7 TCU rifle?

[awp101]

I saw where someone put together a 7 TCU bolt action with a 21" or 22" barrel and it struck me as an unusual choice. I thought the TCU cartridges were optimized for 12-14" barrels and you'd hit a point of diminishing returns in a 20+" barrel.

Do the TCU's see a major benefit going to a rifle length barrel?

[Encore64]

Yes indeed. I can't quote numbers on the 7mm TCU, but I've had a 257 TCU Carbine for years. It crowds a 250 Savage close. An 85 gr BT at 2900 fps and 100 gr BT at 2700 fps.

[magnumwheelman]

I would think powder selection would make a big difference... I don't use the same powders on some cartridges between a 10" & 14" Contender

actually several of my favorite bolt action rifles use small case cartridges... 17 Fireball, 22 K Hornet, 223, 6.8 SPC...

been working with a buddy that has a 22 TCM semi auto & bought an Early TCM bolt action rifle... machining is really rough, but he can fix anything there himself... but I've been working with him on brass prep & loading details, bullet choices... factory ammo shows excessive pressure in both guns ( think they are having to load too hot to meet their expectations ) even on a lil cartridge like the 22 TCM, he's safely getting 400 fps faster speeds in the rifle...

[awp101]

Thanks, I thought powder selection might play into it but I didn't know how fast you'd hit the point of more powder for less gain.

It doesn't surprise me the machining is rough. As much as I like my RIA GI model, refined it's not. That's interesting and a little concerning that factory TCM is showing pressure signs in factory firearms. Fortunately the TCM hasn't grabbed me but I'll file that away in case someone asks me about the round.

[bradshaw]

Ben ”Bear Man” Kilham barreled a SAKO L461 .222 Remington to 7mm TCU, not long after T/C built a pair of bull barrel Contenders----10” for IHMSA Production, and 14” for the Unlimited category----in 1979. As we step past shells like the .45 ACP into magnum revolver rounds, a carbine or rifle barrel quickly ramps velocity. In 7mm TCU, a load which clocks 1,700 fps from the 10” barrel, may read 1,850 fps from the Super 14-inch. A 16 or 18” carbine adds more. To look for a powder for the 7mm TCU, make Hodgdon or IMR 4895 the hub of the wheel. Branch from there. Numerous medium burn powders provide accuracy with a spectrum of bullets.

Magnum revolver round jump 300 fps and more from revolver to carbine. Hell, two revolvers may register 300 fps difference for the same load. Trouble lurks for those who play the velocity game with fast powders.

The 7mm TCU (7mm/223 with 40-degree shoulder) is a fabulous single-shot pistol cartridge and a fine carbine round.
David Bradshaw

[awp101]

Thanks!

With a couple of .223 rifles already in hand and a different .223 based wildcat that just made it's way into the safe, I might look into this a little deeper since a common case would make logistics a little easier.