Point of impact

[williaada]

I am stumped on what is going on with my rifle. I bought a new scope and had to install a rail system this year using the same loads my rifle liked last year. I am using .280ai

I have my gun sited in at 100 yards dead on. When I go out to 200 yards I get a drop of 7” and have had confirmed this on 3 different occasions. Any help is appreciated.

 

[williaada]

Need more info

-What was your rifle/ammo drop last year before you switched scopes?
-Sighted-in at 100 yards with how many rounds? Group size? Pictures?
-How were target ranges established?
-What is your muzzle velocity and what bullet? Hand loads or factory ammo?
-Confirmed drop at 200 yards with how many rounds? Group size? How was drop determined (dialed, held-over, held-on target and observed impact shift, etc)?
-How are group sizes/locations varying trip-to-trip?
-What rifle/mount/ring/optic are you using?
-Do you have a baseline rifle/optic/ammo set-up?

My rifle dropped 1.5 inches using vortex Talley rings at 200 yards and then 7” at 300, closer to 12” at 420 yards using a holdover.
Targets and range were at shooting club I belong to that does state matches. Stand and target do not move.
-hand load Hs4831- FPS 2875 ttsx 150 gr barnes
- 200 yards 4 groups 4 rounds- each.
Grouping was 1.5inches. Match targets with 1” squares.
Optic Zeiss- conquest 30mm zero stop larue rail 0 MAO. Warner 30mm rings for rail medium height.

 

[williaada]

I am sorry I miss typed earlier. Dead on at 200 with the vortex Talley ring set up.The the drops as described is what I used for hunting based on the vortex measurement hash marks from the manual. Not very precise, but I was able to hit a 3” circle out 400 yards consistently.

I have not started to dial with scope to make up the difference. My concern was the fact there was such a drop using the new scope. I had hoped to dial the vertical to be more percise than using holdovers.
The scope is set up with MOA.

 

[Northpark]

Double check velocity of your loads. Then take the scope off, bed the rail on top of the receiver, lap the rings and torque things to spec with a torque wrench. My first suspicion would be a improperly torqued scope tube.

 

[Dhbwa]

Scope doesn’t determine drop…….

 

[williaada]

If you have established drops prior to swapping scopes, that should hopefully trim down error potentials. However, your previous drop doesn't sound right. Zero'd at 100 yards, 1.5" (~0.2 mil or ~3/4 MOA) at 200 yards, 7" (~0.7 mil or ~2 1/4 MOA) at 300 yards, and 12" (~0.8 mil or ~2 3/4 MOA) at 420 yards? There's 100% something wrong with that data set.

With your previous set-up using hold-overs, did you verify that the reticle subtended correctly? If you're using SFP, did you calibrate to see what magnification setting you needed to be on? It also becomes difficult to establish good drop data using holdovers unless you have a specific hold that actually lines-up dead nuts exact (pretty rare). Also, it is extremely rare for anyone to have an exact 100-yard zero - you almost certainly have a zero offset.

I asked about distance to targets because I've seen established ranges be about 5 - 10% off from what they think their ranges are. Unless you verify with a known rangefinder/tape/etc., you may be gathering bad data. Obviously, even if the ranges are incorrect, you can compare the previous drops to what you're currently experiencing (but again, there's an error in your previous data).

Assuming your four 4-round groups maintained about 1.5-inch aggregate group in the same location on target, you may not have an issue with fasteners being loose or a scope issue. If the 'groups' are floating all over, you might check torque on everything as well as barrel/bolt/etc. to see if there is unwanted contact anywhere, and you might look harder at the scope to see if there's an error.

Although not stated, I assume you are holding over with your new optic? Have you checked to see if the reticle subtended correctly? Have you calibrated to find the correct magnification that the reticle in that Zeiss should subtend?

Obviously not knowing you or your set-up it could be a handful of things. Right now, based on that previous data set and what you're currently experiencing, I'm wondering if it isn't an error in how you are using your optics to hold over. You could dial the optic to take out the potential of error that could arise from holding over. However, you should also check that your optic actually tracks correctly before doing that. So, you might consider setting-up tall targets at 200 and 300 yards and aiming exactly at center of target and then measure the drop. I'd guess you should be about 3-inches(ish) low at 200 yards and about 12-inches(ish) low at 300 yards. From there, confirm that you are using the reticle correctly, and that the reticle also subtends what you think it should.

thanks for the Suggestion on tracking with the scope.

 

[williaada]

Wanted to provide an update after all the help. I made it out back to the range and got my brother who is very well versed in firearms after in the marines and becoming a very strong shooter.

my brother was able to determine the following. At 100 yards the bullet was still on an upward trajectory, and had my gun pointed down. This problem was corrected by zeroing the rifle in at 200 yards. After getting the 200 yards distance squared away. My brother went to 100 yards and the bullet was hitting 1.5” above bulls eyes. The. We went out to 300 yards and confirmed a 9 inch drop.

then to make sure the scope and mounting was correct, we stopped and shot a few different firearms and then came back and the scope and rifle hit zero again.