Perge, scelus, mihi diem perficias.
Here's the "original 10mm Supermag based off the 8mm case.
Ease of feeding from mags!
Ease of proper feed into chamber through AK trunnion opening!
Ease of case sizing.
It looks cool...very similar to 401 win self-loading
8mm brass designed for high pressures and should last for many reloads.
Hard to find good brass.
Most brass is berdan primed
Tends to be expensive.
Wide variety in wall thicknesses below bottleneck on the 8mm brass experimented with.
I still kind of like this one. I had originally planned on using off the shelf 8mm dies for sizing which left it just a hair loose and would have required a special taper crimp or roll crimp. That was what the casemouth headspacing concern was. Now that I'm doing custom reamers and sizing dies, I could adjust the taper on the forming die a hair and make for tighter neck. Getting boxer primed, once-fired 8mm brass is still a challenge, though.
Like all projects, every aspect of this has had its good and bad points. Getting a blunt nosed cartridge with a .532" base to feed from a mag,through the lug opening, and into the chamber reliably is still a looming concern. I should have the reamer done this weekend and should be able to test some of this next week. The barrel can still get another couple inches chopped off if I end up needing to rechamber.
Why can't you use .30-06 brass?
Perge, scelus, mihi diem perficias.
I went through several dozen 30-06 and 270 cases with a variety of forming dies. The problem is that the Neck OD needs to be ~.430-.432 depending on case wall thickness for the 40 cal. The 30-06 is ~.441 at the shoulder. Trimming it back to 1.75" long and the OD is ~.445-.448". That only gives a shoulder of ~5-8 thousanths. I made an expander to widen out the brass and remove the taper so I would have an OD of ~.460". That would at least give me a .015" wide shoulder (more of a bump than a shoulder, though). The problem came when doing the forming. The wall thickness is pretty thick at 1.75" on a 30-06 case. Getting it to reliably and consistently form a concentric shoulder just wasn't happening for me. I had four different makes of brass and they all varied a few thousandths on thickness. When you're dealing with a shoulder only 10-15 thousandths...it makes a difference.
I made a few that would have been usable, but the amount of work to get there was a real pain. The 300 wm brass was very, very simple to do, and came out great consistently.
I wish there was a *readily available, inexpensive", cartridge with a .495 base tapering down to .480 over 1.75". That would be perfect!
added: I had to go back and look...I had wanted to try necking up a 338 Marlin and trimming it down to 1.750"....but it seems those don't exist anymore.
what about Inside reaming to thin the brass on a 30-06 case ??
that what I have done to make my 6mmBRX varaint .
the brass cant be thick or it wont expand an seal against the chamber . this was one of my concerns with the 444???
6.5x55 has a bigger case head than 30-06 an 8mm . its suspoed to be about .480" asI recall how ever most US commercial brass is not .
I looked at 6.5x55 with the idea of running the 6mmBRX reamer in even further an making a even longer case an the bigger case head would fill in the larger chamebr area due to the taper. I was also considering swaging it down to fit my existing chamber if needed .
how about a 375 or 358 cal version . A 358 Bench rest would be just about perfect . then again on A AK a 35 remington or 358 win is cheaper an easier .
could a 41 version be done on 30 -06 brass an just head space off the case mouth easier / I agree there not much of a shoulder . I was thinking abuthat back when I was workign on the 444??
what is 284 win brass like? its a larger OD has no belt an almost fits the bolt . would it work better than mag brass ??
BTW the Handloader's manual of cartridge conversion shows a .40x2" based on cut down 7mmmag brass it was done by AO winters in 1976
it has a neck diamiter of .446 an as shoulder dia of .498" shows a 300gr doing 2332 FPS
there is a 41 Juass that is made from 308 win brass is 1.298' HAS A .436 NECK DIAMETER /.AN A .460 SHOULDER DIAMETER. It calls for the cases to be inside reamed. I see no reason why this round cant be made longer. the brass needs to be thinner in the neck IMO
284 win has a case head of .500" thats only .005 bigger than what your asking for I tcan be swedged down but why bother? . its got a rebated rim thats .470 an will work on a slightly modified AKM bolt or a galil 308 bolt as is .I wish there was a *readily available, inexpensive", cartridge with a .495 base tapering down to .480 over 1.75". That would be perfect!
the shoulder starts at 1.775" from the end of the case an is .475" if cut at 1.775" you would remove the entire neck am you would have a diameter of about .475 . thats just under the .480" your asking for go back a little more an you will have your size right abut the the 1.75"mark .
the brass is not super cheap but its out there . also high quality lapua an norma 6.5x-284 would work also . i doubt its much more than new mag brass an there is no belt to deal with .
I see the 6.5 -284 is just slightly different .
I looked at this round hard for a 44 cal version so i already knew most of the specs
I have always thought a 358 version with a over all length of 2.250" would be the a sweet spot for a big bore vs good speed in a AK/AR length mag well an give a good shoulder . a 40 cal or41 would be about as good . a necked down 458 socom or 50 beowulf basicaly
I believe that is based off the 376 styer brass. There were a few like that. It's actually the perfect parent brass. Again though, the goal was to use something commonly available and inexpensive. Unfortunately, non of these fit that bill.
I'm sticking with the belted mag version. I'll have to look up the AO Winters info. He got 2300+ out of a 2", so I should be pretty well on 2200 for the 1.73" version.
Those seem awfully thick for necks. I use .432" and it seats and grips a 40 cal perfect. That keeps a case wall of ~0.016". pretty close to the .012-.014 of other factory cases I've measured. Those others must have a wall of 0.020+". That seems unusually thick.
Midway shows .376 Steyr at $57 per 50. That's right in line with .50 Beowulf or new .45-70 brass I bought recently.
If I ever get the Beowulf finished, I'll probably wind up shooting it with the gas shutoff closed so I don't wind up chasing empties worth a dollar each...
Perge, scelus, mihi diem perficias.
Hah...yeah and it's also been "out of stock and overdue" since late 2010!
I'm sticking with the belted case. I got the reamer blank heat treated last night and will grind/turn the profile this evening. If USPS will ever deliver my special cutter, I'll get the flutes cut this week and be able to use the reamer this coming weekend. I'm really anxious to get this project moving forward!
I'll do a test chamber in a 1050 steel "barrel" first to make sure it polishes up and is smooth. Might even make a "fire-forming" barrel assembly. The 4th is coming up....think I could do some fire forming in the backyard without concern from the neighbors? Hah!
The heat treated blank. Finish turning between centers and grinding down to final dimensions will remove the decarb surface and true it up if there is any slight warp. Then the cutting flutes will be milled in using an indexable carbide mill.