Improved M1 Carbine

[GrumpyOlGuy]

Developed a wildcat for the M1 Carbine using .30 cal Blackout shortened to 1.220 case length. Used NATO 556 for parent case. Allows a higher ballistic coefficient bullet (~0.293, 110 grn). Velcity ~2000 fps, energy ~975 ft.-lb. Ballistic calcs show 9mm muzzle velocity at 380 yds. The cases are very easy to make. Cycle fine.

Another development - M1 Carbine in 256 Win Mag Rimless (also based on 5.56 NATO parent case.) Velocity~ 2400 (75 gr bullet), or 2230 (85 gr). Used a 5.7mm Johnson for the barrel. Very accurate (for a carbine) - ~1.5-2 MoA. Ballistic coefficient still around 0.3. Also a 400 yd round (using the 9mm MV as a metric). Cases are a little harder to produce than the Short BlkOut cases. Maybe some overpressure signs with standard propellant. Have used AA1680 to reduce pressure.

 

[1KPerDay]

Sounds cool! What's the bullet for the first one?

 

[GrumpyOlGuy]

There are only a couple of options: speer Spire Point, 110 gr #1855, Hornady 110gr Vmax #23010. Bullet length is the big issue (normal Carbine bullet is about 0.68 in. long; the Speer is about 0.82. Have to find some way to squeeze the longer bullet in and leave volume for the propellant.

Lower drag leads to longer effective range. The other basic fact is that the carbine was only moderately accurate (best I can get is ~2.5-3 MoA. Some might be able to do better)

 

[bersaguy]

Tell me more about making 30 carbine brass from 556. I have dies and projectiles for 30 carbine, but not a ton of brass. Are the heads the same, or close enough?

 

[1KPerDay]

Got any pics of the modified cartridge next to a .30 Carbine?

 

[GrumpyOlGuy]

For the modified Blackout, I used a Blackout reamer and dies, shortened to a 1.22" case length. I just cut 5.56 cases to approximate length and size with a shortened BO sizing die.

I had to modify the carbine bolt (to accept the ~0.380 case base) and the bolt's extractor (about 0.010, as I recall).

 

[GrumpyOlGuy]

So -- this is NOT .30 M1 Carbine! It is a wildcat cartridge. The OAL is 1.69 inch. Case length is shorter than the standard M1 Carbine (by about .060). The case powder volume (with the bullet seated) is about the same as the M1 Carbine.

I only did this to show what could have been done in 1940 -- produce a cartridge that would provide for a slightly greater range (about 375+ yards), instead of the ~250 yds of the M1 Carbine. A tiny bit of additional work would have produced a game-changing weapon (like the STG-44), versus the very good weapon that the M1 Carbine was.

 

[Jim Watson]

Tell me more about making 30 carbine brass from 556. I have dies and projectiles for 30 carbine, but not a ton of brass. Are the heads the same, or close enough?

He's not.
Look at the picture of the slight bottleneck.


I recall an old gunzine article about converting a Carbine to .221 Fireball. He had to load it with roundnose Hornet bullets to fit the magazine.

There were some strange things done to those $20 DCM Carbines. One guy put in a .375" barrel which he chambered for .38-40. He cut .30-06 brass to .38-40 length and crammed it into the sizing die. The unturned brass was so thick that he could seat a .375" bullet instead of the regular .38-40's .401". Loading by guess and by God, he approached .35 Rem. ballistics.
Same approach in the .30 barrel produced the .30 Kurtz. Pressures were no doubt high and the larger case head increased bolt thrust; undoubtedly treading hard on the Carbine action's safety margins. Ackley's book has several other Carbine length wildcats.

 

[GrumpyOlGuy]

The are just like the 300 blackout, only a little shorter - so, yes, it is a slightly bottle-necked case. My chrony indicates velocities are in the M1 Carbine range (anywhere from about 1900 to 2000 fps depending on powder load, 110gr bullet). The max loads are what I use in M1 Carbine reloads (about 13.4 gr WC820 pulldown). Any greater load, and the primers and cases start showing pressure signs. If the powder load is too low, the action won't cycle. So, I keep the loads within the usual Carbine range (I haven't tried to push the load beyond that). It seems pretty good performance from a small cartridge, and rifle.

The ballistics calcs are done using Hornady's online calculator.

 

[748]

I think they should have just made the 30 carbine the 9x33 carbine.

 

[Jim Watson]

The French had it about right with the 1918 8mm Ribeyroles based on the .351 WSL necked down a bit.
We looked at the 1917 .345 Burton which was a .351 WSL firing incendiary spitzers at Zeps.
But in the end, for a pistol substitute we scaled it back to a .30 developed from the .32 WSL.

 

[1KPerDay]

This is pretty nifty.

 

[GrumpyOlGuy]

I know that this has been discussed to death, but as a pistol substitute, the Carbine is pretty astounding. I can hit 200+ yard targets within a pie plate with my old Inland. Not too many people can do that with a 1911 (hmmm -- maybe there are a few).

And - as the comments above indicate, there are many ways to mod the thing.

Maybe you can tell that I'm a fan.

 

[GrumpyOlGuy]

I know this is an old thread -- but here are some pics: Standard M1 Carbine, 256 Win Mag Rimless (87gr), and Sbort Blackout. Also the rifles, and the cartridges in the chambers

 

[GrumpyOlGuy]

BTW - the 256WMR gets up to ~2240fps using AA1680 with an 87gr bullet. WIth a 75 gr, gets to a little over 2400fps. Accuracy can be pretty good (around 1.5-2" MoA at 100). I think the barrel is a little stiffer with the 256 (same outer diameter as a standard carbine, with a bore diameter 0.050 less, so a little more metal in the cross section). According to hornady's calculator, the bullet drop at 300 yds would be about 25" (compared to twice that for the standard carbine at 300) so definitely flatter. I've never actually measured this at the range though.

 

[Jim Watson]

Back when the NRA/DCM was selling carbines for $20 there were all manner of wildcats; anything that would fit the magazine.
Several bottleneck .30s on '06 cases. Open the bolt face, rechamber, and Bob's your uncle. Seven rounds in a GI 15.
The weirdest one was the guy who monobloced the barrel and set in a .375" tube. He cut off .30-06 and crammed it into a .38-40 die. Without neck turning or reaming, it accepted a .375" bullet which he loaded to .35 Remington ballistics. He didn't come back to report on durability, though.
One gunsmith did the same with a .224" tube and chambered and opened up the bolt for .221 Fireball. He had to load it with roundnose Bee bullets to fit the magazine, though.