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

 
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Old 02-22-2012, 09:56 PM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

All my brass is fired in cycles of 50, so all the cases right now are on there second fire.

I havent been keeping track of how much Im bumping the shoulder back, simply because I dont have the tools to do it really accuately. Do you guys just eyeball up the shoulder line and thats what you go with?

I think that the shoulder bumping could be the problem, I was always taught to run through a FL Die each time for reliable cycleing, but I think Im gonna start partial FL sizeing bumping back very little. What would you guys suggest for bumping back?

Though its a good suggestion, I doubt that the rounds are being cooked. I developed the load in +35*C and was shooting the loads three weels ago at -20*C leaving the bolt open between shots, and never shoothing back to back more than two rounds (I leave it sit for about 5 min between when its cool out, if its warm 15 min).

Thanks for the help guys, I appreciate it. Im gonna get some better reloading gear in time.
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Old 02-22-2012, 10:20 PM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

I make a dummy round with the proper setback so I can be sure the die is set correctly each time. I usually compare a case that was shot through my gun, in your case one that wasn't giving you a heavy bolt lift, and a sammi spec case I have for my OAL gauge and then determine where I want my setback to be. Then I make the dummy round from there.

Scot E.
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Old 02-23-2012, 08:43 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

If you are full length sizing I doubt it is a shoulder problem. I have seen this happen with cases that were getting long on the shoulder, where it was time for a shoulder bump. But these cases also closed a little stiff too. Most lesser expensive dies do plenty of shoulder bump to be sure to cover a wide varience in chamber dimentions. If your rounds are chambering and the bolt closes easy and smooth I would be looking at the powder or charge. Like Autorotate and I sated earlier. This is pretty common with running Retumbo at or close to max. There is a fine line with a spike just waiting to happen. I would drop back 3 grains or so, or look at loading some H-1000.

Jeff
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Old 02-23-2012, 09:36 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

If your pushing the bolt forward and hearing a click and the problem is gone it sounds like a pure mechanical issue to me, try cycling some cases through after sizing and see if you have one fail to extract that may help narrow it down.
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Old 02-23-2012, 09:39 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

Quote:
Originally Posted by bigngreen View Post
If your pushing the bolt forward and hearing a click and the problem is gone it sounds like a pure mechanical issue to me, try cycling some cases through after sizing and see if you have one fail to extract that may help narrow it down.
Yeah, good suggestion. This crossed my mind too. If the front action screw is a bit long it can touch a lug and cause a hardspot and click at the top of bolt lift. But that usually does it every time.

Jeff
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Old 02-23-2012, 09:48 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

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Originally Posted by Broz View Post
Yeah, good suggestion. This crossed my mind too. If the front action screw is a bit long it can touch a lug and cause a hardspot and click at the top of bolt lift. But that usually does it every time.

Jeff
Ohh I like that one, gotta remember that!!
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Old 02-23-2012, 09:55 AM
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Re: .338 RUM with 300gr SMK and Retumbo... over pressure?

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Originally Posted by bigngreen View Post
Ohh I like that one, gotta remember that!!
Yup, last 7mm-300 did it. Could easily be confused with a hard bolt lift. Just a few thousands polished off the front screw, smooth and hard spot gone.

Jeff
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