IMR 4227 is suitable for supersonic and subsonic loads. The relatively fast burn rate makes it suitable for loading various varmint and intermediate rifle cartridges with limited case capacity, such as. It is a classic reloading powder that should be on the shelves of any handloading enthusiast. IMR 4227 is a pistol powder with a medium burn rate, primarily intended for use in Magnum pistol and revolver cartridges. Today, IMR is a trademark of the IMR Powder Company, a Hodgdon brand. IMR propellants have long been used to manufacture US military service ammunition, such as. As always if you have any questions please feel free to reach out to us anytime.DuPont initially developed the first Improved Military Rifle (IMR) powders between World War I and World War II as miniaturized versions of US artillery extruded propellants. It is no means a comprehensive guide to every little quirk you could possibly encounter. This article is meant to be a quick overview of the main points to look at when building/buying a 300BLK gun. Just understand the limitations of that barrel and gas system as described above. We would still recommend a shorter barrel in this setup no longer than 11”, however that is not to say you could not run a 16” barrel. The tradeoff being made is the gun will be a bit overgassed and run a bit harsh. As long as you ensure your gun functions with the weakest ammo you will be shooting, you can then just load a magazine of the supersonic rounds and the gun will cycle. You will need to set your gun up the same way as if you were only going to shoot subsonic loads. If you are looking to be flexible between super and subsonic loads please understand there are tradeoffs to be made. In return the gun will be very smooth shooting. That will allow you to keep the gas tuned relatively low because there is less mass to move. You’ll only need to run a standard carbine buffer and buffer spring with this setup. We recommend fine tuning this setup with just an adjustable gas block. Make sure your barrel is Pistol Gas length because subsonic ammo does not have the pressure to cycle properly with any other gas length. We would not recommend going over an 11” barrel for this application and please use a 1:7” or faster Twist if you are going to shoot 220gr as that is required to properly stabilize the projectile. You can SBR the gun if you want to, however with the invention of really great pistol braces there is no need to. This allows room to put a suppressor on it so that you have the full benefits of that specific load. If you are only shooting suppressed with subsonic loads, we highly recommend keeping your gun as short as possible. You can fine tune that setup with either an adjustable gas block, adjustable bolt carrier group, or your buffer weight. If you wish to suppress that setup, it will work fine the way it is. You can run a standard carbine buffer and spring with that setup no problem. However if you are adamant about your gun being chambered in 300BLK and you are only going to shoot supersonic loads, get a gun with a 16” barrel, 1:8” Twist, and carbine length gas system. This keeps you from having to buy proprietary AR mags for 7.62x39 that can cause numerous headaches. There are plenty of great builds on the market that feed from AK magazines. If you are only going to shoot supersonic only, my suggestion is just save yourself the money and buy a 7.62x39 AR. Going on to mirror that depending on whether your intended use is supersonic, subsonic, or flexibility between the two your gun should be built a specific way. To quickly recap from last week, 300BLK is a specialized cartridge with loads built for specific reasons. This week we are going to expand on that point and talk about how your gun should be built to shoot your chosen load. Last week on Ballistic Theory we talked about choosing the correct 300BLK load for your intended use.
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