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Old February 3, 2013, 12:35 PM   #5
Unclenick
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Join Date: March 4, 2005
Location: Ohio
Posts: 10,175
CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assume any liability for any damage or injury resulting from use of this information.

Trooper2,

Welcome to the forum.

Nobody's recipe will be exactly suited to your rifle but the one you find best in it. Too much depends on your individual chamber dimensions.

As suggested, that 55 grain V-max bullet is a bit short for the 7" twist, and you'll probably get best accuracy from something like the 77 grain Sierra MatchKing. But for the 55 grain V-max bullets you have, seated to 2.250" COL (Hornady's recommendation for this bullet) and given the various reloading supply shortages, I would combine the TulAmmo KVB556M primer or the Federal GMM205MAR (not the same as the GMM205M without the AR suffix) with IMR4198 for a load. A book recommendation would be to start at about 18 grains of powder and work up toward about 20 grains, looking for a best accuracy point.

Different sources have different starting loads and maximum loads. My own last best load in that bullet weight was 20.7 grains, which exceeds some published maximums by a little bit, and can run slightly over SAAMI MAP (Maximum Average Pressure) in a tight match chamber. But keep in mind that while SAAMI puts a 55,000 psi pressure limit on this cartridge, NATO and the CIP put a higher 62,336 psi (430 MPa) limit on both the .223 Rem and 5.56 NATO rounds, so from a safety standpoint you have some headroom in your gun. Just work up in steps no greater than 2%, while watching for pressure signs. I don't think you'll see any unless you get soft brass like Federal and some recent production Winchester. If you are looking for an accuracy load, makes the steps smaller at 0.2 to 0.3 grains per step. I'd be surprised if something between 19 and 21 grains didn't do well.

The nice features of IMR 4198 are that, like a lot of accuracy powders, it doesn't cause as large a change in velocity per grain in the top operating pressure range as some others do. It is bulky and fills the case in the 90% range at the upper loads, which is good, even though these are two to six grain lighter charges than a number of other powders require to achieve the same pressure with a 55 grain bullet. The lighter charges are economical (more loads per pound). The only limitation is you will not maximize velocity with it within reasonable pressures. But it should still put them out plenty fast enough to stay supersonic to 500 yards and maybe even to 600, and nothing you hit with it to 300 yards is going to notice the difference. This is one of the powders Eugene Stoner worked with and liked in the AR for light bullets.
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