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Discussion Starter #1
Are there any common calibers that are made by opening up a 5.56 mm cartage. The same way that a .35 Whelen is a opened up 30-06?
 

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The 7mm TCU is probably the best known and most popular. Preformed cases are available and even pre-chambered barrels can be had for some rifles. Some 7mm TCU loads rival the .30-30 in terms of power but with a flatter trajectory.
 

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Unlike the .30-06 case which had fairly large case capacity the little .223rem doesn't lend itself to larger/heavier bullets so well.Altho in wildcats I always thought some of the 6mm,6.5mm,and 7mm were fairly good,I guess most didn't agree with me so there is only a passing demand by wildcatters and none commercially.Still,the lil .222rem case has been bumped up and down in all kinds of borings up to .30cal,and some fairly sucessfully,and in the .17,.20,.22 cal, commercially.
 

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you have the 6mmX45 that has gained popularity. The 300 whisper is another real popular round that can be made on the .223 cartridge.
 

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^True about the .300 Whisper,a really wierd one,(someone with lots of time on his hands) But it,s parent case was the .221Fireball which had the .222rem for a parent case.I wonder if they knew what they were starting with the .222rem.Maybe I just am not paying attention,but I don't hear much about the .300Whisper anymore.
 

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Discussion Starter #7
I ask because at work I was reading about how the Army is trying to beef up their M4s to make them better suited for modern warfare and that Commandant of the Marine Corps stated that the Marines were going to get all that they could out of their weapons before doing any changes. So my thoughts were something along the lines of a 6.5 or 6.8mm bullet weighing somewhere between 120-140gr and seat it so that it would be able to accommodate use of the standard magazine, the only change that would be needed is a different barrel on the M16/M4 upper receiver, but the ability to keep the same lower, same upper, same mags, and the same cartages but with the newer projectile would equal a huge savings to the American tax payers while giving the U.S. Military a better weapon system.
 

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Discussion Starter #9
I was thinking more like putting the 6.5 or 6.8mm projo into the 5.56 cartage and seating that so that it will fit into the mag.
 

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There's already a 6.5 223. The 6.5 TCU. I have a TC contender in 7mm TCU. I necked up remington 223 brass to 7mm in a 7mm TCU FL sizing die, and then fire-formed them to achieve the 40* shoulder. Cool cartridge. I'm running H322 under a 120gr. sierra prohunter.
The case on the left has been necked up and fire-formed, the case on the right has only been necked up and not fire-formed.

 

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Discussion Starter #11 (Edited)
ok thats pretty much what I am thinking of then. Any idea how well those will fit into a AR mag or how well they preform out of a 20 inch barrel? Cool looking pistol by the way. I don't know hardly anything about the TC contender line of weapons but I have heard good things
 

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No idea how they'd perform in an AR mag. Longer than the standard 223 case, may work in a 6.8 mag or 308 mag. They'd probably do just fine in a 223 mag though. From what I've heard the lighter bullets can rival the 7mm mauser in the right length barrel, out of a 20" though, not sure.
 

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Mmmm,

you have raised an interesting point. As others have noted the five point five six case is not so adaptable to a wide creative range of bullet designs.

Personally, I feel Thompson Center has pretty much explored the creative limits of this case.

I do admire your post.
 

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... From what I've heard the lighter bullets can rival the 7mm mauser in the right length barrel, out of a 20" though, not sure.
this is difficult to believe. with 32 gr water case capacity vs. 58 gr with the 7x57 Mauser it really isn't a fair comparison. the 6.5 TCU gives slightly more energy at the muzzle than the 7 TCU, but even so it is 800 ft-lbs less than the 100 gr 7mm Mauser at 2200+ ft-lbs ME. The 6mm-223 with 80 gr. bullets can go over 1400 ft-lbs ME, and the 223 itself goes into the 1200+ ft-lbs area with maybe the odd hot load getting over 1300, so the improvement is at best 20% with these wildcats. The 6.8 SPC can go over 1700 ft-lbs so it shows a significant improvement over the 223, and AR uppers are available. Not to rain on the parade, but even this relatively simple change has not been accepted and a lot of research went into its design to make as much use as possible of the AR platform.
 

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The 7mm TCU was never meant to be accepted by the masses. It was created simply out of a need for a light recoiling cartridge that could be fired out of a thompson center pistol and still have enough energy to knock the rams down at 300 yards. That's the whole point of the caliber. Just because the TCU calibers are not accepted does not mean they are bad calibers and have no place in the shooters world. They're excellent very efficient calibers, and the way I see it, if a TC contender in 7mm TCU can drive a 100-120gr. jacketed bullet out of a 14" barrel roughly 1900 for the heavier weight up to 2200 for the lighter weights, I see no reason for it to not rival the 7mm mauser in velocity with a rifle length barrel.

EDIT: With the right powders, even out of the 10" barrels like mine, with lighter bullets the velocities get on up there.
 

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Great read guys !! Very informative. A 6x45 sounds interesting.
 

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Great read guys !! Very informative. A 6x45 sounds interesting.
Look up the 6mm TCU. Wes Ugalde did quite a few things with the 223, and although simple it's still all very interesting. I love the 7mm TCU and loading for it has taught me a lot about wild catting and even more about reloading.
 

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my online loading data program didn't list the 6 TCU, but did the 6-233 so that's why I posted that.

I just don't think there is room enough in the 7 TCU case to take advantage of significantly longer barrels.

the best data I found was (rounded):

7 TCU 100 gr. bullet 2440 fts and 1322 ft-lb ME using 14" barrel
------ 120 gr. bullet 2100 fps and 1200 ft-lb ME

7x57 100 gr. bullet 3256 fps and 2346 ft-lb ME using 24" barrel
------ 120 gr. bullet 2900 fps and 2200 ft-lb ME

that's a significant difference. Now put the 7x57 in a 14" barrel and it would lose a lot simply because only so much powder can get burned in the shorter barrel. So, yes, the 7x57 in a 14" barrel might approximate the 7 TCU, which obviously would be more efficient. Stated another way, using a 14" barrel for a 7x57 Mauser would be pointless.

But the other way round is what I think is doubtful. Adding barrel length for the 7 TCU wouldn't yield anything close to what the almost 2x case volume of the 7x57 can do in the longer barrel. You just can't pack enough more powder in there to take advantage of the longer barrels.

But to get back on point, the 7 TCU, the 6.5 TCU, and the 6 TCU (or 6-223) would be better than the 223, but not as much better as the 6.8 SPC and that has already been nixed.
 

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There is plenty of room in the 7mm TCU case to take advantage of longer barrels. All it simply is, is a 223 case, necked up to 7mm, with a 40* shoulder to take up for lost space. Ever loaded for it? Most powders will fill the case almost 100% with slightly compressed charges. 2100fps in 14" barrel is fast, and it's not much less in a 10" barrel. Put it in a 22-24" barrel and you'll be getting very close to 7x57 velocities with the lighter bullets. The only place it won't beat a 7x57 is with larger bullets, because there's simply not enough case capacity there anymore to propel the larger bullets even out of a longer barrel at speeds close to the 7x57. Maybe the 7x57 is not a good comparison, maybe the 7mm-08 would be a better comparison. Those who doubt the capabilites of the cartridges Wes Ugalde created off of the 223 obviously just don't have a lot of experience with them. There's a reason they were created based off of the need to have a light recoiling cartridge pushed out of a 10-14" barrel with enough velocity to knock rams down in 300-600 yard silhouette. I'm not insulting you in any way so please don't take it that way. I just have done a lot of experimenting with the 7mm TCU in the short time I've had one and it has seriously surprised me.
 

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Maybe the powders in Hornaday's new superperformance loadings will make a significant improvement. I think I read here somewhere that those are going to become available to handloaders.
 
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