Zero shift

[char]

Hi all

 

Having an issue with my RPA you may be able to shed some light on!

Been using it to good effect for some time with no problems what so ever.

Went and had a day at the wms with Andrew venables , checked zero upon arrival and found it to be 14 moa to the right at 100yds which bottomed out my windage turret ( 12-42 nxs). I have changed nothing on the rifle for at least 12 months which was a thirdeye unimount .

Scope has been back to nightforce twice and returned with a letter saying it's working 100% as it should do.

I have tried both my other nightforce scopes and various rails and mounts, only to get to the same result.

Have shot it with the moderator on and off with it making no difference to poi.

 

I haven't a clue as to what's causing it.????

 

Any ideas???

[ejg223]

14 Moa one should see something without shooting, loose barrel? cracked action? bullet not stabilising?

Only time I had anything like that it was a loose lens in the Leupold scope.

edi

[Guest Stacka]

Is it grouping ok?

[gbal]

Hmmm...there are five major systems that directly affect precision:the shooter,and shooter style;the conditions during shooting;the ammunition;the scope/mounts;the rifle.

Let's consider each;

 

Can we assume you,and your shooting style,have not changed substantially?

Can we assume weather conditions/shooting rest etc were quite similar?

Has there been any changes in the ammunition?

 

The scope has been checked by NF,twice,and two other NF scopes used too.Same problem;and likewise different mounts have not solved it. Therefore,seems unlikely.

 

The rifle: possible,as we know only that the problem was not there a year ago,but is now though after a year unused....(and it is not the moderator).....

 

Given that performance was good a year ago,and that it would need a big change in most of the factors to give 14 moa (though scope/mounts could-unlikely that 3 NF are equally off,and several combinations of scope and mounting give same problem,not different problems),and big changes seem unlikely for most of them,that leaves the rifle...(and bedding etc)....

 

Just want to be clear about the basics,to reduce possible speculative explanations that are a priori very unlikely,or already checked...

 

there has to be a physical cause....

[srvet]

Change the scope and mounts and recheck

[srvet]

Change the scope and mounts and recheck

Sorry should have read OP better!

[char]

Is it grouping ok?

[char]

It's accuracy has not changed, it's still shooting tiny groups.

My other two rifles are still shooting as they always do (22br, 17rem) so I wouldn't say it's me. Have also had someone else that I know can shoot, shoot it and still the same result.

My reloading regime has not changed and am still using the original load that I worked up for it when I first had it about 3 years ago ( .243ai. 47.6 n165 105amax)

I will strip it down again this evening to see if I've missed something obvious but failing that I'll send it to a smith.

[Jagged 77]

14 MOA at 100 yards is a substantial shift in POI. If you've ruled out the scope and rings, ammunition is unlikely to cause such a shift so there must be a problem with the rifle hardware. Check scope rail, action screws and bedding, recoil lug and then make sure the barrel hasn't started to come loose from the receiver. Then check for any visible defects such a ding in the crown or any other damage to the barrel, bolt or receiver. Do a visual alignment check with the scope off looking from the back of the rifle to the muzzle from over the top. The eye is pretty good a detecting anything off centre.

[char]

Thank you for all responses so far, I will look into all ideas . I'm thinking barell tightness could be favourite !!

[brown dog]

Thank you for all responses so far, I will look into all ideas . I'm thinking barell tightness could be favourite !!

 

 

Have you had the action out of the stock? Have you checked stock action screw torque? I'd put money on one of the action screws being under-torqued.

[char]

Action has been out of stock, and been put back with the correct torque. It will be coming out again later to double check everything

[gbal]

Thanks for all this extra evidence,which confirms that the explanation is not the shooter etc,and is very unlikely to be scope,or a flaw in the barrel-the groups are too consistent,and small. So maybe bedding or action -looseness is less likely,as the grouping is so consistent and good....more a fairly stable 'distorted' pressure on barrel action-like a warped stock-unlikely since it's been in storage-(reasonable storage conditions?) or action screws reset to a different torque-"pushing barrel ",as it were-but consistently...?

Anyhow,suspicions are in that area-I suppose removing stock and redoing acton screws but less (at first) tight might change POI,maybe not back spot on,first time but would indicate that's where the cause is located (though how that occured remains mysterious).

gbal

[Jagged 77]

Some good points raised, something interfering with the barrel externally could be the culprit as Gbal has mentioned above. Check for free float with a thin piece of card all the down the barrel to the action.

[brown dog]

Thanks for all this extra evidence,which confirms that the explanation is not the shooter etc,and is very unlikely to be scope,or a flaw in the barrel-the groups are too consistent,and small. So maybe bedding or action -looseness is less likely,as the grouping is so consistent and good....more a fairly stable 'distorted' pressure on barrel action-like a warped stock-unlikely since it's been in storage-(reasonable storage conditions?) or action screws reset to a different torque-"pushing barrel ",as it were-but consistently...?

Anyhow,suspicions are in that area-I suppose removing stock and redoing acton screws but less (at first) tight might change POI,maybe not back spot on,first time but would indicate that's where the cause is located (though how that occured remains mysterious).

gbal

 

Have a look at the targets posted here: http://ukvarminting.com/forums/topic/24228-the-importance-of-stock-bolt-torque/?hl=torque

 

I had something similar happen to me - Started a day at extended range next to 2 chaps firing same calibre, same mv etc - we were all on same elevation and windage data for each target. By lunchtime, I suddenly became aware that I was applying 1.3mils more windage that the others - reason? The front action screw on the rifle I was using had loosened off. Hand tightened it and I returned to the same POI as the others.

[CRUACH]

Out of interest does anyone know the correct action screw torque settings for an rpa t/h hunter? Or is it down to trial and error ...thanks

[char]

Gbal, the rifle has not been in storage, it was in regular use until this problem cropped up ( end of June) with no issues what so ever.

Used it for a couple of evenings prior to going to the WMS just to make sure all was well, which it was.

Checked zero upon arrival and found to be 14 moa to the right??????

 

It's in an aics stock which was bedded by a well known smith so I dont think stock warping is an issue.

Have just come in from checking the pheasants and just about to strip it down , again..

Will let you know if I find anything.

 

Thanks all

Chris

[Guest Stacka]

In the old L98 you would get a issue from the barrel harmonics.

 

If the barrel was put under lots of heat stress you would get a thermal shift. This would cause to POI to shift dramatically with the change of temp. Especially the first shot on target.

[gbal]

Gbal, the rifle has not been in storage, it was in regular use until this problem cropped up ( end of June) with no issues what so ever.

Used it for a couple of evenings prior to going to the WMS just to make sure all was well, which it was.

Checked zero upon arrival and found to be 14 moa to the right??????

It's in an aics stock which was bedded by a well known smith so I dont think stock warping is an issue.

Have just come in from checking the pheasants and just about to strip it down , again..

Will let you know if I find anything.

Thanks all

Chris

Sorry,Chris ...I misinterpreted 'for some time' and '12 months'. So presumably 'used it prior to WMS' and "checked zero on arrival" are very close in time.And nothing was done in that time,like stock removed. That is potentially important,since it excludes any mi-tightening of bolts,or indeed any upset of the stock/bedding,since it was not changed in any known way (and not by firing it. which might have allowed BD's screw to slacken).

g

[char]

I have just stripped and reassembled the rifle and found everything as it should be.

Have just spoken to the smith that I use and he thinks it sounds like the barrel has come loose which he has not known with one of his re barrels . Going to see if I can find time to shoot it again tomorrow just in case anything has changed with the reassembly, but if not it looks like I'm in for a 600 mile round trip to the rifle smiths.

[Tony.H]

if your barrel might be loose then dont shoot it.... id send or take to your gunsmith asap.

 

atb

tony