Not enough gas on 20" 5.56?

[Not a Clue]

I'm not sure I'm even qualified to be in the junior league here and hate to ask such a simple question because it exposes my complete lack of knowledge.

I've built a few 5.56 pistols, successfully, all gassed right and functioning well. Thought I'd step over into the long barrel side and build an actual rifle. 20" barrel with rifle length gas tube, Aero lower and upper, non-adjustable gas block (didn't think I'd need to dial it down), Toolcraft bolt carrier. Took it out for it's madien voyage and it's not cycling the bolt carrier far enough back to pick up the next round. It's not even getting close enough to jam up the whole works like happens with some gas issues. Each time, I had to shoot a round, then pull the charging handle back to load a round.

Carbine buffer tube and stock mil spec carbine buffer spring running a standard mil spec buffer (I have a heavier one bought didn't try that).

In looking at the gas block, it appears to be on there right, in the right place and not misaligned that I can tell. The carbon shadow on the hole looks to be good so I'm guessing it's not the gas block location?

My current thoughts are possibly the wrong buffer spring or the gas port in the barrel is too small. I didn't measure that but that's my only guesses.

Forgive me for my newbieness.

Thanks for taking the time to read this!

 

[TonyTheTiger]

Check your gas key and rings before you start drilling out the port.

 

[loveha]

Good quality match ammo?

 

[The DFC]

Should be getting plenty of dwell time with the rifle length system. Pretty much has to be a gas port/block issue right?

 

[Lawless]

Exactly what spring did you use?

It would be unusual for a gas port to be drilled that much too small.

 

[Not a Clue]

No, just Winchester target ammo. Just trying to cycle a few rounds through it. Not doing any precision shooting quite yet.

Maybe I'm missing something, maybe the port is blocked or partially blocked. I'll go back and check the gas key and rings. I would think they are okay, I pulled it out of a working gun that had about 75 rounds on it, but that was from a pistol so maybe overgassing did some damage I didn't see before putting it into this rifle.

I don't know the specific spring, which I think might be the problem. I had a couple I had bought when I built my pistols and I think they just said "Carbine length springs". I tried to look it up and find a recommended spring that was light but it all got over my head quickly and lots of recommendations for high end spring setups.

 

[XLR308]

Just out of curiosity are using a Nitrided barrel ?

 

[Not a Clue]

Yes, I believe it is.

Update: Just double checked, it is.

 

[loveha]

If you are unsure about the spring, go here and order a white/carbine or green/rifle one if you are concerned about it.

Sprinco USA -- Recoil Solutions

Run a pin gauge into the gas port or bore scope the barrel and check if the gas port was drilled all the way through. It does happen once in a blue moon.

Can you blow air through the gas tube and block easily enough?

 

[XLR308]

Yes, I believe it is.

Update: Just double checked, it is.

If you didn't thoroughly clean the chamber it can cause issues with short stroking from the residue left over from the nitride process.
Does your fired brass have a smoked look to it ?
If it does give the chamber a good cleaning before shooting again.
I had the same thing happen with the first nitride barrel I built an upper with, after stripping the rifle down and checking everything over at least once I gave it a good cleaning with Hoppes and a chamber brush and it functioned fine afterwards.

 

[Not a Clue]

Thanks guys, I'll check into those things and report back. Might be another week or two before I can talk my buddy into taking me along to the range. He just got into the 6.5 Creedmoor and I thought I'd build this so I'd have something to take while shooting with him.

 

[MontanaMan]

You have a lot going on, but here's what I suggest, some already suggested above:

1. Clean the chamber with a bronze brush; clean the barrel with a nylon brush & JB, lot of residue in many nitrided barrels
2. Verify the gas port size (should be around .093-.096") & GB alignment by measuring the distance from the shoulder on the barrel to the center of the gas port & the end of the GB to the center of the hole in the GB & position it accordingly so that you know the holes are aligned
3. Someone above mentioned a white spring from Springco....that's standard weight spring, get that as well as a yellow one which is one step softer
4. Verify that you have a 3 ounce carbine buffer
5. Lose the Win ammo, especially if it's 223 & get some genuine 5.56 ammo
6. Last ditch effort if all above fails, before you open up the gas port, try a lightweight bolt carrier

Good Luck

MM

 

[Not a Clue]

Thanks! I’ll give it a good scrubbing and get a lighter spring and give it a run, with some better ammo as well. It was 5.56 but still Wally World stuff.