As has already been mentioned, the screw you're looking for is available from Williams but you'll have to call them to order it. It's the one that goes in the side of their deluxe target sight, and you'll definitely have to shorten it (grind or dremel cutting wheel) for it to work. I have those screws in all three of my lever gun sights now and it's a lot easier to use.
I'd also recommend that you get some "appliance touch-up" paint to mark the elevation knob on your sight. Nothing that I've seen is tougher and it just costs a couple bucks for a "white-out" size bottle at Home Depot or Lowes. That makes it a lot easier to be sure where you sight is at any time. For instance, my Marlin 39a's chicken setting is "white mark toward muzzle, 2 1/8 turns from bottomed out." Then I set the other settings based on that settings. Just a glance down at the sight lets me know if I've adjusted the sight for my next animal yet.
As for ammo, I tried out a total of 18 different types of ammo initially in the Marlion 39a and have tried 6 more since then. The WMT didn't shoot significantly better than a few other types, like CCI Silhouette (just mini-mags with less flyers) or Federal Lightning. Since I use it for my scoped silhouette rifle, I decided to use WMT anyway. My first two matches, I rang two rams and then three. A couple other very good shooters up here had told me I might have that problem, but I had the mindset that I'd rather hit the animals and have them not fall than miss them due to inaccuracy. Needless to say, I changed my mind just as they predicted I would. I'm not good enough a shooter to be able to lose points on animals that I hit well, so I switched to something a little faster. Last month, I shot a 35 with the Federal Automatch and won the match. This month, I shot a 32 (mind was off, as baby was due anytime) and only lost by a point or two. If you use standard velocity ammo, keep in mind that the lever action targets are MUCH larger and heavier than the scoped rifle targets that will fall with nearly any hit at all. Hitting the lever action ram targets low in the body, especially toward the front leg, with standard velocity ammo can lead to frustration.
