New Brass vs Old Brass

[Oklahunter1]

I tried searching but I guess I don't know what to search for.
My question to the guru's is my groups change from using new brass to old brass. I full length size both my new and old brass. Use same load, same bullet(I weigh the bullets). My group size at 100 yds is 3/4" with new brass and 1.1" group with old brass. I have verified this doing it more than once. What causes this?
Thanks!

 

[Rick Richard]

Same batch and/or name brand? How many firings on old brass? Quick guess would be difference in neck tension from new to old.

 

[Oklahunter1]

Yes, powder out of same can and bullets out of same box. I am a rookie to reloading, how do I determine if it's neck tension?

 

[Rick Richard]

Yes, powder out of same can and bullets out of same box. I am a rookie to reloading, how do I determine if it's neck tension?

How many firings on old brass?

 

[can1010]

if new brass means unfired and old brass means fired in your gun one or more times then it is a pressure problem.
unfired brass lowers pressure when expanding to fill chamber for the first time
once brass is fired it needs less powder to reach same pressure
lower your fired brass a few tenths powder charge and look for same velocity as unfired brass should solve your problem

 

[Oklahunter1]

How many firings on old brass?

If my memory is good the old brass had 3 firings and the new brass had 0.

 

[Longtine88]

check your case volumes of the new brass vs the older brass. My bet is you gained volumed and changed your density and in turn changed your node you were on with your powder. Neck tension another cause. Fixed by annealing and a mandrel die to make them consistent. Lots of variable and welcome to reloading.

And what Can1010 said

 

[Rick Richard]

Ok. That may not be enough firings and resizing to hardened the brass, which could effect spring back on the neck. I Would then have to agree with can1010.

 

[lancetkenyon]

What cartridge?
If a belted magnum, you are drastically changing shoulder length between virgin and once fired brass.
Also, a lot to do with neck tension I am betting. New brass almost always has higher neck tension than FL sized.

 

[Longtine88]

I tried searching but I guess I don't know what to search for.
My question to the guru's is my groups change from using new brass to old brass. I full length size both my new and old brass. Use same load, same bullet(I weigh the bullets). My group size at 100 yds is 3/4" with new brass and 1.1" group with old brass. I have verified this doing it more than once. What causes this?
Thanks!

What brass are you using and caliber?

 

[Oklahunter1]

What brass are you using and caliber?

I'm using nosler brass with a 25-06 browning x-bolt.

 

[ChiefStone]

I'm using nosler brass with a 25-06 browning x-bolt.

Are you measuring how much you are bumping back the shoulder when you resize?

 

[Oklahunter1]

Are you measuring how much you are bumping back the shoulder when you resize?

No sir

 

[LRNut]

I always thought new brass gave reduced velocities, but last week I chrono'd some Lapua loads with new brass and got exactly the same velocity as old. FWIW, I anneal every time with AMP and use a mandrel, but that said, new brass always seems to have higher neck tension; perhaps that "evens" things out. Again, it was only one test.