That is indeed a great looking mould. I have a Lyman #515139 in 350gr. coming from Buffalo Arms. In the mean time, I trimmed some .515141's from .970" to .740" at roughly 415gr. These I loaded up with H4895 using Fed 210 primers. I should have used my 215's due to some propensity towards hangfires unless I pointed the muzzle up before touching them off.
I set up a "25 yard Timed and Rapid Fire Handgun Target at 100 meters (109yards) and proceeded to test my new Uberti M76 rifle & the ammo ammo with it's factory sights. The black bull (9 and 10 rings only) on this target is 5 1/2" wide and made a decent aiming point for the open sights, shot off the bench.
The 300gr. .512" RFN's did not shoot very well at all, scattering around - perhaps 3foot group - all round the target and none of the first 10 rounds on it - both high and low, side to side - LOL, however they did not lead the bore, which surprised me. I merely blasted the rest of them off- 30 - to fireform the shortened .50/90 brass, of which I had 40. the other 60 brass I have, is Jamison, .50/95 WCF. Nice brass. The .50/90's also fireformed nicely, by the way.
When I first received the rifle, I ran a square of red Scotch Brite through the bore - perhaps 30 strokes, lubed only with WD40 then I cleaned it well with Patch-out and oiled with Kroil. The bore feels very smooth and even. It lacks the loose spot my brother's model 76 had, which we fire-lapped out, BTW.
The shortened #515141's, weighing from a low of 410gr. to a maximum of 420gr. I lubed them by hand, with a mix. of 60% (good) beeswax, 40" Vaseline which had worked for me, for 20years or more, smokeless or black powder. I made 2 deliberate, 5 shot groups, off the bags (resting the back of my left hand on the bench-rest's bag) ran a horizontal group 3 1/2" wide C to C and only 1 5/8" high, then the nasty, gusting cross wind shifted, to directly behind us & gusting making a group 2.9" C to C and only 2.3" wide.
For the first day at the range with a new rifle and new loads, I was quite pleased. Nice trigger and minor boot in recoil. After arriving home, a very tight dry patch removed one small sliver of lead - that was it, for 60 shots total. There was no other lead in the barrel and not much carbon fouling either. An easy cleanup.
It will be fun to test with the new mould when it arrives.
My brothers rifle, with the mid range aperture sights and Hadley eye piece put 10 shots (both he and I shooting) into 2.465" X 1.337", again, a horizontal group in the cross wind. The load in that .45/60 was a 300gr. FN with 14.0gr. of Trail Boss.