barrel throat wear on new barrel

[babyrou]

I have just completed barrel break in, load developement, + sight in of new broughton 5c barrel in 300 ultra mag. 80 total rounds fired. Bullet ogive to lands was originaly set @ .010 jump to lands. After 80 rounds I now have .020 jump to lands. Or about .010 throat wear in 80 rounds. Does anyone consider this excessive or should I consider this normal? Will throat wear slow down? This particular barrel produces 3 shot groups @ .428 outside to outside @ widest point no matter were I seat the bullet. Have tried seating into lands .005, jump to lands .005,.010,.015,.020,.030. No matter what I give it I am extremely pleased with accuracy. Just concerned about that much wear with 80 rounds. Load is 95.5 grains retumbo, 180 swift Sirroco @ 3350fps. Any opinions appreciated.

 

[mikecr]

How much time between shots?

 

[Spotcheck_Billy]

That's a lot of throat wear for only 80 rounds down the tube, but it's quite possible that it's normal for a .300 RUM!

Just for comparason, I started a new Pac-Nor fast twist .243 barrel last summer shooting 115gr. DTAC's with hot loads of Re25,3050fps MV) and the throat moved .005" after the first 230 rounds. A hot loaded .243 is supposed to be a barrel burner, but I'd imagine it to be no where near a .300 RUM.

 

[babyrou]

First 5 shots 4 hours in between shots[to clean barrel], next 10 shots 3-4 minutes between each shot[2 shots then 4 hours, 2 shots then 4 hours to clean barrel. Next 15 shots 3-4 minutes in between shots [5 shot group then clean aprox. 4 hours between 5 shot groups] All others 3-4 minutes between each shot then a 15 minute cool down time after every 3 shot string. Barrel never got to warm @ any time to put any part of it against your face + hold it there tight with any discomfort.

 

[techshooter]

If the barrel was brand new - just chambered - when the seating depth was measured/set, then this amount of change in 80 rounds is not that unexpected in my experience. I believe that this is due to the very fresh tooling marks and resulting roughness on the new throat leading to the bullet not going in as far to first contact as when the throat is smoothed out after a few rounds. My 6 Dasher moved about 0.015" in the first 25 rounds, then hardly at all over the next 300.

Hope that this helps

Cheers,