6mm TCU

[kevinbear]

I've been thinking about a 6mm tcu or 6x45 with a fast twist barrel because it might take a few years for the tenderness to go away from my rotator cuff surgery {the attachment screw is right where the recoil pad contacts my shoulder}, anyone ever had one?
I've shot a few matches with a .223 and 69grain MK's, sometimes they knock the rams down if the wind isn't from behind the targets. In a rifle the recoil shouldn't be much more that a .223, right now I can only stand about 10 shots from a 7-08 before it tells me it's time to quit.

[DanDeMan]

KB,

I'd recommend the 6mm BR if you want to go 6mm. But, if you have a 223 bolt face, have at it with a 6mm TCU. But, one needs a properly designed chamber reamer. The off-the-shelf reamers will be sorely lacking due to chamber front-ends that are not optimal for shooting 105 grain Scenars or 107 SMK's. But, I strongly recommend the 6.5mm TCU. With a properly designed chamber reamer, they are a joy to shoot and perform very well on rams. Even the ram load is so mild it will make you laugh the first time you pull the trigger. My 8-twist, 6.5mm TCU was a tack-driver. Here are my match loads using the 6.5mm TCU. I wanted to use just the 140 A-Max bullets, very cheap and oh so accurate. Lapua 223 cases are the only way to go. The chamber reamer was designed for the Lapua cases and the ram cases will last a long time compared to other cases, loose primer pockets being the problem with the other brands. I used Remington cases for CPT and the Lapua cases for the Ram load. You could lower MV of the CPT load down to 1,800 fps and still have excellent CPT knockdown. Man, would that ever be a mild load. Plus, given the much higher BC of the 140 A-Max compared to say the 6mm, 107 SMK's, you'll have less recoil at your shoulder for the momentum delivered to the rams due to the higher BC. I'll run some recoil terminal momentum numbers for you in a bit.

6.5mm TCU Ram Load
MV 2,520 fps; 29.0 N150; F205M; 140 A-MAX (VarGet can be used for the Ram load, but MV will be about 50 to 60 fps lower at the same pressure as the N150 load)
Range - Vel - Drop
200 2218 - 0.0
300 2071 - 3.3
385 1949 - 6.5
500 1790 - 11.3

6.5mm TCU C, P & T Load
MV 2,250 fps; 26.0 N140; F205M; 140 A-MAX (VarGet and RL-15 work just as well)
Range - Vel - Drop
200 1958 - 0.0
300 1819 - 4.25
385 1702 - 8.5
500 1551 - 14.75

[kevinbear]

Almost 1800fps at the rams for the top load, that's pretty darn good for a 223 case.
I've always wanted a 6x223 because it's the smallest legal gun for silhouette, what % of the rams hit dead center would fall....25-30%? I turned a pig last time with a 69gr.MK, hopefully the 107's would topple them 100% of the time.

[kevinbear]

Thanks for taking the time to post the loads Dan.

[DanDeMan]

Thanks for taking the time to post the loads Dan.

KB,

You're welcome. I think you will have much fun with this HP silhouette project, no matter which cartridge you choose. If you want some help designing a 6mm TCU reamer for silhouette, let me know, can do. And, such a rifle would be most excellent for enticing youngsters and petite wives/girlfriends into "pulling HP silhouette triggers." My guesstimate is that with a properly designed chamber reamer, proper powder, 105 Scenar or 107 SMK bullets and 26", 8-twist barrel, you should be able to launch them to 2,800 fps. Ram performance would be on the order of 80 to 90 % at ranges that have good rams and stands. I'd use the same heavy bullet for CPT only at about 2,200 fps for reduced recoil, longer barrel life and yet have great knockdown performance.

[DanDeMan]

KB,

Here are some numbers to chew on regarding ram performance, recoil and wind deflection for typical loads out of the 7-08, 6.5mm TCU and 6mm TCU. As I posted before, proper chamber design for the TCU's is paramount for satisfactory performance. Most TCU reamers were designed for handguns, not rifles.

7-08
37.5 IMR 4064 = 2,466 fps
168 SMK BC = 0.490
Recoil 10 lb rifle = 11.1 ft-lbs
500m Terminal Momentum = 1.197 lb-s
Terminal Momentum / ft-lbs Recoil = 0.108 ft-s/ft-lb (larger is better)
500m Wind Deflection in 10mph, 9 o’clock wind = 5.0 MOA

6.5mm TCU
27.0 VarGet = 2,450 fps
140 A-Max BC = 0.585
Recoil 10 lb rifle = 7.0 ft-lbs; 7-08 load has 59% more recoil
500m Terminal Momentum = 1.066 ft-s; 7-08 has only 12% more momentum
Terminal Momentum / ft-lbs Recoil = 1.52 ft-s/ft-lb (larger is better)
500m Wind Deflection in 10mph, 9 o’clock wind = 4.1

6mm TCU
27.0 VarGet = 2,750 fps
107 SMK BC = 0.400
Recoil 10 lb rifle = 5.7 ft-lbs; 7-08 load has 95% & 6.5mm TCU has 23% more recoil
500m Terminal Momentum = 0.783 ft-s; 7-08 has 53% & 6.5mm TCU has 36% more momentum
Terminal Momentum / ft-lbs Recoil = 1.374 ft-s/ft-lb (larger is better)
500m Wind Deflection in 10mph, 9 o’clock wind = 5.4 MOA

[DanDeMan]

KB,

Here's a picture to drool over.

----- 7-08/177 Cauterucio ---- 6.5TCU/140 A-Max ---- 6TCU/107 SMK

[malinois]

The 6mm TCU should work pretty good and with the improved chamber if needed. I shot a 6br for a little bit and I did not even push it that hard I was only loading for about 2500 fps with A-Max 105 and the rams were going down good with very little recoil. I would say go for it.

[Bob Mc Alice]

Real good post, Dan. Why dont you edit it to include your 7-04 with same data and a picture. Talk about something to drool over. I am considering looking for an older 700 small base action right now....really!

[DanDeMan]

Real good post, Dan. Why dont you edit it to include your 7-04 with same data and a picture. Talk about something to drool over. I am considering looking for an older 700 small base action right now....really!

Bob,

See if you can find a used Remington XR-100 Rangemaster with 223 bolt face. That's what I'm using for mine. The single-shot, XR-100 action is relatively light and very stiff. And, the thumbhole stock can be lightened to make weight for Standard and still have a nice, beefy, 26" barrel.

When I get the 7-04 back from Pharr I'll be posting load data and ram performance.

[kevinbear]

What's a 7-04?

[DanDeMan]

KB,

The 7-04 is a 7mm TCU on steroids. It is based on 204 Ruger brass opened up to 7mm, hence the designation of 7-04, the little brother of the 7-08. When fire-formed, 7mm TCU brass is about 44 mm long; 7-04 brass is about 46 mm long. The chamber reamer was designed to accommodate the heavy 7mm bullets and use Hornady's very nicely made 204 Ruger brass. Typical off-the-shelf TCU chamber reamers were designed for handguns launching much lighter bullets than what we use for HP silhouette. That's why custom TCU chamber reamer designs are necessary for our application. These diminutive cartridges will shock the heck out of folks if they are designed and loaded optimally. Nothing like "the guys" laughing their collective asses off at you before you clean the ram line with one of these little puppies. Nothing but crickets after that happens, I know. And then, after the match you let'em fire a few at rams, way too much fun for my evil, twisted mind.

Bob,

Below is a picture with all 4 cartridges, including the 7-04 loaded with 30.0 grains of VarGet, 100 % load density pre-fire-forming, under the 177-gr Cauterucio. The brass should allow for another grain or two of powder after fire-forming, not that I think more VarGet will be necessary. Estimated MV = 2,300 fps. If using the heavy Hornady bullets, 2,400 fps should be in the realm of the possible. Here are the estimated stats in the same format as posted in one of my previous posts.

7-04
30.0-gr VarGet = 2,300 fps
177-gr Cauterucio BC = 0.670
Recoil 10 lb rifle = 9.5 ft-lbs
500m Terminal Momentum = 1.317 lb-s
Terminal Momentum / ft-lbs Recoil = 0.1386 ft-s/ft-lb (larger is better)
500m Wind Deflection in 10mph, 9 o’clock wind = 3.8 MOA

As you can see, the stats look might tasty. And, if the bullets are pointed the stats look even better because the BC goes from 0.670 up to 0.720.

7-08/177 Cauterucio * 7-04/177 Cauterucio * 6.5TCU/140 A-Max * 6TCU/107 SMK

[DanDeMan]

Bob,

During the first cup of coffee this morning I got to thinking...always a bad sign in this house. "I wonder how the 162 A-Max would do when launched by the 7-04???", came to mind, when run through the same analysis as was done for the 177-gr Cauterucio. I'll be shooting the Cauterucio bullets because I have a boatload of them begging to slam steel.

The below results look mighty tasty, no???

7-04
30.0-gr VarGet = 2,350 fps
162 A-Max BC = 0.625
Recoil 10 lb rifle = 8.6 ft-lbs
500m Terminal Momentum = 1.206 lb-s - Right at the RAMENTUM LINE
Terminal Momentum / ft-lbs Recoil = 0.140 ft-s/ft-lb (larger is better)
500m Wind Deflection in 10mph, 9 o’clock wind = 4.0 MOA

Oh, oh...more thinking, time for a second cup of joe. I think the 04 family of cartridges for HP Rifle Silhouette is taking shape in my demented brain. Can you say 6.5-04 and 6-04??? OK, designing will be begin shortly.

[kevinbear]

One of the criteria these cartridges would have to meet for me is that they don't exceed 2.80 because I myself like to load the magazine with all 5 rounds during the ready and then just shoot like smallbore. And yes it bothers me to eject those precious labor intensively made cases on the ground but usually the worst that happens is an occasional dent neck.

[DanDeMan]

KB,

The 6mm TCU loaded optimally with the 107 SMK is 2.71" long. That is, only the BT is below the neck-shoulder junction for excellent cartridge concentrically and optimum powder capacity when using the heavy bullets.

Also, so far it looks like VarGet would be an excellent powder to start with for the heavy bullets.