Once fired brass vs New brass

[355sigfan]

I got some new Lake City brass and loaded my pet loads that are usually .65 to .75 moa and the loads opened up to 1 to 1.2 moa. I then reloaded the same loads in once fired Lake City brass and they shrank right back down. I use dillon carbide dies that full length resize. Whats causes this accuracy difference. Is it because the once fired cases fit the chamber better?
Load with Once fired Lake City brass I purchased. (good)

Loaded with new Lake City (Bad)

Loaded with Lake city brass that was new that I fired and reloaded (now once fired) (good again)

So do you guys only use once fired brass for your reloads or is this an issue with certain brass vs other brands?

 

[shoepop]

Re: Once fired brass vs New brass

My bet new batch had bad run out once fired now straight "fit the chamber better" and back to normal. I see this all the time. You have to shoot once to get once fired.

 

[TexIndian]

Re: Once fired brass vs New brass

With a bolt gun and neck sizing, I'd say the once-fired fits your chamber better. But with an auto-loader like the stealth (assuming full length resizing), I don't see that as the answer unless you are carefully setting your head space to fit the gun's chamber. I usually think of that as a means to extend case life rather than an accuracy thing, but it might factor in somewhere.

Are you running the new brass through a sizer before firing? That would eliminate any issues like the one Mark 5 mentioned - irregular new brass.

 

[5R Milspec]

Re: Once fired brass vs New brass

it could be the case of neck tention.the older brass has gotton hard in the necks.and the newer brass thats softer giveing the necks a better grip on the bullet.

I would anneal some of the older brass to see what happens.