Nem,
Indeed this thread is still breathing. Perhaps just getting going....
I have two 336's, both are Cowboys - 24" octagonal barrels, conversions done by Marlin while still in New Haven. One in 30-30. The other in 38-55.
LOVE both of them. The practical side of me has great appreciation for the 30-30. Might be on of the most accurate rifles I've ever owned. A rare variation for sure and those that have them don't typically let go of them. I've had both the Original and the conversion (originally a 336 Texan, sent back to Marlin where the craftsmen there converted it to a Cowboy). I did sell the original (mistake... but it went to a good guy). For the silhoutte game you really can't beat a 30-30 Cowboy...
I later discovered the 38-55 Cowboy. Less practical. Way more fun. Provided that you are a reloader and caster.
The 38-55 is definitely NOT for those with short attention spans. It takes work - if you call experimentation (shooting) work. Each 38-55 is a story unto it's own. First you must find the bullet diameter it likes, .379-.382", the weight, the charge...
Once you get it right, Life is good
It was the first caliber I was able to reach out to 1,000 yards with. and I frequently use it in Silhouette matches, Long Range Matches and Hunting.
800 yards with a Marlin 336 Video:
http://www.youtube.com/watch?v=1bN2Gcd3OGw
Now if I could only have one, it'd be the 30-30. But since I have both, I must admit that the 38-55 gets a vast majority of the attention.
Montana Vintage Arms Tange sight. Zero to 1,000+ yards. Gotta love it!