The barrel is a barrel liner from Chaszel. I bored and reamed the original Hi Point barrel to 5/8 ID and turned the liner a few thousands smaller and epoxied it in the original barrel. The muzzle thread is 5/8 x 24 and I have several “ toys “ I made to fit it, a compansator, a micro red dot mount, a oil filter attachment ( you need this ) and I did some work on the trigger.
On a hog hunt several years ago there were 10 of us guys together and several of the guys had high dollar handguns and most were 30 + years younger with better eyes. At the range we were shooting at 50 yards and the Hi point out shoot all of the other handguns shooting some under 3” groups at 50 yards with arms resting on the table but not by me.
To answer the question of velocity reached, I don’t know I tried loads up to 45 super level and at that point I was getting failure to feed problems probably way to hot for the standard recoil spring in the gun. Hi Point advertises they are good for plus P loads and it works fine with them. I believe I can easily top 1000 FPS with 200 gr. FN cast hi tek coated bollits it likes. The gun will feed and fire almost anything you put in it within reason.
Jedman