weather vs group size....
 

I spend alot of time shooting in the off season and have noticed that some of my rifles shoot better in temp changes than others. I' m not talking about when the barrels get overheated, just casual shooting. For instance I have 2 .270' s of different makes. One shoots 1" groups no matter what the temp changes seem to be. Maybe a slight change in where the bullets hit on the target but groups stay tight.

The other shoots good as well, but seems to throw out a flyer every 4 to 5 rounds that will open the group. But in cold weather in doesn' t ever throw flyers.

Anyone care to throw their 2 cents in?

RE: weather vs group size....
 

Any wind involved? The only thing I can think of that would cause a flyer, other than shooter error, is a gust of wind somewhere between you and the target. It doesn' t take but a 10mph crosswind to screw up your groups, even at 100 yards. Especially if it' s sporadic.

RE: weather vs group size....
 

It all depends on your load.I test my loads in various temperatures before deciding which load that I will hunt with.I have seen loads though that change dramatically with temperature .These same unstable loads also seem to change dramatically with small changes in the powder charge while the loads that are temperature stable also will tolerate changes in the powder charge without affecting group size.

RE: weather vs group size....
 

There is usually always a wind of some kind at this particular range, so I didn' t consider that a factor seeing as how I zero them in at the same range.

And why shooter error with one rifle and not the other?

RE: weather vs group size....
 

I try to do that too! I was just thinking how strange it is that one rifle reacts so much to temp changes and the other doesn' t. But the rifle that reacts to temp change also shoots great groups using the same load when cooler outside, but shoots even better with a factory load than the other one. i guess it just goes to show how finicky certain guns can be and how a slight change can effect the accuracy.

RE: weather vs group size....
 

I am betting that your load if at fault not the gun.Your load is causing the bullet to leave the barrel at a point where the barrel harmonics are in transition so any slight change causes big changes in your groups.You simply need to do some more load development to find a more stable load in that gun.

RE: weather vs group size....
 

Your rifles need to have the receivers pillar bedded, the forearm bedded, and the barrel free floated. It is the inconsistant or irrattic contact and pressure of the stock and barrel that is causing your problems, not your loads. Your best load is your best load. Only extreme changes in weather conditions would cause loads to be suspect. But let the humidity get extremely high or extremely low for a couple days, or let the rifle(s) get wet, then you will have problems. The only way to eliminate that problem is to pillar bed the receiver, bed the forearm, and free float the barrel. I have shot enough benchrest competition to know that a good accurate load, will remain accurate over a wide temperature range, say 50 degress + or - 20 to 30 degrees. Some powders tend to be more stable over a wider range of temps than others, so some loads developement may require hot versuses cold weather testing.

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RE: weather vs group size....
 

Actually the most accurate load in one of my rifles is the one that is the most unstable.If I add or subtract a grain of powder or it warms up the groups open up dramatically.I have another load for the same gun that is almost as good as the first load at it' s best but is far more stable.I can add or subtract a grain of powder with no real change in group size.Temperature also seems to have very little effect on this load as well.Naturally I now only load and hunt with the more stable load.There is nothing wrong with the rifle as it is pillar bedded into a mcmillan stock and the barrel(pac-nor) is floated.The sensitive load does under 1/2" at it' s best(from just above freezing to 50 degrees or so but opens up to an inch by 80 degrees.The stable load holds about 1/2" in all temperatures tested.If the gun in question shoots erratically with all loads with changes in temperature or humidity the most likely cause would be bedding as previously mentioned.If however the gun shoots consistantly through variations in temperature with some loads but is inconsistant with others the fault could very likely be the loads.

RE: weather vs group size....
 

Thanks for the advice, but bedding is NOT the problem with either rifle.They are both bedded.