barrel length vs gas block location vs port size

[txjm]

"Is this a new bolt and extractor, or did it come from a previously used rifle? Having the extractor come of makes it sound like it or it's springs are worn. I would say it isn't just an issue of gas port location as the carrier is moving enough to feed a new round. It could be that the bolt is unlocking while there is still too much pressure, what weight buffer are you using? You might try a heavier one if possible to try to keep the bolt locked in place a little longer."

All the parts on the upper are new. Most of it is dpms, I think the bolt and carrier group is bushmaster. My buffer is the standard carbine buffer. It does seem that the bolt is unlocking while the case is under too much pressure or the extractor isn't grabbing well. It does work when I manually cycle the action after a jam and the case is still in the chamber. Would a pigtail type gas tube or a fatboy gas tube change anything?

"Whats your load? Ill pop it in quickload to see approx what pressures your running. "

From memory it is a starting load of h335 - 23.5G and a max load of 25.5G. The bullet is a SGK 85G. The oal is max mag. 2.262" Other than OAL I pulled it out of the Lee manual. Maybe the oal is driving the pressure up. I had problems with the starting load doing the same thing. The primer on the starting load looked fine. the max load was a flat.

"Also whose reamer did you use for the chamber?"

The reamer is a PTG.

Thanks Chip

[Colohunter]

The pigtail gas tube could help to delay the ejection a little, though I don't have any experience with those. You an also try an H or H2 buffer to delay the carrier a little bit.

Maybe I missed it, but did you ever mention if you were checking velocity on these loads? If you know velocity numbers that can also show a little more info, especially when checked against the quickload predictions.

[txjm]

Originally Posted by Colohunter

The pigtail gas tube could help to delay the ejection a little, though I don't have any experience with those. You an also try an H or H2 buffer to delay the carrier a little bit.

Maybe I missed it, but did you ever mention if you were checking velocity on these loads? If you know velocity numbers that can also show a little more info, especially when checked against the quickload predictions.

The book values start load - 23.5G - 2587 fps and max load - 25.5G - 2818 fps. The oal in the manual is 2.350". My chronograph was messing up and I got one reading at the 24.5G load and the velocity was 2649 fps. That seemed to fall fairly close to the expected. My oal is shorter and I would imagine my 18" barrel is shorter than the Lees test gun.
Thanks Chip

[cav_scout_tj]

I say confirm the extractor parts, if its a new bolt, then the spring and insert should be ok, but an o-ring could help. The o-ring is standard hardware store stuff, 1/4" outside diam, 1/8" inside diam. Slip it over the extractor spring.

Polishing the chamber will help too.

If the whole thing is new, then it probably needs a few rounds to knock the park off the parts. And make sure its WET with oil.

[txjm]

What parts should be wet? bolt and barrel extension?

[cav_scout_tj]

wet: bolt lugs, cam pin area, bolt body inside carrier, a few drops down the carrier key hole. Put a drop in the holes on the side of the carrier. The rails down the carrier bottom and around the key on top.

Basically you could dunk the while bolt carrier group in a quart of oil and that would work fine.

Dont wear a nice shirt when you shoot it. First rounds will blow off any excess.

[leo6223]

Sounds to me like it might be trying to unlock too early when the pressure is still too high.

That can be a tough fix