well, it is going to shoot pretty well from all preliminary indications, and the question remains as to just how well it will eventually shoot. but, the early results are heartening.
i took the little dear to the shooting range the other day to shoot some formal targets ... no ditch bank results to be reported this post. laughing.
i set the target up on the 100 yard target standards, and the rifle up on a shooting bench with a wool blanket on top, and bb shot filled shooting bags to steady my aim. i made some brass out of loads that were not to be, and then took 9 bullets of "jj's .284 brit" ™ and shot three 3-shot groups. nothing elaborate, no need to be doing anything fancier at this stage.
the loads were from cases fabricated w/ remington-peters .243 winchester brass, presumably once-fired, using 130 grain sierra match king bullets (stock no. 1903), in front of 29 grains of h-4198 powder, topped off with standard cci large rifle primers. related post, regarding the .284 caliber 120 grain nosler ballistic tip.-- http://wintersoldier2008.typepad.com/summer_patriot_winter_sol/2012/05/beginning-ballistics-jjs-brit-preliminary-accuracy-testing-w-the-120-grain-nosler-bt-.html
an index of articles on "jj's brit." ™ --- http://wintersoldier2008.typepad.com/summer_patriot_winter_sol/2012/05/jjs-brit-is-a-trademark-symbol-denoting-the-intellectual-property-of-john-joseph-jay-in-the-rifle-ca.html
admonition. i am not a ballistician, nor a reloading manual, and i do not have a ballistics laboratory. use these loads at you own risk, observe proper reloading technique and beginning your loading about 3 grains below my listed maximum, and proceed at your own risk, watching for signs of excessive pressure. wear shooting glasses. be advised that if you use other cases to make your own "jj's brit" ™ you run the risk of dangerous pressure spikes. have fun. end admonition.
the first group went into 2.160". nothing particularly good about that, but, for the first group, o.k. the rifle had been apart, so that i could relieve a little wood around the barrel nut still making contact with the action. nor had the barrel been swabbed out for a while.
the second group went into 1.441" . better. i found the rifle to have a little more "soup" to it than the size of the case might suggest. it has a bit of recoil, a little more than my 6.8mm remington spc shot through the ar-15 upper. i was using my left hand to steady the boot stock, and upon firing the bottom of the pistol grip was striking bone on the back of my hand, not altogether pleasant, though hardly agonizing.
i decided to change that grip a bit.
the third group, after deciding upon a little better rifle management, went into a nice round cluster measuring .950" in diameter. nothing astounding, but very decent, and a harbinger of things to come, i should think. again, the rifle was not shot in a mechanical rest, shot in shirt sleeves, and with no attempt made to read the wind or wait for better conditions. i did allow the barrel to cool a bit, but, it was still warm to the touch.
click on the picture for a full screen view.
caption: the first two groups were shot using the large orange plaster as an aiming point, while the third group was shot using the small "right eye" plaster as the aiming point. as you can see, the bullet strike is about 2" or so above the point of aim, which is intended, and of great utility for shooting at intermediate ranges in the neighborhood of 2 to 300 yards. bullet impact is also to the left of the point of aim, which will have to be corrected at subsequent sessions. for reference, the little plaster is about 15/16th's in diameter, and is largely obscured by the intersection of the cross hairs on the scope. a little more high power scope might conceivably have extracted a bit smaller group from the shooting session, but, not a whole bunch.
in sum, i am quite pleased with the shooting results so far. the load that i am using shows no signs of pressure in the brass, and the bullet is showing itself to travel true. the velocity is holding very steady right at 2600 fps over the chronograph.
at this point, i will adjust the powder charge up & down a little bit, to see if i can find a sweet spot that will give even better accuracy.
john jay @ 05.22.2012
p.s. i have an ar-15 upper in 6.8mm remington spc that i am quite fond of. if i do my part, the rifle shoots under a minute of angle for me, i.e., < 1.00" approximately at 100 yards, and others can shoot it even more accurately. i seem to be the fly in the ointment, insofar as accuracy goes.
it took me forever to find a load that would shoot in that upper, and i used up a lot of powder and a lot of bullets getting it to shoot, over the better part of a couple years. until i developed the present load, the rifle shot "minute of grapefruit" to barely better than an ak. that was not good.
this rifle, in "jj's brit" ™ has proved, by contrast, ridiculously easy to get to shoot this well. the first powder i tried, h-322 was just too slow a burning rate, and i ran out of room in the cartridge to even approach the speeds i wanted from it.
the load used above in "jj's brit" ™ is comprised of the second powder i tried, h-4198 and not more than 7 or 8 shots bumped up 1/2 grain at a time to get the 2600 feet per second velocity at the muzzle that was the performance target. i have no doubt that the velocity could be bumped up a bit, but, i don't want to even try to make the cartridge any more potent that what it is.
the whole project has just gone like that, with every step of the way being with a struggle to make the cartridge perform as intended.
it has proved an extremely tractable round, indeed.
and, all of this at an overall cartridge length of 2.260", designed to fit in the magazine/magazine well of an ar-15 rifle. it will seat the bullet i am shooting to about a 2.400" overall length in the bolt action rifle, my little "rem-chester", that is being used at the test mule for the project. and, yes, i could extract more velocity from the cartridge at this overall length if i wanted, quite easily, i suspect.
but, that is for another day. right now, the goal is to chamber the round in an ar-15, or perhaps an fn scar.