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300 RUM - Pressure Problems

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Unread 12-19-2010, 01:42 PM
Junior Member
Join Date: Oct 2010
Location: Elizabeth City, NC
Posts: 11
300 RUM - Pressure Problems

I have sent old Bessie to the gun doctor, still running into some type of pressure or head space problems.

Tried working up loads with RL- 25, Retumbo and Magnum, started off at min loads and every primer is cratered heavy which is an improvement over the flat primers that started growing lips and rims of their own two weeks ago.

I started out with 180 gr Accubonds, and may have had them set a tweed to long two weeks ago, however the last batch I ran were 200 Accubonds O.A.L. 3.600, Fed 215M in a 300 Rem Sendero 26 in bar. all three powders listed above min loads cratered hard. Cant get this out of the starting block.

The smith looked at a sample of fired casings, said it was pressure and not from head space problems although he has not really gotten that far yet , guess when he starts on the action the truth will come out.

I doubt the chamber is bench rest tight however after inspecting some fired rounds I found two sets of chamber marks printed on the cases a quarter to half inch a part a full 360 degrees. After looking at the chamber mouth, unless they have changed manufacturing procedures, looks like to me that someone at the factory either used a reamer on one to many barrels, reversed it or plain stuck it.

If it's not head space , not sure what the next step is, I can't see three different powders running hot on the lot.

Anybody got any suggestions or had similar problems sure could use it.
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Unread 12-19-2010, 01:54 PM
Platinum Member
Join Date: Jul 2004
Location: OHIO
Posts: 2,417
Re: 300 RUM - Pressure Problems

My 300 RUM was chambered by Shilen and it must be a tighter chamber because a lot guys talk about getting over 90 gr of Re25 with a 200 AB. Max in my rifle is 89.0 gr.

I had a Lilja barrel installed on a rifle by a smith who didn't check the chamber. There was a CHUNK of metal out of the chamber and it left a good bump on the brass, making it near impossible to eject shells. Apparently, this is due to the type of steel Lilja uses according to some other rifle builders I've used. I've heard a few stories now where his barrels have done this type of thing.

Sounds to me like the manufacturer did not chamber your rifle very well. Send it back.
Derek M.
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Unread 12-19-2010, 07:48 PM
Bronze Member
Join Date: Nov 2010
Posts: 65
Re: 300 RUM - Pressure Problems

My 7mm Rem Ultra Mag does show pressure signs with factory remington ammo. Havn't had any problems with handloads though. Maybe my handloads are minimum, I'd have to go look at my records...

I always thought it unusual the primers were so cratered and a little ejector-mark on the case-heads with factory ammo, but I just figured it was hot, new caliber and they loaded the factory stuff at max I guess...
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Unread 12-22-2010, 02:31 AM
Silver Member
Join Date: Jan 2009
Posts: 139
Re: 300 RUM - Pressure Problems

I'll throw one out of left field..Is it a Remington 700 which I assume it is >>

How much slop is around the firing pin hole? I had the same issue with my Edge. I have had the pin rebushed/ re done and made smaller similar to the Lawton firing pin size spec.
Eager to try it after Christmas...lets see if it can shrink my group size to 1/2 MOA at 300!
Mine was a brand new cut chamber and it was doing this with low pressure loads.It was a used 2nd hand 300rum! My action is fully blue printed and bolt has been retimed etc..

My gunsmith has seen group sizes shrink dramatically in F class .308's so he thought he would give mine a go.. Mind you he has won Gold in Full bore events on the World stage!

Just a thought.. this is what we here down under suspect onmy rifle .. worn sloppy pin!
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Unread 12-22-2010, 09:56 AM
Junior Member
Join Date: Dec 2009
Location: Nebraska
Posts: 6
Re: 300 RUM - Pressure Problems

I'm going to kind of agree with what has been posted already. I've got a 700p in .300 rum. that showed craters with Rem. power level 1 factory ammo. This is that stuff that is reduced recoil etc. The next thing is that I had problems with dented cases when I switched to rem. mag primers from winchester. After I studied the dented cases more I coud tell from the "smoke" on the case around the dent it was a LOW pressure problem. Those cases have the same cratered primers. I'm thinking it's just a overly large firing pin hole.
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Unread 12-22-2010, 11:31 AM
Junior Member
Join Date: Mar 2009
Location: Travis AFB California
Posts: 11
Re: 300 RUM - Pressure Problems

I have had my 300 RUM for 5 years now and love it. I sent it to COR BON ammo a few years ago and had them work up a load for it. I am shooting the 180 gr. TTSX bullets at 3200 = FPS. Thats using Rem brass, Rem primer, and 96 gr. of H Retumbo powder. I have a plain 700 BDL with no work done and it and I have not seen anything wrong with any of mine, so hopefully it is something with the gun and the Mfgr. will fix it.
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Unread 12-22-2010, 03:59 PM
Silver Member
Join Date: Jan 2009
Posts: 139
Re: 300 RUM - Pressure Problems


My Edge is doing it with low and warm loads...the only way to check pressure is to measure the case expanion... Tried 90 to 94 gn of H1000....300 gn SMK's

Shoots really well though! No extractor marks yet. 94 is kind of max in most Edges..

It does it with Nosler brass and 250gn pills as well..

I'll report back after christmas how the firing pin mods went!

For my next build I will be going a custom action or Howa .

Benchmark APS carbon barrell is being shipped in January,, 300 rum or 300 Dakota is on the cards.
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