Type 316 stainless steel expands about 9 millionths of an inch per degree F rise in its temperature. Going from 60 to 150 degrees F., a 30 caliber barrel (.3000" & .3080" numbers) will expand to about .300275" bore and .308276" groove diameters. Enough to have its effect of larger diameters drop muzzle velocity a dozen fps, in my opinion. But that's probably masked by the powder's higher temperature.
Temp sensitivity
- Thread starter Thumper1991
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azsugarbear
Well-Known Member
Bart B,
Good catch. I know several of us following this thread were about to call you on that one.
Good catch. I know several of us following this thread were about to call you on that one.
My buddy just told me they use Rl-22?
He says and that he has a reliable source on that one...Will let you know what I find out.
You may well be right and I may well be wrong. That was some years ago.
That ammo in my Obermeyer barrel did not shoot all that exciting when I put 20 rounds of it down range at 1000 yards. Regular 190's with IMR4350 shot a lot better with new cases.
Sierra Bullets' would sometimes get a batch of bullet jacket material that varied a bit in quality. When it was coined, cupped, drawn and shaped over lead cores, testing a production run was made with 10-shot groups using bullets coming right out of the final pointing die. Sometimes those groups would be under 2/10ths inch (in the "ones" in their 100 yard test range with 30 caliber HPMK's during the run. Then they would go larger to 3/10ths or more. That was attributed to the jacket material not being uniform enough in thickness and the bullets shooting less accurate were more unbalanced than those shooting very tiny groups. If a lot of 168 HPMK's averaged over 1/4 inch, it would be sold as "seconds" in bulk and not packaged in green boxes for retail sales.
Sometimes their 30 caliber HPMK bullets would continue shooting in the ones and those would be set aside, never polished shiny bright, packaged in plain brown boxes of 1000 each then sold to one retailer for sale at high power rifle matches. They still had the greasy sizing lube on them, a special type of lanolin, but they shot 30 to 40 percent better than what was sold in retail green boxes. That all stopped when Sierra moved to Missouri from their California plant.
Those greasy, ugly bullets had meplats identical to the others from that run that didn't shoot as accurate. Some folks claim the lanolin on them helped them shoot more accurate, but properly cleaning that lube off of them did not make them shoot less accurate. Only problem was, sometimes one in a box may have a jacket fold or other defect and you had to inspect them to find those then toss them in the trash just like Sierra inspectors did at the plant.
I understand the part in the old thread. I have know this on powder from about yr 1998. Blow a primer out of a rifle in change of 60 degrees in temp. Never used bouble based powder again.
