barrel length vs gas block location vs port size

[txjm]

The brass I am using is Speer 07. It has a military crimp and it was real consistent in weight. The rim isn't ripping off but it is leaving a burr when it jumps over it. You can see where a little of the metal is gone on the inside of the rim. It is a new chamber and I think it would benefit from polishing and cleaning. I will try the extractor kit. Does it come with the extractor? Are all extractors the same?

[Colohunter]

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.

[MIKEONE]

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

Also whose reamer did you use for the chamber?

Mike

[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]

Originally Posted by MIKEONE

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

Also whose reamer did you use for the chamber?

Mike

I would love to see what you came up with on the H335 loads. 2.262 oal. 85SGK, 23.5G and 25.5G o powder.

Thanks Chip

[txjm]

I did 3 things and shot some more this morning. All cases ejected and all but one fed properly. I tried the first load as a single in the mag and it even locked the bolt back. The rims look good, no metal missing where the extractor jumped. One thing odd that I noticed was the primers were not as flat with the same load. It was maybe 5 degrees cooler, not enough to make that much differance.
I oiled the BCG.
I polished the chamber with JB.
The barrel is a nonstandard profile and very thin. The gas block is modified to fit the barrel. I played around with limiting the gas flow through the gas block. I blocked almost half the port.
I think the main problem is the required port size must be tied to barrel diameter. In fluid flow it is not only the diameter of the oriface but also the length. I think the thin barrel really needed a much smaller port. I am going to go adjustable in some form and tweak the gas flow. I think my results this morning show that I may have limited the gas flow a little too much. Maybe the first one locked back because of the oil. Maybe I am running on the edge of functioning and the one failure to feed completely was caused by not enough gas flow. It almost fed the bolt just didn't close completely.

Thanks for all the help. I will be doing some more testing.
Chip

[txjm]

Originally Posted by txjm

I did 3 things and shot some more this morning. All cases ejected and all but one fed properly. I tried the first load as a single in the mag and it even locked the bolt back. The rims look good, no metal missing where the extractor jumped. One thing odd that I noticed was the primers were not as flat with the same load. It was maybe 5 degrees cooler, not enough to make that much differance.
I oiled the BCG.
I polished the chamber with JB.
The barrel is a nonstandard profile and very thin. The gas block is modified to fit the barrel. I played around with limiting the gas flow through the gas block. I blocked almost half the port.

Thanks for all the help. I will be doing some more testing.
Chip

I modified my gas block to be adjustable. I started with lower end loads from above and adjusted until the rifle functioned. Everything seems to be happy now. 85G SGK don't seem to shoot as well as 80G Rem CL. H4895 seems to shoot better than 335. The 80G @ 27K + in the 18" barrel seems to be about it.

Thanks
Chip