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Old February 3, 2013, 10:25 AM   #15
Dan Newberry
Senior Member
 
Join Date: October 3, 2012
Location: Wytheville, VA
Posts: 215
It should be pointed out that unless otherwise specified, match load data would assume Winchester brass. Lapua or Federal or even RP cases will alter the pressure and therefore require a different powder charge.

When you develop your load and properly interpret your target data per the instructions at my OCW load development site... http://optimalchargeweight.embarqspace.com/

,,.you will find, even as a rule, that loads developed at 100 yards will hold tight even out to 1000 yards--provided that the bullet is moving fast enough not to be too close to the speed of sound. As to velocity extreme spread, the OCW system will find a node where velocity is relatively tight (low ES)... so even if you don't own a chronograph, using the OCW load development system will get you a tight shooting load with a low ES, which will equate to good long range accuracy.

Varget... it's a great .308 powder, and I use a good bit of it. Varget likes to be loaded to higher load densities, however. The max charge with 175's according to Hodgdon is 45 grains, and this is where most folks find their best accuracy (again, always assume Winchester brass unless otherwise mentioned). Varget does not work well at lower density charges, and this is the reason that many folks find poor accuracy when they try it. Sierra has some really anemic Varget data published for some reason... so I would not count on Sierra's load data with regard to Varget in the .308 win.

IMR 4064 burns pretty much like Varget. In all likelihood, Varget was created to work like 4064, while being more temperature stable. With 4064, you can get great accuracy without "driving it like you stole it"... and lower density loads work very well. 4064 does not do well with heavy charges in warmish climate... and you'll find that pressures will increase too much for good brass life if you try to run much more than 43 grains of 4064 with 175's. But the 43 grain charge area does work well (with 175's)...

Reloder 15 (never understood why Alliant left the "a" out of reloader)... ... works great as a .308 powder, and that is the current powder that our military is using in their M118LR load (the standard sniper load). They are using LC (Lake City) brass... and that brass is thicker than Winchester, and uses less powder for a given pressure level. They started with 44.3 grains of RL15 in the LC cases with the 175 SMK's, but when they got into the hot desert climates of the Middle East, pressures spiked and accuracy was degraded. They then chose to drop the charge to what is now reported to be a little over 43 grains of the RL15. In my opinion, they're not using an OCW charge there... likely, a charge of around 42.8 grains would be more stable, and give better accuracy across a large range of temperatures.

One of my favorite .308 powders is IMR 4895. It meters well, and I usually throw all my 4895 charges and have never had a problem with accuracy. 42.4 grains of IMR 4895 should shoot bug holes with 175's from a good rifle. If you have some Lake City brass, the 4895 charge is 42.0 grains (which is the old M118LR load from when DuPont had the contract... and I don't think they've had as good a long range load since then!)...

All of this said... IMR 4064 is still the .308 powder by which all others are measured... so you'll never go wrong by choosing that powder. You will need to weigh each charge, as it doesn't meter well, but if you're really serious about accuracy, you'll be weighing each charge anyway...

Dan
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