barrel length vs gas block location vs port size

[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