Issues may be scope?

[bkondeff]

Bought a new to me, custom, that includes Stillar Predator action, Manners stock, etc. all put together by Stiller. Gun topped with FFP Vortex Viper HS LR with XLR reticle.

Loaded some Berger 168 Classic Hunters behind Retumbo, and grabbed some 150 TSX loads for another 7mm RM I have to help sight it in. After a few shot's to be sure scope was aligned, I put 3 TSX's under .5moa at 200. I then moved to 500 and proceeded to do a ladder test on Retumbo between 69.0-71.0gr at .4 gr increments. Decide to shoot one of each load up the string, then one of each back down. First 5 shots are .5MOA, but really much underr given almost all spread was horiz and with the gusting 3-7mph wind. Vertical spread about 1.5". Needess to say I was ecstatic.

The next shot goes about 6" due south. The next 4 after that, mind of the same loads that made up the first 5, spread out over 12". Mind you I kept my shots spread out by a few min for barre to cool. At no point in my load development process did I run out of a lot of any component, nor did I change anything else in my process and started in stopped in one session, so no changes whatsoever to components or process. Brass was brand new.

So, I've seen something similar when action screws come loose, or when the BOSS on my A-Bot come loose. I head the 1mi to my home and shop and check all action, ring, and mounting screws. I find my rings(TPS) are mounted under 10lbs of torque, but nothing else is not at least hand tight. So I tighten TPS rings to 15fps. Back out I go. Still about the same.

I checked the bedding before original session and all seemed well, and with the custom action and Manners stock, don't see bedding being the issue, especiay so suddently.

All I can figure is the scope. Haven't seen posts of FFP Vortex Viper having particular issues and the other 3 Vortexx Viper(non-FFP), have certainly not given me any issues.

Anyone think of any other obvious items to check. Seems like there's always some kind of gremlin messing things up that has to be worked out, just unsure this time.

Here is a pic, sorry it is posting sideways due to pic height. You can see the five strung horizontal. Ignore the two in the orange bull, that's from my A-Bolt. All 500 yds.

 

[Barrelnut]

Seems like the problem came on suddenly with that shot that was 6" low. You've checked all the nuts and bolts. I would try a different scope and see if that eliminated the problem.

 

[LeddSlinger]

So you checked the top screws on the rings....always add a mild thread locker such as your wire's nail polish so they stay tight. I also always hand lap and bed my rings with JB Weld for maximum contact and non-slip hold on heavy recoiling rifles.

Did you bother to check the torque of the base screws or the bottom nut on the cross bolt of the rings? i torque mine to about 60 in lbs. and again, apply something mild like nail polish to help hold the threads.

Also check to make sure you have and adequate amount of thread engagement with the action screws. I've seen problems in magnums when the front action screw was only holding on by one or two threads.

Other than that, try a new scope like the other fella stated.

 

[86alaskan]

I too would suggest another scope. Also, it wouldn't hurt to inspect the bore condition, particularly fouling. It seems to me that if all else was in order, maybe the TSX's laid down a layer of copper fouling that the bergers may have stacked. You're nott too far off of 1moa at that 500, so something as little as extra copper in the wrong spot could easily blow you off 1 click.