A True Mystery

[psteinmayer]

Ok, I have a Toyo Kogyo Series 31 that get shot on a regular bases in CMP Vintage Matches throughout the year. Last year, I had an interesting phenomenon where I had burned discoloration of the upper portion of some of my cases. I posted this here last year when it happened: http://www.jouster.com/forums/showthread.php?58695-Strange-Phenomenon. My load at the time was a Hornady 174 gr .3105 dia FMJBT bullet over 40.0 grains of 4064 and a CCI-200 primer.

Going with some of the advice I received, I changed to a slightly hotter load and more accurate bullet thinking that my case necks may not have been expanding enough to seal. The new load is a Hornady 174 gr .312 dia HPBT Match bullet over 42.0 grains of IMR 4064 and a CCI-200 primer. This proved to be considerably more accurate! However, things have gone from strange to downright weird. My son shot it on Saturday with the new load for the first time and here's what we have now:

I'm no longer getting that burned appearance on the upper portion of the case and neck. Now, I'm getting a considerable amount of carbon on the rim, head, and bolt head. I have no flattened primers, no pierced primers, no bulging cases, no split cases, no cracked case necks... in short, I have no indication what-so-ever of where this carbon is coming from. My only guess is it's leaking past the shoulder... but I have nothing on the upper portion of the cases. When my son shot it on Saturday, he gave me no indication that there were hot gases blowing out of the receiver either. After cleaning and inspecting the rifle, the bolt and chamber both look fine! Everything appears to be normal. Could it be that I'm moving the shoulder too far back when resizing, and the cases are not fire-forming to the chamber? I'm sizing the same way I have for several years, and this only started last year with the original problem. Dies are LEE Pacesetter 7.7x58 Jap. Brass is both PPU and Norma, and the results are the same for both.

I welcome all discussions

[Tuna]

Have you tried neck sizing the cases and see if they come out the same way?

[psteinmayer]

Going to try that. It's possible that I set the shoulder slightly back a hair and it's not fire-forming to the chamber like it should.

[bruce]

Have you got any Jap ball on hand? Have you got any equivalent foreign/domestic production ammo on hand? Shoot either or both. Are the results the same as your handloads? How do the fired cases compare to your brass? Would be a start to diagnosing what is going on. Have occasionally had foreign military rifles with chamber dimensions that were not standard to the caliber. Never had this with a German rifle. Common to SMLE, similar types. Possibly the case with Jap rifles. Neck sizing would be one step to take as it would eliminate possiblity of pushing the shoulder a bit to far back. Will follow this thread with interest. Sincerely. bruce.

[fguffey]

I welcome all discussions

When checking a Japanese rifle I cover the receiver with a white towel. When the case does not seal the chamber the white towel has two distinct black dots and on occasion I get a very distinct black outline of the receiver. When checking the rifle I find the barrel is too large in diameter for the bullet. I had a 7mm Remington Mag that blackened the case neck meaning the powder was burning too slow to seal the neck but fast enough to seal the case body from the shoulder back, removing the carbon is not easy.

F. Guffey

[PWC]

Do you leave the die in the press when through reloading, or do you take it out and put it back before beginning reloading? If it just started something has changed and it sounds like your 'fixed' die adjustment has slipped down on the shoulder. As recommended above, use some new or comm'l brass and neck size only on the first reload to see if the problem still xists.

[psteinmayer]

Do you leave the die in the press when through reloading, or do you take it out and put it back before beginning reloading? If it just started something has changed and it sounds like your 'fixed' die adjustment has slipped down on the shoulder. As recommended above, use some new or comm'l brass and neck size only on the first reload to see if the problem still xists.

Actually, I do take the die out because I load for several different rifle and pistol rounds. However, I have a locking nut installed so the measurement never changes. I also mark my dies with reference lines so I can quickly verify that my settings are correct. I also mark my bullet seating dies as well as the bullet depth settings.

[psteinmayer]

Just a quick update:

I started using a slightly larger bullet: Previously, I was using a Hornady 174 gr FMJBT sized to .3105 with 40.1 grains of IMR-4064. I've started loading a Hornady 174 gr HPBT Match bullet sized to .312 with 42.0 grains of IMR-4064.

I cleaned everything very thoroughly and polished the brass make certain there is no signs of previous black or discoloration. The result? Not only is there almost no signs of any blow-by... but the accuracy has improved quite a lot! There was still a tiny amount of carbon on the brass, but it was in patterns that suggested that it was a result of remaining soot mixed with gun oil (I usually oil thing up pretty well when cleaning) that happened during ejection. There was no discoloration at all. My son shot it in the Vintage Rifle Match at Perry, and everything worked great and looked fine. I'm still going to keep an eye on things though...

Many thanks to everyone for the help and advice!