View Full Version : Tempature Sensativity Question

04-14-2013, 11:46 AM
Looking for some generic advice, because I simply don't have the time (or weather at the moment) any more to perform the necessary testing.

With N133 and a 6BR (or 6PPC), how many clicks on my Harrell's would you guess I need to take out for a 20 degree tempature difference? In othe words, if I tuned my load in 60 degree weather, but I end up shooting in 80 degree weather...would I maybe take out 1/2 of a click (from 46 1/2 to 46 for instance?

I'm going on a 3 day P-dog blasting trip and am pre-loading all my ammo now...and I just tuned up a couple loads for a 20 TAC, 6BR and 6PPC with Benchmark and N133. However, my "tuning" weather has been in the low 60s and I expect some of my actual shooting to be in much warmer weather, so I wanted to load up a few hundred "reduced" rounds in case I find myself shooting in the mid-80degree weather...trying to guess for "optimal tuning".


04-14-2013, 12:53 PM
Okay, for 6PPC, what's the general rule in regards to velocity difference with respect to tempature difference and powder charge?

For instance, for every 10 degrees in tempature increase, how much can we expect velocity to increase? I.e., 20fps per 10 degree changes?

How about for changing powder (with N133, 8208 and the like)? Maybe guess 10-15fps for every 1/10th of a grain?

04-14-2013, 01:58 PM
I.e., 20fps per 10 degree changes?

That's pretty close. Hatcher's Notebook (page 399, it's amazing how much good info is in this book) gives 1.55-1.83 fps/ F for 30-06 with unspecified powder. Maybe someone can offer some measurements for 6PPC with 133.


PS, you can download Hatcher's for free.

04-14-2013, 05:13 PM
The more powders I test (I'm down to about 25 on the shelf, working towards maybe 5 types) the more I'm convinced that "powder is powder" and that inflated claims of "less temperature sensitive" and "more stable" and "more powerful" and "makes more velocity with less pressure" are just that, inflated.

Which may be exactly why it's unspecified :)


04-14-2013, 09:07 PM
I'm guessing this will be your 1st pd trip. Depending on when & where you are going, it's just as likely that you get temps past 100 as anything else. If you are tuning your loads like you are going to a match, you are wasting your time. You will be shooting at unknown distances and in unreadable wind. The dogs won't know if your load is in tune and niether will you. My suggestion is that you back off from the raggedyass edge and get a good solid middle of the road load for each of your rifles. You will shoot just as many dogs and you won't be stuck out on the prairie with a bunch of ammo that's too damn hot too shoot.


04-14-2013, 11:50 PM
Greyfox brings up a great point.

Don't leave your ammunition out in the sun!

Bring coolers, seriously.

A friend of mine builds RC planes. He was recently studying flex characteristics on large wings and taking temp readings in the sun. He found that a sunny day can easily produce 300F temp readings on the underside of wings left out in the sun! Stuff in the sun SUCKS UP ENERGY to get a lot hotter than the sun itself. You really could fry an egg on an airplane wing.

Or on your blued gun barrel, without you firing a shot.