HasegawaYamato
Regular
- Location
- Great Vancouver
When I fired the arisaka type 99 with my hand reloads (all parameters exactly go by the book, 41 gr H4895 with 150 gr Hornady interlock), I experienced excessive gas blow back from the chamber that kinda hurts my forehead, and the brass came out excessively black.
As a completely newbie in reloading I got bit nervous about it.
First thought was there is a problem with the gun, then I did some research and found this old thread described the exact same problem:
https://www.canadiangunnutz.com/forum/showthread.php/1214728-Never-Assume
I made the exact mistake just like the OP - I did not trim the PPU 7.7 Jap brass. As I measured the PPU 6.5 Jap brass, they are good, so I automatically assumed the 7.7 will be in spec as well, and it turns out amost every 7.7 brass is longer than it should be.
But I found no conclusion about whether it is the problem with the brass or insufficient pressure build-up to seal the chamber, so I decided to test it out.
To be on the safe side, I trimmer all the brass, and load 10 with 41 gr H4895, 10 with 42.5 gr (mid value between starting load 41 gr and max load 44 gr).
Here is the result:
Back up link to the pic: https://photos.app.goo.gl/Pu3EJKgSqHo7vGmh6
The top is the 10 brass with hotter load, bottom 10 went with starting load, and they were much more blacker when they popped out of the chamber.
Clearly 42.5 gr load wins for cleanliness.
So in sum, the problem is due to insufficient pressure in the chamber to deform the brass for sealing. By adding more charge or seat the bullet deeper or crimp the brass will reduce but may not completely solve the leaking prblem. And the over-lengthed brass seems has no effect on it (if I remember it correctly, arisakas tend to have larger chamber).
Please point out if I made any mistake here, advises are always welcome for a rookie like me
As a completely newbie in reloading I got bit nervous about it.
First thought was there is a problem with the gun, then I did some research and found this old thread described the exact same problem:
https://www.canadiangunnutz.com/forum/showthread.php/1214728-Never-Assume
I made the exact mistake just like the OP - I did not trim the PPU 7.7 Jap brass. As I measured the PPU 6.5 Jap brass, they are good, so I automatically assumed the 7.7 will be in spec as well, and it turns out amost every 7.7 brass is longer than it should be.
But I found no conclusion about whether it is the problem with the brass or insufficient pressure build-up to seal the chamber, so I decided to test it out.
To be on the safe side, I trimmer all the brass, and load 10 with 41 gr H4895, 10 with 42.5 gr (mid value between starting load 41 gr and max load 44 gr).
Here is the result:
Back up link to the pic: https://photos.app.goo.gl/Pu3EJKgSqHo7vGmh6
The top is the 10 brass with hotter load, bottom 10 went with starting load, and they were much more blacker when they popped out of the chamber.
Clearly 42.5 gr load wins for cleanliness.
So in sum, the problem is due to insufficient pressure in the chamber to deform the brass for sealing. By adding more charge or seat the bullet deeper or crimp the brass will reduce but may not completely solve the leaking prblem. And the over-lengthed brass seems has no effect on it (if I remember it correctly, arisakas tend to have larger chamber).
Please point out if I made any mistake here, advises are always welcome for a rookie like me
