This was the first try with cast boolits in my brand-new M1A, which has had a tad less than 500 jacketed rounds through the tube. It wears the issue iron sights.
For the first 'go', I took a leaf from BobS' Garand book, and went with olde H4831, charge weight 35.0 grains with both designs fired today. This load was the subject of much thought before I chose the charge weight, because it's basically uncharted ground. This is why I'm pleased to be able to post about it, so others don't have to do the same "interpolation" schtick.
The bullet designs were Lyman's 311672 and 311299. 672 is a bore-riding 167-grain job much like a SAECO RG-4 in profile, to my eye at least. 311299 is a reduced-diameter version of 314299, a famous bullet intended for the .303 British and other "fat .30s". My 311299s weigh 210 grains, cast hot and fast, and water-dropped in straight WW alloy, as were the 672s. Lube was the Felix stuff, of course. All bullets were sized at .311". Primers were CCI #34 "military" type. All rounds were fired with a timed one minute interval between shots, with ambient temperature at 59 degrees and NO wind. The barrel never got more than comfortably warm...easy to touch, in other words. Cases are unfired (new) pull-down Lake City 1988.
For the 311672s, I loaded two ten-round batches, one batch with a TINY dacron tuft (because there's not much room in a 7.62 NATO case above 35 grains of bulky powder) and the other batch without dacron.
I fired five rounds of the NO-dacron rounds first. The initial two rounds went through the same hole from 50 yards, PRECISELY on the point of aim/zero for 168 Matchkings at 2600 fps! "OOOooooh", sez I. The next three rounds landed progressively further down the target, and ended in a total group of about 3.5 inches.
Average: 1414fps; extreme spread: 102 fps; standard deviation: 47 fps
Hmmm. So, I switched to the 311672 WITH dacron, and this time the first THREE rounds cut into a single hole on point of aim, followed by one hole an inch out at 4:00 and the fifth an inch out at 10:00, for just over a two-inch group. Now, check out the readings WITH dacron, after the group being barely HALF of the no-dacron group:
Average: 1524 fps; extreme spread: 60 fps; SD: 22 fps
I admit to being surprised here. Over 100 fps higher speed, and about HALF the ES and SD, all for a truly MINISCULE bit of dacron!?!?
I refired both loads on the original target for each, and the groups did not enlarge over the initial five rounds. The chronograph readings also stayed very close to the original results.
Shifting to the 311299 load, the group formed about 1.5" above where the 672s were landing on their targets. 299s did not demonstrate the movement of successive impacts, and the entire ten rounds ended up making a 1.5" group These rounds had NO dacron.
311299, average: 1546 fps; ES: 117 fps; SD: 36.
Notice that with this same charge and a bullet 43 grains heavier than 311672, the velocity was just about the same as the 311672 with dacron..
Pressure with all loads was very mild. The cases were FILTHY, indicating marginal obturation (based on observations with the service-level Matchking loads). The primers are also VERY rounded compared to those same jacketed loads. Ejection was a great deal softer than with the jacketed loads, especially with 311672. The 299s were much snappier than the 672s, but still nowhere near the functioning speed with Matchkings.
It's my conclusion that these carefully-figured loads are operating on very safe ground, pressure-wise, and I can safely work them up without worry.
Here's one of the neat parts: even with some rounds dropping down into the high 1300s for speed, the rifle functioned PERFECTLY, even to the point of locking open on the empty magazine! This is awesome, to me.
On inspecting the rifle afterwards, (only 30 rounds fired, of course) I found no evidence of leading or excessive fouling anywhere. Since the flash suppressor prevents looking sideways at the surface of the bore at the muzzle, I contented myself with a hard look down the barrel and saw no visible leading. The inside of the suppressor can sometimes tell us a tale, but in this case I found it totally clean, without any of the gray wash I've seen in similar places on other rifles.
Am I happy? You bet! I've been looking forward to this day for months, and it went very well indeed. This is one IMPRESSIVE rifle. By the time NCBS 2006 rolls around, I'll be sure to have plenty of good, tested loads for y'all to shoot.