Having trouble getting my 7 LRM to shoot

[Dhughes]

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.

 

[stanley52]

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.

 

[AZShooter]

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.

 

[John-Pure Precision]

.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

 

[Dhughes]

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.

 

[RockZ]

Try retumbo... Should get more velocity and less pressure as well as better time pressure curves for that cartridge.

 

[stanley52]

.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 **** 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.

 

[Dhughes]

I thought I would give an update.

I had a loose cross bolt on one of my rings, so we took the gun a part, checked everything out and torqued all the nuts/bolts/screws.

Before I found the loose bolts/nuts, I tried probably 10 different loads with the berger 180 hybrids, 180 berger hunters and 162 amax's at .010, .020 and .030 off. I also tried different charges of H1000 and retumbo. Everything shot about 1.5"-2". It didn't matter what the load was.

I went and shot 2 groups this morning. It shot about 1.25-1.5" on both. That was with 71.2 grains of H1000 20 thousandths off the lands. I'm still getting a little pressure so I'll back off a little more. I'm going to play with the seating depths this evening and see if it will get any better.

I'll let you guys know what I come up with.

 

[Nimrodmar10]

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.

Great advice. This should be a STICKY somewhere.

 

[Dhughes]

I played with the gun a little more this weekend.
I tried a couple different charges of H1000 with some 168 bergers and the 162 amax again.
I tried 70 and 69 grains. I also took the brake off just in case it was causing some trouble. It still shot the same 2" group.

It shot a pretty good group the other day, so I loaded 9 more exactly the same and this is what it did.

This is the target I shot with the 168 bergers(middle and bottom left) and the 162 amaxs(top two).

I took the scope off and put it on my 6x47 to make sure it was good. I shot about a 1" group with it and the wind was blowing pretty hard.

I don't know what to do now. Anymore suggestions?

 

[stanley52]

Well... Maybe there's stress in the barrel/bad chamber/bad action.

 

[IdahoCTD]

I would change the powder. If it won't shoot another powder then there is something wrong with the gun. Some guns just don't like certain powders. I have 2 30-8mm Magnums and one shoots R-22 into 3/8" and the other shoots it into 1.5". It's not the end of the world. I would try Retumbo, R-25, or R-33.

 

[John-Pure Precision]

Make sure you are getting all copper fouling out of the barrel. If you don't it can destroy your load development. I don't remember reading but on the bergers try getting about .002 to .004 off the lands. .020 is a mile off the lands for bergers. Just my .02 cents

 

[ramrod79]

Sorry to here you are having this trouble. I have recently just had a 7 saum built ,and had the exact same results using 5 different powders and 5 different bullets , the build was crap to say the least , I finally ended up rebedding the gun as there was not an ounce of bedding inside stock , the action was rocking so hard in the stock it was rubbing the stock inside smooth,and every time I shot it the guard screws came loose . I went through everything from bullet runout to my scope, after I had gun re-bedded it shot very well, I aslo had other issues with a tight neck but thats a different ball game that would not let me load near the top end of the loading data. I even put another scope on my rig with the same results, I do have a short action and I dont care for berger bullets so I cannot help you there , but this was my dilemma and my targets used to look like yours , and I was very frustrated after 200 rounds check to make sure evrything is tight , check your bedding go through gun top to bottom , there is alot of good advise from these other guys try all your options if it still does noty shoot take back to smith.