Strange Custom rifle pressure issue.

[TikkaTac]

Not sure if this belongs here but here goes....

Here's the story. I picked up a used custom Remington rifle off the EE last year for what I thought was a good deal so I figured what the heck. This was during hunting season so I didn't have a terrible amount of time or ambition to take it out and play with it.

Here's the details on the rifle.

Rem 700 LA REP
B&C stock
24" Fluted KS Bbl
Cadex 2 stg trigger
Unknown Bottom metal
Cartridge - 338 Sherman Short mag (Basically a necked up and improved 7mmSAUM for those wondering)

Here's my problem. I researched load data online and found a lot of loads for 250gr Bergers, however, I'm using the Hornady 230gr ELDX. Now the consensus on best loads for the Bergers were using varget from 58-63gr charge at 2800-2880fps. This seemed absurd to me so I went another route.

Knowing the case is an improved SAUM and knowing a larger projectile will offer less pressure I simply used the load data for the standard 300SAUM of the same weight projectile.

So I started with N550 at 54gr. The brass in the photo is Brand new unfired with proper 338 Sherman Short headstamp. No indication as to manufacturer on the head so not sure about that. Bertram maybe??

Loaded up 3 rounds at 54gr using 215M primers and 230gr ELDX at .25mm off the lands.

Went to the range and fired a round. Looked at my chrony... 2820fps... That can't be right I said to myself... Let's try another.

That's when things got strange. The bolt was really stiff to open, like really stiff. Now I'm thinking pressure issue... Damn... Put on sad face, Packed up and went home to investigate.

I went through the entire rifle, cleaned it again. Bore scoped it. all looked good. So next step, disassemble everything and chamber cast.

Well, here's what I found in the photo below. Chamber cast compared to new brass. The substantial difference in the case head dimensions is what has me concerned. I feel like that's way too sloppy of a chamber??? or is it???

Here's what I think happened. When the individual was reaming the chamber the tool was not concentric to the bore and made an oversized chamber, As well it took a mere 15ftlb to remove the barrel from the action.

What are your thoughts?? Would this issue cause that kind of pressure spike? Is the chamber too sloppy? Is there something else going on I missed?

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[emerson]

Who did the chambering? The Sherman stuff is “known” by many to be BS, but that may not be the issue here.

 

[TikkaTac]

Who did the chambering? The Sherman stuff is “known” by many to be BS, but that may not be the issue here.

Not entirely sure. I looked back at my PMs but cleaned them out in the new year so I don't even recall who the gentleman was who I bought it from.

Maybe he'll see this post and come forward with the info of who chambered it.

As far as the sherman stuff goes, I just thought it would be a neat cartridge to mess around with. I would agree with you, looking back, I don't see much point in this cartridge. Especially in a long action..

In all honesty, I'll probably end up rechambering in 338WM and call is done.

 

[bearhunter]

This can be an issue with "custom" chambers.

This just might be a symptom of a reamer cut to maximum dimensions.

Once the cases are fire-formed, you should be good to go.

As for pressure, once that bolt gets sticky to lift, it's a pretty good sign your load is too hot for those bullets/cases back it off 5% and I'm willing to bet your velocities won't be that much different.

The cases you have on hand could easily be quite a bit heavier than those used for the tables you gleaned the loading information from.

From what I can see on your chamber cast, your rifle has a very short throat and the rifle used for working up loads for the tables may have had much more free bore, helping to keep pressures lower

 

[6.5 shooter]

Certain chamber casting mixtures are known to give inflated numbers as the mixture hardens. This may be what your seeing? Check the instructions on the packaging (Or phone the manufacturer) to be sure this is not the problem. IF not, then just fireform the brass and see what happens.

 

[Meroh]

I agree with what is written so far; drop your powder by at least 5% and work up.

Once brass is fireformed, check cartridge length and trim if required, then neck size only. Full length resizing could caust metal fatigue if the cases are a bit on the fat size, reducing their useful life.

 

[Eagleye]

.009" [.23mm] does seem pretty generous to me, but I have seen plenty of custom rifles with generous chambers.
I have also seen many with very tight chambers and short throats.
Your load is obviously too hot. The suggestion is sound....back off 5-6% and start there. Dave.

 

[TikkaTac]

.009" [.23mm] does seem pretty generous to me, but I have seen plenty of custom rifles with generous chambers.
I have also seen many with very tight chambers and short throats.
Your load is obviously too hot. The suggestion is sound....back off 5-6% and start there. Dave.

That's my thought. I feel like having that much movement at the base of the case is going to lead to case head separation much sooner than I want.

I'll do up some lighter loads and update once think warm up outside. I'm a fair weather shooter...

 

[The Lou]

That's my thought. I feel like having that much movement at the base of the case is going to lead to case head separation much sooner than I want.

I'll do up some lighter loads and update once think warm up outside. I'm a fair weather shooter...

I would be inclined to do a false shoulder on the neck to fire form, as well as back your charge down. I went through something of this nature on a custom once. I was getting the very bright line towards the case head when fire forming. Going to the false shoulder was a bit more work but, my brass was very much useable vs being ruined.