I just bought a small quantity of "Sighting Target for Cal. .30 M1 Rifle Using M72 Match Ammunition at 50 Yards" as printed by the National Target Co.  These are on heavy buff paper with a sighting bull at the bottom with gradations for 200, 300, 500, 600, and 1000 yds and inch rulings at the side for equivalent rear sight clicks (½" = 1 elevation click).  
Since M72 Match ammo is as rare as hens teeth and twice the cost, is there a commercial ammo equivalent using the 173 gr bullet?

The projo itself is the same in 7.62mm M118 Match, so there should be commercial loadings.  M118, though, has been largely superseded by better bullets a couple of grains lighter with tiny hollow points.

I'd see what's available pre-loaded in the "170ish" bullet weight range.  This target will still get you close, but reduced range shooting is never, ever going to product X-rings at long ranges.

-- Chuck