Barrel constriction in cold weather?

[Stooxie]

Hi all,

I've read lots of posts/articles/blogs about cold weather POI shift and there's always talk about how temps will affect powder burn rates, air density, barrel stiffness, stock reactions, etc. One thing I haven't seen is the effect of barrel constriction, meaning the bore being a tiny bit smaller due to the contracted metal. So I guess I have a few questions.

1. Does this even happen? The barrel is a tube so I suppose contracting metal could make the bore a tiny bit wider, but that wouldn't account for the typical drop in POI. There are calculators on the internet that will show how a length of steel will change at different temps, but not sure how that might apply to a barrel.

2. If this is happening, how much would it affect engraving force and muzzle velocity?

3. Just like brake pads lose their efficiency when hot, is a colder barrel "stickier"? Does it have higher engraving force simply because it's not warm. I suppose the same can be said of the copper on the bullet as well.

4. Would it even matter under 200 yards? I ask because I've seen as much as 4" drops at 20-30 degrees on cartridges that are 2700-2900fps at 50-60 degrees. That could totally just be user error as well (i.e. shooting differently while freezing one's ass off) but I thought I'd get some other opinions as well.

Thanks,
-Stooxie

 

[Steel head]

Dense air and reduced speeds from cold powder.

 

[SupressYourself]

Probably temperature sensitive powder or you. Shooting H4350 out of a 6.5 Creed, I've only seen like 10-20fps loss from 80 to 0 degrees (F). I haven't been looking for it, but POI did not seem to shift much.

 

[chevy_man]

Some powders are scary different over a 100* swing.

It's the main reason temp sensitivity is the first thing I look for in a powder. I don't want summer and winter loads, so I don't shoot powders that require it even if they would get more velocity or potential accuracy.

 

[E. Bryant]

The bore gets smaller at colder temperatures by around 0.000007" per linear inch of nominal dimension per degree F. A 0.264" nominal bore at 68F becomes 0.26387” at 0F. In other words, this change is relatively small compared to the other effects already mentioned in this thread.

 

[LawnMM]

Steel Head already nailed it

 

[1moaoff]

The bore restricts radially very minimally by comparison to how much it shrinks in length. This is simply because it's the same tiny percentage of a larger number.

 

[captainmorgan460]

Im going to say not enough of a thing to worry about. Physics tells us it would shrink some, but not gonna notice it. Power burn rate is what is going to cause the biggest shift in POI.

 

[LR51]

It’s not the bore it’s the boom

 

[1moaoff]

That was just my attempt to convey that the tiny tiny amount was inconsequential to other things gs in reality!!!!

 

[lanwickum]

my barrel constricts in cold water. It still works if I need it to.