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.338 RUM with 300gr SMK and Retumbo... over pressure?

 
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Old 02-21-2012, 11:14 PM
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.338 RUM with 300gr SMK and Retumbo... over pressure?

The senario is I have a factory .338 RUM (XCR) that shoot stupid good. Ive actually been trying to justify re-barreling it but just cant...if it aint broke dont fix it. It shoots three SMK's into under 3/4 MOA at its worst, usually much better.

The problem is I believe the load that it likes is HOT. Im running 94 grains Retumbo with CCI 250's and 300 SMK's at 2800 (3000 ft. elevation). There is not sign of flattened primers and I get five loadings of the cheap Rem brass.

I suspect over pressure because of a slightly sticky bolt, but its not really sticky. It seem more like mechanical lock up, and it only does it every 6-7 shots. the bolt needs a little nudge forward, but then it extracts perfectly. The bolt isnt hard to lift, or even sticky as long as I push the bolt forward a bit. and when I do I can feel a very slight click.

So is this a mechanical problem with the extrator hanging up, or am I way over pressure causeing the bolt to set back?
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Old 02-22-2012, 12:18 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

94 of retumbo is a good load for the 338 RUM and I have used it often. 93-94 grains is actually my best load for it. Retumbo always did better for me than H-1000 in the 338-300 RUM and the 338 RUM. 94 grains is a max load but not dangerous in the rifles I have shot it in. If it is shooting good I would stick with it. It shouldn't cause the sticky bolt but could in some rifles because it is right at max. I guess you could try a few groups at 92 grains and see if the sticky bolt stops. Then you will know for sure. That load shoots fine in my rem 700 factory rifle. Your velocity is right in there for the cartridge. With a 26" barrel factory rifle 2725-2775 fps is average with a few that do better at 2700 and some better at 2800 fps.
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Old 02-22-2012, 09:25 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

Thanks LTLR,
I did actually down load it to 92grains and found I had the same problem, just not as often. I figured that it wasnt over pressure by too much and have been hunting with the load for awhile, but thought I should ask just in case. Thank you, I can go press up some more without concern.
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Old 02-22-2012, 09:32 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

Quote:
Originally Posted by angus-5024 View Post
It seem more like mechanical lock up, and it only does it every 6-7 shots. the bolt needs a little nudge forward, but then it extracts perfectly. The bolt isnt hard to lift, or even sticky as long as I push the bolt forward a bit. and when I do I can feel a very slight click.

So is this a mechanical problem with the extrator hanging up, or am I way over pressure causeing the bolt to set back?
The " only every 6-7 shots" tells the story for me. Although I like Retumbo, I have found this to be a character trait of this powder. Especially prevelant when running close to max and is aggravated durring a range session where the chamber is warm. This is why I left Retumbo for H-1000. You can get a very accurate and more consistant load worked up with H-1000. Start at 89 gr and work up in 1/2 gr increments. Your extractor in your Rem 700 is only going to put up with this for so long. Next it will most likely start leaving cases in the chamber and a rod will be needed to remove them. If it seems wrong it usually is. If any form of force is needed to extcact a case or release a bolt there IS a problem. These are not the kind of things am willing to risk an trophy on.

Jeff
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Old 02-22-2012, 11:13 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

Just like Broz posted....I agree...It may very well be a temp sensitivity thing with Retumbo. Actually it's my experience Retumbo and H1000 share very similar temp resilence properties, but Retumbo does go "super nova" (sometimes in as little as .5 to .75 of a grain) when you step over a certain threshold. The heat soak of the 6th or 7th round might be just enough to push you over that edge your riding with your lot of retumbo and this load with your rifle.

I'd look at a change in velocity when shooting that "hot" 6th or 7th round, and measure the case web diameter just north of the extraction groove, and see if you don't see some correlation with pressure before you gave up on Retumbo though.

Your post about not seeing an extractor mark, or any cratering primers is conflicting.... but you might not be seeing enough pressure for those overpressure indicators.

Grab a chrono and a set of calipers next time your out....see if those don't point to pressure.

If not, maybe look elsewhere....example....How much are you bumping the shoulder? What type of sizing are you doing?
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Old 02-22-2012, 01:47 PM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

Quote:
Originally Posted by Autorotate View Post
How much are you bumping the shoulder? What type of sizing are you doing?
This shouldn't be overlooked. I just helped a guy get a bit more consistent on his reloading and found that he was having a similar issue as to what is described by the OP. Come to find out he wasn't keeping very good track of his casings and was loading some cases that had been shot just once while some others had been shot 5 or 6 times. Needless to say he wasn't setting the shoulder back and the multiple reloaded cases were causing a heavy bolt lift which he thought was a pressure sign. After getting things fixed the issue went away.

Scot E.
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Old 02-22-2012, 05:00 PM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

Guys have been seeing a difference with old h1000 and Retumbo, having to download a few grains, seen it posted a few times lately. Versus new lots
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