Weird scope issue (I think)...

daved20319 · Jan 22, 2022

So I have a Sightron S-TAC 4-20x50, this one of the nicer scopes I've owed, good glass, excellent reticle, and accurate tracking. But the problem is, occasionally it seems like I just can't get it in focus. I say seems, because I'm not totally certain it isn't something with my eyes

. And not just a focus issue, it's almost as if the erector tube in the scope is oscillating for no reason, or I've got lots of heat mirage off the barrel (I don't). Not much rhyme or reason to it, it comes and goes.

Yesterday was the first time I got a hint that this could be impacting my accuracy. I haven't been able to get to the range for months, but finally made it yesterday. Had some middle of the range loads put together with 3 different bullets, nothing I'd call a proper load workup, more barrel break-in/extended function test. Rifle is an AR in 6.5 Grendel, BCA side charging upper on an Aero M4E1 lower. This was only my second outing with this rifle, the first time out I was only able to put about 30 rounds through it, and I had lots of extraction issues. But that's another story. Groups then weren't impressive, but I wasn't expecting much, I was shooting left over reloads from my previous Grendel, had no clue as to what they were, and it was a brand new rifle.

So fast forward to yesterday. Get to the range, get setup, put the first 5 rounds down range, and all 5 went into a nice tight sub-1/2" cluster

. I'm thinking YES!!, gonna have to buy some more of those 123 gr. SST's. But after that, the groups went to just ho-hum, maybe 1-1.5", some a little bigger. Focus issue would come and go, sometimes changing position cleared it up, sometimes not.

So has anyone had anything similar? I know, the obvious test is try a different scope, and I will, but I'm just curious, and it'll help me decide if I need to contact Sightron or my eye doc

. Later.

Dave

Member 34319 · Jan 23, 2022

Hard to say.

Did you do your due diligence setting up the scope? Set up the eye relief correctly? Set up the reticle focus correctly?

Could be something like cheek placement.

Could be you never focused the reticle.

My bet is you never focused the reticle. As your eye will focus to an out of focus reticle.

To focus the reticle. Back out the focus all the way. Point the scope at a white wall or the sky. If 1st focal, zoom in enough to where the reticle is big. Close your eyes. Open. If out of focus, close your eyes and turn the focus 1/2 complete turn. Repeat until the reticle is clear. DO NOT keep your eyes open while doing this, your eyes will adjust to an out of focus reticle and lose focus on the background, however once you look at the background/target the reticle will go out of focus.

It could be the eye relief too, but my guess is you mounted the scope and never adjusted the focus.

daved20319 · Jan 23, 2022

You'd have lost that bet, Reno :s0114:

. I've mounted a LOT of scopes over the last couple of decades, focusing the reticle is the first thing I do when it comes out of the box, even before mounting it. Eye relief is second, although I'll admit to a tendency to just eyeball leveling the reticle. Won't argue with cheek placement, definite possibility, but I've had this scope on two very different rifles, a Savage bolt action and now this AR, and I've seen the same thing with both. Not temperature related, either, I've had the same issue at 80+ degrees as I did at 20 something the other day. Like I said, I'm going to switch scopes and see if that makes a difference, just waiting on a 1" mount for the AR. If I get the same thing with the other scope, it'll be time to make an appt. with the eye doc. Thanks for the ideas, appreciate your time. Later.

Dave

Member 34319 · Jan 23, 2022

daved20319 said:
You'd have lost that bet, Reno . I've mounted a LOT of scopes over the last couple of decades, focusing the reticle is the first thing I do when it comes out of the box, even before mounting it. Eye relief is second, although I'll admit to a tendency to just eyeball leveling the reticle. Won't argue with cheek placement, definite possibility, but I've had this scope on two very different rifles, a Savage bolt action and now this AR, and I've seen the same thing with both. Not temperature related, either, I've had the same issue at 80+ degrees as I did at 20 something the other day. Like I said, I'm going to switch scopes and see if that makes a difference, just waiting on a 1" mount for the AR. If I get the same thing with the other scope, it'll be time to make an appt. with the eye doc. Thanks for the ideas, appreciate your time. Later.

Dave

Dang!

Hopefully it's the scope and not your eyes!