6MM TCU Verses 6X45

[pistolman44]

Is a 6MM TCU the same as a 6X45 They use the same 223 brass that is necked up to a .243 boolit. What I'm asking is can you shoot a 6MM TCU in a AR 15 chambered for the 6X45?

[madsenshooter]

No, the TCU has a slightly larger shoulder diameter and a different shoulder angle. Not much of a difference in capacity. To complicate the validity of that statement, at one time I think the TCU was the 6x45, then they decided to give it the same treatment as the rest of the line. So you might find some that would fit. One could size the TCU down to make 6x45. I've been shooting an AR in 6x45 with an Obermeyer barrel. It's not wanting to go very fast with cast, don't know if it's the tight twist, the 5R rifling or a bit of both, 1700-1800 seems the best for accuracy. By the way, the Lyman 245498 when seated to the crimp groove, will just fit into a steel magazine. And, BaBore sells a mold designed for the 6x45 ARs. I've gotten my best so far with an Eagan design that I have the cherry for, but it isn't for everyone, seems to have been made for the Obermeyer's .233 bore. Most 6mm barrels have a larger bore diameter. Here's some of the results I'm getting: http://castboolits.gunloads.com/showthread.php?p=1227207#post1227207

[pistolman44]

Thanks for the info. I want to build an Ar15 in a 6X45 caliber. I have a Encore in the 6MM TCU caliber and thought It was the same. But you cleared that up for me.

[madsenshooter]

I'm beginning to like mine. The twist on the Obermeyer is tight enough, 1-8, that I should be able to shoot 105gr A-max bullets out of it, got some, but been busy trying to get it to shoot cast. It loves 87gr jacketed bullets.

[Moonie]

I would think running a 6mm tcu finishing reamer into the 6x45 chamber would be enough to convert it to 6mm tcu.

Just a thought if you wanted to keep the ammo the same between them, and the dies...

[madsenshooter]

I don't know what effect that would have on feeding. Might work, I don't know.

[Bullshop]

I am not sure on this but I think a big difference between the two is in the throating. To my understanding all the TCU cartridges are very long throated because they were intended for single shot TC Contenders so the over all length did not matter.
If you chamber a TCU cartridge in an auto loader your OAL is limited so the bullet/boolit will have quite a long jump through a long throat to engage the rifling. Not a good arrangement for accuracy.

[45r]

I'd go with the 6x45 over the 6tcu in a AR.It is easy to make and throated right,doesn't need to be fire-formed.In a magazine article I got a 6x45 AR from LBC shot half inch groups at 200 yards with BlackHills ammo.Wish I had 2200 bucks to spare.

[27judge]

check out my pm to you on a ar15 6x45 tks ken

[madsenshooter]

One thing I've discovered, you'll want to anneal the necks after necking up the 223 to 6mm. I didn't and I'm loosing a lot of cases to neck splits. 45r, get with 82nd Airborne, he built the upper for me with my $10 Obermeyer barrel.

[45r]

One thing I've discovered, you'll want to anneal the necks after necking up the 223 to 6mm. I didn't and I'm loosing a lot of cases to neck splits. 45r, get with 82nd Airborne, he built the upper for me with my $10 Obermeyer barrel.

I talked to Aaron about the 6x45 and he said it was one of his favorites.I'm waiting on a .45x284(450BM) he said he would make for me.I've been playing with my 24 inch Colt H-bar Elite untill I hear from him.Its been shooting real well,under an inch with Hornady 55 grain J-words with H-4895.It shoots half inch with 52 grain SMK's with Vitt-133.I'm ready for the woodchucks.I'd like to get a 18 or 20 inch 6x45 for coyotes and deer.After I get a big-bore AR a 6mm is next on my wish list.

[madsenshooter]

If you plan on using cast in the 6x45, don't make the mistake I did. I know the twist in that Obermeyer is at least 1-8, maybe tighter. So far best accuracy is coming at only 1650-1700fps. Could be the fast twist, might be the 5R rifling. The design of the bullets I'm using might be a part of it too. The Eagan is a bore rider with very little in the way of driving bands and the Lyman 245498 has a lot of unsupported nose. Also, if you want yours to cycle with cast, I'd recommend a carbine length gas system. I had a rifle length tube put on mine, 4198 with 55gr j-words won't cycle it. 2015 will. For my cast loads, it becomes a straight pull bolt action. I've got a new convection oven coming, maybe with some oven heat treating I can get a bit more speed out of the boolits.

[madsenshooter]

Here's what will probably be the best you're going to be able to do with cast, if you get your 6x45 with a tight twist barrel that will stabilize 105gr j-words: http://castboolits.gunloads.com/showthread.php?t=104680&page=6 See post #118. You might find a better combination, but I doubt the possibility. I guess minute of coyote noggin at 200yd isn't bad, but I'd like to be able to pick which eye.

[gee-gaw]

I've been runnin a 6MMX45MM ( 6X.223 ) for a couple of years on an AR platform and have been real pleased. First off, I don't consider it a heavy bullet cartridge. You have a relatively small combustion chamber, and even in a bolt action, there just isn't enough powder to launch heavies at a useful velocity. I varmint hunt with 58 gr. V-max at a true 3400 FPS. That's kinda hard on WW cases and I only get 3-4 loadings from them before they hit the scrap bin. I deer hunt with Speer 80 gr. Hotcores at 2950 FPS. These do a good job at the short ranges that I hunt in East Tenn. On my hunt in West Texas for varmints, this was my go to gun. I killed several coyotes and a huge bobcat with those V-max, and found that they do real good out to 200 yards if I do my part. I didn't try them beyond that range. Up close, say inside 70 yards, they are devastating, blowing legs nearly off and making large wounds that anchor the critters right there.
My barrel is a 1 in 12" twist Krieger that is just over 23" long. while shes not a benchrest gun, I can count on 1/2" to 3/4" groups at 100 yards with my magazine length rounds. With the relativly slow twist rate, I've not tried cast bullets in it, as most are heavier than 90 gr.
The TCU looks to be the 6x.223 that has been ackleyized ( is that a word? ) with the straight body and 40 degree shoulder. My friend Brad Richardson of long Range Precision, say the .223 Ackley feeds fine from regular magazines in the ARs he has built on this cartridge.
All this is just my experiences with this round, your mileage may vary.
Wayne