7mm-223 wildcats

[Carlos]

What about the 7mm T/CU or .223/7mm from a 20" barrel?? I looked at the published data but it was all for 14" Contender barrels; out of a 20" w/ 150s it would appear to make major & the drop at 300 appeared to be 18" over 12" for the .223. Seems like it would feed from AR maks just like .223. I understand it is common to split necks on .223 necked up that much but beyond that . . .?

[ErikW]

As I understand it, the 7mm TCU is too long for M16 magazines. I'm not sure if this is just with the heavy (long) bullets or if it also applies to lighter (shorter) bullets. If you look at the heavy 7mm bullets you'll see there's no way.

130 gr

150 gr

But, check out the 7x40 Improved.

This cartridge is formed by full length sizing 223 brass in a 7x40 improved die and trimming to 1.590"

The cartridge is derived from the 7mmTCU, shortened to feed in the AR15 action.

When loading, start with 10% less powder than similar 7TCU starting loads.

Powder capacity is about 3 grains less than 7TCU.

Velocities in rifle barrels will exceed the 7TCU pistol barrel data that is commonly available.

I am awaiting a reply to my e-mail asking for details of this wildcat, including the heaviest magazine-fed bullets and typical velocities. I'm wondering if it's the same or similar to one of these:

7mm-223

7mm-223 Improved 30-degree

7mm-223 Improved 40-degree

Edited March 29, 2004 by Erik Warren

[Carlos]

Quite promising! I noticed that the "long" data for 7 T/CU is all for 14" barrels & while I can't say for certain, it would appear to easily exceed major in an 18 or 20" barrel. Even if 7x40 gives up a little case volume to the TCU, it may still comfortably exceed major w/ a couple of bullet weights.

7x40 cost? For brass, its 223 w/ one extra reloading step (necking up) some trimming and fire forming (plus die cost & bullet expense). There would also be the cost of the new upper. A benefit would be simple practice by switching to a similarly set up top end & using cheap .223 (though the recoil would obviously not be the same). Reloads & trigger would match though. Personally, I have WAY too many projects on the back burners to tackle this one. Erik? Kelly? Erik L.? Mig? Anyone??

[ErikW]

Randall at AR15barrels.com replied to my questions... (quoting from 2 e-mails)

>The 7x40 is one of those interesting ideas that I had that never really came

to be finished.

>I started an upper, but never finished it out.

>It uses cut down 7TCU dies and 223 cases to form.

>Think of it as a necked down, blown out and forward 7mm whisper.

>You can use just about any weight bullet you want and load to magazine

length.

>Keep in mind that the bullet will impede into the powder just like it does

in the whisper when you run heavy bullets.

[Bear1142]

Carlos,

I have plans for a 7mm whisper. I think it has some real potential, but it's a back burner project right now. I'm hoping to start preliminary work on it at the end of this season.

Erik