AR just for fun boolit gun - 7 TCU

[P Flados]

My boy and I shoot together on a regular basis.

Mostly handguns at the local indoor range. We also (not to infrequently) shoot at an outdoor range North of town and maybe a couple of times per year we did an IHMSA match.

He pushed for more guns, specifically ARs. I was never a fan of the 223, but found the 357AR interesting. About a year and a half ago, his bad influence won out and we jumped into the AR world.

I got a 357AR working pretty good, but it is a bit much for a "fun to shoot" gun. I was also not real happy with the cost per round given the amount and cost of the powders required for full power accurate loads.

In my quest for an AR fun gun, I tried just a few boolits in 223, but gave up quick.

We got a 300 BO hoping for boolit happiness, but the 1 in 7 twist barrel seems to hate boolits.

With my 7x14 mini lathe and a bunch of lost cost "gab bag" barrels, I wanted to try making an AR barrel. I took a 30-06 pull and made a 8" 300 BO that I hoped would shoot boolits. I never got the accuracy I wanted and the short case in combination with the light/med boolits I wanted to used just did not want to feed well.

After playing with the 357AR and the 300 BO, I eventually decided that easy boolit feeding was most likely to happen with full length rounds with some amount of bottle neck. I also thought it would be real nice to find a round that would do well with surplus powder originally intended for 5.56 ammo.

I looked around at the various 223 case based rounds. I would have liked a full length 30 cal, but there are really no "standard rounds" that meet this description. The next closest was the 7 TCU. I have one in a TC contender with dies etc and my barrel grab bag purchases included one never used 7 mm stainless blank. It seems that a few have done the 7 TCU in an AR, but these guys were j word shooters and they were not real happy with bullet choices (few have a short enough nose section to work in an AR magazine). I was not concerned with projectiles as I would be making my own custom NLG molds for use with PC boolits.

I found a used chamber reamer, and made a 16" barrel. I have cut a number of 7mm cavities in Lee (or my own) blanks to check out feeding and accuracy with different meplat sizes.

With an altered P-mag (side ribs trimmed down just a little), most all of the boolits have fed very good.

Right now, my most accurate load is with a 128 gr small meplat boolit loaded over WC 844 for a Quick Load estimated 1850 fps. My best group is right at 2 MOA but it has only been 25 yards at the indoor gun range. When the outdoor range re-opens (it was closed for Covid 19) I am hoping to get regular 2 MOA shooting using the better bench rest provisions.

Gun:



Target:



Some of the Boolits tried:



A couple of loaded rounds

[corbinace]

Very interesting. Thank you for bringing us along on the journey.

[toallmy]

I have a 223 case necked up , with a 132 gr Thor seated in it sitting by my loading bench . I definitely think it's a good idea fun gun .

[P Flados]

My ability to pursue this line of experimentation is mostly due to those innovative guys that worked out ASBB PC.

Making NLG molds that work for applications like this allows for very cost effective custom boolit molds tailored to specific custom gun applications.

Thanks again to the PC pioneers.

[rockrat]

Check into the 30 Apache, if you want a 30 cal. Based on the 223 case

[P Flados]

Check into the 30 Apache, if you want a 30 cal. Based on the 223 case

I actually have an 8" barrel that I tried as a 300 BO and then later ran a 300 BO reamer in deep enough to shoot 233 necked up to 30. Using a 300 BO reamer allows use of my existing loading dies (backed way off of course) if I need to. For now, I have fired it some and just neck sized between loadings. I started testing with Tight Group. Based on QL I found that Tightgroup would do good for fireforming and actually my fireforming loads were over 1500 fps. Even though my WC 844 will produce a good bit more velocity (more than I really need) I am not sure I want to deal with the blast & fireball from an 8" barrel. So far accuracy has not been great, but I am still working with it.

[P Flados]

The outdoor range re-opened this week

The weather was great with negligible wind.

However, I really struggled to hold the gun steady. My sandbag setup was not real good and there was a noticeable side to side wobble with every heartbeat.

Most groups were 3 to 4 MOA. A couple of groups were better. One was an outstanding 1.4 MOA.

We will have wait & see if I can get my shooting act together with consistent results before I declare how good the gun is.

[EMC45]

Well done! The TCU was something I thought would be great years ago. I didn't have the tooling or the skills that you have to make it happen though.

[TCLouis]

Look for the post by Junior1942 for his last foray in loading this round with the "Soup Can" boolit.

WC820 (N) got him about that same velocity out of his Contender.

Always thought the 7mm TCU could be a performer out of a rifle.