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