Rifle Scopes New scope and adverse effects on groups?

[Fishbaum]

Wanted to see if anyone else experienced this.

I install a new scope on my rifle. I have my favorite hand loads ready to go for the range. These 2 loads on the previous trip to the range a week ago with my old scope shot very well out of this rifle. One shot in the high .2's while the other made a 15 shot group well under .75". I load these same loads up to get my new really nice scope sighted in. To my suprise, my group sizes more then tripled. Could no get a better group then about 1" today.

I did not clean the barrel between last range trip and today's to eliminate any need to foul the barrel before groups settled in.

The weight difference between the two scopes is pretty significant but I would not expect the harmonics to be affected this drastically.

I will mention, another variable that changed in my loading practice was that I resized the brass to bump the shoulder back. This is all that changed along with the scope change. Having said this, what do you believe could have caused this huge change in group sizes?

 

[IanHusaberg]

What scope new/old and rifle? Caliber?

 

[Fishbaum]

What scope new/old and rifle? Caliber?

New scope is a Gen 2 Razor 4.5-27. Old scope was a Gen 1 PST 4-16.

Rifle is an FN SPR with a bedded action in its factory McMillan stock and a Bartlein 260 barrel 27" medium Palma.

 

[diverdon]

If you can go back to the old scope and see what happens then that might be something to try. If your accuracy improves then ditch the new scope. If not then try to examine your reloading.

 

[IanHusaberg]

Have you inspected your rings/mount, pic rail? Brand new or used scope? More weight isn't your problem.

 

[Fishbaum]

Have you inspected your rings/mount, pic rail? Brand new or used scope? More weight isn't your problem.

Brand new. Rings are vortex precision rings mount is badger ordnance 20 moa. Mount was loctited and torqued to spec with recoil lug up against the receiver. Ring bases were mounted forward against picitanny rail and torqued to spec. Ring tops were mounted such that there was an even amount of gap between the tops and bases. Also torqued to spec.

 

[IanHusaberg]

?????? Bad day of shooting? .2's?? .75 sounds more like reality. Pics? Windy day?

 

[Fishbaum]

?????? Bad day of shooting? .2's?? .75 sounds more like reality. Pics? Windy day?

It was very windy. I'm going to leave it as it was probably just a bad day of shooting. Had ar's to the left and right of me with muzzle brakes doing mag dumps and it was cold and damp. Have brand new brass coming in this week. Going to do it all over again next weekend and see what happens. Just seeing if there was some off chance that someone else experienced this.

 

[Snuby642]

Does that change effect neck tension from the flr you were doing?

 

[Fishbaum]

Does that change effect neck tension from the flr you were doing?

I use a body die and do my neck sizing separately with a neck die. Used the same tension as last time.

I'm starting to think I might have had excessive head space since I sized by bolt feel. Had to bump shoulder 4 thou back to get the bolt to close without resistance instead of the recommended 2 thou bump.

 

[IanHusaberg]

I shoot bullets in one hole all the time. But, the next shot is thrown off. Happens all the time. I don't think people here weight sort bullets/brass and are anal bench rests shooters. Variables add up sometimes and the stars align other times. Shoot on!

 

[Fishbaum]

I shoot bullets in one hole all the time. But, the next shot is thrown off. Happens all the time. I don't think people here weight sort bullets/brass and are anal bench rests shooters. Variables add up sometimes and the stars align other times. Shoot on!

Agreed, I have a hard time believing my new razor is causing issues. Just had a crap day.

 

[M77]

torque settings on the rings?

 

[Fishbaum]

torque settings on the rings?

45 in-lbs for bases to rail. 18 in-lbs for the caps.

 

[Mordamer]

Did you check parallax or did you just set it to the yardage mark on the turret? Parallax can easily add 1/2 MOA to your group sizes and many times the factory yardage marks on the parallax knob are off.

 

[Fishbaum]

Did you check parallax or did you just set it to the yardage mark on the turret? Parallax can easily add 1/2 MOA to your group sizes and many times the factory yardage marks on the parallax knob are off.

Come to think of it, something strange happened with this. I originally had it set somewhere between 100 and 150 yards because that is what was clear to me. As the day went on I found it was getting blurry on the adjustment I had at the beginning of the day. I turned the knob to 100 because that was what cleared it up. I thought it was just my eyes getting tired or something.

 

[Mordamer]

Come to think of it, something strange happened with this. I originally had it set somewhere between 100 and 150 yards because that is what was clear to me. As the day went on I found it was getting blurry on the adjustment I had at the beginning of the day. I turned the knob to 100 because that was what cleared it up. I thought it was just my eyes getting tired or something.

It is a mistake to set the parallax knob by how clear the focus is. The parallax knob should be used to eliminate parallax. It takes about 3 seconds to check for parallax while prone behind a rifle. Let the rifle sit with no contact from your body, move your head left to right or up and down and see if the cross hair moves relative to the target. I do not know if this was your issue with getting the larger groups, but it will at least eliminate a variable from your testing. Generally, when the parallax is adjusted perfectly the sight picture will also be very clear.

 

[Delta Hotel]

This is Dave at Vortex,

Give us a call tomorrow and ask for Scott Parks (1-800-426-0048...ask for Scott). He can walk you through everything and help troubleshoot this. There are so many variables that can cause bad groups that even switching back and forth between two scopes you may not find the root cause. For example, just to name a few: How tight did you torque down the turret set screws and how did you do it? How close is the objective bell to your barrel? This just barely scratches the surface. Scott can walk you through a ton more than that and help you figure it out.

Dave

 

[Fishbaum]

This is Dave at Vortex,

Give us a call tomorrow and ask for Scott Parks (1-800-426-0048...ask for Scott). He can walk you through everything and help troubleshoot this. There are so many variables that can cause bad groups that even switching back and forth between two scopes you may not find the root cause. For example, just to name a few: How tight did you torque down the turret set screws and how did you do it? How close is the objective bell to your barrel? This just barely scratches the surface. Scott can walk you through a ton more than that and help you figure it out.

Dave

Thank you Dave. I am currently loading up the same load that I know the rifle loves with 3 different stages of sizing. I did full length resize for the first time on this range trip so I may have messed that up. To see if that was the issue I am loading identical loads with the shoulder bumped back 5 thou, 2 thou, and no bump (fire formed) to see the affects on accuracy there. If I get bad groups across the board I will give Scott a call. I appreciate you for coming on here and giving advice. Please don't take my post as me blaming my new scope on this I was just asking if others had this experience with any other new scope.

 

[Delta Hotel]

Thank you Dave. I am currently loading up the same load that I know the rifle loves with 3 different stages of sizing. I did full length resize for the first time on this range trip so I may have messed that up. To see if that was the issue I am loading identical loads with the shoulder bumped back 5 thou, 2 thou, and no bump (fire formed) to see the affects on accuracy there. If I get bad groups across the board I will give Scott a call. I appreciate you for coming on here and giving advice. Please don't take my post as me blaming my new scope on this I was just asking if others had this experience with any other new scope.

Sounds great! We got your back!

 

[EnXCess]

I don't even try to shoot accurately when I have muzzle-breaks going off near me. I think the concussion pushes/pulls my bullets around. Or maybe I just flinch. I wait for their mag-changes to shoot.

That said, I do think different scopes affect harmonics differently.

 

[Fishbaum]

Hi guys, just an update. Definitely not a scope issue. Swapped on multiple scopes and had the same inconsistent results. Need to re-examine my reloading practices and shoot through a chrono to see what the sd is on the load in question. I was basing my accuracy expectations on a few fluke 5 shot excellent groups. Loading 50 of the same thing and shooting really revealed what was actually going on. Back to the drawing board!