The most simple method of performing this "conversion" is to purchase an entire new complete upper assembly (and magazines if needed), and put this new upper assembly on to your AR-15 lower. I may suggest that this is the safest way as well...but more on that later. There are a variety of conversion calibers from which to select, but the most popular have been the 7.62X39, 6.8 SPC, 6.5 Grendel, and the .300 Blackout. For training and shooting fun, rimfire caliber conversions are popular, but less so now that rimfire ammunition is more costly and difficult to acquire. Much larger calibers like the .450 Bushmaster, .458 SOCOM, and .50 Beowulf are also options, but they have a very specific application and the same issues with ammunition cost and availability can affect the success or popularity of those calibers.
|5.56x45, 6.5 Grendel, 6.8 SPC, 450 Bushmaster|
If purchasing a new complete upper assembly is not a cost effective option, one can disassemble their AR-15 upper and use many of the parts to build an upper in this new caliber. For the 7.62X39, 6.8 SPC, 6.5 Grendel calibers mentioned, a new BARREL (including muzzle device), BOLT, and MAGAZINE are required. The .450/.458/.50 offerings require a new barrel/muzzle device and bolt, but use the same magazine, albeit at a 60%+ drop in capacity. In reality, the upper receiver, bolt carrier, gas tube, firing pin, etc...are the few parts that you can use for the new caliber. If a new barrel/muzzle device, bolt, magazine (s), and possibly other parts (buffer) are required, I stand by the premise that losing a 5.56X45 complete upper assembly is not worth any cost savings that such a modification would provide.
We didn't skip the .300 Blackout, we saved it for last. This relatively new caliber uses the same (though modified) case as the 5.56X45 cartridge and offers a promising .30 caliber bullet option in an AR-15 size package without using a different magazine. It uses the standard AR-15 bolt and magazine, but a new barrel and muzzle device IS required. Herein lies some risk for this particular caliber. Because it uses the same magazine and bolt and only requires a new barrel and muzzle device, BAD mistakes can happen. The .300 Blackout cartridge can be loaded into and fired in a 5.56X45 weapon, but SHOULD NOT BE. It will cause dangerous and potentially fatal results. Below is an image from such an event. Fortunately, the weapon was the only thing damaged. Almost all other conversion calibers require a new bolt and barrel, and maybe a new magazine. This particular one only requires a new barrel and muzzle device. There have been a number of negative experiences resulting from an individual with misinformation attempting to use this caliber in a standard 5.56X45 chambered AR-15 or having weapons chambered in both calibers and a dangerous mix of ammunition and magazines. A magazine that you mark or specifically designated for ONLY one caliber is one way of helping to prevent a catastrophic failure of this nature, but an intent focus on safety is the only sure way to prevent dangerous situations when using firearms.
|.300 Blackout Bullet Lodged in 5.56X45 Chamber-cross section|
Conversion calibers offer a definite benefit to many applications, but if not installed as a complete upper assembly or built on your current AR-15 platform and used with a focus on firearms safety, they do present a possible risk. My wife bought a new hair dryer a while back. It had an adhesive warning tag on the cord that stated in large font red lettering, "Not to be used in the shower" and "Not to be used while sleeping"...why were those warnings there? Because someone had used them in such a manner.
This blog post was not designed to be a definitive guide on AR-15 conversion calibers. The idea for and general purpose of it is to provide an online "adhesive warning tag" regarding conversion calibers and what you need for parts (at a minimum) to safely use them with your AR-15 rifle. The internet can be an incredible source of free and valuable knowledge. It can also contain information that lacks truth and is dangerous. This is what led to the negative, conversion caliber related event described and displayed above. The sheer volume of information online can be confusing, so when it comes to firearms safety, make sure the information is from a reliable source. Research. A lot.
Thanks for reading our blog. DTI carries some parts for conversion calibers with more being added soon. Many of our current products exist because we listened to suggestions from our customers, so let us hear from you regarding what calibers in an AR platform you would like to see. If you have any questions about the AR-15 rifles we manufacture or the parts we offer at www.del-ton.com, please feel free to contact us.