Ballistics question

[AZ223]

I have a .223 Ultra with an inexpensive Bushnell Trophy 3-9X40 scope. Sighted it in back in December, and wasn't able to shoot much recently. The last two times I've been out, the groups aren't quite as good as before (out of practice on my part, I assume), but what surprised me is it's shooting about 0.5-1" or so higher than before at 100yds, and about 1.5" higher at 200yds. In January when I zeroed it in, the temperature was around 65F; now it's close to 100. I would have thought the higher temperature would cause the bullets to drop, not rise.

Anyone have experience with this? It's a minor change; but I'm curious. Also, I'm using factory ammunition: Winchester 45gr JHP Valu-Pak, and Ultramax 40gr NBT. I'm at the same range, same set-up, and same position as before.

Thanks in advance...

[Ditchdigger]

Loads I chrono during cold weather will be 75 to 100 fps faster in the summer, in some calibers.  Higher temps. will make the powders burn different sometimes, usually with higher pressures.  Digger

[safetysheriff]

I am guessing that if you were working with a larger projectile than the .223 at 40 to 45 grs', and out of a lighter barrel, that you'd see the results (lower point of impact due to greater velocity with same bullet weight) you have expected.     Get some 55 and 60 gr' loads and see how they do between now and next January.    Barrel harmonics, however, as well as recoil/projectile velocity are also part of the sight-in picture.    

ps: in n.e. Ohio, in January, we can oftentimes expect the high temps' to be in the 20's !      you've got it made!    

you've gotta' be tough to live in n.e. Ohio!    that's why i'll be leaving! :-D

[AZ223]

I am guessing that if you were working with a larger projectile than the .223 at 40 to 45 grs', and out of a lighter barrel, that you'd see the results (lower point of impact due to greater velocity with same bullet weight) you have expected.     Get some 55 and 60 gr' loads and see how they do between now and next January.    Barrel harmonics, however, as well as recoil/projectile velocity are also part of the sight-in picture.    

ps: in n.e. Ohio, in January, we can oftentimes expect the high temps' to be in the 20's !      you've got it made!    

you've gotta' be tough to live in n.e. Ohio!    that's why i'll be leaving! :-D

Thanks; I'm going to keep track of where the shots go as the temperature varies. While it stayed below 80 degrees here, not much changed. But now that spring is here (!) :eek:  I'll see what happens.  The Win & Ultramax loads are my favorites, and coyotes don't get that big around these parts, but I may pick up some of the Ultra 55gr PSP's when I can find them. The Win 55gr FMJ's are too inconsistent to tell me much, and until I start reloading, I have to make to.

I know what you mean about highs in the 20's; I grew up in Southern WI, and winters at 40 below were not uncommon. I don't mind the heat any more; as long as you don't touch the asphalt or anything metal, you're alright.  

[safetysheriff]

the Winchester 55 gr fmj's have all that exposed lead at the back of the bullet, unlike the properly-finished-off Remington's i've seen, and that lead really plays hob with the accuracy when if gets cooked off the bullet and onto the barrel.    i stopped shooting them.    much easier to clean the barrel as well.......