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Barrel constriction in cold weather?

Stooxie

Sergeant of the Hide
Full Member
Minuteman
Oct 11, 2018
450
302
Northern VA
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
 
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.
 
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.
 
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.