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Having trouble getting my 7 LRM to shoot

 
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  #1  
Old 10-21-2013, 09:48 PM
Bronze Member
 
Join Date: Feb 2010
Posts: 88
Having trouble getting my 7 LRM to shoot

I'm having some trouble getting my 7 LRM to shoot like I want it to.
The specs are:
Bighorn action
Broughton barrel with 1-8.4 twist
McMillan stock
Jewel trigger
Nightforce 5.5-22x56

I'm trying to get the 180 berger hybrids to shoot using H1000. I started out with 72 grains since thats what everybody else seemed to be using, but I'm getting pressure signs until I get down to about 71.4 grains. I've got them seated about 20 thousandths off the lands. It shot the best with 72 grains but it had a pretty hard bolt lift.
Has anybody else had trouble getting the 180 hybrids to run? I'm going to try some different bullets, but would really like to run the hybrids.

Here's a picture of the target. Its at 200 yards.
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  #2  
Old 10-21-2013, 11:20 PM
Silver Member
 
Join Date: Jan 2013
Location: Southeast Kansas
Posts: 185
Re: Having trouble getting my 7 LRM to shoot

Gunwerks factory ammo for 7LRM is 72gr H100 with a 180gr Berger Hybrid. They seat them .080 from the lands, yes you read that correctly. Try using 71, 71.5, 72gr of powder at .080 back and just see what happens.
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  #3  
Old 10-22-2013, 05:15 AM
Platinum Member
 
Join Date: Dec 2005
Location: Tucson Az
Posts: 1,279
Re: Having trouble getting my 7 LRM to shoot

First off I am sorry to hear of your problem. Many of us have gone through the agonizing process of trying to figure out why a rifle won't shoot. Perhaps one of the members here can help you solve things.

If this is a new rifle you might want to go through a checklist of possible issues before you continue to shoot. Regardless of who built the rifle or how good the work sometimes small things slip by.

I ended up putting a checklist in my documents to refer to when a rifle doesn't perform as it should:

If any action screw holes are blind holes check for debris or bedding material in bottom which can cause a false tightness
Action screw bottoming out in blind hole by being too long
Holes for action screws too small allowing screw to touch sides of hole
Action screws improperly torqued


Forward most scope base machine screw touching threads of barrel causing a false tightness
Leupold windage style base, windage screws not tight

Bolt handle touching stock
Mag box must not bind
Uneven bedding--- tighten one action screw at at a time to see if the action pulls up at other end.
trigger group must not touch stock
Trigger guard must not touch trigger

Clean bore and good crown

-------------------------------------------------------------

I am very interested in how you solve your accuracy issue. Will be watching this thread.

Hope you can solve it easily.
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  #4  
Old 10-22-2013, 08:31 AM
Silver Member
 
Join Date: Feb 2009
Posts: 474
Re: Having trouble getting my 7 LRM to shoot

.080 seems like a ton of jump.? I have had all my rifles shoot the best with .002 to .004 jump with Berbers. Not saying you are not correct, just trying to understand how they are getting such great results with so much jump. I also found out I have an easier time picking out a "in the middle" powder charge and adjusting my seating depth starting .002 off lands and moving in .002 increments. Once group shrinks to a group that is close to expected I then adjust powder charge until it is a horizontal masterpiece! I shoot all group at 200 yards to easier see groups.

I'm no expert at all this has just worked for me
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  #5  
Old 10-22-2013, 08:33 AM
Bronze Member
 
Join Date: Feb 2010
Posts: 88
Re: Having trouble getting my 7 LRM to shoot

Thanks for the info. I didn't know they were seating them that far off the lands. I'll try that.
Thanks for the checklist too. I'll try all of this and let you know how it turns out.
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  #6  
Old 10-22-2013, 08:34 AM
Gold Member
 
Join Date: Mar 2006
Posts: 848
Re: Having trouble getting my 7 LRM to shoot

Try retumbo... Should get more velocity and less pressure as well as better time pressure curves for that cartridge.
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  #7  
Old 10-22-2013, 09:19 AM
Silver Member
 
Join Date: Jan 2013
Location: Southeast Kansas
Posts: 185
Re: Having trouble getting my 7 LRM to shoot

Quote:
Originally Posted by TrophyHunter_colorado View Post
.080 seems like a ton of jump.? I have had all my rifles shoot the best with .002 to .004 jump with Berbers. Not saying you are not correct, just trying to understand how they are getting such great results with so much jump. I also found out I have an easier time picking out a "in the middle" powder charge and adjusting my seating depth starting .002 off lands and moving in .002 increments. Once group shrinks to a group that is close to expected I then adjust powder charge until it is a horizontal masterpiece! I shoot all group at 200 yards to easier see groups.

I'm no expert at all this has just worked for me
I totally understand your questioning that, the same goes for me. My 168gr bergers kiss the lands, but that is what they load there ammo to, and their rifles shoot pretty damn good... Also, the Retumbo is a good idea if the 0.080 seating depth doesn't work. There's a stick at the top of the reloading section about Berger seating depth, it's worth a read.
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