Shifting Zero 338 RUM 300 gr Berger

[D.Camilleri]

I went out yesterday morning to double check my 100 yard zero and send a couple of bullets down range to around 700 yards getting ready for my Western Wyoming high country mule deer hunt. I got out the G7 rangefinder, shot my target and dialed 14 moa and sent two shots. I went down range and saw that both shots hit 8 inches high. I scratched my head and wondered what happened. I went back to the bench and sent a shot at 100 yards and it hit 1 inch high. This has happened before and I am convinced it is a problem with my Sightron SIII. I even went so far as contacting Sightron and their tech told me it must be the gun. After it happened the last time, I could not get the problem to repeat itself. I would shoot 700 yards, zero my turret and shoot 100 yards and put the shot in the bullseye. I have carefully made sure that my 100 yard zero is dead on. I thought that maybe the elevation mechanism in the scope had possibly gotten stuck or something and after running through the moving of the turret several times it would track perfectly. This afternoon I went out to solve the problem. Instead of the problem getting solved quickly, another problem came up and everything went to crap. My groups started opening up, shots started stringing and nothing was working the way it should. Then my bolt wouldn't go into the receiver, WTH. I looked and the tab that keeps the bolt from coming out was sticking up. I pulled the scope off of the rail and checked the screws, all were tight. I removed the action from the stock and found the rear pin that holds the trigger in place and also locates the lever that prevents the bolt from falling out was not engaged with the pin. I put the pin back in and put a drop of blue loctite on the end of it to help prevent it from walking out again. Put the gun back together and it started grouping again like normal. I was starting to question the last batch of 300 grain bergers that I had loaded. I double checked my zero at 100 and it was 1 inch high, so I took out 1 moa from the G7 solution and sent two, much better. I am not quite sure what is going on. I cleaned my barrel again and I will attempt a sight in and down range verification again tomorrow. What I don't understand is how my scope can be zeroed exactly at 100 yards and track perfect to 700, bring it back to 100 and hit perfect. Put the gun away, shoot 100 and hit one inch high and then when I dial up for a 700 yard shot, the scope tracks 14 moa just like dialed. How can the zero be shifting? The barrel is free floated and checked, the stock is a bell and Carlson Alaskan with full pillar bedding, I have a picatinny rail and burris tactical rings. I still suspect the scope, but I need to confirm.

 

[RockyMtnMT]

I feel your frustration. I have been chasing the same **** for a few years now. Sent the scope in, got it back, told everything checks out. Must be the rifle, right? Every time I am convinced the scope is bad, something else is found. Long story short, I should have mounted a diff scope long ago to know for sure. I will be doing that tomorrow.

I hope you figure it out faster than I.

Steve

 

[ShtrRdy]

If you have a solid bench to work off of you might consider throwing together a scope test fixture to check the tracking, return to zero, and holding zero of the scope. I'll try attaching a picture of one I made a few years ago.

 

[arrow]

I had the exact same problem. Everything good one day, come back and everything went to hell. My rifle was custom built on a 700 action chambered in .300 win mag. Was in badger hardware and everything was tight on the rifle. The rifle was extremely accurate shooting tiny groups, but zero was always shifting. This meant the night force had to be bad. After many long conversations with night force I finally sent in the scope to be looked at. After their full inspection there was nothing wrong. I assumed my "smith" who built the rifle blue printed the action properly like I paid him to do. Well after almost 2 years of this inconsistency I completely gave up on the rifle and was going to start over. Ordered a new barrel and brought it to a reputable smith. Explained my problems and he never heard of anything like that. He unscrewed the barrel and saw the first hint. The threads of the action haven't been touched and they were tapered. The barrel tenon was cut small enough so it would fit the smallest part of the tapered action threads. So after a couple twist of loosening the whole barrel would wobble in the action. Then after checking other parts of the action that were suppose to be square, weren't even close. I watched him as he set up my action in the lathe with .0001" run out. That's one tenth of a thousandth of and inch then he recut all surfaces and re cut the threads. The rifle should be done any day now and I'm assuming that was my problem of inconsistency. Is your rifle a factory rifle or was it built up properly by a reputable smith?

 

[rafterfp]

Does your rifle have factory barrel?

 

[bigngreen]

Next time dial the scope up then back down to zero and see if it shoots at the correct zero.

 

[barefooter56]

I went out yesterday morning to double check my 100 yard zero and send a couple of bullets down range to around 700 yards getting ready for my Western Wyoming high country mule deer hunt. I got out the G7 rangefinder, shot my target and dialed 14 moa and sent two shots. I went down range and saw that both shots hit 8 inches high. I scratched my head and wondered what happened. I went back to the bench and sent a shot at 100 yards and it hit 1 inch high. This has happened before and I am convinced it is a problem with my Sightron SIII. I even went so far as contacting Sightron and their tech told me it must be the gun. After it happened the last time, I could not get the problem to repeat itself. I would shoot 700 yards, zero my turret and shoot 100 yards and put the shot in the bullseye. I have carefully made sure that my 100 yard zero is dead on. I thought that maybe the elevation mechanism in the scope had possibly gotten stuck or something and after running through the moving of the turret several times it would track perfectly. This afternoon I went out to solve the problem. Instead of the problem getting solved quickly, another problem came up and everything went to crap. My groups started opening up, shots started stringing and nothing was working the way it should. Then my bolt wouldn't go into the receiver, WTH. I looked and the tab that keeps the bolt from coming out was sticking up. I pulled the scope off of the rail and checked the screws, all were tight. I removed the action from the stock and found the rear pin that holds the trigger in place and also locates the lever that prevents the bolt from falling out was not engaged with the pin. I put the pin back in and put a drop of blue loctite on the end of it to help prevent it from walking out again. Put the gun back together and it started grouping again like normal. I was starting to question the last batch of 300 grain bergers that I had loaded. I double checked my zero at 100 and it was 1 inch high, so I took out 1 moa from the G7 solution and sent two, much better. I am not quite sure what is going on. I cleaned my barrel again and I will attempt a sight in and down range verification again tomorrow. What I don't understand is how my scope can be zeroed exactly at 100 yards and track perfect to 700, bring it back to 100 and hit perfect. Put the gun away, shoot 100 and hit one inch high and then when I dial up for a 700 yard shot, the scope tracks 14 moa just like dialed. How can the zero be shifting? The barrel is free floated and checked, the stock is a bell and Carlson Alaskan with full pillar bedding, I have a picatinny rail and burris tactical rings. I still suspect the scope, but I need to confirm.

D. Camilleri,
Looks like you have found part/all of the problem by fixing the trigger issue. I would suggest you go to the range and do a " BOX" and "TALL TARGET" test to make sure the scope is tracking as it should. Sometimes the erector system can "stick" and affect your first adjustments before it becomes unstuck. Also you MAY want to try checking to see if your rifle likes a "cold clean barrel" or "cold fouled barrel" when you take it out into the field. The way I test this is Shooting a 3 shot group on a target. Then I shoot at a practice target until my bullet strikes stop rising and begin to cluster. Take it home. Don't clean it and go out to the range in the next day or so and shoot another 3 shot group. Compare to the first group.

 

[Bravo 4]

If you suspect the scope (and all the mounting hardware was tight) then mount a different scope to check. My last Leupold MK4 would adjust fine and return to zero but the zero that would be good one day would be off the next. It seemed like every time I would go shoot I had to re-zero (usually 1-4" off in multiple directions), but the rifle grouped well and the shooting session would go without a hitch. After checking everything multiple times I ended up sending the scope to Leupold and they sent me a brand new one instead of fixing the one I sent (wouldn't tell me what was wrong with it, just said it was nothing I did). I sold that one and put that money towards a Nightforce.