Change brass Change accuracy?

nitis · Feb 14, 2010

OK so we were at the range yesterday looking for a load for my buddys 300 win so I took my 257bee and I wanted to try the loads I had loaded using 7 mag brass. The brass was new winchester brass resized in the sizer die only difference I could see was the necks were a little short.

So they were shooting at 50 yards trying different loads looking for potential candidates. So I took the opportunity to shoot the loads in 7 mag brass at that yardage since the load was proven in wby brass. Bam 1 hole group!

Not sure why but I shot a group of the wby brass later and it opened up to like 3 inches argh! this load had shot a dime size group at 100 yds previously.

Load is a max load of imr 4831 and 100 gr ballistic tips. One thing I am worried about now is the powder I used in development was about 15 years or older now that is used up and I need to use new stuff.

Anyone care to comment?

JD338 · Feb 14, 2010

New powder, new load development.

How much shorter is the 7mm RM fire formed case?

JD338

nitis · Feb 14, 2010

they werent fireformed

I will have to measure but I am guessing 3-4 thousandths and its just the neck so the only difference is how much of the bullet is in brass in one vs the other overall length is the same

Charlie-NY · Feb 14, 2010

3-4 thousandths is nothing but the brass may shoot differently anyway. Typically, you will have a difference in case capacity and that could result in more or less pressure with the same load. That's one reason why you shouldn't mix brass from different manufacturers. Reforming brass from a different cartridge is more likely to result in a change in capacity IMO.

While many guys may use old powder I can't waste my time and energy with a powder that may be as good as new, and then again may not. Particularly when your working up a load and will have to switch to a new can that has likely changed a bit over 10-15-20 years.

I have given lots of powder to our local range officer to use at his discretion because I just don't have the desire to meticulously assemble my handloads with old powder.

kraky · Feb 15, 2010

This is where using a chrono is important. I still have a batch of remington brass that was made for the 7mm wby. I use it to make my 270 wby. That brass has way less capacity and if I load it with the same grains as genuine wby brass it is like like adding about 2 grains of powder.
So.....if the rem brass is like what I experienced you may find that if you had 70 grains of 4831 in ea case the rem would have been much faster....like putting another 2 grains into your wby brass.
All this is theory until you chrono the loads but I will bet the rem loads are hotter than the wby brass.