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Too much pressure, throw the cases out?

 
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  #1  
Old 08-17-2003, 09:50 PM
dwm dwm is offline
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Too much pressure, throw the cases out?

I have been shooting a 7MM RUM with 89 grains of Retumbo behind a 168 grain MatchKing. This is Hodgdon's minimum load for the 168 MK and Retumbo.

I have been experiencing a bit of pressure with this load. Ending up with a bunch of cases with extractor marks stamped into the case heads.

I have heard someone suggest filing the extractor mark off the case head. What is the case good for after that? 1/4 MOA, 1/2MOA, 1 MOA, Fouler shots, or toss it?

What kind of damage does the extractor mark do? Will it get stamped/flattened out the next time the case is fired? The case surely won't sit in the chamber squarely against the bolt face with that bump on the head.

The primers are backing out a bit and flattening also. Does this mean the primer pockets are oversize now? How can I tell? They seem to seat with a normal amount of force.

I am a bit curious about why the pressure is so high with the minimum load.

The cases are timmed to 2.840" each time and the shoulders are bumped with a Redding body die a bit so that headspace is maintained.

I know lot's of questions, sorry.

Probably should back down to 87 grains and start over. But should I throw out the cases too?

Doug
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Old 08-17-2003, 10:18 PM
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Re: Too much pressure, throw the cases out?

Doug,

As long as the primers take a little pressure to seat when new, the pockets are still good. At least to me.

If I threw out brass every time I got a flattened or cratered primer, my two favorite rifles would only be shooting virgin brass.

Retumbo is an odd powder. I keep hearing how one guy gets pressure signs, while another guy can shoot 2 grains more in a different rifle of the same caliber and get none. It's a good powder, if your rifle likes it, but it doesn't seem to like all rifles.

Tim
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Old 08-17-2003, 10:26 PM
dwm dwm is offline
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Re: Too much pressure, throw the cases out?

What if I can't get the cases in the RCBS TrimPro trimmer shell holder? I think some of the case heads have expanded some also, not all of them.

I filed the ejector marks down so they are pretty flat. That's not a real problem.

Tim, your shooting a 300 RUM or a 7MM RUM?

Doug
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Old 08-19-2003, 11:11 PM
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Re: Too much pressure, throw the cases out?

you can use either steel wool or fine sandpaper to take a little extra off the heads so they fit. when i was testing loads in my 300RUM i had ejector marks, cratered primers and expanded heads myself. as long as theres a little pressue while seating the primers, they shot fine. in fact, even the ones with easily seating primers shot fine as well, just needed 2-3 extra clicks out around 500-600 as compared to the normal ones. for finding out initial drops for my working load, they were good enough to get by.

-brian
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Old 08-19-2003, 11:16 PM
dwm dwm is offline
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Re: Too much pressure, throw the cases out?

Thanks, that's what I needed to know. I have 75 - 7MM RUM cases in this condition now.

Put them aside last night and started prepping some new brass. Got 25 trimmed to length, FL sized, and neck turned last night.

They fit much better in the trimmer shell holder than the ones with the ejector marks.

Doug
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Old 08-19-2003, 11:58 PM
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Re: Too much pressure, throw the cases out?

once you get everything figured out- drops, slight wind drift, etc, then i'd say ditch the old ones and focus on good brass, but for getting all the tweeks worked out, they're ok in my book. i have a bunch that i still shoot around 3/4MOA with as long as the primers hold a little resistance when seating. i think i'm on round 9-10 for them. the main thing to remember is you're going to lose a shade bit of accuracy, but keep that in mind, and you'll be alright.

-brian
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Old 08-20-2003, 09:49 PM
dwm dwm is offline
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Re: Too much pressure, throw the cases out?

Figured out where all the pressure was coming from. Think I was seating the bullets a bit long.

Took the firing pin out of the bolt to get a good feel for closing the bolt and then started working seating depth again. Last time I tried this I was using a Sharpie to color the bullets so that the land marks would be visible. Had a misreable time with the Sharpie. Wouldn't paint well at all on the bullet, etc.

This time I tried putting the seated bullets in a candle flame to coat them black with carbon. This worked great. Saw the land marks really great for once.

At an overal length to ogive of 3.120 I could see small land marks almost all the way around the bullet. Well I was shooting groups with the overal length to ogive of 3.131 and 3.136. This is at least 0.011 and 0.016 into the lands.

(I have a custom chamber reamed with a short freebore reamer so please don't use these dimensions for your loads. Check the length to ogive on your rifle.)

That could easily explain the high pressures with the Hodgdon recommended minimum load of 89 grains Retumbo. It didn't make sense that a minimum load should stamp the cases and flatten primers so bad.

I think someone on the site suggest I seat the bullets deeper and they were definitely right.

Thanks to who ever said that.

Anyway this time I'm going to seat them at 3.120 to ogive and start over again. Maybe even load a few with H50BMG just for fun.

Doug

[ 08-20-2003: Message edited by: dwm ]
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