Has this been done? Has anyone put a 6.8 spc bullet in a .223 case? Sorta like the 300blk which has a 7.62mm bullet inside a .223 case.
I believe that Constructor who posts here & owns ARPreformance has worked up a barrel/load combo for this one!
There are one or two people who have done this and documented it pretty well on TOS in the AR Variants section. I’m in the process of doing it right now, myself. I have the case geometry just about set in my mind and have assembled a couple of dummy rounds with both Speer 100gr Varminter and Sierra 90gr Varmint bullets. I should be good up to about 115gr (for the SMK) with the way I have the brass set up.
Case capacity should be somewhere around 25gr, give or take.
Awesome. I m thinking it would be a better round than .223, 6.8spc, 6.5 grendel and 300blk. All in a AR15 platform using standard bolts and mags.
It is not clear standard mags would work as the rib would hit the larger neck.
Also, this case would want to be shorter than a 5.56mm case.
In order for them to stack correctly the case needs to be cut back to 1.6", that puts the neck behind the first rib and only the bullet touches the rib. The shoulder needs to be pushed back .100-.150 by shortening a 5.56 bushing die. The bullets can be loaded longer where the base is at the donut to keep as much powder capacity as possible. The 6.8 bullets are the correct weight and length so the 223 case gives decent super-sonic performance. For sub work the 300 would be a better choice.
5.56 mags, bolt and cheap brass but is it worth the trimming, sizing and reloading ?
Right now I have my case length at right around 41mm (1.61") and have the bullets seated at 2.255". I used an RCBS 7mm TCU neck (shortened 0.080" bushing die with a .270 tapered expander) for brass forming and a standard 7mm TCU seating die. So far, it seems to work pretty well. I picked up a Lee 6.8mm SPC FCD for crimping when I start building rounds.
Yesterday I tried running unshortend, necked-up cartridges in some of my mags and, while a little tight, they seemed to stack pretty well. Constructor is absolutely correct in that the necks are hitting the ribs in the magazine if the brass is not trimmed shorter. I might build up some dummy rounds for feed checking this weekend and see how they go through both USGI mags and PMags. I will get one each of the Lancer and TangoDown mags for comparison later, as well.
I plan on running this in a 12.5" barrel for comparison with a 5.56 upper I have right now. My velocity target is 2300fps but I’ve got no solid data to support that yet (i.e. no access to ballistics software). I want to see how close I can come to the performance of a 6.8 SPC with what I build. Will this be the new “wonder cartridge”? Probably not and that’s not what I’m trying to do. I just want to build something for myself and see how it works out.
As for the question of is it worth it, for me it is. I enjoy the tinkering and pride that goes into making something on your own. I like the detailed process of reloading. The brass forms pretty easily when properly lubed and, aside from the trimming, there really isn’t that much more to do when compared to a commercially-available round.
You can do 0.20 cal in a 223 case, and have something like a 204 Ruger. You can do 6mm, 6.5mm, 6.8mm, 7mm, or 7.62mm. So many choices.
Where could I possibly find more info on 6.5’s in 5.56 cases?
The AR Variants section on the TOS. There’s two or three that guys are currently working on there.
What does TOS mean?
I refuse to visit that site under any circumstance.:suicide:
Haha, me neither!
I know the guy who owns that site. I have heard rummor they are opening a store in Farmington NY. sorry random
I’ve heard of one person who ironed the .223 case out to a straightwall for a 9mm wildcat. Conceivably, you could do a .311, 8mm or .338 as well. J.D. Jones has a .338 Whisper Mk2 based on the .221 Fireball necked out.
The expander on the left is 270 cal.
Maybe for long bullets?
I remember reading about someone trying this once. I saw it Guns and Ammo, or Special Weapons, or something like that. While I don’t usually put too much stock into those magazines, I did find this idea interesting.
It was called the 6.86mm, IIRC. Whoever made it cut the case down to 41 or 40mm to fit the standard magazines. Out of a 16" barrel, I think the MV was something like 2400 fps with a 110 grain round. From what I understand, that’s about what the .300 Blackout is getting with a 110 grain, and the 6.8mm would probably have better BC than a 7.62mm and thus, would probably be more accurate, better at longer ranges, and providing equal, if not better, terminal ballistics. Actually the only things I could see the .300 BLK having over a 6.8 in a .223 case would be a heavier, more effective subsonic round (On that note, how heavy could one get a .270 cal bullet?)
All this, of course, is theory, but it’s an interesting concept I think.
The heaviest .277 I’ve seen available are:
Woodleigh 180 gr bullets .334 sectional density & .513 BC
Nosler also makes a 169 gr semi-spitzer partition .298 SD & .434 BC
Both are relatively expensive ($35 plus for a box of 50).
The guy who has the big thread on TOS on developing a cartridge like this has stated that he hit 2900 fps with a Speer 90gr TNT bullet out of 16" barrel. With that info, I’m looking for around 2500fps out of the 13" SBR build I’m planning for my cartridge.