I have had a 6.8 SPC stainless heavy varmit barrel (remington take off) for over 2 years and a 223 Bulgy bolt to enlarge for a 6.8 SPC build. time and other projects have been infront of it. I posted here and on another site several times abought it.
A AR to AK mag adapter was the original plan but those all got bought up and now are really pricey.
I have put 4 rounds of 6.8 into a unknown steel 5 round 223 mag and they seem fine to me. they dont fit well in my bulgy plastig mags as well the lips are just a little to far apart to hold them in they jump out easly. Now here is some thing interesting. In the only 223 ProMag I own I can easly get a whole box of twenty rounds in to the 30 round mag and they seem to not bind or jump out This may be a doable cheap USA mag for this build (I am very aware of Pro mags poor reputation and this mag works poorly in my 223)
my plan was to use a Rommy kit and add the bulgy bolt just like my 223 varmit build. however I can say that a 7.62x39 bolt will pull a 6.8 round round out of a normal AK I just put a round in the barrel (it wont fit all the way in ) and closed the bolt by hand and it will catch and pull and eject it with no mods!!! HMMMMM I cant say what it will do with a fired and expanded case fully seated in the correct chamber however, IT IS POSSABLE THAT A 7.62X39 BOLT WILL WORK AS IS OR MAYBE WITH A MODIFED EXTRACTOR POSSABLY A TRIMMED 223 OR 5.45 ONE. I get a .418 rim on my silver state armory brass and I have seen 7.62x39 brass as small as .440 so were only talking
.022 differance here. If a 7.62 bolt will work this will make this a lot easyer and cheaper build IF IF IF.
also any 270 winchester barrel could be rechamberd to this round for a dirt cheap build
to be honest I dont see the 6.8 nearly as good as a 308 the trajectory is close only when you compare the 115 GR 6.8 to a 150 GR 308. and even then at 300 meters the the 308 is faster an has 200lbs more energy. at 100 meters the 308 has a lot more energy almost 500lbs thats a lot IMOA.
were the 6.8 rally shines is over the 5.56 77 gr were it has very simular velocitys clear out to 1000 meters but at that range has nearly twice the energy (228 LBS )
dont get me wrong the 6.8 spc is a lot better than a 223/5.56 but is to far from the 308 IMOA to be in the same class. also if a lighter 308 bullet were compared the 308 really out shines the 6.8 with a lot more speed.
As far as on A AK platform pressures are no issue as the reduced rim size equates to 7.62x39 bolt thrust pressures. as far as the 5.45 pressures giving the velocity these shoot I, suspect it is right at 50,000 PSI as well. This is a build I am going to do at some point. likely in a hunting pistol. I really would rather have a 6.5 Grendal or a 243,260 remington, 250 savage ,300 savage, or a 308 even loaded to a lower pressure over the 6.8 SPC IMOA