How bad is bad?

[gih]

Hi there!

First time poster with a technical question.

If a scope does not hold zero (lost 5" of elevation without any known cause - no drops - non-magnum rifle), and then comes up 6" when it is only adjusted to come up 5", then can I basically write off all results from this scope? I feel like I can not differentiate shooter error from the potentially random effects of my optics. I can say that I shoot much better with what should be an inferior rifle, and have been struggling to tighten up groups on this new gun.

Thanks!

[kweidner]

I am afraid we might need some more info to try to accurately help you out. What kind of rifle, scope, mounts are you using? Is this new ammo or previously tested? This being said though the first thing I would check is the mounts. Just a couple thousandths movement can cause inches at 100 yds as well as inconsistency. Is the scope touching the bbl?

[gih]

Bases were professionally installed by a trusted and regionally respected gunsmith and there is no movement that I can detect by hand.

Burris signature Zee rings on 2 piece Warne steel bases.

Scope does not touch the barrel.

Barrel is fully free floated, all the way back to the recoil lug.

Rifle is a brand new savage model 10. Rear tang is also floated.

This problem has been observed with Federal, Remington, Fiocci, and Winchester factory hunting ammo from 150 grain ballistic tips to 180 grain round nose.

I don't want to get into the scope brand because I don't want to start off a "me too, those are junk"/"mine works fine" thread. I have observed a problem with my rifle that I am trying to diagnose. I have a problem that cropped up with my scope along the way. My question is, given the problem with the scope, should I throw out all previous results with the rifle pending installation of a replacement scope.

[kweidner]

If it acts that way with all loads, I would probably suspect scope. Some things I would also try, I would check the crown. All it takes is a little tiny burr to cause erratic results. Use a jewelers loop and inspect the crown. You might also want to check the torque of the action screws. Unequal torque on an action can cause crazy results. I use an craftsman inch pound wrench and set them consistent. One of my benchrest rigs can go from shooting the same hole to just barely under an inch without the right torque setting on the action bolts. If you have another scope try it. You would just be out of some time. Another thought is this. I once experienced this problem with too long screws in the scope mount. They felt tight but were bottomed out. I tried three different scopes on it before I found what the heck was going on. Good luck and keep us posted.

[gih]

Hi, thanks for the help!

I actually re-installed the barreled action on Friday after reducing the tang area removing material from the stock wherever a rub mark was evident except I did not touch the recoil lug inlet, which was sufficiently wide. I have an Armstrong Industries inch pound torque wrench, both screws set to 55 inch pounds. brought them both down by 1/4 turn until finger tight, then torqued both to 50, then both to 55, rear screw first as recommended by the majority of Savage nerds I have read.

I haven't checked the crown yet. I did not realize a small burr could make such a big problem. If there is an imperfection of the crown, what is the best way to cure it? I have looked at it but not at magnification. It looks "fine" to the naked eye.

[kweidner]

Hart makes a crown lapping tool you can use by hand. I have fixed many a friends truck gun with that thing. Check this link MidwayUSA - R W Hart Barrel Muzzle Crown Lapping Tool Complete Set with 4 Inserts for 22 to 35 Caliber As a matter of fact my gunsmith borrows it from me quite regularly. To answer your question a tiny nick causes an irregular gas release at the muzzle. The most important area to be sure. The bullet needs to leave the bbl the same way every time for consistent groups. One tiny nick will wreak havoc on group size. This tool beats taking the bbl off and turning a new crown.

[glockman55]

Try a different scope.