Can a gas leak affect bullet velocity?

[ABNAK]

Or is the bullet gone before any of the effects of a gas leak take place? Like short-stroking, etc.

Long story short I shot a new Brownell's XM177E2 upper today (1:7 twist). I only put about 80rds downrange; 40 of it Federal M855, maybe 30 of IMI Mk262, and about 10 of Mk318.

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. Noticeable "lame" feel to the shot. Also, it only occurred with the Federal M855, not the others. There was a little gas residue around the bottom of the FSB on both sides, front of the rear "strut" and back of the front "strut". I did not take off the handguards.

Maybe a little leak in the rear of the gas tube or in the interface between the rear ring of the FSB and the barrel making it squirt forward (front of the back strut, rear of the front strut). Either way it wasn't a huge amount but I did notice it. The Mk262 and the Mk318 didn't have any issues.

So the reason for this thread is that the specific rounds that malfunctioned also deviated from the impact of all the other rounds. To differentiate between it being the big coincidence of it only just happening to the M855, or some lame-ass M855 ammo causing it, I was wondering if the residue I saw (indicative of a gas leak to whatever degree) could affect bullet velocity (and it's subsequent impact on POI) or if the bullet has departed before the short-stroking is showing itself. If a leak would NOT affect velocity, and therefore the leak isn't hurting much accuracy-wise, then the fault lies with the ammo, correct?

[TomMcC]

Deleted

[georgeib]

Some gas leakage is normal until enough carbon has built up in order to create a good seal. However, it shouldn't leak so much as to cause the short stroking you describe.

My guess is bad ammo. Especially given your description of it feeling lame when firing.

[ABNAK]

Some gas leakage is normal until enough carbon has built up in order to create a good seal. However, it shouldn't leak so much as to cause the short stroking you describe.

My guess is bad ammo. Especially given your description of it feeling lame when firing.

Yes, and deviating from the others in the shot group. I took a closer look at the ammo with a magnifying glass and the bottom of the case rim, where the headstamp is, has a bunch of little circles stamped into it all the way around the rim. It's to the point that you can barely read the headstamp. This is Federal M855 bulk pack of 1000rds. Maybe those little circles stamped into the rim show it's some kind of factory seconds? (although it doesn't say so on the box)

[georgeib]

Post a couple pics please. I'm curious.

[ABNAK]

Post a couple pics please. I'm curious.

There is no way my crappy cellphone camera would show what I'm talking about. Look at the link below and scroll down to the Federal American Eagle pic of the rim. See the little circles? Only on mine they go pretty much all the way around the rim and make it very difficult to even see the headstamp:

https://www.ocabj.net/55gr-5-56-nato...on-comparison/

[Averageman]

Well, that's disturbing. I would do some further testing by pulling bullets charge weights on cartridges with those head stamps and then pulling a few without that stamp to compare them to.
If there is any deviation, I would note it and get back with the manufacturer with your information. If they can throw a light charge, they can certainly give you a squib.

[twm134]

Those stamped circles are just a way for the manufacturer to tell which line that particular piece of ammo was produced on. Sort of like a watermark for each round.

[ABNAK]

Those stamped circles are just a way for the manufacturer to tell which line that particular piece of ammo was produced on. Sort of like a watermark for each round.

Sounds plausible, but they pretty much obliterate the rest of the headstamp info. I checked about 5 random rounds from the 1000rd box last night and they all looked like I'm describing. Maybe these were factory seconds? The fact it only occurred with the M855 and not the Mk262 or Mk318 kind of makes a coincidence unlikely.

[twm134]

I agree with the other posts that it initially seems like a problem with that ammo, however the markings don't indicate it is factory second ammo. I would try the ammo in a different rifle and try a different lot of M855 in the rifle to make sure it is isolated to that lot of ammo and not a problem with the rifle.