Shimming Help Please

[LRDGCO]

Firearm: Recent PTR91 GI 308 with Rail

Optic: Sightmark Photon 6.5x50 ST

Rings: A.R.M.S . QD (Warne steel QD also tried)

Issue: The scope is running out of elevation such that at 50 yards and max elevation adjustment on scope, POI is @ .5" - 1" low. This with both 150 grs .308 Win Federal Fusion and handloads 43.5 grs IMR4064, LC 7.62 brass, General Dynamics 147 grs FMJ.

The scope has been back to Sightmark twice and seemed in parameters by their techs. The second time came back with a target shot with a Savage in .308 on the money. The Sightmark techs admit that the elevation adjustment is very limited in the digital scope. PTR admits that their rail could be slightly rear high but say they have never had this problem. I have been able to zero conventional scopes and a red dot 3" high at 100 yards on the rifle.

I have spent the money on the digital scope and would like to use it hog hunting at night. Comments bashing the Sightmark scope, PTR, and me are all welcome, provided they are accompanied by practical and useful advice to resolve the problem. Bashing without useful advice is not welcome.

I am assuming that my only practical solution is shimming the scope. If there are other realistic,cost effective options, please advise. If not, can the process of shimming the scope be explained in very simple, step by step detail, assuming that I know nothing please.

Thank you for your assistance.

 

[243winxb]

Set scope adjustments so they are in the middle. Shim and bore sight by looking thru both barrel and scope at 100 yards. A black bullseye small enough to center it in the bore.

Or shim and test fire if you cant bore sight rifle.

I cut strips from a soda can. They are around .004" thick. Place 2 or 3 in the bottom of the rear ring. This is if the base cant be shimmed?

Its easier to do it, then tell some one how. Good luck.

 

[Blue68f100]

Another option is the Burris XTR Signature series rings. These use inserts that allow you to adj the scope elevation and windage just by positioning the inserts. I have them on 2 of my rifles I use for long range shooting. You able to do a 40 moa shift with these rings.

https://www.burrisoptics.com/mounting-systems/rings/xtr-signature-rings

 

[entropy]

Shimming the base on a PTR91 is much more involved, if it's the STANAG base; sounds like yours is built into the receiver, so shimming the rings is about your only option. As 243xb says, cut pieces from pop cans that match the base of the rings, and experiment with the number of shims needed. Or try the Burris rings mentioned by Blue68f100.

 

[LRDGCO]

Thanks very much. 243Winxb those are the instructions I was looking for. Correct picture of rings was a very nice touch. Thank you all.