I'm wildcatting both short and long 375 Rugers. I use the 300 RCM for the shorty's. I'm using one case taper in all of them. And this taper follows the old 8 x 68 S Schuler's.
With my taper, my 243 VampKat will feed out of a M-98 Mauser's box magazine, and is one holy terror. In a previously taken off target barrel, with 1 in 14 inch twist, at 26 inches, it does stabilize Speer 105 R.N.'s out to beyond 500 yards. My newest loads are using Hornady GMX 80 gr. Spitzers, as they are long for their weight. If this rifle barrel will stabilize 100 gr. lead cored, flat based spitzers, I will re-order a new Barrel with the 1 in 14 twist. If not, then I'll order a quicker twist.
While I'm waiting until Sept. for Neil Jones Products to return my second fitting bushing die, I bobbed off a couple of old military stepped M-98 barrels in 7 and 8 mm., and chambered them, using oversized pilots, on my PT&G wildcat reamer. When the take off Shilen barrel is done in, it will become a .277.
This 243 VampKat has 70.5 grs. of H2O to the case mouth sans meniscus. The short 8mm has about 76 grains of water. Even with my severe case taper, I can still make a 44 cal. wildcat, which is a rimless 444 Marlin on steroids, and which will feed through most bolt action's magazines. It will dish out Hornady 265 gr. Flex Tips at more velocity than they are designed to handle. And in a light rifle, more recoil than I am designed to handle.
But for the rest of you, unless you are being really anal about reliably feeding through CRF bolt magazines, once you get above the factory's 308 caliber, the stock RCM's case taper and Go gauges will work fine. These can form shoulders which will adequately head space rimless cartridges in the old 375 and 400 Whelens. But a 400 Whelen nips right at the 416 Taylors, so "short, & light", may be too much of a good thing.
I think its really dumb to cuss out this cartridge, which will, at the very least, duplicate the 9.3 x 62mm, and do it in a short action. Dave Kiff and I designed this little beast to elongate these 300 RCM's out to an honest 55mm. But with the first stage bushing and button dies, we stalled at 53.94 mm. I'm hoping my new full length chambered PT&G die blank in 270 cal. will put this in order. Obviously, above .308", the Ruger's 53mm will start to shorten up a bit.
All in all, the Rugers are better designs than either of the two rebated short magnums. Simply put, Ruger and Hornady didn't have to bullet proof their case heads using their purely rimless design. So this means that the 300 RCM case has nearly as much volume as the rebated rimmed 300 RSAUM does.
I lose two grains for my extra case taper, and about the normal amounts for necking down from a 308 neck. I'm left handed, so when I've worked up some winners, I'll have a do over with left hand bolt rifles. As I said, after re-chambering my Rem6mmBR Shilen take off barrel, the difference between the little Remington target round and my 243 VampKat, which sports 6 grains more capacity than the 240 Weatherby, is astounding.
I feel that I'm knocking on the doors of the legendary David Lloyd's 240 H & H Magnum rifles. I think that shooting the 80 gr. GMX's and mating it with my Nikon 1000 laser range finder, will let me range and smoke, Yotes and Lopes, out to about 700 meters. Without a good reflective surface, this is a good maximum range for this ambi. laser range finder.
So I will be searching for a really stiff action, with a 3 inch long magazine in a left handed bolt action rifle. It will probably be one of the newer Savages. Last but not least, the Ruger case design is made to go up to 60,000 + M.A.P. The 300 RCM's neck wall is 0.014" and going down makes them a little thicker. So Neil is setting me up to do both inside and outside neck work to keep my neck walls down to his approved 0.012". My PT&G chamber's 243 VampKat's neck diameter is .2775". F.W.I.W. The free online Powley Powder Computer which I use, goes off scale with my 243 VampKat, right in between the 85 and 87 grain bullets.
