Bolt wont lock back.

[budlight]

Pulled the gas tube re-installed it and tried again with the rifle buffer tube/spring/buffer wallah....runs like a top with proper gas. Switched back to the carbine gas tube/spring/buffer and again same as before 3-330 and wont lock it back.

I don't have the test to post, but the highest peak pressure is after the bullet first starts to travel down the barrel and then with more bullet travel distance pressure decreases.

Carbine length gas tubes are hit with @30,000 psi
Mid length gas tubes are hit with @ 22,000 psi
Rifle and even the rifle plus 2 inch at subjected to less than 14,000 psi and 11,000 respectively.

These are not exacting figures because of the many variables. Like powder type, bullet weight , barrel temperature, and friction.

This is why the buffer assembly differences and BCG weight. All my stuff is rifle and rifle +2 to not beat up my buffer weight faces...... You get higher velocity using longer gas system and that includes buying barrels with the smaller diameter gas ports

 

[xsn10s]

I'd play with magazine catch assembly. If in too deep on the magazine it can drag on the spring enough to allow feeding, but slowing the floorplate enough to not pop up fast enough to hold bolt open. Try turning the assembly out a turn at a time and test firing. It's the cheap, easy, and least invasive thing to do.

 

[ARlife4me]

and yet back to post #13 for answers. that would help

 

[UncleDano]

And another one goes to hell.

 

[Reelamin]

Sorry all was on a little trip to enjoy warm water and sunburn. I don't do internet when I can leave home. Apologize to all just enjoyed time away and thought I had time to resolve such a minor issue.

bolt traveling too fast will override the catch. very important question...........what cartridge!

AR15 223 and used range reload, 2 factory 55gr, 1 factory 64gr.

DITCH the SA gas block and buy a better 1. I've had 3 and all were bad. I have several AP barrels and components and all work great. I don't use or need an adjustable gb for any AP setup I have and that includes 3 6.5creed barrels without + length gas systems. All have carbine stocks with standard weight buffers and springs.

This may be the issue as this is the only one I have tried and it is the first rifle I have had not work from the get go. I'll start back on it ASAP...spring is here so projects to complete.

So, what you are saying is that you don't know if your barrel takes a carbine or mid-length gas tube?

Sorry, I know what it takes carbine, I was just swapping parts (Buffer/Spring) to try to get it to work.

Ar15 or Ar10? If ar10 my guess is ar15 length carbine buffer instead of ar10 carbine buffer. Just throwing my guess out there.

Thanks....my fault for not answering.

I'd play with magazine catch assembly. If in too deep on the magazine it can drag on the spring enough to allow feeding, but slowing the floorplate enough to not pop up fast enough to hold bolt open. Try turning the assembly out a turn at a time and test firing. It's the cheap, easy, and least invasive thing to do.

I did and will continue to do so. Even with brand new mags no luck. I installed a PDQ (never had issue on previous installs) now I will pull it and go with a standard bolt release.