ttolliver Posted January 3, 2014 Share Posted January 3, 2014 I'm working up a 40 major load and thinking through how to adequately allow for powder temperature sensitivity when doing chrono work in the winter. I'm not going to surf so close to PF 165 that I'm worried about velocity. I just want to make sure I'm getting summer case pressure levels for over pressure evaluation. Sticking to VV powders reduces the issue significantly, but even VV has some temperature sensitivity. Their manual lists a 1% velocity increase and 3% case pressure increase with each 18 degree (f) increase. Using round numbers, a load that produces 1000fps at 20 degrees would develop 5% more velocity (1050fps) and 15% more case pressure at 110 degrees. If I increase the powder charge to give 1050fps at 20 degrees, would I be producing the 15% additional pressure at the lower temperature as well? And would this allow me to evaluate the case pressure signs I would experience at 110 degrees? That being said, I don't plan on trusting those extremes. I'm just wondering if that logic is sound. For now my goal is to produce indoor practice ammo that's close to the what I'll shoot this summer. So I'll be doing chrono work at 30-35 degrees for what I'll initially be shooting around 70 degrees. And obviously once it's being shot indoors it'll get real case pressure evaluation at 70 degrees. Then once outdoor temperatures come up I'll run the same incremental test again. Thanks! Link to comment Share on other sites More sharing options...
George Post Posted January 4, 2014 Share Posted January 4, 2014 You know you could just warm your ammo to summer time temperatures then shoot it and measure it's speed. Link to comment Share on other sites More sharing options...
ttolliver Posted January 4, 2014 Author Share Posted January 4, 2014 Why is it the simplest solutions sometimes escape us?!? Thanks George! Just need to do a little experimentation on how well some gel packs hold temperature in a small cooler. Link to comment Share on other sites More sharing options...
caspian guy Posted January 4, 2014 Share Posted January 4, 2014 I try to crono my ammo at 3 different temperatures. I put one batch in a ziplock bag in a cooler with ice. I put one batch in a bag with a hand warmer pack and one at ambient ( I usually crono in the spring). That covers all the conditions I am apt to see. Link to comment Share on other sites More sharing options...
Hi-Power Jack Posted January 4, 2014 Share Posted January 4, 2014 I wonder if the temp of the gun might be a part of the equation? Possible that a hot gun might have different "velocity" than a cold gun, or vice versus? Might be good idea to freeze the gun with the ammo, and heat the gun with the ammo - see if that makes a difference? Link to comment Share on other sites More sharing options...
kneelingatlas Posted January 4, 2014 Share Posted January 4, 2014 Jack raises an interesting question: are variations in velocity due primarily to the temperature of the powder or the temperature of the barrel? I suspect the former. Link to comment Share on other sites More sharing options...
GrumpyOne Posted January 4, 2014 Share Posted January 4, 2014 Metal shrinks as it cools and expands as it warms...I would think even with warm ammo and a cold gun, the barrel would be ever so slightly smaller, causing greater pressure on the case...but also causing a lower velocity because of the constriction. ..it would be interesting to see some hard data on the matter. Link to comment Share on other sites More sharing options...
9146gt Posted January 4, 2014 Share Posted January 4, 2014 I wonder if the temp of the gun might be a part of the equation? Possible that a hot gun might have different "velocity" than a cold gun, or vice versus? Might be good idea to freeze the gun with the ammo, and heat the gun with the ammo - see if that makes a difference? I wish all manufactures would published temp>velocity pressure specs! A while back I tried this experiment with a 6" S&W 686 used in NRA Action Pistol Production class 120 PF min. Over a couple 95 degree days I tried a lot of temp issues. Take gun and ammo out of the house and shoot,leave ammo on tailgate for two hours and shoot,very hot to hold,put ammo in freezer, put gun in freezer for two hours Did not see and significant difference in chrono results. Only significant changes (both lower FPS} were not keeping barrel tillted back between shots and keeping the gun on the tailgate for two hours then shooting (ammo that was in the feezer ,ambient temp, ammo left on tailgate). Tom Link to comment Share on other sites More sharing options...
9146gt Posted January 4, 2014 Share Posted January 4, 2014 Western Powder used to pressure check samples sent to them for a fee, last time I asked they stopped that service. Tom Link to comment Share on other sites More sharing options...
ttolliver Posted January 5, 2014 Author Share Posted January 5, 2014 Great ideas to kick around -- thanks guys. When I was noodling about the effect of the temperature extremes on metal, my thoughts went to the colder brass being ever so slightly more brittle. That made me suspect that some sort of brass failure (case rupture or head separation) might occur at a slightly lower pressure level when shooting really cold brass. Link to comment Share on other sites More sharing options...
Mpie427 Posted January 20, 2014 Share Posted January 20, 2014 George Post, awesome reply and so simple...."Just warm" the ammo...thanks Link to comment Share on other sites More sharing options...
jmbaccolyte Posted January 20, 2014 Share Posted January 20, 2014 You know you could just warm your ammo to summer time temperatures then shoot it and measure it's speed. George Post, awesome reply and so simple...."Just warm" the ammo...thanks +1 or 2. The temperature of the cartridge or maybe the gunpowder is the controlling factor. Link to comment Share on other sites More sharing options...
Recommended Posts
Create an account or sign in to comment
You need to be a member in order to leave a comment
Create an account
Sign up for a new account in our community. It's easy!
Register a new accountSign in
Already have an account? Sign in here.
Sign In Now