What if...for slimjim by request, or anyone else, feel free.

fnuser

This is in relation to A.R.'s. What if you could use standard everything i.e. mags, bolts, uppers, lowers, the only thing different was the cartridge and barrel, moving a bullet of @90 g at a velocity of @2700f.p.s. conservatively with a b.c. of greater then .320. Wouldn't that be cool? I'm still cranking #'s but have ordered the dies, upper,bolt carrier group, and am drawing barrel contours in my sleep. So I'm pretty serious. .25 UGALDE, basically an ackley improved .223 Remington case necked up to .257 bullet dia. produced mostly for the contender crowd , thus the moniker .25 T.C.U. Has proven itself in 14" guns already so a 20" or 21" in a basic H-Bar config might be just the ticket. You got one Pumpkin? I only found it in c.o.t.w.#7 so the loads are few but it looks promising. I'll keep you posted.

Pumpkinslinger

I looked briefly at the 7mm TCU for an AR but the OAL is too long. A quick check didn't find an OAL for the .25 TCU but you'll want to keep that in mind.

slimjim

from .25 Ugalde

The 25 Ugalde, also known as the Thompson/Center Ugalde, was developed by Wes Ugalde of Fallon, Nevada, in 1987. The cartridge, like other TCU cartridges, is based on the necked up and Improved 223 Remington case. The 25 TCU is intended for metallic silhouette shooting, but would also make a good varmint cartridge at moderate ranges. There is a good selection of 25 caliber bullets available in weights from 60 to 120 grains. By the standard of today, ballistics are not spectacular, but quite adequate for the intended purpose. Dean Grennell reported less than minute of angle groups. It is in about the same class as the old 25-35 and would be marginal for deer.

This text is based on information from “Cartridges of the World”, Hodgdon reloading manual, the cartridge designer and/or own resources.

slimjim

Ok, fnuser, why did you pick the .257 vs .243? The 6mm/223 or 6mm TCU has gained a lot of interest.

www.ar15armory.com/for...48703.html

slimjim

As I've been looking at alternative calibers for the AR, I've had one criteria - its got to be able to shoot the lighter bullets at velocities greater than 3000 fps. That has ruled out the 6.5 Grendel for me. The 6mm Turbo 40 Improved has sparked my interest.

However, if you are going to use all common components but the barrel, its impressive to see how much more performance one can get with the 6mm/223 over the standard AR cartridge. Makes you wonder why the US Military has hung on to the 5.56 for so long when they can do so much more with just a bullet diameter change and get out of the realm of being a "poodle shooter"

Am very interested to see how your project moves along.

fnuser

pumpkin I did before i ordered the dies this time. Actually the 85g Nosler offering looks custom made for this. Slimjim yeah the 6.5grendal attracted me too, also the 6.8 but neither were quite "it" for one reason or another. i am basing my necking up project on past experience of other wildcats i have tried, take the 35 whelen for example it is about as familiar as its parent. once you enlarge the case neck much further it starts to act more like a straight case then a bottleneck internally speaking and externally speaking the geometry of the .223 case is very similar to a shortnecked 30-06 in its various ratio's so if you factor this approximately (1.16) you get .257.

fnuser

75g's will get close to 3000 but it is all speculative until i actually chono my results with loads that work, I won't use a load based only on velocity.

PaulS

I tried the 6mm TCU in a 24" barrel and couldn't get the velocity anywhere near what I wanted. I had to go to a 30-30 case necked down to get the 3000 fps that I was wanting. Not only did the velocity come up but the groups shrunk down to a nice cloverleaf hole at 100 yards and about 1/4 MOA at 200 using 85 grain Sierra bullets.

fnuser · Last edited by fnuser on Thu Jul 15, 2010 6:07 pm; edited 2 times in total

were you using 85's in the 6tcu also? what did you actually get? .25 t.c.u. load= 24.5gr IMR 4198 85gr Nosler BT--2800fps this data came from another site seems a little hot to me, this was a 21" contender. he didn't list his c.o.a.l. so he might have been seating them out a little to get some volume.

slimjim

Yes, PaulS, this sounds very interesting! Any pictures of the cartridges for comparison? Picture of the rifle? Please tell us more!!

fnuser

slim, I just got a chance to look at the h335 and w748 loads you referenced and 2400+f.p.s. out of a 12" tube sounds promisingthey are seated out though 2.48" probably the longest i could go would be @ .25" shorter 2.245"-2.247"Hopefully you can see the ring I made on the .250 "

fnuser

maybe the 75's without a boattail? I may have to dig around and see if I have some sierra 87g. softpoints if I remember right they don't have a boattail. The rings on the bullets show approximate land contact if I build a gun dedicated to 75g hps it would take alot of experimentation out but might actually simplify stuff, too soon to know but a slow twist might be neat 1-11" or 1-12"

slimjim

fnuser, do you have an on-line source for looking at the .257 TCU load data?

chambered221

What is the intended purpose of this rig ???

PaulS

The only way to get up to even the minimum velocity that we wanted was to go with a 60 grain bullet in the TCU. That got 2850 fps with 26.8 gr of H335. The 85 grain loads were below 2650 fps. This was all in the Contender carbine.
The difference between 30-30 and the 6mm-30 is only the neck - the overall length is the standard length and no angles were changed. It does shorten the neck a little but it is still longer than the one caliber dimension with the 6mm bullet.
One surprising thing we found with the 6mm-30 was that even with starting loads of H335 we had cratered primers from beginning loads to maximum listed loads. We went to H4064 32.1gr and the Sierra 85 grain 1520 bullet and got 3002 fps. A real tack driver that can shoot out to an honest 200 yards on deer or down to ground squirrels.