So I just finished a 10" 300 blackout and it cycles, ejects and locks the bolt open just fine shooting supersonic ammo but is short stroking with subsonic. Went through the upper and bcg and all is good. My guess is the standard carbine buffer I'm running is too heavy for subsonic ammo so I was thinking about replacing a weight or two with a chunk of plastic or wood, anyone else had to do this?
300 blackout short stroking subsonic ammo
- Thread starter Ms359
- Start date
An adjustable gas block would help for hot loads but not so much for his low powered subs since the setup has full gas (or what's available) right now. While not fully ruling out an adjustable gas block, if OP was to have the gas port opened up on his barrel and get the adjustable gas block, he can run it wide open and hopefully it's still enough to cycle the BCG then close it down for supers. Hopefully he remembers to dial down the block when he switches out from subs to supers or there's might be a little bit of banging going on with his BCG.
There may be a couple cheaper routes to take. One would be to slowly increase the powder load in his subs to a point where it can successfully cycle the BCG so it locks back on an empty mag. The OP might even have to switch to a different powder and it might be a little on the hotter side for subs. The other option would be to use a lighter buffer (if possible) and/or experiment with cutting a ring or so off his buffer spring until it cycles and just replace the buffer and spring with stock ones when he switches to supers.
I'm sure someone here more well versed in this will jump in...
There may be a couple cheaper routes to take. One would be to slowly increase the powder load in his subs to a point where it can successfully cycle the BCG so it locks back on an empty mag. The OP might even have to switch to a different powder and it might be a little on the hotter side for subs. The other option would be to use a lighter buffer (if possible) and/or experiment with cutting a ring or so off his buffer spring until it cycles and just replace the buffer and spring with stock ones when he switches to supers.
I'm sure someone here more well versed in this will jump in...
A 10inch bbl rifle running subsonic 300 blackout/whisper is always tricky for proper cycling, even though 300 blackout was designed just for the purpose of both sub/supersonic loads. In a reasonable world, you would probably be using a suppressor to offset the change in pressure needed for cycling. But in this case, you may need to increase the gas port diameter to compensate. Noveske makes a switchblock to accommodate both sub/supersonic loads, not sure how and where to get one.
I'm pretty sure most 300BLK barrels under 16" would be a pistol length in order to get reliable cycling.
You'd be surprised how many are carbine length.....and you hear about the problems.
lol, this is very true too.
Have the gas hole opened up and run an adjustable block. Like others have said the subsonics really are meant to run with a can adding back pressure. You'll make it work, but many of them need a little fiddling around.
Powder is another issue, slower burning powders tend to give you more pressure at the gas port. According to Quickload.
http://4.bp.########.com/-WquNoElkdSM/VP1GrcEYj9I/AAAAAAAACJs/nHa6cCI-h9U/s1600/pressure.png
I got an adjustable gas block from CTCS about 2 weeks ago.
http://4.bp.########.com/-WquNoElkdSM/VP1GrcEYj9I/AAAAAAAACJs/nHa6cCI-h9U/s1600/pressure.png
I got an adjustable gas block from CTCS about 2 weeks ago.
What ammo are you using? My rifles wouldn't cycle factory Hornady 208gr subsonic loads but I can easily get 208gr Hornady pills to cycle using A1680 powder.
You have to remember that not all ammo is designed to be used in a semi auto rifle and the same goes for reloading data you find in your books. Sometimes you get lucky and it functions fine and other times it doesn't.
I have found that H110 is the best powder for 110-130 grain projectiles and Lil'gun and A1680 are best for the heavier stuff with A1680 being best for 200+ grain subsonic loads. I have been told 4227 is a good powder for mid weight projectiles but haven't tested with it yet.
If your rifle won't cycle factory subsonic loads then don't buy them, you still need to wear hearing protection anyway.
The best way to shoot subsonic is to handload and if you don't then just be happy with what it will cycle and stick with that.
Good luck
You have to remember that not all ammo is designed to be used in a semi auto rifle and the same goes for reloading data you find in your books. Sometimes you get lucky and it functions fine and other times it doesn't.
I have found that H110 is the best powder for 110-130 grain projectiles and Lil'gun and A1680 are best for the heavier stuff with A1680 being best for 200+ grain subsonic loads. I have been told 4227 is a good powder for mid weight projectiles but haven't tested with it yet.
If your rifle won't cycle factory subsonic loads then don't buy them, you still need to wear hearing protection anyway.
The best way to shoot subsonic is to handload and if you don't then just be happy with what it will cycle and stick with that.
Good luck
Hornady factory 208 subs don't cycle for me as well. I only shot 2 rnds from the box so I think I'm just going to pull the pills, dump the powder and reload using some 1680.
I use H110/W296 for 150gr FMJs without any problems.
I don't bother much about subs anymore since I can't shoot suppressed and as CR5 pointed out, you still need ear pro anyway.
I use H110/W296 for 150gr FMJs without any problems.
I don't bother much about subs anymore since I can't shoot suppressed and as CR5 pointed out, you still need ear pro anyway.
OP we need two pieces of information to render a verdic on yer problem.
1. Who made the bbl - secondarily, what is gas port size?
2. What subsonic ammo are you using? Factory or handloads?
Either one of these can be tweaked to improve cycling. Best case is to tweak both. My 10" BLK will reliably cycle 150gr subsonics but that is using taylor made handloads, adj gasblock and a very trick adjustable recoil setup of my own design.
1. Who made the bbl - secondarily, what is gas port size?
2. What subsonic ammo are you using? Factory or handloads?
Either one of these can be tweaked to improve cycling. Best case is to tweak both. My 10" BLK will reliably cycle 150gr subsonics but that is using taylor made handloads, adj gasblock and a very trick adjustable recoil setup of my own design.
Thanks for all the info. Looks like the issue was the factory ammo, tried out a few mags of a friends hand loads today and it cycled fine. I was initially going to sell the rifle but it's kind of grow on me so it's off to pick up some dies and powder and like others have said we can't shoot suppressed so I'm fine with supersonic ammo.
There is nothing wrong with his rifle, What would you tell the retailer? It works great but when I try this one type of ammo it won't work so I want a refund? He'll tell you not to run that ammo and to have a nice day.
You can't expect a semi auto rifle to cycle every type and brand of factory ammo available. Ammo manufacturers could never take every factor into account to make sure that every rifle available works with their ammo.
Really? you only buy factory rifles? Your ACR with the Herron 450 Bushmaster conversion isn't factory. Do you think Ian is going to give you your money back if you find a factory load out there that doesn't cycle well?
That factory Hornady 208gr works great in my Remington 700 bolt action 300BLK
I'm sure it would work in an AR with a suppressor as well. Just needs a little more backpressure.
Semi auto subsonic is a matter of degrees. That one type will or won't cycle doesn't make a rifle "NFG".
