Rifle changing zero suddenly

[timelinex]

I had this post in the optics section, but realized it is better placed in the rifle section so I deleted it and moved it here.

The gear in question is a 308 savage FCP-K(~750 rounds or so) with a vortex PST 6-24 FFP attached with burris XTR rings on an EGW rail.

I generally clean my rifle around 300 rounds or so and this time I didnt clean it for 390 rounds. The accuracy did NOT get any worse but for some reason that last time I went out the zero changed on me at 100 yards. The elevation was around the same but the windage changed .5mils. I thought that this might be because its finally time for a cleaning.

So I cleaned my rifle and went to the range again and even though it got closer back to zero, the zero did change. It went down .2mils and to the left .2 mils.

What could possibly cause this?? This is what I have went through so far
- I double checked that everything is tight
- The rifle was never dropped or hit hard against something, but even if it was, its a quality scope and should hold zero.
- The accuracy is just as good, in fact printed one of my best 200 yard groups ever while rechecking drops.
- Tracking remained the same.
- Its not a change in technique because the zero changed with a different user as well.
- Same ammo, not that ammo should make a difference in windage.
- The change was sudden, so it's not like the bore has been wearing in or something and gradually changing.

 

[freereload]

Re: Rifle changing zero suddenly

Did somebody else handle your rifle and check out your scope adjustments? Had that happen once.

 

[timelinex]

Re: Rifle changing zero suddenly

No, I'm the only one that handles it.

 

[Shortdraw]

Re: Rifle changing zero suddenly

Wild temperature swing? Elevation, conditions??

 

[CavRed3]

Re: Rifle changing zero suddenly

stupid question was it really windy last time u zero

 

[bowslngr]

Re: Rifle changing zero suddenly

My guess is that you are not getting completely repeatable positioning behind the rifle or are applying different amounts of pressure with your shooting hand or cheek each time you go out. The differences you are seeing are really pretty small.

 

[BigJohn141]

Re: Rifle changing zero suddenly

What did you clean it with? If you removed all the copper fouling it COULD throw your gun off for a few shots till the copper fills in all the small imperfections in the barrel.

 

[skog]

Re: Rifle changing zero suddenly

Is the gun bedded?

 

[timelinex]

Re: Rifle changing zero suddenly

Conditions where close to the same.

As for positioning, I have been been working on trigger work and form, so I would have contributed it to that, EXCEPT it was confirmed by someone else as well.

I usually zero the windage at 50, to ensure wind doesn't play a role.

I cleaned it with wipeout foam. Thats the same thing I have been cleaning with always. But again, this shift happened before I even cleaned.

The gun is NOT glass bedded, but its the savage accustock which is pillar bedded and freefloated. Should I be investigating this? As I said, accuracy does not seem to have suffered at all.

I'll probably end up just scratching this up to 'unknown' as it isnt a big difference at all, as someone else stated, I just wanted to hear your guys' opinion, to sooth the curious mind.

 

[Lowlight]

Re: Rifle changing zero suddenly

A lot of people's systems are not as bulletproof as they think. Shooter can matter, ammo can, there are a host of issues that can come into play, but at the end of the day you get what you pay for which is why you don't see lesser systems excelling. This is why....

 

[Trevor300wsm]

Re: Rifle changing zero suddenly

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">My guess is that you are not getting completely repeatable positioning behind the rifle or are applying different amounts of pressure with your shooting hand or cheek each time you go out. The differences you are seeing are really pretty small.</div></div>

I am thinking the same thing.^^^^^^^^
At one time I would have disagreed and blamed it on equipment, but experiance has taught me otherwise.

Re-zero and check repeatability to see if it's maintained. If you still get variations after you re-zero and confirm, then the next step I'd take is to remove the shooter and any variable he may be adding to the equation. Put the rifle in a vise/sled and let it print.

 

[Chanonry]

Re: Rifle changing zero suddenly

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">This is why.... </div></div>

I own so many AI's ?????

 

[flyboy10]

Re: Rifle changing zero suddenly

You said it was the same ammo - does that mean it's the same everything? Same case and lot number if factory? Same lot number of components and loading conditions (temperature and humidity) if handloaded?

 

[oneshot onekill]

Re: Rifle changing zero suddenly

You guys are really splitting hairs here. I think Lowlight nailed it.

 

[timelinex]

Re: Rifle changing zero suddenly

It's southwest 175SMK load. Maybe it is a different lot # though. Again, elvation change isn't what bothers me since that hsa to do with load. But I was under the impression that windage zero is zero'd to all loads.

It hasn't changed on me since I reset it it a couple range sessions ago, so it is what it is.

 

[Sidk]

Re: Rifle changing zero suddenly

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">My guess is that you are not getting completely repeatable positioning behind the rifle or are applying different amounts of pressure with your shooting hand or cheek each time you go out. The differences you are seeing are really pretty small. </div></div>

I don't know about you, but that was my exact problem this weekend with a new 700. I've really got to work on getting behind the rifle correctly. I have back problems so sometimes for comfort I will not get straight. It sure throws the shots off.

 

[bowslngr]

Re: Rifle changing zero suddenly

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Sin City Shooter</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bowslngr</div><div class="ubbcode-body">My guess is that you are not getting completely repeatable positioning behind the rifle or are applying different amounts of pressure with your shooting hand or cheek each time you go out. The differences you are seeing are really pretty small. </div></div>

I don't know about you, but that was my exact problem this weekend with a new 700. I've really got to work on getting behind the rifle correctly. I have back problems so sometimes for comfort I will not get straight. It sure throws the shots off. </div></div>

To varying degrees, I struggle with this every time I go to the range. And the effect is more pronounced with lighter rifles.

 

[PeterN]

Re: Rifle changing zero suddenly

I have a Remmington 5R which comes standard with an HS Precision stock with an aluminum bed. From day one it has been a 1/2 MOA or better with FGMM and my hand loads. However every once in a while my 100 yd zero would change for no apparent reason .My smith suggested skim bedding on top of the aluminum. Problem solved!!! No more zero change

 

[bowslngr]

Re: Rifle changing zero suddenly

What's the theory behind that?

 

[Rprecision]

Re: Rifle changing zero suddenly

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: timelinex</div><div class="ubbcode-body">Conditions where close to the same.

As for positioning, I have been been working on trigger work and form, so I would have contributed it to that, EXCEPT it was confirmed by someone else as well.

I usually zero the windage at 50, to ensure wind doesn't play a role.

I cleaned it with wipeout foam. Thats the same thing I have been cleaning with always. But again, this shift happened before I even cleaned.

The gun is NOT glass bedded, but its the savage accustock which is pillar bedded and freefloated. Should I be investigating this? As I said, accuracy does not seem to have suffered at all.

I'll probably end up just scratching this up to 'unknown' as it isnt a big difference at all, as someone else stated, I just wanted to hear your guys' opinion, to sooth the curious mind.</div></div>

I would be inclined to look into bedding

Sure, a AI would be one way to resolve any problems. A ferreri also ensures a effective way drive to work. But this little pesky thing called money causes us lesser folk to make the best of what we have.

 

[PeterN]

Re: Rifle changing zero suddenly

Between the machining tolerances on the action and the additional tolerances on the aluminum bedding block there is some tolerance stacking. The skim bedding makes for a perfect fit. My smith has done a lot of these and he said that some come from the factory pretty good and some don't Mine was one that that wasn't so good

 

[timelinex]

Re: Rifle changing zero suddenly

Ok, I think I will look into skim bedding. I know there are 1001 how-to's out there, but do any of you any links to a how-to that does it on a pillar bedded savage that you would recommend.

I've never done anything like it, so it would be my first!