Re: Cases bulging near head. .357 Magnum R92
Posted: 13 Jul 2017 07:42
Toddm,
I strongly advise againgt going to the 360DW chamber. I'm still trying to get my gun to feed the longer round "reliably". And the 100-150 fps gain in bullet speed is just not worth all that trouble.
I have lost a lot of my 360 brass to the same problem as you are having. The quest for more velocity means higher pressures, and this makes my cases bulge exactly like yours are doing. If I back off, the brass does ok, but then whats the point in that? And no, it's not because I cut the chamber out. It was already like that at the rear end of the hole, I only reamed a little out at the front of the chamber, and reamed a new longer throat section.
I think they make the chamber that way to help getting the round into and out of the chamber. A perfectly straight walled chamber would be a lot harder to deal with especially since most of us reloaders like to use oversized bullets too. SAAMI specs also show some taper in a "perfect" chamber. .0008" of taper, which really isn't very much. SAAMI also shows that all chamber mesurements can be up to plus .004" over, but no undersize allowed, understandably. And looking at your case mesurements, you appear to be right on the maximum allowed size of .3849-.385 since your largest bulge measures .384.
One thing that adds to the bulge looking so big is that rarely are new cases at the .379 size. I measured a handful of new 360s and they were all .3765". If they were at the full .379, that bulge would look a lot smaller. But again SAAMI specs say this measurement can go as much as .006 smaller than .379, so imagine what that brass would look like with the same amoult of bulge in it.
I strongly advise againgt going to the 360DW chamber. I'm still trying to get my gun to feed the longer round "reliably". And the 100-150 fps gain in bullet speed is just not worth all that trouble.
I have lost a lot of my 360 brass to the same problem as you are having. The quest for more velocity means higher pressures, and this makes my cases bulge exactly like yours are doing. If I back off, the brass does ok, but then whats the point in that? And no, it's not because I cut the chamber out. It was already like that at the rear end of the hole, I only reamed a little out at the front of the chamber, and reamed a new longer throat section.
I think they make the chamber that way to help getting the round into and out of the chamber. A perfectly straight walled chamber would be a lot harder to deal with especially since most of us reloaders like to use oversized bullets too. SAAMI specs also show some taper in a "perfect" chamber. .0008" of taper, which really isn't very much. SAAMI also shows that all chamber mesurements can be up to plus .004" over, but no undersize allowed, understandably. And looking at your case mesurements, you appear to be right on the maximum allowed size of .3849-.385 since your largest bulge measures .384.
One thing that adds to the bulge looking so big is that rarely are new cases at the .379 size. I measured a handful of new 360s and they were all .3765". If they were at the full .379, that bulge would look a lot smaller. But again SAAMI specs say this measurement can go as much as .006 smaller than .379, so imagine what that brass would look like with the same amoult of bulge in it.