It is expensive shooting these premium slugs and that's good advise. What I do is shoot my first two shots at 50 yrds on a 1 inch grided target then make a adjustment according to the scope turret adjustments ( 1/4" at 100yards will be 1/8" at 50 yards) then move back to 100 and fire two more...
I use a TC 20ga and have had great results with Hornady SST 20ga 2 3/4 " or Federal Barnes Expander 3". I have made kill shots out to 184 yards with the Hornady's on whitetails. The Hornady load shoots 1" at 100 yards, this would be my choice. Hope this helps.:D
I have used several calibers from 25-06 to 7mm RUM and have found them all to be very good for pronghorns. Having said that I have three favorites .270 WSM, .257 Weatherby mag.,7mm RUM. Hope this helps Richgun)
I also have a Model 7 and my best load is a 140 TSX with 64.0 gr. of RL- 19 a Federal GM215M primer and Rem. cases . It is a top end load but I have no preasure signs at all. I am getting 1.5 in. at 200 yards. Good luckgun)