53.5gr of VV N560 was my accurate charge for the JLK 140gr VLD, and to boot it produced 3060fps.
When I ran of out JLK's 400 rounds later I decided to try some other bullets at the same charge, as it is still 2.5gr short of the published maximum by Vhita Vuori for the 139 scenar. CCI magnum primers used throughout.
So I tried the Scenars and the 142 SMK. They both shot well in terms of accuracy but I noticed about half the cases were engraving and flattening the primers.
Then I got some 140 Berger hunting bullets and just went ahead and loaded some up. With a .01" jump to the lands. All brass get FL sized.

When I tried the Bergers, I had to knock the bolt
Open, and found the primer had blown out! This is the first time in 15 years of reloading exclusively that I have ever had this happen.

Certain that I must have made a mistake, I went back to my shed, checked the chamber length again, and my COAL (off the ogive, not the tip) which that was fine, so I pulled some bullets and weighed the charges which were spot on. I suspected it might have been due to the brass, which has quite a few firings and I'd just annealed it with a new method that I think overlooked them. So I got some new cases - same result.

Unfortunately my chrono is playing up, but the shooting was done at 300m and 600m on large steel targets, so I can gauge the speed by the drop, and nothing seems to be inconsisted there.

I tried the Bergers with 51.5gr and 52.5gr and some cases showed light flattening of the primers, but nothing like what was happening earlier. The ballists also indicated there was a drop in speed with an impact 3" low at 300 and about 14" low at 600m.

So what have I overlooked? Is it possible that the Berger bullets are the cause of so much difference in pressure? I know I should try another powder but That won't answer the question.

What cartridge?

6.5-284 Norma

Every different brand of bullet can cause this. Difference is jacket hardness, bearing surface, jacket thickness and so on. It also sounds like you are right at the absolute max with your loads so a slight difference in bullets could run pressures over the top. Even though you have same weight bullet you should work up a load for a different bullet.

Very true. Berger hunting and match bullets have jackets of different thickness.

quote:

Originally posted by srose:
Every different brand of bullet can cause this. Difference is jacket hardness, bearing surface, jacket thickness and so on. It also sounds like you are right at the absolute max with your loads so a slight difference in bullets could run pressures over the top. Even though you have same weight bullet you should work up a load for a different bullet.

Plus Sierra uses 4 different lead alloys for there cores. Makes a difference if running at maximum pressures.