Cold bore zero all over the place?

[EXPRESS]

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.

 

[paphil]

Sounds like loose base screws or a defective scope! that is a lot of movement.

 

[EXPRESS]

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.

 

[Greyfox]

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.

 

[WildRose]

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.

 

[EXPRESS]

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.

 

[Bravo 4]

Sounds like loose base screws or a defective scope! that is a lot of movement.

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.

 

[ICANHITHIMMAN]

I have to say, based on your story, to me it sounds like there is not a single thing wrong with the rifle. The reason I say this is because you changed so many things, there is no consistency to your shooting, therefore we can not definitively conclude any of this is a result of anything more than environment conditions and travel.

 

[EXPRESS]

ICAN, I'm not really sure what you mean by that, the rifle was set up and shooting consistently during load development, and the only change was the addition of muzzle break which went on for a after the hunt.

What I have now gone and changed is the bedding. For reasons known only to him, the gunsmith who did the work milled out the recoil lug area and more of the already weak barrel channel. He probably planned on bedding it again after changing the recoil lug and didn't get around to it.

So I bedded the recoil lug properly and laid up the forend with a good carbon fibre reinforcement. which has made a noticeable difference to the rigidity of the Whole forend, and will probably induce some change in POI from the previous, but may resolve the cold bore inconsistency issue.

I'll test it this weekend and come back with the results.

 

[WildRose]

Installing a muzzle brake will change your POI from what it was. If however the rifle is put back together properly it will not cause your cold bore POI to be all over the place. You may have to tweak your load because the harmonics of the barrel will be different than before installation but it can't make a shooter go bad unless something is very, very wrong with the installation such as being off center and the exiting bullet striking it.

If you are switching back and forth zeroing without the brake and then putting it on to hunt, that is going to cause a serious issue in a lot of rifles because again, the harmonics of the barrel will be different with it installed vs just a thread protector installed.

It sounds to me like somehow your action is binding and stressed due to either improper bedding or uneven torquing of the action screws.

What kind of stock do you have and is it pillar bedded?

 

[EXPRESS]

There is no switching back and forth with the brake, I had it and screwed it on for the first and only time, and because I did it on the range, I was checking to see if it would change the POI significantly.

The strange thing that then happened was that the first two shots, which could both be considered cold bore, having a good five minutes between them in near freezing temps, were on top of each other at 300 yards, the first was without brake and the second was with brake.

Both these shots however were off by half a MIL, then, the rifle went back to shooting to the zeroed POI, and continued to do so for the whole LR session of 25 rounds, from 310 out to 800 yards.

Previously, the rifle had behaved in a similar manner. Now that I have redone the bedding and reinforced the forend, as per the previous post, I hope the cold bore will be consistent.

Just for keeping tabs on the cold bore shots I have prepared a big (40x40") gong to hang at around 600 yards from my house so I can check on it without having to get out for a full blown range session.

 

[WildRose]

Sounds good. Going at it in a stepwise manner is the way to go. If your problem now isn't solved I'd look at the scope as possibly being the problem, but a full MIL as an awful lot of shift in POI.

I had a 7mm 700bdl that was actually far worse. After multiple trips back to Remington and to 3 different gunsmiths it was finally determined it was just junk. The action was so far out of true with the barrel we finally just gave up and sold it and started over.

 

[EXPRESS]

I'll be ordering a new stock for this rifle, probably a Manners.
After re l re-bedding and reinforcing the forend, it shot cold bore off the target, then after chasing a few rounds I was back to the original zero, with a pattern developing that seemed to follow shooting snake eyes, then one shot would be way off. Shooter error probably isn't the problem either. I had two other rifles, a 6PPC and .338 Lapua which were happily, consistently ringing the gongs outgo 750.
I hate this rifle.

 

[WildRose]

I'll be ordering a new stock for this rifle, probably a Manners.
After re l re-bedding and reinforcing the forend, it shot cold bore off the target, then after chasing a few rounds I was back to the original zero, with a pattern developing that seemed to follow shooting snake eyes, then one shot would be way off. Shooter error probably isn't the problem either. I had two other rifles, a 6PPC and .338 Lapua which were happily, consistently ringing the gongs outgo 750.
I hate this rifle.

Check your bolt face and see if by chance it's shaving brass. Do you ever seen evidence of small amounts of brass filings left in the chamber when cleaning?

Unfortunately your rifle sounds a lot like my first M700. For one shot it was dead on perfect every time. Fire more than that and I chased it all around in circles.

One of the big problems though which was easily solved was that the bolt face was just a hair under large enough in diameter and depth so it was either shaving off little pieces of brass and leaving them in the chamber or building up around the cut out and extractor.

Most aggravating weapon I ever owned.