hot weather shooting ?

[kidcoltoutlaw]

it was hot today 90 or so .i needed 21.5 moa higher than my 100 yard zero to be on target at 1000 yards.then latter in the day as the sun was going down i need 26 moa above my 100 zero to get me on at 1000 yards.same load but a different case was quite a bit lower i know the pressure can be different in a different case but i never seen it that bad.i know the heat can push a load to higher pressure and boost you fps but i never seen it that bad before.has anybody else.it may have needed a good cleaning to i put 24 rounds through it today its a .50bmg amax 750 molly with h50bmg 222.5 grains.shoots great just cant figure out the fps change.im shooting up hill i may not be getting back in the same spot on the bags,thanks,keith

 

[Brent]

I show a MV of about 2885 FPS needed with the 750 A-Max at a BC of 1.05 to be zeroed at 1000yds with 21.5 moa dialed in.

Drop the MV to 2680 and you need 26.0 moa now and that's still at 90 deg. F too.

I would say in a case that large, you could expect velocity variations of a couple hundred FPS with different lots of brass pretty easily.

Combine that with a slight loss of velocity from the cartridge cooling off in the evening also.

A check of water capacity in each case lot of fired cases could verify it real quickly.

What angle uphill are you shooting?

An Oehler 35 would be earning it's keep in this situation for less than the price of two cans of ball ammo.

What type 50 do you have, and what length barrel? My brother has the LAR Grizzly with a 36" with the new style muzzle brake and a Nightforce 5.5-22. Bitchin to shoot!!

 

[Roadrunner]

I was just doing my ballistics tables for hunting elk in the mountains this fall with my fifty. I was doing a whole series of ballistic tables to cover variables of distance, elevation (5000 ft to 13,000) and temperature (0-70 degrees). While I was looking over the tables, I noticed that the biggest effect on MOA, other then range, was temperature. The differences in MOA at a fixed range and altitude, for a difference in temperature of say 30 degrees to 70 degrees was amazingly large. Altitude had much less effect on MOA. Throw in a difference in ammo temperature, and yea, I could easily see how you could get this much difference in MOA. Additionally, if your ammo was sitting in a fifty cal ammo can, in the sun, with the air temp being 90 degrees. The ammo ain't at 90 degrees, it's probably at 150 degrees.

 

[kidcoltoutlaw]

i do have a 35 p choronograph on the way.it's a mcbros light benchrest 32 inch barrel.nightforce 8x32x56.in this months issue of fcsa they did a test with an armalite ar-50 at 500 yards.they got groups some under 2 inches the biggest was just over 6 inches.the loads with the biggest es one of the had an es of 179 shot the best.i would have thought the vertical would have ate there lunch,but not so .maybe it would have at 1000.im going to try to get the least amount of sd and es then shoot it on paper to see if a group can be made by es and sd alone.

 

[kidcoltoutlaw]

i dont know the up hill it must be at least 25 degrees.no they were not in a ammo box.