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7mm STW - Low Pressure??

 
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  #1  
Old 07-23-2012, 09:39 AM
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Join Date: Jul 2012
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7mm STW - Low Pressure??

Hey guys. I have been a long time reader at this site but this is my first post.

Yesterday I was at the range and started load development in my 7mm STW shooting 168gr Berger VLDs.

The first batch of loads I was shooting I was using RL-25. The maximum charge Berger recommended was 75.3 grs. I started lower and was working my way up. At 73.0 grs I started to get alot of burnt powder residue all the way down the casing. With 73.5 grs I had 2 cases where there was a large dent in the shoulder (the dent was running vertically). Unfortunately I wasn't running these loads across a chronograph so I am missing that piece of the puzzle.

What would be the cause of this? Low pressure?

I was checking each case after firing and I didn't have any flattened primers or sticky bolt lifts.

I was using CCI 250 Magnum primers, Remington once fired brass.

To touch the rifling with the Berger in my rifle the COAL is 3.865" but to have them fit in the magazine I had to seat them at 3.660". Would this have something to do with the issues I was having? I know Bergers like to be seated alot closer to the lands but I just wanted to try jumping them this far to see how they shoot in my rifle.

Does anyone have any insight or past experience with issues like this?
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  #2  
Old 07-23-2012, 06:45 PM
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Join Date: May 2012
Location: N.D.
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Re: 7mm STW - Low Pressure??

Quote:
Originally Posted by PaHuntin View Post
Hey guys. I have been a long time reader at this site but this is my first post.

Yesterday I was at the range and started load development in my 7mm STW shooting 168gr Berger VLDs.

The first batch of loads I was shooting I was using RL-25. The maximum charge Berger recommended was 75.3 grs. I started lower and was working my way up. At 73.0 grs I started to get alot of burnt powder residue all the way down the casing. With 73.5 grs I had 2 cases where there was a large dent in the shoulder (the dent was running vertically). Unfortunately I wasn't running these loads across a chronograph so I am missing that piece of the puzzle.

What would be the cause of this? Low pressure?

I was checking each case after firing and I didn't have any flattened primers or sticky bolt lifts.

I was using CCI 250 Magnum primers, Remington once fired brass.

To touch the rifling with the Berger in my rifle the COAL is 3.865" but to have them fit in the magazine I had to seat them at 3.660". Would this have something to do with the issues I was having? I know Bergers like to be seated alot closer to the lands but I just wanted to try jumping them this far to see how they shoot in my rifle.

Does anyone have any insight or past experience with issues like this?
I'm shooting 75.0 of rl25 in my 7stw with the 171 barnes matchburner, a 215, and rem brass and it's just fine at 3.685" oal.. I'm getting 2950 fps and .3" groups at 100 yards from a 24" barrel. It doesn't like hot weather to well, but no overbore does. I've taken the 171 to 78 grains, but it got a bit warm pressure wise, not high pressure, but the accuracy was gone. I had started at 70 or so and jumped at least a grain per group 'till I found the 75 grain load.
It sounds like with that bullet you either aren't developing enough pressure, or aren't getting a good seal at the neck of the chamber. You said you are using once fired brass, what is the neck condition; have you turned them, annealed them, etc. Sometimes a factory chamber doesn't like brass with worked necks. Low pressure when the bullet leaves the case from mild ignition can cause this too.
The last time I saw that I was playing with my 300 win with 125 grain nosler bt's and 4895 with a cci 250. It was cured by switching primers to a 215 and going to a slower powder(rl19) with better case fill, but rl25 should be fine here.
Post on the stw brotherhood thread for other's ideas on this. From what you've said, this should be a good load.
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  #3  
Old 11-03-2012, 09:16 PM
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Join Date: Nov 2012
Location: East Central Ks.
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Re: 7mm STW - Low Pressure??

Sounds to me like the case was pushed too deep into the fl resizing die & pressure went around the case to dent it inward.!! Not a good situation.
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  #4  
Old 11-04-2012, 01:14 PM
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Join Date: Feb 2008
Location: IOWA
Posts: 1,874
Re: 7mm STW - Low Pressure??

Quote:
Originally Posted by seedfarm View Post
Sounds to me like the case was pushed too deep into the fl resizing die & pressure went around the case to dent it inward.!! Not a good situation.
Agreed.
Try to neck size only,and only bump the shoulder .001-.002 if you resize.
Try single feeding with the bullets seated on the lands to see if that helps your soot problem.
When I was running an STW, I used a wyatt box to be able to seat closer to the lands.
I was using Retumbo with no problems.
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