6mm TCU in an AR, anyone try it?

204 AR

204 AR

Well-known member
Basically a 6x45 improved. I already have a pair of 223 AI's, so I know they will work. And a long barreled, accurate 6x45 that I'm considering having a local guy ream out to 6 TCU. Any thought?
 
Originally Posted By: 204 ARBasically a 6x45 improved. I already have a pair of 223 AI's, so I know they will work. And a long barreled, accurate 6x45 that I'm considering having a local guy ream out to 6 TCU. Any thought?

the big question is why, I don't see what a 6x45 offers over a 223, in order to wildcat I think you need to have the new case give you something that you don't already have. You can't really run a heavier bullet or substantially heavier bullet because you will loose case space. The only 6 I am seeing that makes sense in an AR is the 6x6.8 several guys around here have been talking about. That does offer something although I don't think even it is as much as most people think if you load both rounds to equal pressure.
 
You would see some minimal gains wuth the TCU but I don't think it would be worth the fireform issue. I shoot four 6X45 rifles and enjoy them greatly but the 6X6.8 has mine setting on the shelf now. The moving up in power is noticeable. As a big game cartidge it shines and leaves the 223 based rounds in the dirt for long range predator hunting.

The 6X6.8 is loaded to higher pressures than the others and with that you do get real world quantifiable performance boosts.

Greg
 
Um well I'm sure a lot of people will beg to differ. I was testing 87 and 85 gr hpbt's in my 6x45 yesterday afternoon. It seems 2800 is attainable, maybe more. I modded an aluminum mag and can load to 2.350" oal now. The question I'm asking is how much more does the improved version offer, and has anyone built or tested one and how well did it work. I'm guessing you could see an additional 100 to 150 fps. That would put 55's and 58's close to 3400 fps+.
 
Oops we were typing at the same time Greg, my post was a response to Steve.

Greg what speeds are your most accurate loads in, say, a 22" 6x6.8? with various bullet weights.
 
don't know anything on the tcu but from the way it sounds the 6x6.8 would maybe give it a fairly good black eye in a dual.

fwiw: from my 22" I can get 3500+fps with 58s, 3300fps with 75s and the very limited testing I did with 87s 3100fps isn't out of the question.
 
You can push the 87's harder without a doubt. A 5% increase in speed might be a bit optimistic. Most gains tend to be in the 4% volume increase yields about a1% velocity increase. I would say that the 50's can be pushed pretty fast since the expansion ratio is so good.

Greg

PS: MWP has the speeds down at a reasonable sane level BTW.
 
Those speeds you're talking put the 6x6.8 pretty close to 243 territory. That's impressive. I was simply looking to get an increase out of the barrel/upper I already have. And add the benefit of not having to trim brass, improved rounds don't ever seem to grow in length.
 
Tcu probably wouldn't be a bad way to go but for the costs of a re chamber, you could probably buy a 6x6.8 barrel and bolt and sell your 6x45 barrel and not be out much more money. Either way you will need New dies and although 6.8 brass does cost more than 223, the extra performance is worth it.

Also, I have not seen a whole lot of case stretch in my 6x6.8.
 
Those are good points also, I'll consider that. Truth is if the barrels were readily available I would probably buy one as an impulse buy. Just when I go to order one I chicken out bc I need another AR like a hole in the head, lol. Right now Midway has factory AA 6.5 Grendel uppers for $717 and it's all I can do to hold off!
 
One thing that just occured to me is that all the data I have seen on the TCU was shot with a single shot pistol oriented reamer loading out to as much as 2.500" A TCU rifle would have to be done with a dedicated rifle chamber reamer or a live, I think that's the term, pilot and a throating reamer.

If this project goes forward I am really interested in the report on performance.

Greg
 


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