So I worked up some 223 loads for shooting last weekend. 75 gr Hornady BTHP, Fed brass (FL sized, trimmed, flash hole uniformed), and some of the Alliant 2000MR. Charges were 5 rounds each of 23.8, 24.2, 24.6, 25, and 25.4 grains (based off configuring the 77SMK load to a 75 gr bullet) at 2.26 OAL. Expected velocity from 25.2 grains should have yielded around 2850 FPS from a 24 inch barrel. I was indeed shooting a Stag 6h upper (24 inch, 1/8 twist) with RRA match trigger off bench rest with rear bag.
So here are the problems. First off, my 25.4 grain charge only yielded around 2750 FPS, and I didn't get a single group to get under about an inch. It has to be the cartridge, since this rifle will shoot my cheapo 55gr FMJ plinking load under 3/4 inch. It was breezy, 10-20 mph winds from left to right, but I was attempting to put my rounds off in a timely fashion during consistent wind conditions, and besides, it was only at 100 yards. That shouldn't make a full inch worth of difference. The vertical spreads and STD were pretty good (my notebook with the data is elsewhere right now), but the left/right spreads were pretty terrible. Parralax was confirmed GTD each time.
Anyone have any ideas on the velocity problem? The book says to use Winchester brass, and I do have a good bit of LC '06 in a bucket that could be used. With the capacity and sturdiness (and the fact that this rifle is actually chambered 5.56 NATO), could I up the charge some more and perhaps locate a higher node? I didn't see any pressure issues all the way up to 25.4 grains. My 308 165gr hunting and 175 SMK loads (both with 2000MR) all hit the book max velocity 1.5 grains below the book max charge, so I was very much hoping the same would occur with this load/rifle. (I'd REALLY like a mag length 1000 yard 223 load).
Was it the wind, or seating depth, that was at issue with the left-right spread in the grouping? Loading these to mag length doesn't leave me a whole lot of play with the seating depth thing.
Any help or information would be greatly appreciated.
So here are the problems. First off, my 25.4 grain charge only yielded around 2750 FPS, and I didn't get a single group to get under about an inch. It has to be the cartridge, since this rifle will shoot my cheapo 55gr FMJ plinking load under 3/4 inch. It was breezy, 10-20 mph winds from left to right, but I was attempting to put my rounds off in a timely fashion during consistent wind conditions, and besides, it was only at 100 yards. That shouldn't make a full inch worth of difference. The vertical spreads and STD were pretty good (my notebook with the data is elsewhere right now), but the left/right spreads were pretty terrible. Parralax was confirmed GTD each time.
Anyone have any ideas on the velocity problem? The book says to use Winchester brass, and I do have a good bit of LC '06 in a bucket that could be used. With the capacity and sturdiness (and the fact that this rifle is actually chambered 5.56 NATO), could I up the charge some more and perhaps locate a higher node? I didn't see any pressure issues all the way up to 25.4 grains. My 308 165gr hunting and 175 SMK loads (both with 2000MR) all hit the book max velocity 1.5 grains below the book max charge, so I was very much hoping the same would occur with this load/rifle. (I'd REALLY like a mag length 1000 yard 223 load).
Was it the wind, or seating depth, that was at issue with the left-right spread in the grouping? Loading these to mag length doesn't leave me a whole lot of play with the seating depth thing.
Any help or information would be greatly appreciated.
