Rifling Deterioration?

[highfinblue]

This is a 7stw using N570 and Berger 195's.
Knowing the powder eats barrels, I measured the throat at 80 shots, then measured again at 432. I burned away .100" of the throat in those last 350 shots, never firing more than 2 then using the chamber chiller. I rarely shoot more than 15 shots in a range session.
At 432 I set the 195's out to the new lands ( 3.275 CBTO ) then pulled back .020". With the extended throat I finally got the boat tail above the case neck/shoulder jct, then I re shot my powder charges to see how bad it was going to be.

This rife has never produced the 3 shot groups seen at 81.5 and 82, which have been replicated. So far, it seems the bullet placement in the case has more influence on this rifles groups than fire cracking and throat erosion.

View attachment 628016

I know it's apples and oranges, but my 28 Nosler loved 81.5 grains of N570 and Berger 195's. Don't know much about an STW, but I find that kind of odd. No other load comes close in my 28, 0.020 off lands. I'm at around 200 on the round count and it really is a tack driver. I only use it to hunt, so hopefully it will last a while. I have lots of littles and a 7 PRC to shoot often.

 

[WapitiBob]

I know it's apples and oranges, but my 28 Nosler loved 81.5 grains of N570 and Berger 195's. Don't know much about an STW, but I find that kind of odd. No other load comes close in my 28, 0.020 off lands. I'm at around 200 on the round count and it really is a tack driver. I only use it to hunt, so hopefully it will last a while. I have lots of littles and a 7 PRC to shoot often.

This last bullet position within the case neck is within about .005" of a cpl top end 28Nosler rifle builders configurations. Could be a fluke but I'll take the results. It won't last very long as hot as this powder burns.