Can a gas leak affect bullet velocity?

[1168]

Those circles are normal on military issued M855.

[MistWolf]

...I ran into a couple of short-stroking failures.....spent cartridge not ejected (but extracted) and the bolt resting on the back half of the next round...

Did you perform a lock back check? Your symptoms do not automatically mean short stroking.

[TomMcC]

Related to the lock back test...I rebuilt a rifle with a new bolt and it had intermittent short stroking. It also had intermittent lock back. I spent some time hand racking the BCG (like a 1k times) and never had anymore problems, my theory was the gas rings needed a bit of break-in. Since the OP's gun was new maybe this would help. Still doesn't explain flyers in his group though.

[ABNAK]

Did you perform a lock back check? Your symptoms do not automatically mean short stroking.

Yeah, the last round in the mag would lock back, even when I had the malfunctions. It's a brand new Colt 20rd magazine too.

Again, the malf rounds would fly out of the general group.

[hotrodder636]

Pardon my ignorance here, but how would one identify factory seconds by looking at headstamp?

[MistWolf]

...is the bullet gone before any of the effects of a gas leak take place?

The effect the leak would have on velocity would be consistent. It would affect each round the same.

...the reason for this thread is that the specific rounds that malfunctioned also deviated from the impact of all the other rounds...

Before going down the rabbit hole, it's a good idea to troubleshoot each problem one at a time-
1) The extractor spring may not be causing the problem, but it could be. Replacing it with a Colt extractor spring eliminates it from the equation. Colt extractor springs cost so very little and perform so well, the peace of mind they bring is well worth the effort.

2) Perform a lock back check. If the rifle fails lock back check, go to Step 3. If it passes, go to Step 4.

3) Check for and eliminate leaks and blockages in the gas system. When repaired, repeat Step 2.

4) Verify function.

5) Test ammo for precision.

[MistWolf]

Yeah, the last round in the mag would lock back, even when I had the malfunctions. It's a brand new Colt 20rd magazine too.

Again, the malf rounds would fly out of the general group.

The possibilities are-
1) Bad ammo
2) Weak hammer spring
3) Out of spec firing pin

Primers need a solid, consistent whack for consistent ignition. A weak or inconsistent hit from the firing pin sometimes results in weak ignition resulting in erratic pressure. This leads to flyers. Combined with cheap blaster ammo, the possibility of a flyer is even greater.

[ABNAK]

The effect the leak would have on velocity would be consistent. It would affect each round the same.

That's what I was thinking.

I was only loading 3 to 5 rounds at a time as I was just trying to zero the weapon. It would happen and affect (short stroke) the first two rounds in the mag, then the third would lock back. It never happened to just one round, it was always the first 2 of a 3 round loading but only with the M855. It also did not do it with every mag of M855 I tried, only every now and then. Weird, it would happen with some pairs (the first 2 of 3 rounds) and only with M855.

Shoot first round....stoppage

Clear stoppage

Chamber second round and shoot it.....stoppage

Clear stoppage

Chamber third round and shoot it.....lock-back on empty mag.

Only with M855, but not every time I tried it. Always did it in pairs though, no "one-sies". If it did it on the first round, it WOULD do it on the second one also.

Used the same new Colt 20rd mag the entire time.

[GH41]

Do you guys mean XM193/855? The "X" signifies it is NOT mil spec ammunition. The "X" rating may be applied for many reasons. I don't know what the sample rate is for the mil but it is said if a lot of many thousands shows one QC example the whole lot would not be accepted by the gov.

[ABNAK]

Do you guys mean XM193/855? The "X" signifies it is NOT mil spec ammunition. The "X" rating may be applied for many reasons. I don't know what the sample rate is for the mil but it is said if a lot of many thousands shows one QC example the whole lot would not be accepted by the gov.

Nope, the box is marked "M855 LCAAP RIFLE CARTRIDGES". The X was the first thing I looked for after I came back in the house from shooting but there wasn't one.