I'm loving the results I get from my Green Mtn. drop-in's.
In 50 cal, mounted in my T/C Hawkens I'm using a .500 RB, dead soft lead, .020 patching. For 50 yds, 65 gns or so of Goex 2f or 3f. I've been successful with several lubes, so try what you like. 7:1 water Ballistol on a "dry patch"(THANK YOU Dutch..!!) works great for example. I use a composite mallet and special short starter to get the ball just started into the end of the bbl, then a conventional short starter to push it down 5-6 in., then a 3/8th's solid brass range rod to solidly seat on the powder.
From a decent rest, when my 64 yr old eyes are having a good day...that sort of combo produces "one ragged hole" 5 shot groups with almost :wink: boring regularity.
My combination and loading regimen isn't for everyone, but it works for me.
Your experience might be different.