Avalon Hill's super-detailed Gunslinger and Worthington's Cowboys: The Way of the Gun cover much the same ground, both being skirmish-level wargames depicting Old West gunfights. Cowboys is the newer and more streamlined design. It's primarily designed as a two-player game with each player able to handle up to a dozen cowboys and town folk, while Gunslinger depicts the action in painstaking and loving detail to the point where it plays best as multi-player game with each player controlling the actions of a single individual or two.
Both include a number of historical scenarios and even include many of the same fights.
Here's brief rundown of the scenarios in Cowboys and and the equivalent scenario is Gunslinger:
Scenario 3 : Shootout at the OK Corral covers the same incident as Gunslinger Variant Showdown One Gunfight at the O.K. Corral. Probably the most famous single gunfight of the Old West, the showdown between the Earps/Doc Holliday and the Mclaurys/Clantons in Tombstone Arizona on Oct. 26, 1881, is a straightforward close-range slugfest.
In Gunslinger the action happens within the confines of the corral on Map A, while in Cowboys it's on the open-terrain on Board K, but there's no practical difference as the corral terrain is unlikely to come into play with both groups of gunfighters set up facing each other at close range in the open.
The Gunslinger Scenario has Wyatt, Virgil and Moragn Earp with Doc Holliday facing Frank and Tom McLaury and Billy Clanton. The Cowboys scenario adds an unarmed Ike Clanton. In both games everyone (except Ike C.) is armed with pistols except for Doc Holliday who has a shotgun. In both scenarios there's also an unpossessed rifle available nearby. The characters used in the Gunslinger scenario for Doc Holliday (Gambler) and Wyatt Earp (Dude) are the best while the Cowboys scenario makes Doc H. and Morgan Earp the best on that side. Frank McLaury is the best character on that side in Gunslinger while Cowboys makes Billy Clanton the top guy among that gang. Gunslinger is more "historical" giving the Earps the advantage of starting "alerted" where in the cowboys scenario both sides have an equal chance of shooting first.
Scenario 4: "You're My Huckleberry" is depicted by one of the small versions of Showdown 1: Gunfight in Gunslinger, a face-off between Doc Holliday and Johnny Ringo on July 13, 1882. This is probably the simplest scenario in both games, with a single gunfighter one each side facing his opponent at close range in the open with holstered pistols. Both use the most open maps (A in Gunslinger and K in Cowboys).
Scenario 6: Commodore Owens vs. The Blevins Boys is the same incident as the small version of Gunslinger Showdown 25: Robber's Roost as Sheriff Commodore Perry Owens tangles with some horse thieves. Oddly enough, the Gunslinger scenario is much more expansive -- using all 8 mapboards -- than the Cowboys version which takes place on just one. But in both cases the focus of the action is a small clutch of buildings and a corral where the four thieves are set up as theya re surprised by Sheriff Owens. In both games Owens is a high-powered guy (+2 in Cowboys and the Marshal +3 in Gunslinger) who is well-armed with a rifle and two pistols but the Gunslinger scenario makes the thieves better armed with some long arms while the Cowboys bad guys just have pistols. The scenario victory conditions are different as well. In Gunslinger the thieves are trying to escape -- any left on the map at game end are captured whereas in Cowboys the thieves must eliminate the sheriff and he has to eliminate one particular horse thief to win, with mutual failure by Turn 15 being a draw.
Scenario 9: The Ambush of Wyatt Earp at Mescal Springs is small version 2 of Showdown 16: Bushwacking from Gunslinger. Both depict the ambush of Wyatt Earp and his companions at Mescal Springs Ariz. on March 24, 1882. There are considerable differences between the two, however. The Gunslinger scenario map set up shows the ambush happening near a stable with other buildings nearby while the Cowboys scenario happens in open country from a rocky area. The Gunslinger scenario shows just Wyatt Earp and his brother Morgan alone facing three Bshwackers while the Cowboys scenario adds Doc Holliday, Warren Earp, Sherm McMasters and Jack Johnson to Wyatt's party while leaving out Morgan. The ambushers number five in the Cowboys version. In the Gunslinger scenario both sides are armed with an assortment of long arms while the Cowboys battle includes only pistols except for Wyatt Earp, who also has a shotgun. Finally, the Cowboys scenario includes a special rule that has combatants fleeing the fight based on a die roll.
Scenario 21: The Dalton Gang's Last Ride depicts the infamous Oct. 9, 1892, Coffeyville, Kansas, Raid, also shown in part in Showdown 9: Bank Robbery in Gunslinger. Both games show the main street of an Old West town, using 8 maps for Gunslinger and five for Cowboys. The tightly focused nature of Gunslinger works against that game here as its forced to focus on the action at just one bank with two members of the Dalton Gang facing five townsfolk. In contrast the Cowboys scenario shows five Dalton gangsters robbing both banks facing the sheriff and four townsfolk with more showing up each turn. In both games the robbers are trying to escape but Gunslinger adds a colorful touch with money bags in the bank.
Scenario 22: Buckshot vs. The Regulators is the same as Gunslinger Variant Showdown 20: The Regulators. Both show Buckshot Rogers alone facing a posse of Regulators (six in Gunslinger and eight in Cowboys) at Blazers Mill, N.M. on April 4, 1878. Both maps feature scattered buildings separated by considerable open space (eight in Gunslinger and six in Cowboys). The posse's target is set up in a building while the Regulators have to try to cross the open ground to get to him. In the Cowboys scenario casualties may caise the other posse members to lose heart and flee, which is an interesting touch.
Scenario 25: Billy's Escape depicts the same July 19, 1878 incident in Lincoln County, N,M, as Gunslinger Showdown 20: Lincoln County War. Billy the Kid is trapped in a burning building, surrounded by enemies, and has to escape. The Gunslinger map is the same setup used for the Regulators scenario, showing a large farmhouse surrounded by outbuildings and countryside. The Cowboys map shows another town setup, using six maps. The Gunslinger scenario includes extensive special rules for darkness falling and the house burning, while Cowboys dispenses with all that and simply requires Billy or two other Regulators to get off the map. The limits of Gunslinger forces it to show a "simplified version of the incidents" with Billy the Kid and one compatriots facing off against five opponents. The Cowboys version shows Billy with four Regulator cowboys and two "townsfolk" against five cowboys and three townsfolk.
Overall, with the exception of Scenario 9, the scenarios shared between the two games are similar enough to clearly represent the same incident while showing some interpretive differences and highlighting the strengths and weaknesses of each game system. Gunslinger's forte is detail and intimacy, which serves it well for tight close-quarter fights like the OK Corral which can be interesting, but force it to compromise when depicting a large event sch as the Coffeyville Raid or Billy the Kid's stand. In contrast Cowboys is a little too streamlined to do OK Corral justice while allowing the whole of something like the Dalton Gang 2-bank heist to be shown.
I'm surprised there isn't more overlap between the two games, as each has several other historical incidents included among its scenarios. It's also worth noting that both games seem to include a scenario inspired by the movie High Noon. In Gunslinger it's rather obviously also called Showdown 23: High Noon, while Cowboys similar treatment is Scenario 15: Gunnin' for the Sheriff. In both a single lawman opposes four outlaws, although the Gunslinger scenario adds some colorful touches with "reinforcements" for the Sheriff comprising a "Lady" and a "Running Boy."