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Posted: 8/20/2010 7:29:13 AM EDT
Ok went out shooting with a buddy (he is on this site and might chime in as well), and he has an 18 inch SPRish gun that shoots like a dream. Specs on the gun are 18 inch Saber Barrel, Troy Rifle+ length handguard, Vltor Mur upper. It shoots just fine without a can on it, but the second we throw his AAC M4-SPR can on it there are problems. It will eject the fired round, then to reloads the next round and totally mangles the next cartridge. and jams it into the chamber, will not fire and we have to Yank on the CH to pull it out rather forcefully. We have tride carbine buffers and heavy buffers and they dont work. Any ideas on what to do? I am stumped... Here is a pic of the gun in question:
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Buffers tried:
Carbine Heavy Spikes magic tungsten powder Two carbine buffer springs Ammo used: Black Hills 75gr Black Hills 55gr Privi 55gr Federal 55gr WalMart special WWB 556 55gr 5 different pmags used 1 CProducts SS 20 The 18" Sabre barrel is a Mid Length gas system. Any help would be appreciated. |
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Suppressor is going to cause more barrel bore back pressure, hence raise the action pressure at the gas port, speed up the unlock at cycle with the can in play.
If the gun is dialed in unsuppressed with a standard buffer, then going to a H-3 will make it run the same with the can in place. Chances are he is now having to use a heaver buffer unsuppressed due to the gas port being too large, and you don't have the option of finding a new buffer the same math stated above to normal it all back out with the can in play. So if the above it true, then the simple fix is to just to go to an adjustable gas tube system so you can dial the action cycle pressure now to allow the gun to run with a standard buffer, then either readjust the gas tube setting or add the H-3 buffer for the can. |
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You need an adjustable gas tube. They run about $38. The problem is that you have an 18 inch barrel, and they make the adjustable gas tubes in 20 inch and 16 inch. I guess you could buy a 20 inch and cut it down. If you have a good machinist or gunsmith, they could even put the little bulge in the end to help seal the gas tube with the bolt carrier key. I used to use the adjustable gas tubes when I shot suppressors a lot on my M16, and they worked really well.
Charles Tatum |
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I am also running an AAC SPR-M4 on a 16" Armalite carbine upper 1 in 9 twist carbine gas length. The SPR-M4 creates lots of back pressure, so I went with the JP adjustable gas block $70.00 at Brownells. The rifle runs silky smooth now. I am in the process of having a cut rifled barrel built which will be an 18" rifle length gas system and it will carry the Noveske switchblock system. Expensive, but worth it. ne other option which has not been mentioned is using the Tubb Carrier weigth suystem $50. This allows for several variable weights to balance the rifles action against the ammunition being used. Increasing the mas and delaying the bolt motion. I would definately get an adjustable gas block of one type, not just the tube. |
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The only thing that I do not like about the Tubbs carrier weight system is that the weight carrier sticks out the back of the carrier, and you have to trim the buffer bumper the same amount for such.
Hence, when you pull the weight insert to take it out of play in the rig, you have to change out either the buffer or end bumper that you shortened since it will allow the back of the bolt to retract back past the back edge of the ejection port and cause ejection problems (spent case path being changed since the case is now striking the back of the ejection port). Note: Brownells sell an end of buffer plastic silencer cap piece (front of buffer), and J&T has there anti-sprong device that goes on the other end, ether of which could be use to gain the needed over all length as well. |
| Dano, While I have heard about the possible need to trim the buffer I have never experienced a need to do so in a half dozen AR's which I have run the Tubb CWS in, both rifle and carbine variations in multiple calibers as well. The main concern was to have enough rearward travel to be able to catch the bolt stop on the last round. |
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