rookie dealing with possible pressure signs

[skuna boy]

I'm new to reloading and long range shooting in general. I recently had a 300 rum put together and loaded some base loads up for it. Using Hornady reloading manual and a base load for 180 bullet, I got one casing that had 2 major dents/creases starting at the neck and running half way down to the base of the case.

My gun smith initially got a few pressure signs with factory ammo on the rim of the case, but he was able to adjust the head space and correct the issue and had no more pressure signs after that.


i think this was shot #8 of the day and shot a couple more times after this casing and didnt see any more issues.

I have searched and searched and have yet to find an example and explaination on the web.

Any ideas?

thanks,

 

[SpikeSniper]

S.B.-
I've seen similar results when I attempted to seat long bullets (VLD's, etc) to magazine capacity in large/belted magnums. In other words, a load that normally showed no pressure signs when seated to lands or jumped slightly has cratered shell casings when the bullet base was seated below the neck junction. Obviously deeper seating creates more neck tension and greater friction, therefore greater pressures. But typically you will experience sticky bolt lift, cratered or loose primers, or other pressure signs as well. My advice would be to start with lower charge weights and work up in .5-1 grain increments while watching for pressure indications. Keep in mind that just because a load shoots well from my rifle, it may not be safe in yours due to faster twist, tighter headspacing, etc. And primer selection, seating depth, neck tension, etc. can cause large increases in pressure within loads.

 

[skuna boy]

thanks I do plan on backing down on charge, but what concerns me with this is that the loads were loaded to factory ammo specs.

 

[bigngreen]

A picture of the cases would help!

 

[skuna boy]

not the best, but you can see the two identions.

 

[Nimrodmar10]

I've experienced the same thing with my 7 RUM. Only one so far out of about 150 shots. From what I have been able to find out searching the internet it's caused by the .400" of freebore used in the Ultra Magnum chambers. When the bullet is seated out longer than normal the neck of the brass does not seal the chamber and it allow the gas to flow back between the chamber wall and the brass collapseing the brass. Or at least that what the consensus seems to be. You can find about as many explanations as there are responders. I'd really like to talk to a Remington engineer about it.

 

[SpikeSniper]

SB-
There is a similar thread on this page with a 30-378 cartridge. There are several possibilities, but I would be willing to bet that you made a very simple and common mistake when you begin reloading. It looks to me like the crater starts just above the shoulder junction. You may be getting too much lube on your cartridge, or your die vent may be clogged during resizing. This will create small dents in the slope of the shoulder, which will allow a seep in pressure from the chamber into action. Pressure theoretically should push the case out against the chamber and prevent this from happening when all is well. But if there is enough gap in headspace for one reason or another, the result will be blow by and a deformed case as you have. I have made this mistake myself starting out. Often, the shoulder will just appear slightly dimpled. Try cleaning your dies with a fast drying solvent like gun scrubber and blowing them dry. Then only apply enough lube to the case sides to keep them from sticking. If there is extra lube on the shoulder or neck after you pull it outdryer running a dry case through but don't force it or it will stick. If that's not it, try cleaning your chamber. Debris or moisture in the chamber could cause the same issue. Keep me updated.

 

[skuna boy]

thanks for all the replies. I will look into all suggestions. I know the gun smith had to lengthen the head space a little to get rid of some pressure signs and accuracy issues so I'm thinking that may have more to do wit it.

 

[skuna boy]

I have dropped in powder charge and went from 210 bergers to 185's and this issue continues and actually gotten worse.

Next i will try some factory loads to see what will happens.


if it continues with factory loads, i'm going to be looking at sending the rifle in to someone for a look.

 

[justgoto]

not the best, but you can see the two identions.

I've always heard that collapsed case walls are caused by too light a load.
Need your input [Archive] - Benchrest Central Forums

Dennis Sorensen
11-22-2007, 10:49 AM

Yup - too light of a load... the case did not expand quick enough to seal the gases from leaking back a bit and collapsing the brass.

That amount of powder in such a large case does not seem appropriate. I am not familiar with loading for the STW nor that particular powder but it can be dangerous to use reduced loads in large capacity cases. Where did you get your loading data?

keithcandler
11-22-2007, 11:27 AM

Way below minimum load, slow burning powder, large capacity case.....all the ingredients for implosion.

It seems there are a few causes.
Strange dents in my brass. - AR15.Com Archive

OP, that is the classic sign of low chamber pressure. There can be multiple causes and combination of causes but the most common is too light of a bullet with a too slow burning powder.

Your bullet is too light for your chamber, powder, throat combination.

I think your fix may actually be the cause. Tell us all your specifics.

 

[Bart B]

My gun smith initially got a few pressure signs with factory ammo on the rim of the case, but he was able to adjust the head space and correct the issue and had no more pressure signs after that.

This doesn't make sense to me at all.

If headspace is changed to make it longer/greater, peak pressure will go down for a given load. If it's made shorter/smaller (setting the barrel back?), peak pressure will go up. But a few thousandths either way will not make any significant difference in peak pressure.

Note that that rimless bottleneck case is driven full forward in the chamber seating its shoulder hard against the chamber shoulder when the round fires. And the case shoulder stays hard against the chamber shoulder while the round fires. As the case expands from pressure buildup, its shoulder slides on the chamber shoulder sucking shoulder and neck brass back as the case body stretches back until the case head stops against the bolt face. This ends up making the case length shorter after firing.

By the looks of the case in the picture, there may have been a lube dimple in it before it was fired and peak pressure wasn't eough to flatten it out against the chamber wall. Your load may have been very much reduced.

 

[skuna boy]

the rounds I fired last were 88.3 grains of Retumbo pushing a 210 grain Berger with a CCI 250 magnum primer.....COL 3.65"......when I posted last I night I was thinking the 185 Bergers did this, but after going back and looking tonight it was actually the 210's.

I dont think there were any dented places on these casings from lube because since this was suggested as a possible cause in an earlier post, I was very careful and looked at each casing carefully after seating the bullet.

3 out of 5 of these rounds collasped.

should I try increasing the charge?

 

[skuna boy]

what about the primer? Could the CCI not be enough?

 

[justgoto]

88.3 grains of Retumbo pushing a 210 grain Berger

I would think that isn't too low a charge.

Here is what some others use in their 300RUMs, maybe that will help?

http://www.longrangehunting.com/forums/f28/300-rum-berger-210-load-data-73343/