Huge poi shift and bore sight oddity

[freddiej]

So I'll try to explain as short as possible, buddy just bought a Christensen Mesa 338. He shot a few groups not so hot but breaking in the rifle as Christensen states. I go there today and he says shoot it, so I did. Peterson brass, rel 33, Berger 300 otm, misses 100 yd target completely to the right twice. Dial it over and can't tell where it's going. Loaded some more, here's where it gets weird. Bore sighted as I do with every gun every time with no issues. Look through bore and align bullseye with scope. Usually always within a few inches of center and never off paper, until now, at 50 yds. Over 12 inches left. Now to center it we had to max out windage in the scope and found that the 40 min NF rail was too much for the scope and didn't allow for enough horizontal travel. Tried another scope to be sure it wasn't just the scope. Replaced with 20 min rail and was able to move over enough to sight in. Same thing bore sight looked good, shot way left. We then sighted in at 100 and shot 3 shot group, not great but consistent. Decided to load a few Barnes lrxs 265, same powder, case, primer, brass, poi shifts over 10 inches right at 100 yds. Dumbfounded by this we fired another Berger to be sure scope didn't shift and it had not, that bulletin fired back in the group of bergers. Any ideas?

Grizz, David has the right idea to track down your problem. but if that was so the POI versus POA would not be shifting so wildly.
here is my suggestion.
take the MOA offset bases off, put on a standard 0MOA base on-remount the scope and zero
take various ammunition;
shoot at 50 yards on a 2' target.
see where the various ammo shoots.
if there is no consistency then I would start suspecting the barrel.
I just had a $3,000.00 precision AR come in with a similar problem. the barrel was a reject. it's possible to get a trashy barrel from anyone every now and then.

 

[Frog4aday]

Maybe I missed it, but did someone suggest ensuring the barrel channel is well and clear of the barrel the full length? And I'm not talking the old "ran a $1 bill down and it was good to go" kind of gap. I'm thinking at least a full millimeter or more gap at the narrowest spot. It is a 338 (win mag?) Any contact between barrel and stock as the bullet makes its way down and out (like a snake swallowing an egg while whipping up and down slightly) will drastically change POI.

If it isn't that (a 'free-float' issue) my next thought is you have a barrel that has a slight curve to it. If the curve pointed up or down, you'd get dramatic vertical changes. But if the curve goes slightly left (or right) you would get dramatic horizontal POI changes as you indicate. And what a 'mess' that is. A good gunsmith should be able to check it for concentricity/runout and let you know.

 

[Killertraylor]

What brand of scopes? If they weren't Nightforce, March, Kahles or Swarovski, POI shifts can be more common than people think, especially on a .338 bore.

 

[7mmTikkaShooter]

Sounds kinda wild. With a lateral poi shift like that I would first check stock/barrel clearance. Could there be contact between them? That seems like a likely suspect especially considering the shift after a bullet change. Also would check every torqued and threaded component including the barrel to the action.

 

[Chesterrose79]

I'd try new rings and a different scope that you know is accurate. Had a set of scope rings that wasn't' too happy with magnum charges. Start there to eliminate them as the problem.

 

[30BR]

"Bore sighted as I do with every gun every time with no issues. Look through bore and align bullseye with scope. Usually always within a few inches of center and never off paper, until now, at 50 yds."
But you said he was shooting at 100... Is your 100 yard bore sight 12" off paper at 50?

12" left at 50 yards is 24 moa at 50....

A 40 moa rail refers to elevation, not windage; has no impact on windage.
Swapping to a 20 MOA rail validated that.

So how did you "then sight in at 100"?

A bullet change resulted in 34" of windage at 100 yards? (12" at 50; 24 at 100, plus 10" right for the Barnes)???

I would not shoot that gun until a good smith tears it down.

 

[Gunpowder]

I've had this happen where a barrel shot way different than where it "looked" by bore sighting. It was a bent barrel in both situations.

 

[WildRose]

Loads were built for this gun. Gun is new. Thanks for the reply

Try a different load then, something is very wrong here.

I wouldn't put too much more into this before calling Bergarra and making arrangements to send it back for evaluation and repair/replacement.

 

[Greyfox]

Just a long shot. There was no mention of the support system(Bench, Bipod, etc). My buddy had a similar issue with random flyers of the type you describe his 300WM. After pulling our hair out, checking the scope, mounts, etc, it turned out the fore-arm pic rail mount was not fully tightened. It was barely noticeable but enough to throw the shots considerably. After we snugged the rail down, all was good. I have seen this happen with mechanical front rests like the Caldwell when the main stud is not fully locked down.

 

[Rich Coyle]

I've had this happen where a barrel shot way different than where it "looked" by bore sighting. It was a bent barrel in both situations.

I had the same thing happen. Once I discovered it I could see an oval shape to the barrel rather than a perfectly round bore.

 

[WildRose]

Grizz, David has the right idea to track down your problem. but if that was so the POI versus POA would not be shifting so wildly.
here is my suggestion.
take the MOA offset bases off, put on a standard 0MOA base on-remount the scope and zero
take various ammunition;
shoot at 50 yards on a 2' target.
see where the various ammo shoots.
if there is no consistency then I would start suspecting the barrel.
I just had a $3,000.00 precision AR come in with a similar problem. the barrel was a reject. it's possible to get a trashy barrel from anyone every now and then.

It shouldn't be but as long as we rely on humans for quality control it's inevitable that everyone is going to have a bad one get out occasionally except perhaps for the very small family shops.

 

[MagMan]

I'm guessing it has a brake on it. Just see if a bullet will fit through it without rubbing.

 

[26Reload]

Sounds like the barrel is falling off.....