barrel firecracking

[boiler_house7]

I was wondering if excess case chamber length will attribute to more firecracking in the throat area, or is more specific to the longer shot strings, powder, velocity? I have a 7saum with a little over 300 rounds through one barrel and the throat is cracked fairly bad at chamber case mouth. My reamer is cutting .020 longer than had specified and have around .035 case length to chamber clearance. running the 180's around 3025 with 4831 SC, 1.250 barrel. have ran several 15 round strings so don't know if this is part of it. I'm going to spec another reamer out and hopefully this one be right.

 

[L.Sherm]

I would suspect those 15 round strings are contibuteing to the fire cracking.

 

[Preacher]

15 quick ones out of a 7 mm SAUM sure won't do it any good....
A 7mm Weatherby is hard pressed to average over 3000 FPS with a 180...
Are you saying the reamer is cutting the chamber .020 longer than a normal 7 MM SAUM ?

 

[fdshuster]

boiler_house7: If the cracking you are seeing at the chamber mouth is straight-line linear in the direction of bullet travel, that is completely normal. That's where I see the first signs of usage. The alligator firecracking will soon follow in the leade area.

I see the straight-line cracking beginning around 700 rounds fired out of my 8 twist 6BR's, and around 1000 with the 308's.

 

[boiler_house7]

You hit it on the head, the cracking is starting right where a carbon rings forms going straight forward as you mentioned. The barrel is still shooting well but just was not for sure if the excess length would contribute more to cracking. My chamber length is 2.038 and case trim is 2.010. I had my reamer specified at 2.025. I think I'm going to look at a lower node and see if it will help with the longer strings. Just had my concern with a little over 300 rounds. I guess like the old saying goes got to pay the fiddler to play.

 

[Erik Cortina]

Excess chamber length is not causing the fire cracking, it's caused by the overbore cartridge pushing bullets that fast.

Change to a slower powder (H1000, Retumbo, N165, etc.) and slow it down some, it will extend barrel life.