BP temperature vs. velocity

[mnzrxer]

Just wondering if anyone has experimented with velocity loss as temperature drops in a BPCR. I haven't done much shooting lately, but want to get out soon to chrony a load while it is cold here (~0F).

The load I am working with is for the 45-120. 120.0 gr (wt) of GOEX Cartridge (all I could get at the time), single 0.060" fiber wad, 525 gr SAECO boolit and a WLR primer.

I have two data points so far, at 52°F I had an average velocity of 1424 fps and at 35°F an average velocity of 1349 fps. I was very surprised at the huge difference in velocity and the accuracy was terrible, SD and ES doubled at the lower temp as well. In both cases the loaded rounds were left out to make sure they were at ambient temp before shooting.

I realize that powder/primer combo is not ideal and I now have some 1F to load, but mag primers still aren't available to test.

Any similar experience?

[NickSS]

You probably were getting most of your variation from your frozen lube. I have not shot in as cold weather as you are but have had lube failure when it was below freezing. By warming up the rounds in my shirt pocket before shooting everything was back to normal.

[RMulhern]

BILLY DIXON RULE #1:

When cold weather hits.....feed the fire instead of shooting and partake of good whiskey!

[mnzrxer]

I would love to follow Billy's rule #1, but the family doesn't care for me to touch off the big sharps from the house if a deer happens by.

My main reason for asking is that I would like to use this rifle to take a critter at fairly long range, beyond 300 yards, but during deer season here it can be 60° one day and 20° the next. If the temp is affecting velocity that much its tough to know where to set the sight.

Another reason for asking is that I think some of the variation in velocities I have noted while testing are due to the round picking up heat from the chamber before firing. I have seen a string of 5 shots generally get higher velocities with successive shots. My thinking was that fouling should slow following shots not speed them up. Also firing quickly after loading vs letting the round sit in the chamber a minute or so may affect velocity if the barrel is warm.

I am using SPG lube and it still seems pretty soft even at these temps. No problems with leading and I still get a lube star at the muzzle it just doesn't wipe off as easily as when it is warmer.

Well, at this rate I will never run out of things to test with this rifle.

[mnzrxer]

I did get out today and fired the 4 rounds I had loaded. Temp was about 5°F and the ammo may have been slightly warmer since it was in the garage. I ended up with about the same average velocity as what I saw at 35°F, 1356 fps. The first shot was a little higher on velocity with a clean barrel, but the next three were all within 3.5 fps.

Time to go load more rounds and get a larger sample size.