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Especially because you will be hunting with a cold and most likely clean barrel, this is dead on.Quote:
Originally Posted by Big Jack
Also, once you are sighted in then take a few shots to see how the next shots group and if they group at the same POI. Some guns like a dirty bore, a fouling shot if you will. If this is the case then make sure you leave the bore dirty if you can so that your shots land where they should be.
Anyone ever done any cold weather testing?
Reason I ask I lined up gun up around zero degrees Celsius.
Shot a coyote last year at 140 yards with 20guage sabot and just caught him low enough to make him spin and he ran closer so I was able to hit him again.
Cold air is heavier and slows a bullet down, It was almost -20 that day. I figured my impact was 4-6"lower than expected. Has me wondering how it much it really affects my 20guage....
I notice it with my .22 250 shooting over 300 yards on very cold days....
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The changes to muzzle velocity on powders is minimal, even for bad powders but I would think that at longer ranges the air density would actually change the point of impact. To what extent I do not know, but I do know that there is a lot more wind when the leaves are off the trees and since winds are never consistent it may just be that.Quote:
Originally Posted by SongDog
Powder is a funny thing. I have found some to be down right terrible and some with little difference.
Yes sabots will change poi in really cold weather. Keep in mind shotguns have low pressure barrels and loads. It doesn’t take much pressure drop to see the bullet change poi.
They have a rainbow trajectory
I’ll add, I’ve often wondered if the steel barrel being really cold constricts enough to cause more drag on the projectile.
It would seem possible and plausible.
Steel does not move much though, you would see more variation in barrel size after shooting 1 or 2 shots than what would happen with a 40C drop in temperatures.Quote:
Originally Posted by Big Jack
Remember how hot your barrel gets in the heat of the summer when out in the field under the sun, probably hotter than the cold of the winter but still nothing like what is caused by the friction in firing.
Stainless steel would move more than carbon steel, but again not to that much of a degree.
Not sure I would totally agree with that, there's a lot more expansion and contraction in metal than most would think. Like you said though it does depend on the metal, some expand more than others. I couldn't count the amount of times I used a heat gun or a very hot oven to heat up an end bell so I could drop a bearing into the hole without having to force it in using an arbor press. Interference fits would be an example where one part is heated and the other part cooled to make an easy fit that becomes very tight once temps stabilize. I used to measure 1/16" SS pivots for fitting into yokes on a gimbal assy for a nice firm fit. I was measuring these to 5 decimal points and separating them into different bags for fitting selection. The micrometer was mounted in a stand and I had to handle the pivots with tweezers so the heat from my fingers would not affect the measurement reading. Now we're taking fine tolerances here but it was still surprising how much difference in the fit there was between a few hundreds of a thousandth of an inch.Quote:
Originally Posted by Fox
remember though that all the components will expand or contract at their material rate with the temperature change. Therefore the lead core and copper jacket will shrink as well as the steel but lead shrinks at 2.5x the amount that steel does, copper is closer to the steel than the lead. Based on that you would expect the lead to shrink inside the copper jacket and de-laminate, but that is not going to happen at these temperature ranges.Quote:
Originally Posted by smitty55
Plastics with no structural support added, yes you will have a bunch of movement but metals do not expand and contract much. If you are talking extreme temperatures sure but 40, even 60C is not that much, cryogenic temperatures sure.
Yes, put your bearing in the freezer and your pillow block in the oven to be able to assemble them but you are not going to see significant changes in a narrow tube barrel compared to the bullets.
I don’t know guys.
I do know what song dog is talking about and have seen exactly that.
Song Dog, do you reload or buy factory?
If you reload look for an extreme powder or temp insensitive powder which would likely be double based. That is what I typically find best.
The metallurgy matters though, when you are taking steel and steel or even steel and stainless steel the coefficient of linear thermal expansion is very similar. These parts are designed and made to be a tight fit, a fit that requires them to be pressed when at extreme temperature variation. Think about it though, they both change temperature at the same time so the pillow block will shrink with the bearing and expand in a similar manner, this keeps them from breaking or falling apart.Quote:
Originally Posted by Big Jack
Based on the numbers the bullets, of all types, will move more than the barrel itself but they will also move in the same direction at the same time. Based on this the barrel will shrink but the bullets will shrink more, the reverse will happen when you go up in temperature. At the same time though the barrel getting hot by shooting raises the temperature a lot more than just being in the sun, just by friction, so your 2nd and 3rd shot should change POI much more than just shooting in hot or cold weather.
Now the density of the air though increases with lower temperatures but also changed with relative humidity, although I do not think this has that much of an effect. I think that powder and primers, leading to velocity changes and unseen winds make more of a difference than the friction of the air or the barrel getting larger or smaller.