Castle, both my Marlin .30-30, and my Winchester Trapper (a real Win., not USRA), have Williams 5d receiver sights. I don't like a scope on these handy, light rifles. If you do, fine. Here's a quote.
"A .30-30 sighted to hit the point-of-aim at 100 yards will put the bullet almost 10 inches low at 200 yards, whereas a .30-30 sighted in to hit 3 inches high at 100 yards, will be only 3 inches low at 200. The man with a rifle sighted in for the shorter distance will miss a buck with a good hold at 200, whereas the man with the rifle sighted to hit 3 inches high at 100 yards, will connect at both ranges.
"Some hunters will say: 'In my neck of the woods, 200 yard shots are rare. Most of the deer are killed at 100 yards or less. Why sight in like that?'
The answer is that no one can hold well enough on a deer at 100 yards to be aware if his rifle is shooting 3 inches high or not. BUT, on that long shot out around 200 yards, he'll miss every time with a rifle sighted for the short distance."
("No One Else Can Sight A Rifle For You. Here's How You Do It." Written by Jack O'Conner., Outdoor Life, Oct. 1947)
I've been shooting .30-30s for 45 years and I agree with the late, great Jack O'Conner. Mine are sighted for 3" high at 100 yards, and I've never been disappointed with that sighting.
FWIW. J.B.