1000yds with the Mann
 

I've shot it out to 600 several times.
Today we had an informal practice at the 1000yd range so I decided to break out the Mann. I have not developed a load for 1000 in this rifle so I shot a load worked up for the M1A.
45.5g Reloader15 behind a Berger 168 Hybrid. It runs 2780 out of the M1A's 22" barrel. I figured 2750 out of the 20" mann barrel which calculated to 31.5 minutes up from the 200yd zero. That was spot on.
I only shot 20 rounds but every well broken shot was 10 or an X.
There was a couple of hinky shots because I forgot my rear bag and was using a front bag laid on its side. Not the best. If I took the time to situate everything where I wasn't straining to align the shot I got center shots.
Pleasantly surprised. I had never shot it at 1000 because I just didn't think a 20" barrel could get there.
Target pullers reported that my rounds sounded comfortably supersonic.

Impressive. WTG. Is the rifle scoped?

Yes with a Weaver T36.
Harris bi-pod

Why a scope? I used to shoot a M1903 with iron sights from the prone position and M72 Ammo and could get a good 5v count. Of course I was using a Lyman 48 and not that M1905 sight. Elevation was OK with an O’Hare Mike, but windage was was a problem as it does not blow in “points”
FWIW

Have you got a pic or two we can see of that Mann Rifle? I've been thinking of converting mine into a rifle for long range shooting and need a few ideas