Temperature changes impact point in my Model 12 precision varminter

[cooner3]

I have a Model 12 Precision Varminter in .223 with a Leupold 6 1/2 x 20 scope. My problem with this gun is that it shoots a different impact point depending on the ambient temperature. I have tried different powders, different brass, different primers and different bullets in all combinations. The load I settled on when I got the gun was 25 grains of AA2250, 55 grain Hornady V-Max moly, Winchester Brass and Federal Match primers. This load shoots excellent groups for me at 150 yds. when shot in nearly constant temps. With a cold barrel at 70 degrees it shoots on center. The next day at 40 degrees with a cold barrel it will shoot one shot somewhere within an inch or more. I live in Iowa and in the early spring or in winter we can indeed get temperature variances like that from day-to-day. I sent the gun to Savage and they had no problem with it but they shot it in their indoor range over two days with no temperature changes. They don't know or won't talk about what could be causing my problem. Do any of have any ideas as to what could be happening to this gun when the temperature changes?

Thanks.

[xhogboss]

Some powders are more sensitive to temperature extremes than others. Sounds like it's happened with a variety of powders, though.

I'm assuming you have a wood stock. You're keying on temperature variations, and what may be causing your problem is humidity, rather than temperature. If the stock is not sealed property, then the humidity fluctuations will cause changes in impact point - the wood swells and shrinks and changes the action/bedding relationship.

You didn't mention if your rifle was bedded. If not, then that's a great place to start. Then, inspect the barrel channel and action recesses to make sure there isn't any unsealed wood. If there is, get the stock warm and dry, and seal it with a good oil or polyurethane finish to keep the moisture out.

[cooner3]

Synthetic stock. Bedded and checked for clearance.

[ellobo]

You dont have a gun problem, you have a temperature problem. Metal expands and contracts with temp differences, actions, barrels, magazines, optics, all change. Temp changes will, as said, produce differing humidity levels. I think you will hear from a lot of guys who have the same problem. Ammo makers are always looking for powders that arnt affected by temp changes.

El Lobo

[handirifle]

Maybe having the barrel and action cryo treated will resolve most of the issue. Over at the mini 14 forums I frequent, cryo treating works wonders for stringing issues. Stringing is caused by the barrel heating up, same issue though.

[xhogboss]

Synthetic stock. Bedded and checked for clearance.


Blew my theory!

[cornstalker]

Maybe having the barrel and action cryo treated will resolve most of the issue. Over at the mini 14 forums I frequent, cryo treating works wonders for stringing issues. Stringing is caused by the barrel heating up, same issue though.


Is is actually stringing, or is the POI just changing with ambient temp variation, yet still groups the same?

[Three44s]

I'd consider borrowing/buying a different barrel and try it.

The most thought of alternative has already been mentioned: Cryo treatment

There are lot of rifles out there that shift after the first shot, you just make sure you "get em" with the first one (or two or three) ....... after that, you've got a warm walking stick .....


Three 44s

[shoofly]

I have the same rifle. You need to use a powder that isn't temp. sensitive. I use varget 26 gr. with berger 80 gr. vld molly. I have had no problems. My rifle has the 1 in 7 twist.... Hope this helps..........I'm hitting golf balls and clay pigeons at 500 yds.

[mcho]

I know this rifle and it does the same thing with H-4895. I think that powder is about as stable at it gets, is it not? It will shoot good groups with both H-4895 and 2250. However both will change POI with a temp swing of about 30deg. Does this info help? Thank you. Mark

[bushwack]

"Less than an inch" at 150 yards is below MOA & I'm pretty sure that that is within acceptable limits for the factory. It could be something as simple as wearing different clothing, which may be causing you to have a different cheek weld. You only mention cold bore shots. What do your groups look like with these conditions? The only people I know of who are worried about cold bore shoots are hunters & snipers. The kind of accuracy you're speaking of should be within the limits of both. I assume this is a factory rifle.

[helotaxi]

Temp, humidity and barometric pressure are included in ballistic calculations for a reason. Even if you are using a temperature insensitive powder, atmospheric conditions have an effect on the flight of the bullet. A good ballistic program can account for this if you have accurate measurements to plug into it.

[PBinWA]

Temp, humidity and barometric pressure are included in ballistic calculations for a reason. Even if you are using a temperature insensitive powder, atmospheric conditions have an effect on the flight of the bullet. A good ballistic program can account for this if you have accurate measurements to plug into it.


Beat me to it. You should be recording the variations and then you can simply compensate according to the conditions.