammo and magazines are plentiful to say the least. Besides, the 7.62x39mm offers a heavier bullet and more kinetic energy than the 5.56mm.<\/p>\n<p>You can get an upper receiver to handle the comm-block ammo, just be aware that you may have to resort to some tinkering and Dremel tool use to get it humming. The usual reliability problems center around three areas. The AR-type rifle magazine well is straight, which doesn\u2019t always sit well with the tapered cartridge and associated banana clip design of AK magazines. Others have reported problems with feeding related to low gas pressure and have resorted to drilling out the barrel&#8217;s gas port. As for the Dremel? The standard AR design uses a split feed ramp which tends to hang up the larger 7.62x39mm cartridges. Industrious shooters have put Dremel to metal to smooth out the feed ramp area into a single ramp.<\/p>\n<p>Or, you can cheat a little bit and pick up a rifle \u201clike\u201d an AR that\u2019s optimized for the cartridge. <a href=\"https:\/\/www.cmmginc.com\/product-category\/rifles\/7-62x39\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">CMMG\u2019s Mutant<\/a> and the <a href=\"\/blog\/rock-rivers-new-lar-47-line-ar-ak-new-gun-review\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Rock River Arms LAR-47<\/a> both offer lower receivers built specifically for the AK cartridge fan club.<\/p>\n<h2>.458 SOCOM<\/h2>\n<p>If you favor lobbing cinder blocks down range, you might consider one of the standard AR rifle big boy caliber options, .458 SOCOM.<\/p>\n<p>Like other non-traditional AR calibers, this one was developed after complaints of 5.56mm stopping power. This cartridge swings to the polar opposite end of the slow and heavy versus light and fast scale by using a lengthened .50 AE cartridge case and 300 grain bullet moving at 1,900 feet per second. That generates 2,405 foot-pounds of kinetic energy.<\/p>\n<p>The beauty of this one is near complete compatibility with the standard AR, excepting of course the barrel. You don\u2019t want to try and stuff a .458-inch bullet into a .224 inch hole. Everything else, magazines, bolt, buffer and springs, is the same. [Correction: The bolt is not compatible, that&#8217;s a typo!] The big fat cartridges stack singly into a standard AR magazine, so a 30-round 5.56mm magazine ends up holding 10 rounds of .458 SOCOM.<\/p>\n<p>Can you say &#8220;infinite bacon?&#8221;<\/p>\n<div id=\"attachment_39033\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/cartridges-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39033\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39033\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/cartridges-1-1024x873.jpg\" alt=\".308, 300 AAC Blackout and 5.56mm cartridges.\" width=\"1024\" height=\"873\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/cartridges-1-1024x873.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/cartridges-1-150x128.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/cartridges-1-352x300.jpg 352w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/cartridges-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39033\" class=\"wp-caption-text\">.308, 300 AAC Blackout and 5.56mm cartridges.<\/p><\/div>\n<h2>.50 Beowulf<\/h2>\n<p>Not to be outdone by tiny little 300-grain, .458-inch bullets, <a href=\"https:\/\/www.alexanderarms.com\/products\/50-beowulf\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Alexander Arms<\/a> offers complete rifles and uppers in .50 Beowulf. This one is intended to replicate the famous .45-70 Government round.<\/p>\n<p>If you go with the 400 grain bullet option, that\u2019ll lob down range at 1,800 feet per second and deliver 2,878 foot pounds of energy.<\/p>\n<h2>Pistol Cartridges: 9mm, .40 S&amp;W, .45 ACP<\/h2>\n<p>Too many to list here, numerous makers offer upper receivers for standard pistol calibers like 9mm, .40 S&amp;W and .45 ACP. If you want the handling and easy sight picture of a carbine, maybe one that matches your handgun caliber is in order? The longer barrel length will give your pistol rounds a little more velocity, and therefore longer effective range.<\/p>\n<h2>.22LR<\/h2>\n<p>Coincidentally, .22LR has a number of ways to fit into the AR-rifle family. The bore size is pretty darn close to the standard .22LR version anyway. Regardless of the .223 Remington name, the standard AR rifle uses bullets that are .224 inches in diameter. Regular .22LR ammo varies a bit, from .223 to .224 inches in diameter, so you can shoot it through a standard AR barrel with reasonable success. As a result, a bolt and magazine change, combined with a chamber insert, can turn your existing rifle into a .22LR plinker. Of course, dedicated .22LR upper receivers and complete rifles are plentiful too.<\/p>\n<div id=\"attachment_39030\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/22-conversion-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39030\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39030\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/22-conversion-1-1024x768.jpg\" alt=\"The standard AR barrel is close enough in diameter to shoot .22LR ammo through it with a conversion bolt.\" width=\"1024\" height=\"768\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/22-conversion-1-1024x768.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/22-conversion-1-150x113.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/22-conversion-1-400x300.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/22-conversion-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39030\" class=\"wp-caption-text\">The standard AR barrel is close enough in diameter to shoot .22LR ammo through it with a conversion bolt.<\/p><\/div>\n<h2>.410 Shotgun<\/h2>\n<p>In the &#8220;why the hell not?&#8221; category is the <a href=\"https:\/\/www.safirarms.com\/en\/kurumsal-safirsilah\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">.410 shotshell upper from Safir Arms<\/a>. The upper connects to standard AR-type lower receiver and lets you whale away with .410 shot shells or slugs. The magazine is proprietary as you might imagine. You can get magazines in 5, 10 and 13 round versions. Why 13? Maybe the better question is, why not?<\/p>\n<h2>.50 BMG<\/h2>\n<p>In the \u201cBecause \u2018Murica!\u201d category is the <a href=\"https:\/\/www.tactilite.com\/\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">Zel Custom<\/a> &#8211; AR-15\/M16 Tactilite upper receiver. This, like most of the others mentioned here, mounts to a standard AR-type lower receiver.<\/p>\n<p>Th .50 BMG cartridge is just a hair longer than the 5.56mm, so there\u2019s not a snowballs chance in hell that one will go through a standard magazine well without melting it first. As a result, this upper receiver is a single shot only, and you load the .50 BMG cartridge through a bolt action in the upper.<\/p>\n<div id=\"attachment_39036\" style=\"width: 1034px\" class=\"wp-caption aligncenter\"><a href=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/Colt-and-Smith-Wesson-1.jpg\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\"><img loading=\"lazy\" decoding=\"async\" aria-describedby=\"caption-attachment-39036\" title=\"Build an AR-15: AR Calibers\" class=\"size-large wp-image-39036\" src=\"https:\/\/www.gunsamerica.com\/blog\/wp-content\/uploads\/2015\/06\/Colt-and-Smith-Wesson-1-1024x765.jpg\" alt=\"A Smith &amp; Wesson M&amp;P 15 VTAC (top) and Colt M4 chambered in .22LR (below)\" width=\"1024\" height=\"765\" srcset=\"https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Colt-and-Smith-Wesson-1-1024x765.jpg 1024w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Colt-and-Smith-Wesson-1-150x112.jpg 150w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Colt-and-Smith-Wesson-1-400x300.jpg 400w, https:\/\/gunsamerica.com\/digest\/wp-content\/uploads\/2015\/06\/Colt-and-Smith-Wesson-1.jpg 1200w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/a><p id=\"caption-attachment-39036\" class=\"wp-caption-text\">A Smith &amp; Wesson M&amp;P 15 VTAC (top) and Colt M4 chambered in .22LR (below)<\/p><\/div>\n<h2>And many, many more\u2026<\/h2>\n<p>In a quick and very informal count, I found at least 53 other chamberings for the AR-type rifle, ranging from 5.45x39mm to .30 Carbine. Oh, that M&amp;P 338 I mentioned earlier? ArmaLite makes an AR-10 variant called the AR-30A1, chambered in, you guessed it, .338 Lapua Magnum.<\/p>\n<p>Celebrate diversity? Heck yeah! But ask yourself this question: What do you want this rifle to do? If you&#8217;re an experienced shooter, and this won&#8217;t be your first AR, then the sky is the limit. If you&#8217;re just getting into the black rifle game, consider the benefits of sticking with the tried and true. Nothing wrong with the old 5.56.<\/p>\n<h3>More from this Series: <a href=\"https:\/\/www.gunsamerica.com\/blog\/?s=build+an+ar\" target=\"_blank\" class=\"clickTracking\" campaign=\"build-an-ar-15-ar-calibers\" title=\"Build an AR-15: AR Calibers\" target=\"_blank\" rel=\"noopener\">https:\/\/www.gunsamerica.com\/blog\/?s=build+an+ar<\/a><\/h3>\n","protected":false},"excerpt":{"rendered":"<p>Looking to build an AR-15? What caliber will you choose? .223 is just the start. Before you get into the build, you need to know exactly what you want your rifle to do. You can always stick with the traditional 5.56, but is that the right choice? Here&#8217;s a list of the most popular calibers and what they deliver.<\/p>\n","protected":false},"author":25,"featured_media":39119,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_specdata_upc":"","_specdata_placement":"","footnotes":""},"categories":[282,7,891,334,888,72,209],"tags":[724,132,102,108,620],"featured":[],"hunt365":[],"class_list":{"0":"post-39025","1":"post","2":"type-post","3":"status-publish","4":"format-standard","5":"has-post-thumbnail","7":"category-columns-ammo-tests","8":"category-gunsamerica-authors","9":"category-ga-guides-build-ar","10":"category-building-an-ar-15","11":"category-columns-ga-guides","12":"category-columns-gunsmithing","13":"category-tom-mchale","14":"tag-build-an-ar","15":"tag-buzz","16":"tag-feature-articles","17":"tag-guns","18":"tag-tactical"},"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v27.1 (Yoast SEO v27.2) - https:\/\/yoast.com\/product\/yoast-seo-premium-wordpress\/ -->\n<title>Build an AR-15: AR Calibers<\/title>\n<meta name=\"description\" content=\"Looking to build an AR-15? 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