I need some help guys! I know ammo very well, but I don't know the inner workings of an AR as well, like some of you do. I began working on my 223 subs that will cycle an AR. I am working with some custom 87 grain and 94 grain flat base, HP bullets that will stabilize in a 1:8" or 1:7" twist, 16" barrel. I have a working subsonic load with both bullets in a standard M4 type, 16" barrel shooting suppressed. My problem is this. When I get down to the speed I need, I can not get the bolt carrier to fully cycle the next round. It will eject the spent case, but the bolt will not lock back on an empty magazine. When I get my speed up just above 1100 fps (supersonic speed), it will cycle and the bolt will lock back on an empty mag. So, I am almost there. What are some options I can do to help aid the cycling? My goal is to have a subsonic round to sell to any and all shooters who have an AR-15 with 16" barrel and a 1:8" or 1:7" twist barrel shooting suppressed. So, my solution needs to be simple and easily available to all shooters. The idea of changing out the bolt carrier and gas block and such is not an option. I am leaning towards playing with the buffer spring and/or buffer. I need to find a reduced spring that I can try. I have also thought about cutting a few coils off the standard buffer spring to see if this helps. Any ideas?

Send me a few rounds to try in my custom gun with a JP captive spring set. That spring set is very nice.

Buddy of mine's 300BLK would not cycle subs, cut about three coils off his buffer spring, ran fine, I'd try that first, Buffer Springs are cheap.

Chad,
What buffer are you currently using? The CAR buffer is 3.0 oz; if you have an H buffer of heavier change it to a CAR buffer.

The problem you are going to run into is that different manufacturers have different size gas ports and compensate for over gassing with heavier buffers; while others optimize the port size to run with a CAR buffer.
Once you get the load to work in your rifle you might want to try other brands of factory rifle to see if they run better/worse so you can let customers know the parameters to be successful.

My piston rifles run everything with just a CAR buffer, including all the under powered Russian stuff.

A lot of the market base for sub rounds that cycle are going to be the SBR guys; in general most SBR barrels are over gassed which should help you out.

I would say the only other thing you can do is change the buffer/spring or enlarge the gas port, of those two you said you don't want to mess with the gas port so that option is out.

I put a ARES Armor low friction BCG in my AR recently to get it to cycle easier and a Damage Industries spring....

Chad,
Have you tried going to a lower mass buffer?

That might be my next option. I am almost there getting it to cycle. I'm going to try an idea or two in the next day or two to see if I can get it to work. I'm shooting and testing on a mid length system. I'm fairly certain the pistol length system would cycle these rounds with a normal set-up. I need to refine and test (confirm) my load a little more before I know for sure. When I'm at a little over 1100 fps, it will cycle and lock the bolt back. So, I am almost there. After talking to some powder engineers and ballistic guys, I need to change up my primer I'm using. Every single part of this ammo is very sensitive to changes and I'm trying to get the recipe just right.

What primer were you using, and what was suggested? What should the change be?

Chad,

If you're looking for this to be a commercial product, low mass buffers (/adjustable GBs) are probably not the ideal solution. What I would do is paint a straight line down your buffer spring and clip it one coil at a time. Note how many links it takes to get reliable action, and recommend to customers that they shorten up their spring accordingly. It's a cheap wear piece and is easy to change out. Alternatively, think about buying a bulk set of them, cut them yourself and offer the "subsonic-compatible" spring to your cusomers.

Edit -- You'll probably want to do this with more than one buffer weight.

I'd like to hear a lot more about this myself.

Chad, you are going to have to use a light buffer/low mass bolt carrier group, or use a barrel with a oversized gas port which will result in the rifle being over-gassed when using supersonic rounds. If going to the over sized gas port, I would highly recommend using a adjustable gas block or adjustable piston system so you can limit the gas when not needed.

I've spoken to several ballistic engineers and powder engineers about this project, and I am getting really close to working it out. The primer part of it has been a real trick. I have learned more than I ever though about what causes certain reactions with primers and powders. I am still in the R&D side of things, so I don't have a lot of solid data yet. Just a lot of thoughts on what to try and experiment with.



Hey Carl, for this project that's not an option.

The buffer spring and/or the buffer would be the only 2 ways I can change to make it work.