I agree totaly with SASS#23149, I will elaborate a little on his general concept.
This is only my opinion, shared by the small group of cowpokes I shoot with. Feel free to shoot whatever you want, it's more about having fun and being safe than anything else.
If you want to make a lot of noise, shoot .45's
If you don't care about being the fastest, shoot .45's
If historical accuracy is very important to you, shoot .45's
If you already have a nice pair of .45's and don't want to buy new guns, shoot .45's
If you want to compete for ribbon's and trophies, shoot .38's
If you use what most other's use, shoot .38's
If you want to spend alot less $$ on ammo, shoot .38's
If you are a real wuss shoot .32's
If you have incredibly small hands (i.e. female), shoot .32
If you have arthritis, shoot .32's
This is not to say that .45 shooters CAN"T win. Some shooters do quite well with .45's, I just am not one of them.
Basicly the ammo requirements are as follows
Must have muzzle velocity less than 1000fps (safety)
Must be all lead, no jackets allowed (safety again)
Rifle ammo must be flat nosed, i.e. SWC, WC, TC, LFN (by far the most common is the TC Truncated Cone, second is the LFN Lead Flat Nose, this is a safety issue with tube magazines)
Pistol ammo may be any lead bullet, no jacketed rounds. (most folks shoot the same caliber and bullet in both rifle and pistol for the sake of simplicty)
No caliber smaller than .32 or larger than .45
I and the small group of shooters I shoot with all share the same caliber choice, the same reloading press and the same ammo recipie, it may work for others so here it is.
Using good brass for matches, new brass for big matches and old brass for practice,
Federal small pistol primers,
3.1gr of Clay's powder (clean burning, and alot easier to find than the preffered TrailBoss)
125gr Truncated Cone Bullets made by another shooter at our club.(commercialy available bullets work just as good)
Stir vigoursly and viola, ammo!, your milage may vary.
I am not sure exactly on the shotgun ammo requirements, I have never seen anyone shooting magnums, most people use a light target load such as winchester AA light target. or the remington version therof, avoid walmart federal shotgun shells, they are cheap for a reason.
Have fun and be safe
Dalton