6.8 SPC up to 40 for a straight wall AR cartridge.

A friend and I have been piddling around with making a straightwall 40 cal AR cartridge out of the necked up 6.8 SPC. He provided me with some primed cases and I expanded them to 30caliber, then loaded them with some NOE 311284s seated out to the rifling of my Remington Model 14. I used 10gr of 10B101, flake powder from 50BMG plastic training ammo, to blow the shoulder out. It left me a little neck to expand further. I had to single load the rounds and had to use a rod down the barrel to make sure the extractor got over the rim. It shot surprisingly good! I only took 10rds with me and had to walk them up with the first 7rds, but the last three went into about a 2.5" group at 100yds, inside the coffee can lid center of my target. My Model 14 is 109yrs old!

Attachment 302413

I've had that same thought. Since the 6.8(and 10mm) are based on the .30 RR- why couldn't there be a 10x43 mm cartridge for the AR?
Keep it up and keep us posted, please.

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There is:

https://www.thefirearmblog.com/blog/...rtridge-ar-15/

Not based on 6.8/.30 Rem but the article says it could be.

Thanks longbow! I never said the idea was original! The fellow I been working with thought it so. I'll have to get the link to him! They have the bullet I had in mind too, 200gr TC Shockwaves.

Maden-

Howdy !

Great work there !

FWIW -

If you cut-off .35 Remington ( Remington brass ) @ the shoulder / body juncture, you'll find that it has .40" ID, all the way down to just above the web of the case. Straight wall.... straight taper.... no need to expand the brass.

Since that .40" cal ID is constant, one could run the case cut shorter to suit their needs.

Remington 14s and some of their auto-loaders were made chambered for .35 Remington.



With regards,
357Mag

I was looking at using Starline 6.8 Basic brass to do something similar for an Iowa legal deer cartridge. Then the changed the rules again to allow bottle necks 35 cal and larger.

Just buy 6.8 basic brass from Starline and be done with it. I dreamed up .375 on the 6.8 SPC, my friend (he also visits here) Moleman made it a reality for both us, the 375 FUW. Has some case taper to it for feeding easier in AR. Grendel Basic can be used for a forty with slight taper, or cheaper use 308 and cut at the shoulder. Again, NOT cylindrical but is shoulderless, feeds well from taper , cheap or free brass. Can load to a little higher pressure than the 450 Bushmaster, and uses same bolts. Based on Grendel you can use Grendel pressures withGrendel bolt, which is what about 52ksi from memory? On 6.8 brass/bolt you can go to 58ksi. Using the308 base you CAN load to 60ksi IF IF IF you use Oly arms or other oversized bolts/extensions (like they used on their 22-250 ARs). If using standard size diameter bolts/extensions performance will be similar between the three- you just trade larger case volume/lower pressure on 308 case for the inverse on the 6.8 (30 remington ) based wildcats.

Hey stranger! About the same time as the 375FUW I did try a 40-6.8, but MDWS has the 40GPC which is the same thing. The 30-06 case gets you more capacity so that's what another guy and I went with. He's got a 200gr ftx up to 2761 FPS chrony average in a bolt action. Using a 22-250 AR15 bolt and extension with a 16" barrel I'm right at 2600fps with a 200gr xtp. Feeds fine out of 450BM mags with the feed lips bent in slightly and they still work with 450BM. I use the same 450BM mags with the 400FUW, 44x1.8 and 450BM. Built a 22" AR15 last fall but haven't got anything with it yet. Won't be able to hit the same FPS as the bolt action due to magazine length unless stepping up to a 308 framed AR. I've got an extra 308 barrel extension laying around, but haven't found a cheap 40 blank fat enough. Might just use the same GMB 40 gunsmith blank and we've been using and put a savage type locknut on it for the extension to torque against.

Good morning Friend!
Thanks for fleshing out the two 40s you worked with, and for putting up the 40GPC. I’d forgotten they’d done that one until you mentioned it.

Interesting about using the Savage nut as a stop for the extension. Great minds or crazy people think alike I guess! I was considering if that would be viable the other day when I saw some unturned blanks that were on the small size for traditional method.

http://https://mdws.forumchitchat.com/post/40-gpc-load-data-and-tuning-tips-thread-10040804

https://mdws.forumchitchat.com/post/...uilds-10074519

Guys interested in 40 cal SPECIFICALLY on the 6.8 cartridge can look at those links, I used to hang out there. Lots of interesting and useful wildcats in AR15 platform.

http://https://mdws.forumchitchat.com/post/40-gpc-load-data-and-tuning-tips-thread-10040804

https://mdws.forumchitchat.com/post/...uilds-10074519

Guys interested in 40 cal SPECIFICALLY on the 6.8 cartridge can look at those links, I used to hang out there. Lots of interesting and useful wildcats in AR15 platform.

Sorry for the double post on the links guys, it acts crazy on my phone sometimes. @moleman have you tried the 180-200 grain HAP bullets for expansion and holding together? I know on many of your projects you use their XTPs to good effect

Only shot the Hap bullets at targets and they shoot great. I got some Barnes 175 copper bullets (sold as Knight red hot 45 cal 175gr ML sabot bullets) but haven't worked up a load for them. They're the same profile as their 195gr so I coated the 175's to tell them apart.

Well sir those will do nicely, and I imagine at the bore to weight ratio move pretty quick, and Barnes has a good reputation for coppers. I think some of the newer monoliths from the big makers don’t expand as much

Well sir those will do nicely, and I imagine at the bore to weight ratio move pretty quick, and Barnes has a good reputation for coppers. I think some of the newer monoliths from the big makers don’t expand as much. Reason I asked on the HAPs is they look like XTPs which are great, but aren’t skived - it may make the better for these purposes. Or smacking things at 2000fps they may shed their jacks SPECIFICALLY since they weren’t meant for game. The things I ponder when I can’t sleep…..