how much does sun heated loads affect pressure?

[bkondeff]

I shot very well yesterday including groups of 1.0" at 400(only 2 shots), 3.5"at 500, and 3.8" at 600 for 4 shots. I left my ammo in the sun on one of the 1200+ yard round trips to check targets and they went from 75deg to 101deg. Group went up to 5.5" and cases were sticky, when they had not been before.

Seems I have been fairly consistent with this gun and load at .6 to. 8moa from 200 to 600 this summer but when the temps rise groups can be up to 1.25moa. I don't feel its always me.

Seems to also cause POI change to.

So how much do you think over-heated ammo can affect groups and/or POI? PS This not a custom rifle, just an A-bolt with BOSS with an after market trigger and medalist stock.

 

[royinidaho]

The evidence of what sun heated cartridges was proven pretty well by what you did.

Long story short, it makes one helluva difference. And should be avoided at all costs.

Direct sun light can heat an object to well over 130*. I've tested it w/an infrared thermometer.

 

[trebark]

Totally agree with Roy.

Another consideration is the powder you are using. If you are using any of the Reloder powders, they are notoriously temp sensitive, whereas the Hodgdon 'Extreme' powders are far less temp sensitive.

 

[bkondeff]

I use RL19. Tried some hogden loads but cant replicate the low teen ES I have now. Seems it starts to make a diff at 80 degrees.

So while hunting where do you carry ammo?

 

[trebark]

I use RL19. Tried some hogden loads but cant replicate the low teen ES I have now. Seems it starts to make a diff at 80 degrees.

So while hunting where do you carry ammo?

RL19 might provide a good ES, but with it's temp sensitivity, ES doesn't mean much.

I carry ammo where temp can remain stable. Generally an inside pocket.

 

[J E Custom]

101o will/can effect the velocity a load if it was worked up at ambient temps, but when you leave them in the sun they can get much hotter and will definitely have an effect on zeros and groups.

If you have near or max loads you can experance blown primers and stuck cases if the ammo
in allowed to roast in the sun

The only time I have placed my ammo in direct sunlight was when temps were very low.
or I just kept the ammo in my pocket.

J E CUSTOM