Vertical stringing of shots

bpost

I got a very precise vertical string out of my rifle at 100 yards.

XP actioned 8 twist HB 6MMBR with 30.3 Varget pushing a 107SMK.

Any ideas on how to go from vertical to round?

Mk 19

bpost1958, How large was the group? Are we talking about a small amount of variance in the string (1/2") or is it on the larger side (1")?
How do you handle your trigger, do you grip or pinch?

nononsense

bpost1958,

This is the simple and usual cause for vertical stringing but it is not the only significant causal factor:

Vertical stringing may be caused by irregular powder charges, position in the case and ignition problems (inconsistent ignition due to variations in primer pocket depth or primer thickness). It can also occur when the forearm position and pressure is not consistant.

This article covers the subject fairly well:

http://www.6mmbr.com/verticaltips.html

Best.

bpost

This sure sounds like the issue (quoted in red);

Firing Pin--A number of firing-pin issues can cause vertical. First, a firing pin spring that is either too weak or too strong will induce vertical problems. If you think this is the problem change springs and see what happens. Second, a firing pin that is not seated correctly in the bolt (in the cocked position) will cause poor ignition. Take the bolt out of rifle and look in the firing pin hole. If you cannot see the entire end of firing pin it has come out of the hole. Lastly, a firing pin dragging in bolt or shroud can cause vertical. Listen to the sound when you dry fire. If you don't hear the same sound each shot, something is wrong.

I have noted cratering on the primers. Me thinks the firing pin spring is draging. I plan on sending the bolt out to have the pin sleeved. The hole is way too large from what I can tell.

veemax

Maybe it sounds somewhat stupid, but are you sure, the rear action screw is really turned on tight?
Last week we had a similar problem on our shooting range withe a fellow with a nice Sauer 90 rifle in .222Rem.
He shot a vertical line of about 3 inches /100meters, and it turned out, he could turn the rear action screw almost 1 full turn to tighten it. After having done so he shot 1 inch groops 10rounds/100meters.
Over here there is a vast popularity for take off mounts on rifles, I use them myself too, but, if these are not professionally installed, there is a chance there is no room left for expansion of the heated action, which causes the same problem.
The old fashioned "Suhler Einhakmontage" is known and feared for having this problem.
Regards,
Paul Tummers.

JustC

I get vertical with inconsistent cheek weld or positioning in the rest. HTH

buddyb

Hot barrel?

bpost

The more I look at test targets the more I am sure the boys at GRE-TAN will get the issue resolved. The bolt leaves in the morning Priority mail to them.

The firing pin hole is a 5 gallon bucket compared to the base ball bat end of the firing pin. A bushing job with a lightweight firing pin pushed by a strong non-binding spring should take that excuse away from the jerk behind the trigger.

Thanks for all your help. It is appreciated!

nononsense

bpost1958,

"...should take that excuse away from the jerk behind the trigger."

That's being a little hard on yourself, isn't it?[:D] I hope the fix works out correctly.

Best.