300RUM cases denting in after firing

[Rustystud]

The attached picture is a 300RUM after being fired with 90.gr Reloader 25 and 180 Nosler Accubond. The chamber is clean and to spec. No defects or trash in chamber. This doesn't happen with every shot. It happens approximately every 8th to 10th round being fired. The rifle has a 26" 1:10, 5R barrel with muzzlebrake. The rifle shoots .5moa but slow, 3100 fps.

 

[Eddie Harren]

I have seen this happen, in large capacity cases, when the powder charge is too light.

 

[Minesweeper3433]

Are you seating long or seating to sami depth?

 

[Rustystud]

SAAMI Spec chamber and cases.
Nat

 

[XTR]

SAAMI Spec chamber and cases.
Nat

It looks to me like you are getting pressure back past the neck. I've seen something similar once in my 308 when I had a partial case head separation and the outside of the case was deformed in. In your case it looks like the neck isn't sealing allowing pressure back to the point that the case is sealing the chamber.

What is the chamber neck measurement? Is it too large for the brass you are using?

Anneal?

As another poster commented with the large boiler you may not be getting enough pressure to expand the case firmly against the chamber and seal it off at the neck. Considering the cartridge you are running maybe you need to take it up to the next node. I don't load magnums but isn't 90gr in the range of a 300WM load.

 

[dragman]

I think load is too light. I have shot a lot of RUM's and I have never had one that didn't shoot well and with at least 88 grains of powder and I don't go below 210 grains of bullets. should add I seat them long but I gotta think that load is light.

 

[wapiti25]

I have saw dents like that on low pressure loads. you may need to anneal to a softer state in the neck shoulder area. I was working up a reduced recoil load for rapid fire and saw the shoulder's dent, by going up in the powder charge they went away.

 

[dkhunt14]

I have seen two things that caused this. One was cleaning fluid in the chamber and the other was too light of load and they didn't seal off the chamber. Might try annealing a couple. Matt

 

[ShootDots]

I had EXACTLY that happen on my 1st 6.5 x 284 barrel. I had enough throat wear that before the case neck expanded to seal of the gases from escaping, some would escape.. Not only would it "dent" the case, but black soot would be found on the case body. I am sure there are other reasons for this phenomenon, however, mine were full power charges! I simply had too much throat erosion. I know that sounds "silly / not possible" but I guarantee you that very thing happened to me. With a R.U.M. it would not surprise me to see that sort of thing happen around 700 rounds..

 

[Ragnar]

Gonna jump in and say Yes along with the previous replies. I shoot a
300 RUM and the level 1 ( low power) rem brass baged at least 4 cases out of the
100 I bought and fired for the brass. There is some truth in the freebore being
Way long in factory barrels.seemed like those 150's were a foot from the lands. I found great groups and no more dented brass When burning lots of retumbo and barely jumped 210 hunting Bergers or 240 smk's.
Best of luck
Shawn

 

[ebb]

Aliant's load data page lists a load for 300 rum with a Speer 180 gr at 94 grains and 3146 fps. They don't list a min and max just the one load. So I don't see you being to far off on the load. At least not enough to get a problem like the picture. This must be some very small issues stacking up to make a bigger problem. Ive shot a 300 rum since 2004, every one in our group had one back then, never seen any thing like it.

 

[Dgd6mm]

Nat, I ran your load on QL without any defaults, and it said that at an OAL of 3.598 the pressure is 62,651 psi. and FPS 3097. With this kind of pressure it should not be an under charge issue. I've owned 3 of them over the years and still have 1 and have loaded them from lite to heavy and never experienced this.

 

[LHSmith]

FWIW. My load for a Rem. 700 custom shop 300 RUM is 97.0 gr. of Rel. 25, 180 gr. Ballistic Tip, Fed.215, R-P cases which show no over-pressure signs (only shot in cool to cold conditions). In fact some cases have been loaded 6x ( w/o annealing) with no problems.

 

[dkhunt14]

I don't have a 300 RUm but the guys I hunt with all have them. They shoot pretty much year round to practice for out west. I have seen them shoot out to 1000 yards and seen the guns chronographed. All of them shot around 3200 with a 210 Berger. I think the load is light. My 30-338 Win MAG will shoot 3100 with a 180 Ballistic Tip. Matt

 

[Julien]

The gases are getting by the neck so it appears there is not enough pressure to keep it sealed .
I have seen a lot of case head seperations cause the exact same thing .
Maybe like a few others said annealing the necks or maybe more neck tension to build up the pressure.
Another possibility might be trying diferent primers.