Hi Mark. I was confused by the "plugged barrel" note that was sent out, and thought that I had to drill out aluminum from the center. Not sure how to do that, I ordered the Mato 17-pdr barrel just in case. It turned out that the center of the barrel was plugged only with resin, and I managed to bore that out by filing "teeth" onto the end of a 5/32" brass tube. I chucked that in an electric screwdriver, and bored it out easily.
Anyway, as to the Mato barrel. If you have seen the one Tamiya used to make, this is almost dimensionally an exact copy. The extension at the rear is about 1/2" longer, and there is also a smaller 5/8" extension on the rear of that which plugs into the Heng Long recoil housing. Be advised that the larger-diameter part hits the inner mantlet before the smaller part can go go all the way into the recoil unit. And, on recoil, (if you left it partially inserted that way) it would "unplug" itself from the recoil unit. You can carefully drill out the pivoting parts of the inner mantlet for clearance and then it ought to work just fine.
You rarely see the Tamiya ones for sale anymore, so this is a welcome availability. I'll save mine for a future Achilles build. -Mike
Last edited by sassgrunt; 06-02-2016 at 02:42 PM.