Cartridge won't feed into chamber

[MaxG66]

I'm having some trouble with my 168gr BTHP loads. Hopefully someone can point me in the right direction.

I made up 5 rounds of each charge weight of Lil Gun: 14.0, 14.3, 14.6, 14.9, 15.2. All of the rounds chambered and shot when using the charging handle for the first round, but NONE of them picked up the next round from the magazine and chambered. Not once, not any powder weight.

Other details: 16 inch barrel, don't know details of the gas system, COL 2.2", CCI SR primers, a variety of brass. I'm using Magpul 300 BLK mags.

I also shot some Remington 147gr factory ammo which worked perfectly. My 125 gr Nosler Ballistic Tips also work and cycle fine with 19.0 gr Lil Gun under them.

What's happening? It seems something fundamental, which it probably is, but I'm stumped.

Thanks for your advice and enlightenment.

[ReadyAimDuck]

If you load one into the magazine and fire that, are is your BCG locking open on the empty magazine? That would be my first question to check if the bolt is short stroking due to not enough gas pressure.

[MaxG66]

No, it isn't. I have to manually operate the charging handle each round (after checking the mag to see that no round loaded.

MG

[20X11]

1. Measure the length of your gas tube (is it Carbine length or Pistol length?)
2. What buffer weight are you running?

[ReadyAimDuck]

No, it isn't. I have to manually operate the charging handle each round (after checking the mag to see that no round loaded.

MG

Okay, so if it doesn't chamber the next round after fired and it doesn't lock back on an empty magazine that seems to indicate that it is short stroking. What gas length system and buffer weight are you using would be my next question. I'm seeing load data that would indicate that this load should be within the range for proper cycling, but I have no experience with that powder so I can't say for sure.

If we could find out the info about your gas system and buffer it will help indicate whether there may be an issue somewhere, or if you need to make an adjustment. For example, if you had a longer gas system and a heavier buffer, then everything may be in order and you might just need to lighten up the buffer. But if you say you have a pistol gas system and a carbine buffer, then it may indicate a problem somewhere such as an improperly installed gas block causing not enough gas pressure to get back into the gas key.

[dellet]

If the other loads worked after the Lil'gun loads failed,and you used multiple magazines, I would load a round or two at 13.5 grains and check again.

If the Lil'gun loads were the last you tried, Try the others again. Something could have happened to have caused the failures. Gas leak or blockage, probably the most common.

With the wrong buffer and spring combination, it's easy to over gas using Lil'gun and heavy supers. The bolt will travel too fast for the magazine to feed or lift the bolt catch.

[MaxG66]

All the loads I tried were with Lil Gun. The 147 gr factory ammo, while not quite as heavy as the 168 BTHP, functioned perfectly. I've got to think it's something about the rounds themselves. Factory ammo of any weight / brand has never malfunctioned in that gun.

I made up two more test batches (5 ea) with different COLs. I'll try to get to the range this after noon and see if that's it. Very weird.

I will measure the gas tube also. I"m guessing it's carbine length, but I don't know. I know the barrel is 16".

[cdl]

If you're using standard 556 magazines …

When I stick a Sierra 168gr BTHP in a 300 Blk case at 2.20"... and I measure it with a bullet comparator with a 0.27" bushing …  I get 1.770" @ 0.27".
 
Generally, for me, a measurement of 1.598" @ 0.27 would have already started rubbing on the shoulder guide ribs in a 556 magazine. This causes the stack of cartridges to "pigeon toe" in the magazine and impede the feeding of the next round. Can be a problem.

If you're using a 300 Blk magazine, ignore the above...

[popper]

Should be ejecting case about 15 ft. If neck is dinged, under gassed. Neck could hit front of port. Over gassed, may hit deflector and dent neck.you are getting close to overload for 168 gr.

[ReadyAimDuck]

Did you get a chance to do any further testing afternoon that day? Curious where you're at with this.