Changes in bullet drop due to cold

A-zone

A-zone

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Don't know if this is the best place to post this question, but I'm curious about what to expect, in terms of bullet drop, in a rifle that has been zero'd, say at 200 yards, at an ambient temperature of 0 to -5 degrees C, when the rifle is then fired at -20 or -30 degrees C ?

Calibers include: .223 (52 grain HP), .308 (155 grain Sierra) and .243 (100 grain Rem SP), with H-335, H4895 and Varget, respectively.

I've heard to expect a drop in point of impact of one MOA for every 10 degree drop in temperature.

Does that make sense?
 
Well, colder air is more dense. I guess it isn't an impossible assumtion that the colder the air, the greater the drop.
 
Well, i was just goofing around with RCBSload, new to me and I haven't really figured out how to use it. However, on the external ballistics part, I entered the bullet weights you asked for with a 200 yard zero at 60F, and then changed the temp to the max it would go in either direction.

Not very scientific, but here's what I got:

.224 50gr speer tnt hp at 3400fps:

120F +.22"
60F zero
-20F -.30"


.308 155gr sierra hpbt at 2800fps:

120F +.15"
60F zero
-20F -.20"


.243 100gr sierra spz bt at 3000fps:

120F +.13"
60F zero
-20F -.18"

This is at sea level. As far as I can tell with my limited knowledge of this program. Under a full moon. Before I ate supper.:p

Hope it gives you some idea!
Joe
 
A-zone said:
Thanks, Joe:)
Click to expand...

Azone... Don't forget the MV will be slower as well with a colder load. Powder doesn't develop pressure as fast. Striker energy could be lower on primer if lubrication thickens, which could change ignition.

NormB
 
I was shooting my .308 HB with a 168 grain match HPBT today and I found that the moa went up 1/2 a inch for me. I had mine zeroed at 100 yards, but it shot spot on at 200 yards.

Weather conditions, rainy, cloudy, high of -3c.

Any ideas opinions etc?
 
NormB said:
Azone... Don't forget the MV will be slower as well with a colder load. Powder doesn't develop pressure as fast. Striker energy could be lower on primer if lubrication thickens, which could change ignition.

NormB
Click to expand...

Exactly, the velocity is what has the biggest effect on the POI on any load, rifles should be sighted in as close to hunting season as possible. There will often be problems shooting maximum loads developed in the fall or spring when shooting in the summer due simply to the warmer weather. I have found this to be true with all the powders including Hodgdon. My solution has been to develop loads right up to hunting season and sight in just before the hunt. Shooting factory ammo has had the biggest effect in varying temperatures in the POI.
My .02
bigbull
 
I was shooting my 6mm the other day (-20) and it was shooting about 5" lower than when it is zero at 560 yards. I use varget and the cartridges were not cold. I walk out the door of the garage and shoot from my bench 10feet from the door. The change was only do to the dense air.
 
6mm Shooter said:
I was shooting my 6mm the other day (-20) and it was shooting about 5" lower than when it is zero at 560 yards. I use varget and the cartridges were not cold. I walk out the door of the garage and shoot from my bench 10feet from the door. The change was only do to the dense air.
Click to expand...


So going from 0 to -20 deg C. is worth just under 1 min. lower (5 in. at 560yd) with warm loads in your 6mm. As an experiment, if you get a chance, next time cold soak the rifle and cartridges a couple or 3 hours at -20 then see what the drop is.

I bet it's more.

NormB
 
Temp Effect

Powder plays a role here as well, I have found my rifle shoots an inch lower in winter with H4895, with Varget I do not notice the same effect.
 
Well, i shoot cariboo for 5 year in a row in the north, my 300 mag is bulls'eye at 200 yard in the summer, +15 to +25 celsius and when i shoot at -30 to -45 degre celsius, i have to clic the scope at least 3in higher to have the same zero at 200 yard. (i tried it on LG4 reservoir, you can take 1 miles shoot in the winter if you whant)

I use factory federal match 190gr.

Sendero
 
I have noticed similar effects long range shooting in the summer under a cloudy sky, then when the sun comes out it drastically affects the point of impact.
 
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