[The_Eccentric]

Haven't seen it in person, but the Winchester factory 400L ammo is supposedly available.

 

[The_Eccentric]

The base of the case is only 1 thousandth of an inch smaller than the Grendel/ARC case, so that is possible. The odd thing is the 45,000 psi max pressure vs the 52,0000 for the Grendel/ARC. It makes me wonder if there were bullet issues or if the pressure was held down for a particular rifle design. Possibly a lever action?

There may have been bullet issues that influenced that pressure ceiling decision. The 10mm mag is the highest pressure cartridge that any of the available 40 cal bullets were designed for. They may also have held it at 45k to reduce stress on the AR extractor. That's a long, relatively straight case. No shoulder, and no reduced neck section. Much more case wall surface area than on a grendel/ARC, and far beyond what the AR15 extractor was designed to overcome.

The lever gun angle is possible too. Wouldn't take much more than a barrel, a different extractor, and a different cartridge stop to adapt a 35Rem Marlin 336 (or a Henry derivative) to 400L. A Winchester 94 would be a little more involved, but certainly doable. Wouldn't be the first time that an autoloader cartridge was later used in a lever gun. I have a box of 35 Rem factory ammo that is so old that it has spitzer bullets. The 35 Rem wasn't chambered in a lever gun until 1948 in the M336. It was first chambered in the Rem 8/81 autos (with box mags), then the Rem 14/141 slide actions with the spiral 'safety groove' mag tubes to prevent spitzer/primer contact, and various bolt actions (with box mags) for decades until it appeared in the M336 that required round/flat nose bullets for safety.


There's a youtuber that's been shooting a 400L upper that 'someone' built for him. Someone also provided him ammo for it with cases headstamped 6.5 carcano. He's been getting some very impressive ballistics. Funny thing is that he still states that the 400L is 6.8 spc based.....

 

[The_Eccentric]

Are cases going to be makeable from the starline 6.8 basic cases?

Nope, but they can be (and have been) made from 6.5 and 7.35 Carcano cases.

 

[The_Eccentric]

I'm thinking it's probably available bullets is the reason for the low pressure spec.

I hope it could be done. Probably be a PITA. Have to be in stages I'd guess. It's beyond my knowledge or skill currently, but I sure like the idea of a ARC capacity cartridge able to take SPC pressure and maybe squeeze more speed from it than the ARC.

That'll likely be the best thing for AR15 wildcat tinkerers to come from this 400L introduction.

 

[The_Eccentric]

R Spomer and others on youtube are incorrect. The 400L isn't based on the 38-55/30-30/30Rem/10mm/6.8spc/221val case family. The only thing the 400L case shares with those cartridges is the rim diameter.

Rather, this round is based on the 6.5 (and 7.35) Carcano/220Russian/7.62x39/220ppc/5.45x39/9x39/Grendell/ARC case family. Head and body diameters bear this out. The 400L has the rim rebated to .422" from the origional .447" of those cases.

This combination gives a few advantages. The added body taper compared to the 400AR and similar earlier 30Rem/spc/etc based .40 wildcats greatly aids feeding. A 40 cal rifle round based on the 30rem/spc/etc case is basically straight.

The .422" rim of the 400L allows the use of the stronger spc/val bolt in place of a x39 or Grendell AR bolt. As stated earlier, bolt thrust is controlled by case head diameter, rather than rim diameter. The .422" rim diameter just allows more support for the locking lugs at the bolt face. Of course, in a bolt gun or an AR308 based rifle wouldn't benefit from the rebated rim.

I've been pondering a carcano based 1.6" long .400 wildcat with a 30rem/10mm .422" diameter rim for a few years for those very reasons. Never had the time to build it however. Too many other projects. A few folks have used the carcano/Grendell case for .40 cal wildcats already. This is the first I've seen with the .422" rim.