10 degrees F changes accuracy of load???

[cjk]

Ive been working on a load for a 1000yd ar15 .223 p-dog gun. 80gr sierra matchking and ramshot tac powder.

Shooting 300 yards,
Thursday, 75-80 deg F getting 1.65" 5shot group with 23.5gr powder at an av vel of 2736fps. I think I have my load so I load up 5shot groups of 23.3, 23.4, 23.5, 23.6, 23.7 to verify.

Friday, Go with friend to new range, still 300yds, 85-90deg F.
23.3gr 2675 av vel .925" group
23.4gr 2700 1.975"
23.5gr 2718 2.80" former good load
23.6gr 2716 1.975"
23.7gr 2715 1.85"
The only thing that changed was the benches( both pretty solid wood benches), the temp(higher), Humidity(higher),light wind right to left both days and the second shooting range was more level by 20ft. elevation or so.
My plan is to shoot these loads again to see what happens unless the experts here can shed some light on this mystery.

 

[royinidaho]

[ QUOTE ]

My plan is to shoot these loads again to see what happens unless the experts here can shed some light on this mystery.

[/ QUOTE ]

I'll wait until you post results of shooting those loads again.

I guess I think I'm an expert /ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/crazy.gif

 

[davewilson]

not an expert like Roy but i did stay at a holiday inn a while back.i don't think you've really had that much difference in the 2 days.other than one group the others were similar to what you had before.shooting a 22 at 300, let's just say a very small wind change,maybe,just maybe the shooter was a little better one day than he was another.it's not like you shot 1" one day and 4" the next.i have certain places even though i seem to be as comfortable, i can't shoot as well.i'd try things a few more times before panicking.as far as the speeds go,knew a fellow that claimed the humidity when he LOADED his ammo was as important as most other processes.can't say for sure, haven't tested that yet.

 

[Bart B]

I've shot the same load for .308 Win., .30-06 and two 30 caliber magnums from 10 to 110 above and never had a change in each rifle's half MOA accuracy through 600 yards. Ammo shot on hotter days had flatter trajectory but it all performed well.

Don't forget, the shooter is the least repeatable part of the shooting system.

 

[Roll-Yur-Own]

Why don't you try Varget? I found the ramshot powders ok, but not stellar.

 

[cjk]

Ive got a set of shells ready to test once the wind settles down. The reason I didnt go with varget is in my sierra manual tac produced higher velocity, and I had a pile here as it works well with the 50gr blitzking. Even with tac the bullet will barely be supersonic at 1000yds.

I have questions about my load development.
1. Do I have to stay supersonic at 1000yds to be accurate?
2. I assumed the answer to #1 is yes so I skipped the ladder test and went right to a powder charge that would get 1140+fps at 1k yds(23gr max listed in manual). Then worked up till pressure signs showed in .5 grain jumps while shooting 5 shot groups(flat primers at 24gr). I then picked the most accurate load(23.5gr) and loaded 5 rounds at .1 gr intervals 23.3-23.7 to fine tune and verify.

Anything I missed?

 

[cjk]

Today, 70-75deg F 300 yards, very light winds staight downrange.

23.3 2666fps 1.80" with .80" verticle spread
23.4 2671fps 1.50" with .55" vertical spread
23.5 2695fps 2.93" with 2.93" vertical spread
23.6 2722fps 2.57" with 2.57" vert
23.7 2733fps 2.95" with 2.95" vert

It seems to me 23.4 is the way to go with the smallest vertical spread being consistant on all days. The horizontal spread could be wind or the bench. Since I can see my heartbeat in the scope its time for a concrete bench.

 

[Alan Griffith]

Good stuff you've got there! Now go get some H4895, not IMR 4895. I've found TAC and H4895 to give the highest vel w/ big 75-80 gr bullets. Prove to yourself that one is better than the other.

Varget is good for accuracy but it will be hard to put enough into the case to get the vel you want.