POI change with temperature

[JCCinOhio]

I know it's going to be rifle and ammo dependent, but what, on average, can you expect for a 223 POI shift between say 70 and 30 degrees (rifle and ammo at said temp)? For the sake of argument say the powder is Varget, 2900fps average, 55gr v-max. 100yds..

 

[Sheldon N]

You can expect a velocity shift due to temp, which will then result in a POI shift due to the change in velocity. That's part of the reason why you want to look for consistent POI/elevation across multiple charge weights when finding your node during load development.

That being said, Varget is pretty darn temp stable.

 

[IndianaRem5r]

Your muzzle velocity will NOT change significantly with temperature. Varget is very temperature stable. Might be a 10 fps difference in that range of temps. It is all about air density. Colder air is more dense and will decelerate the bullet more. Running your scenario in my ballistic calculator with the temp shift and a 10 fps reduction at 30 deg F: POI shift is 0.04" at 100 yards, 0.90" at 300 yards, 5.60" at 500 yards.

So, it is negligible at 100 yards but becomes much more significant with distance. BTW, that is really slow for a 55 grain bullet. I run just over 3000 fps with a 75 grain bullet in my .223.

 

[DrainTheSwamp]

Your muzzle velocity will NOT change significantly with temperature. Varget is very temperature stable. Might be a 10 fps difference in that range of temps. It is all about air density. Colder air is more dense and will decelerate the bullet more. Running your scenario in my ballistic calculator with the temp shift and a 10 fps reduction at 30 deg F: POI shift is 0.04" at 100 yards, 0.90" at 300 yards, 5.60" at 500 yards.

So, it is negligible at 100 yards but becomes much more significant with distance. BTW, that is really slow for a 55 grain bullet. I run just over 3000 fps with a 75 grain bullet in my .223.

Curious on your combo for a 75 gr?
Out of my 20 inch ar and 24.2 gr varget im only getting 2770.
Thanks

 

[IndianaRem5r]

Curious on your combo for a 75 gr?
Out of my 20 inch ar and 24.2 gr varget im only getting 2770.
Thanks

25.0 grains of Varget in Lapua cases with CCI 450 Magnum Small Rifle primers and 75 grain AMAX bullets. This is from a 26" barrel in bolt-action. It is a compressed load and on the hot side. It does chrono at around 3,000 fps and proven ballistically out to 600 yards. Of course, the usual disclaimer applies...don't use this in your rifle, blah, blah, blah. I have been shooting this combo for over a year (maybe 1,000 rounds).

 

[JCCinOhio]

I'm using a 16" gasser.. XM193 goes about 3200 out of it I think it was, but I matched my load with what the Hornady Varmint Express 55 grains shot out of my rifle, so about 2900fps. This speed gives me real good groups at my 185yd target (~3/4" or .39moa) if I do my part and don't drink too much coffee.

I kept my question general to limit getting off subject.. but main reason I'm asking is I'm getting some POI shift with my thermal based on temp. It's not really consistent, so can't say for sure it's the thermal's fault. Still minute of coyote to 200 yds tho. Need to do more testing, just wanted to see what I could expect.