6x45 vs 6TCU vs 6.5TCU for whitetails - Rifle build

[JD95]

Hi guys!

Im looking for information (especially first hand experience) with 223 based wildcats for White tail deer. Im a lefty, and I have a cz 527 in 223 that wont shoot a reliable sub 2” group with anything Ive tried (many combos of h335, varget, different seating depths, and a variety of Varmint and target bullets from the 53gr vmax up through 69 SMK). I even glass bedded the action to no avail. Now, I want to do a barrel swap to a new cartridge and turn the rifle into a handy deer rifle. Converting the rifle to something that doesn’t use the 223 parent case is significantly more difficult and expensive, so Id like to stick with the 223 case. Id like for the rifle to feed from the magazine. I made up a dummy 223 round and found that the maximum length to function in my magazine is 2.334”. Id like to keep barrel length to 20-22”, but would begrudgingly go to 24” if that will really make the difference. White tail deer under 200 lbs mostly within 100 yds, maybe pigs under 200lbs , and possibly predators inside of 300yds if I see them while hunting deer are the prime targets. Id prefer to send heavier bullets at a max velocity of 2700fps for the sake of avoiding meat damage and maximizing penetration through higher SD in these relatively small projectiles.

So far Ive done a lot of reading about the 6x45 and 6TCU. Im fairly confident that I can seat 90 Ballistic tips, 95 Ballistic tips, or 95 Partitions to magazine length. I suspect I can probably get the 90BT or 95 Partition to about 2700 fps, or the 95BT to 2600+. Out of those options, Im probably most enthused about the 95BT, especially if I can get it to roughly 2600-2650 fps. Has anyone tried something similar to this? Would I need to look into the 6tcu instead of the 6x45 to get this kind of performance? Id like to avoid fireforming brass if I can, but Ill do it if that’s what gets the end result Im after.

Ive also spent some time thinking about the 6.5TCU. In 6.5, Id only really be interested in bullets between 120gr and 125gr. A few options that come to mind would be the 120BT, 125 Partition, or the 123SST. The only issue is Im not sure how fast I can realistically expect to get those bullets moving from a 20-24” barrel and a 6.5TCU case. OAL to fit inside my 527 mag also becomes problematic because I can only afford about 0.590” of bullet outside the case and Im worried these 120 class 6.5 bullets all have longer ogives than that.

How fast do you guys think I can get a 120-125 gr 6.5 bullet moving without exceeding reasonable pressures for a rifle chambered in 5.56? Any ideas on which powders would yield top velocities and workable accuracy for hunting (1 moa or better)? At 2400fps, it probably becomes the winning option. At 2500+fps, it becomes dang near a 6.5 grendel and I would completely stop worrying about terminal ballistics. All load development will be done over a chrono.

If anyone happens to have any of these dimensions, it would really help me out. Covid economy has made purchasing (or even locating) projectiles really difficult and expensive.

6.5 123SST – overall length, ogive length

6.5 125 partition ogive length

6 95 Ballistic tip ogive length

6 90 Ballistic tip ogive length

6 95 partition ogive length

Thanks for any help or advice!

 

[Mike Casselton]

I would think that the 100gr 6.5 ballistic tip would be a perfect match with the 6.5 TCU.
Honestly, you could build the load and hunt with the fire forming rounds without issue.

 

[JD95]

Mike,
Thanks! I considered the 100gr ballistic tip for 6.5TCU, and I agree that it would be much easier to get it to seat at mag length than the 120. Believe it or not, the 95gr 6mm partition is actually shorter than the 100 gr 6.5 ballistic tip with a higher sectional density and ballistic coefficient to boot. Its true that I might get a bit more muzzle velocity with the 100gr 6.5 option but either option is on the verge of exceeding the velocities I want anyhow. In that case, Id probably gravitate towards the 6mm option. This was my train of thought for why I dont want anything lighter than about 120 in 6.5 TCU, I think the 6mm is a little sweeter in that weight range. Thanks for taking some time to help me out!

EDIT - its worth noting that I dont have a lot of experience with this, so maybe my "train of thought" is wrong?

 

[potatojudge]

There is considerable hunting experience with the TCU rounds on the specialty pistols forum.

The key to making these rounds work is to match impact velocity with bullet performance. A fragile varmint bullet slowed down to TCU speeds will remain intact, penetrate, and still expand in deer.

Almost always you'll be looking at light for caliber bullets, often considered unsuitable for deer when fired from 308 or larger sized cases. This works to your benefit since you're looking for a magazine fed rifle. Most of the TCU rounds are fired from Contenders where OAL isn't typically a limitation.

Look at the 25 TCU. The 85 grain ballistic tip has proven a very nice match to this round. In 6mm, ballistic tips in the 70 grain range are effective, and for 6.5 the 100-120 BT works well.

There are many proven combinations in the TCU line. I'd suggest floating this question over on the specialty pistols forum and I think you'll get exactly what you need. The amount of experience those guys have hunting with TCU rounds can't be matched anywhere else.

Then, I'd call Bullberry and arrange for them to rebarrel your rifle. They cut all the TCU chambers and can help with dies, cutaway chambers, etc. Look for used 6mm TCU dies and have your gunsmith open them up to the proper size depending on which round you choose.

 

[Oso]

For what it is worth - Don't make the mistake of trying to over-work the cartridge. It is a 223 based cartridge, and so there is only so much powder capacity even with the improved case, such as 6x45AI or 6TCU. If you aare wanting to use bullets in the 90gr+ category then you really should consider another cartridge, such as a 6mmGrendel/AmmAR/6ARC, which will get you in the 2500-2800 fps range with a +100gr bullet. Again, this gets you away from your 223 parent case objective.

Most of your better hunting bullets are in the low 80gr class used traditionally for 243 Win. These rounds may/may not expand at lower velocities that you'll achieve in a 6x45 variant/6TCU.

There is another cartridge that might fit your needs and it is based on 223 parent case and will work out of a CZ527... 300 HAM'R. 95gr - 150gr .308 bullets doing 2,800fps - 2,300fps, respectively. It is easy conversion... just need a .30 cal barrel (1:15 to 1:13 twist).

 

[mike.e]

I have a Remington SA M700 in 6.5TCU (24 inch barrel) formally chambered in 204Ruger
Have fired over 4K thru it. Mainly 123SST and lately 130RDF.
I have shot a couple of red deer with it and quite a few wallabies, but mainly I use in on the range for target shooting (steel plates).
I find its ballistically similar to 6.5Grendel but with cheap brass.
Its not smooth to feed out of the mag (std floor-plate) with the 130s seated long.
I really like it, as uses very little powder but still does OK velocity wise

123 @ about 2600 and 130s @ about 2500fps from a 24 inch barrel.
Never tried 100gn projectiles yet
I use 8208XBR and ADI BM2 generally. BM2 gets a little bit erratic at max loads.
I just wish I had brought the reamer. for when I wear the barrel out.

 

[lb-ft]

Lots of great guidance here.

I’m stuck on your original post. 53Vmax -69 gr projectiles have all been tried with nothing but poor accuracy.

What is your twist rate? If by chance it’s closer to 1:14 than 1:12, I’d expect the same results you’ve experienced.

Might try a 50 gr FB bullet. It should stabilize just fine if indeed twist is slow.

 

[rjtfroggy]

I would be a little more concerned about bullet weight for White Tails. If it were me I would get an 8twist barrel 6mm and chamber for the 6x45 and use 85 -95 gr. Sierra's.
I know mine shot like a laser beam out to 200 yards.

 

[SVT_Tactical]

A simple 300 Blk Out is also proven to do what you wanting with the 223 bolt, easy to load mag length, and factory ammo availible.

 

[JD95]

lb-ft - The barrel is either a 1:9 or 1:10. Id have to look when I get home to know for sure. not stabilizing the 69smk I understand but I would have thought a 9-10 twist would work with anything below 60gr.

Oso - if only I could snap my fingers and convince the folks at CZ to produce a lefty grendel bolt for this rifle.. I agree though, "more pressure" is a poor answer to using a case too small for your goals. as for 6mm bullets, the 85 partition has wonderful reputation as a deer bullet in the 6x45. The folks at nosler were kind enough to spend a few minutes talking to me and recommended that I consider the 95 ballistic tip, 90 ballistic tip, 95 partition, and 85 partition for muzzle velocities in the 2600-2700 range which seems achievable. I assume the 30 hammr is essentially a "30 TCU"? Ill have to do some reading. Im a little worried about using a really short 30 cal bullet for loss of SD. its certainly worth looking into though. Thanks!

Mike.e - Thanks! that kind of direct experience is really helpful. on your 123 gr load - would you mind sharing your oal for that load? Glad you like your rifle so much!

Potato- Thanks! I did some looking around on the pistol forum and also spend a little more time looking at 25 and 7mm projectiles. I really would prefer to stick to slightly heavier projectiles for deer, its probably silly, but I feel better with a little more weight even at lower speeds. mag length is certainly the constraining factor here.

RJT-
is that what you did with your rifle? if so, did it work out for you in the field? Thanks!

All,
after doing a little more looking and reading Im seriously considering 7TCU. Ive found some printed data showing 120gr nosler bt load data, 2.28" oal and velocities over 2400 fps from a 14" barrel with RL7 and h322. I imagine that going from 14" to a 22" barrel it would be safe to assume Ill be looking at 2550-2600 fps. The 7mm 120 has a slightly lower bc and sd than the 6.5 120 bt, but inside of 200 yards I dont think the deer will ever know the difference. even if I dont get all of the velocity I want the 120 bt 7mm bullet has an excellent reputation as a deer killer our of 10 and 14" tcu barrels. Ive been comparing energies and velocities at various ranges (inside of 200yds) for likely muzzle velocities of various 6, 25, 6.5, 270, 7, and 308 bullets and the 6.5/7 really seems to be a sweet spot where you can get projectiles around 120gr, high BC, reasonable SD, and perhaps reasonable hunting velocities from a rifle.

at this point, Id like to narrow the scope a little bit and only consider a 6.5TCU built around the 120 ballistic tip or 125 partition in the 2450 to 2550 fps range, or a 7TCU built around the 120 ballistic tip at roughly 2500-2600 fps. I think there are lots of good 6mm and 25 cal options (the 25 is a sleeper with lots of really good projectiles) but Ill be more confident with the heavier projectiles afforded by going to 6.5 or 7 and the larger bore area makes it easy to squeeze some speed out of the case.

I suppose I need to identify a source for a barrel, nail down twist rate (8:1 for a 6.5, but what twist for a 7??) and figure out definitively which projectiles are short enough to seat to mag length. if anyone has a good guess or measurement on ogive length for these 3 projectiles Id really appreciate it. I would also really appreciate any further shared experiences or opinions on the matter. Thanks guys!

 

[jasophil1]

Go with the 7 TCU with the 120 Nosler you will be very happy with it there amazing .

 

[mike.e]

Left to right 6.5TCU loaded with 130gn Nosler RDF, 123gn ELD-M, 123Eldm for comparison and .223 factory

 

[mike.e]

OAL
in both Metric and Imperial as I am not sure what you use
I would have no hesitation is using 100gn Nosler Partitions or 125gn Partitions on larger deer species.
They just plain work.

 

[JSH]

I have fooled with all the TCU’s at some time or another. Be aware that the 6.5 and 7mm seats the bullet well out of the case in order to take as much advantage as possible of the case capacity. The CZ’s magazine will put a big limit on what will work.
A 6TCU performs over what it looks like. The Speer Hot Core 80 grain bullets will work well out of the longer barrel.

 

[Ggmac]

6 tcu with the speer 80 . Great

 

[rockhound78]

Don't forget the 25x45 sharps. Load data shows an 87gr @ 2900fps

 

[moorepower]

.300 Hamr drives a 125 grain Sierra PH at 2500 fps. I would agree with many on an 80 grain cup and core bullet as being entirely adequate.

 

[dhagerty40]

I have shot all the TCU calibers over the years in Contenders. And I need to pass on some info for You.

The chambers for factory Contender Barrels are known for Having Very long Throats and a lot of them are known for not able to touch the rifling with any bullet. A trick we found is that they seem to shoot best when the base of the bullet is even with the bottom of the Neck.

The above may all be different in a bolt action Rifle as the CZ.

you are going to have troubles with both the 7TCU and 6.5 TCU with a standard .223 Mag with seating depths.

The below pic, the first is a 7TCU with a Hornady 7mm 154Gr SP. Second is a 7TCU with a Sierra 7mm 150Gr SMK. The third is a 6.5TCU with a Sierra 107Gr SMK. and the last is a .223 with a Sierra 69gr SMK. all are seated even with the bottom of the neck.

 

[stacy]

6TCU FOR ME WITH 85GR BTHP SIERRA'S OVER H-335

 

[PRR1957]

There is considerable hunting experience with the TCU rounds on the specialty pistols forum.

The key to making these rounds work is to match impact velocity with bullet performance. A fragile varmint bullet slowed down to TCU speeds will remain intact, penetrate, and still expand in deer.

Almost always you'll be looking at light for caliber bullets, often considered unsuitable for deer when fired from 308 or larger sized cases. This works to your benefit since you're looking for a magazine fed rifle. Most of the TCU rounds are fired from Contenders where OAL isn't typically a limitation.

Look at the 25 TCU. The 85 grain ballistic tip has proven a very nice match to this round. In 6mm, ballistic tips in the 70 grain range are effective, and for 6.5 the 100-120 BT works well.

There are many proven combinations in the TCU line. I'd suggest floating this question over on the specialty pistols forum and I think you'll get exactly what you need. The amount of experience those guys have hunting with TCU rounds can't be matched anywhere else.

Then, I'd call Bullberry and arrange for them to rebarrel your rifle. They cut all the TCU chambers and can help with dies, cutaway chambers, etc. Look for used 6mm TCU dies and have your gunsmith open them up to the proper size depending on which round you choose.

Bullberry is closed do to the owners retirement.