sufficiently to provide for easy extraction, even with loads generating perfectly normal pressures. To maintain usable extraction, loads at about 3200-fps are maximum with the 130-grain bullet.
Interestingly, with a 28-inch Pac-Nor barrel, launching this bullet at 3200 fps from the 6.5-284 Norma requires top loads – pressures therein are almost certainly close to 65,000 psi. Therefore, it looks as though the 6.5/60 easily produces 100 fps more velocity at any given pressure. Since these cartridges have almost identical usable capacity, we have a tantalizing suggestion that the SMc design does produce superior ballistic efficiency. Of course, we do not yet know and that lack of data is frustrating. Fortunately, Norma will soon begin testing for this effect using a 6mm SMc cartridge designed to duplicate 6mm Remington capacity.
Meanwhile, we have ordered another batch of modified 416 Rigby cases. Buffalo Arms will redraw those, using the least amount of annealing possible (preferably none). We will see how that goes. These will also give us a chance to spend two (more) days making cases!
We hope the result will be worthwhile. These cases should have harder sidewalls and that should allow use of higher pressures with normal extraction. We have returned the reamer and barrel to Pacific Precision and Pac-Nor, respectively. We had a mistake in the throating (far too long) and, inexplicably, one of us (McPherson) cut the case necks 0.050-inch too short on all 100 of the original batch of 6.5/60 cases – you cannot imagine his consternation at that discovery. The modified reamer (to correct both errors) has gone to Pac-Nor, where they have rechambered the barrel – which is on its way to McPherson's shop, as this is written.
We have now fired some of those first-attempt cases six times. Interestingly, none shows any measurable case neck lengthening, despite testing involving a marginal amount of case body resizing, along with a slight shoulder bump before each reloading.
Through careful lathe work and using the finish chamber reamer, we converted a Newlon die body to form a combination neck bushing and shoulder bump die. We now have additional Newlon die blanks. We will use the finish chambering reamer to form a resizing die from the 12L14 steel blank and then have Fireball case-harden it – this will induce sufficient shrinkage to adequately resize the case body. Meanwhile we have been using an unhardened die, which tends to gall cases.
Similarly, we will use the modified chambering reamer to convert the 416 steel blank into a proper seating die, which Fireball will harden through heat-treating. The system we have been using to date has not provided good bullet-to-case alignment. Just one more problem to be overcome.
Following Page
Preliminary 22/28.5 SMc
Ballistics and Accuracy Results
(Note that inconsistent neck tension
and other case quality problems related to case forming almost certainly
limit accuracy potential)
All loads use Sierra 69-gr. MatchKing seated at 1.968-inch OAL (base of bullet flush with internal neck-to-shoulder juncture)
Unless otherwise noted, groups are 5 shots at 100 yards and no called fliers were excluded