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Cold bore zero all over the place?

 
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Old 01-01-2014, 11:49 AM
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Cold bore zero all over the place?

I have just finished setting up my 6.5-284 - the rifle will shoot .5MOA, it's a trued 700 Ti action with a 25" Krieger barrel, in the original factory stock, glass bedded, but I am about to change the stock. TPS one piece base, American Rifleman rings, Leupold Mark 4 with M5 turrets and TMR ret. I really like the setup and there is nothing amiss with the equipment.

I had just been shooting steel with it, until last week when I went on a Spanish Ibex hunt with a friend. Before I left home I zeroed the rifle. We drove to Tortosa, Spain and checked zero in the rifles on the first morning.

It was shooting a full MIL to the left. So I corrected zero and went to hunt.
The following day I got my shot at 340 yards and hit a full MIL to the left. Luckily that put the bullet into the billies' neck and killed him instantly. It was a very windy, gusty day, but where we were there was no apparent movement at the time, and even if there had been wind through the middle part of the path where there was no vegetation, it would have needed to have been something like 30 miles per hour to shift POI by a MIL, considering it could only have effected half of the bullets' flight path.

So today I took the rifle out to see what would happen. there was no wind whatsoever today.
Well, the first shot was exactly half a MIL to the right. I screwed on my new Vektor Maskin muzzle brake and gave it 5 minutes to cool off to cold bore temps. It was only 3 deg C, and I was curious to see if the brake would change POI. The next shot with the brake on hit the exact same spot as the cold bore shot, .5 MIL to the right. A third shot, without moving anything hit dead center. So I moved on to my 3" gong at 310 and hit it, then the 4" at 450 and all the way out to 660 yards.

After shooting 25 rounds I decided to call it a day. Tomorrow I will try to get out again and see if there is a change in cold bore zero.

Can anyone tell me if there is something I am overlooking that is causing cold bore to be all over the place? The rifle can shoot accurately, shooting MOA out to 800 yards. But it seems to throw the first round out with no rhyme or reason.
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Old 01-01-2014, 12:48 PM
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Re: Cold bore zero all over the place?

Sounds like loose base screws or a defective scope! that is a lot of movement.
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Old 01-01-2014, 01:08 PM
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Re: Cold bore zero all over the place?

The screws are all good and snug, and I thought about the scope or base/rings issue, but if it were that, then I shouldn't get good accuracy at all.

Over the next fews days I'll take scope rings & base off, and bed the base so it has no tension in it, and lock tite all the screws. But I don't think there is anything loose.
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Old 01-01-2014, 02:02 PM
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Re: Cold bore zero all over the place?

Cold bore problems are generally tough to figure out if the are no obvious problems. The fact that your bullet is varying laterally with the cold bore shot only is generally not an indication of a barrel/load effect. I have seen this with scope, mounts, or bedding issues. If there is flex or movement somewhere, the recoil of the first shot occurs under a laxed position which is off target, and the subsequent shots maintain the POI until the rifle sits awhile and reestablishes the original position. I had the same issue with my 308 several years ago, with a lateral cold bore shot. While the original stock was bedded, it didn't go away until I replaced the stock. Also had this problem on another rifle with a Mark 4 that had a defective parallax adjustment. Refill would knock it out of adjustment.
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Old 01-01-2014, 04:00 PM
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Re: Cold bore zero all over the place?

Having the actions screws tight doesn't equal "torqued equally".

back them off and then use a torque driver to tighten them back up to the same setting on each.

You didn't mention what stock is on it or if it's been pillar bedded.

Differences in cold bore shots generally come either from inconsistencies in the ammo, or how the action/stock melding is done. If the screws are not torqued the same then the action is going to bend somewhere. If it's a cheap factory plastic or wood stock it's going to change with weather/temps and from being pushed/pulled/torqued by the shooter trying to get braced up for the shot; especially in the field.

The other of course is the least popular to discuss which is shooter error. It's one thing to shoot off of a bench and another to shoot under field conditions when you are out of breath and can't really find a good steady rest.
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Old 01-01-2014, 04:54 PM
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Re: Cold bore zero all over the place?

I've been suspecting the stock might be the culprit, it is the factory offered Bell & Carlson mountain stock which is very soft in the forend though it is pillar bedded. I don't have a torque wrench but I've never experienced this big a problem in any other rifles. I snug them down gradually and gently.

The stock will be replaced with a Manners EH2 or McMillan A3 sporter as soon as possible and I hope that will be the end of the problems.

The ammo is consistent, I usually shoot over a chronograph, and the shooter error element is fairly minimal, as groups are sub MOA with of course the occasional flier or pulled shot.

We'll see il anything changes tomorrow with cold bore.
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Old 01-02-2014, 10:09 PM
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Re: Cold bore zero all over the place?

Quote:
Originally Posted by paphil View Post
Sounds like loose base screws or a defective scope! that is a lot of movement.
Quote:
Originally Posted by EXPRESS View Post
The screws are all good and snug, and I thought about the scope or base/rings issue, but if it were that, then I shouldn't get good accuracy at all.

Over the next fews days I'll take scope rings & base off, and bed the base so it has no tension in it, and lock tite all the screws. But I don't think there is anything loose.
Phil may be on to something, don't overlook the scope just because it will not shift during a group or string. I had to send my MK4 back because it seemed like every time I took it out and shot it the zero would shift .5 to 3 mils. The groups would always run well under 1/2 moa when checking zero. They examined it and wouldn't even tell me what was wrong with it, just said it wasn't something I did. Told me it was unfixable and sent me a new one.
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