Re: Annealing and Velocity Change
essentialy what happens say with factory 6mm BR Lapua cases as they are fired a few times the brass work hardens and they do not seel the chamber as weell some people then use a smaler bushing to get the same neck tension because of spring back, But the problem is that the brass also does not seal to the chamber wall like ti did when it was new so ytou can loose some small amount of velocity. if you anneal the cases you should then regain the same velocity and seal as the factory brass they will not go faster.
The thing with neck tension if you have some that have less tension than others all sized the same and all measuring the same loaded diameter the only diference is the maluability of the brass this is the ability for the brass to form. The harder the brass the less likly it will seel to the chamber and will allow some gasses to flow back towards the boltface.
You can see this also with underloaded cases their is not enough pressure to seel the necks so they are black and sometimes they can actualy colapse the shoulders of the cases inwards. if tyhe cases afre old this cazn occour with starting loads that are not unsafe. I have then annealed cases for some of these tests and geus what the cases sealed and the velocities increased dramaticaly and the extreme spreads and standard deviations shrunk dramaticaly.
Having said that i dont think you have to anneal every 2 or 3 shots but some shooters swear by it and have shot world reccords doing this. i have 6mm dasher cases that have neen fired 30 times and never annealed they only have a total of 1.5 thou clearence so their is less case working and i just shoot them until the primer pockets are to loose then they get ditched. then i have short mag cases i anneal them when forming them as i push the shoulders back and fireform them to my own case dimensions and then will anneal every 5 shots because of the neck thicknesses.
I also have a factory spec chamber reamer for a 7mm rem SAUM i use for F Class after shooting near max loads the case necks are black and i dont want to load them hotter actualy i would have to go to a faster powder because it is already compresed. Now i have fired them twice the first and second times the 1000 yard elevation was 2", I fired the same cases, primers, powder and packet of projectiles on saturday and had 6" elevation so i went home annealed the cases and reloaded them again shot on sunday back to 2" elevation.
I also had chronographed both the annealed and twice fired cases and the annealed cases had an es of 5 the others on the 3rd firing had an es of 38 and were on average 54fps slower.
Neck tension had nothing to do with it as in all cases the projectiles are hard jammed into the lands.
Just in case people think i just hear about these things and have no qualifications i am one of very few people in Australia that has a private firarms licence indorsed for Ballistic testing. I wortk for a gunsmith here and conduct most new calibre development and testing as well as designing my own calibres andhave 4 registered calibres with the police on the Australian firarms and ammunition template. I also write technical articles for Australian target and hunting magazines. And was involved with all of the ballistic testing in a family buisness that was a custom loading company that hand loaded millions of rounds of ammo from 17 hornet to 50BMG including target ammo for commonwelth games gold medalist full bore shooters and big game ammunition for use in Africa where any problems can end in the shooters death and hundreds of thousands of rounds of 308 and 223 for freal pest destruction, the 308 ammo was required to function in semi auto's shooting straight down without any malfunctions from a helicopter.
On top of this i am one of the top Open F Class shooters here in Australia.
So i think i have a bit more knowlidge than most in this department.
Hope this helps but the bottom line if you think your loads are good and your velocities are eratic try to anneal the cases it can help especialy if you have a factory chamber with a larg amount of neck clearence.