What kind of adventures are you looking for? Detectives? Gangsters? Horror? Back of Beyond?
How many models? Massed Armies? Squad on Squad Skirmish? Individual Heroes?
There are set of free intro rules on the Rattrap website so you can give .45 Adventures a go for free. The extra books generally add new settings rather than being needed for most Pulp stories. The Rattrap system is great for Individual Heroes, it covers thinking as well as shooting which is great.
For Skirmishes, Legends of the Old West from Warhammer Historical is a great system, as is the Reaction System from Two Hour Wargames. 2HW have just released a Pulp variant called "Larger Than Life" I've not seen yet but could be worth a look, we've enjoyed using Nuts! the WWII version and 5150 the Sci-Fi one.
For bigger battles, I've not tried as I don't play games that big, but everyone here seems to love Triumph & Tragedy, there is a whole section of this forum dedicated to it.
