I've been working up loads for my .300 RUM and am having trouble reaching the same velocities for the given load of powder as published. I'm getting approximately 100 fps less than what I should be getting per any given load. My load work has been done mostly in 40-45 degree weather as it's been cold up here in the Northeast. Yesterday just for grins, I chronographed some Rem 180 Nosler Partition factory loads and came up with an Avg velocity of 3169 fps, which is a full 100 fps lower than what I expected. Is it the cold or some other factor ?? The rifle is a Savage with 26" barrel. TIA.

bowhuntr

You got it. Cold weather = lower velocity. Fire those same loads when it's 70 or 80 degrees and you'll see a lot higher velocity.

Most "factory" ballistics are calculated at a standard temperature (70 degrees F is the norm, I think). I'm pretty sure there's also a standard for barometric pressure and altitude.

This points up a problem that can occur when we, as handloaders, are working up loads in the cooler fall months, then, for whatever reason, use those same loads in the summer, or, we're at the range on an unusually warm day and the rifle/cartridges are laying out in the sun. All of a sudden we have sticky bolt lift, tough case extraction, etc.. We've gotta be on our toes and adjust accordingly.

Some of the new powders are a lot less sensitive to temperatures. In the latest Handloader, John Barseness has an article in which he mentions testing that shows Hodgdon's "Extreme" line, Ramshot's ball powders and latest lots of RL-15 to be relatively unaffected by temperature variations.

R-WEST

One benefit of NOT owning a chrony, one less thing to worry about.. Small patterns rule!

I was just working with a new .308. I had loaded some stuff near top charges right out of the box and was a little worried exept that all bullets had been moly coated. I went out in 32 degree wether and found most loads were a good 100 fps slower.

WHEN I GOT HOME I CAMPARED MY RESULTS TO QUICKLOAD. When I picked the loads I didn't factor in moly coating. (OR 32 degree weather).
My NEWER quickload lets you figure in temp and moly coating and by golly when I let those things get dialed in it predicted right at what those bullets shot at. Between the two factors loads that should have been at about 57,000 psi were now at about 49,000 psi.

In general what I am seeing is a drop from 70 degree weather to 32 degree's is worth about 50fps and moly coating is worth about 50 fps.