DsGrouse wrote: ↑Mon Jul 21, 2025 10:06 am
rickhem wrote: ↑Mon Jul 21, 2025 8:23 am
I loaded up 25 rounds of 6.8 SPC-II for my final confirmation test, after going through a couple ladder tests. These are loaded with the Speer 90 TNT bullet over a charge of Reloader 7 powder. This should give me just short of 2900 fps in my 18" barrel.
The big deal is that my rifle has the 6.8 SPC-II chamber, and only the original 6.8 SPC chamber is SAAMI certified. The SPC-II is a bit different, in that it has what I'll simplify as an extended chamber. There's more to it, but in short, it allows a round to be loaded longer, and that gives a bit more room for powder, and the charges for the SPC-II chamber frequently go past the published data for the shorter SPC chamber.
So what I'm finding in my rifle, is that I'm not quite at the charge weights that others find optimal, but I'm getting well under MOA at 100 yards with a few loads surrounding this confirmation load. If this works out, I'll have a load that can deliver that kind of performance, even when the charge weight varies by a couple tenths of a grain over or under my targeted charge weight. That means just throwing charges is fine, and it'll make loading much quicker.
The target will be my decider though, and I'll see how that looks in the next couple weeks.
Now you have me interested. I've picked up a .270 die set. One point form for mid weight .270 win bullets, and one shorter spire point for 6.8 spc bullets. I'd like to learn more about the cartridge.
Are you using gordons reloading tool to model the pressure in your SPC II chamber?
I'm not using Gordon's for this. I have been accessing the major bullet and powder company data posted on-line, and have received some from other companies in response to email requests. They've all been great, and Sierra even sent me a PDF of the 6.8 pages from their manual. There is also a very active forum over at 68forum that has a lot of great info, more info than you can imagine on that site.
My rifle was kind of a "right place, right time" deal, where I built up a stripped lower with all parts I selected. I have a Magpul UBR Gen 2 stock and a Geissele High Speed National Match trigger, and all the other lower parts sourced from White Oak Armament. I was intending to use it for a Service Rifle upper, but along came a buddy that had an upper he bought over 15 years ago and had never fired. It was a 18" 6.8 SPC-II that he got from Compass Lake Engineering in Florida, all set up to be used as a service rifle, as this was back when the AMU first proposed the 6.8 as the next version of the M16. He had a full set of Redding dies, and even threw in a pile of brass that he got from some AMU guys way back when. Made me a deal I couldn't pass up, so I bought it.
In short, it's a .270 bullet loaded in a cartridge case designed to fit and function on an AR platform, and provide increased terminal performance over the 5.56 round. It has a max pressure of 55,000 psi, and with a smaller head size, no issues with the bolt like the Grendel size cartridges have. The 6.5 SPC-II has a bit longer freebore, but was never SAAMI certified, so variations exist. (just like .223 chambers) It never really caught on, and has fallen from favor, but is still a fantastic hunting cartridge for hogs and deer.
