New build won't cycle......help

I just finished my first complete build, all the function tests checked out and I am able to cycle rounds in and out of the chamber by hand. However, when I fire the rifle it ejects the spent case but does not feed a new round in or cock the hammer. I guess it's obvious that the bolt carrier isn't going back far enough.

This project has a rifle-length gas system and a colapsable stock with a David Tubbs buffer spring.

Can someone suggest possible causes for this problem and how I might check for said causes?

Thanks!

Try carbine length spring instead of all in one spring like David Tubbs.

Might have to enlarge (haha) the gas ports.

Try a standard carbine spring and carbine buffer. Is the gas block a pinned on FSB or a set-screw lowpro? If It's a set-screw type I'd check to make sure you don't have a gas leak.

Are you using Tula or wolf ammo ?

Could be weak ammo against an XP buffer spring...

Could be not enough gas due to a misaligned gas block, leaking gas from gas tube and or gas block interfaces...

Are you using a Geiselle trigger by chance?

If the buffer or spring were bottoming out the recoil impulse would feel funny and the issues would show on a function check without firing .

I run the Tubb flat wire springs in all my guns with no issue's . My money is on a gas leak some where .

Come see me.

Quote:

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Originally Posted by BPTactical

Come see me.

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+1 [Beer]

Barrel length? Ammo used?

It is an 18 inch DPMS barrel that came with a set screw type non-adjustable standard hight gas block. The gas tube is one Midway recommended for this barrel/gas block.
I've got a Tubbs spring in another carbine and it works great, although it's a 6.8SPC.
I was using Black Hills .223 ammo, which I'm sure isn't the best, but I would expect the rifle to be able to operate with anything I give it.

How does one test for a gas leak?

Thanks

I too advocate stock springs and buffer. They never fail.
Gas block in position and aligned to the port correctly?
Pull the gas block and put a couple of drops of solvent down the gas tube. When it reaches the block you may see a bit of seepage between the tube and block, which is normal. But if it is wet leakage may be excessive.
Gas rings staggered?
Gas key tight? You can check it the same way you did the tube/block.
Then if all that proves ok only then look at the port size, I think it is .080 but don't hold me to that.

Standard port size for rifle gs is 0.110.

I bought a high dollar daniel defense complete bcg for this rifle, so I hope I can assume that everything related to that is OK. I'm pretty sure the gas block is situated correctly. I think what I'll do first is try shooting some more potent ammo and if things work, I'll replace the buffer spring and maybe go with a lighter buffer. If that fails, I guess its off to a smith. Sound reasonable?

Go to the smith first. It may not be your buffer or spring. Don't waste money on parts before diagnosis. Tubb springs work fine with pretty much any buffer. It is more likely gas related than buffer/spring related.

Update..... Shot some Winchester 5.56 62gr penetrator ammo today and everything worked flawlessly. I'm now assuming that if I want the rifle to be able to handle weaker loads, I'm going to have to weaken the buffer spring and possibly lighten the buffer. Thanks for all your input....