SINGLE ACTION SHOOTING SOCIETYTM SASS Range Operations Basic Safety Course
21. Although cross-draw and shoulder holsters are legal, they represent a significant safety concern. No holster may depart from the vertical by more than 30° when worn. Extreme care must be exercised when drawing a firearm from a cross-draw or shoulder holster or returning the firearm to leather. The user must twist” their body, if necessary, to ensure the muzzle never breaks the 170° safety rule during the process. (NOTE: The 170° safety rule means the muzzle of the firearm must always be straight down range +/- 85° in any direction. If a competitor “comes close” to breaking the 180° safety plane, the 170° safety rule has been violated and the competitor is at fault). Shooters competing in the Gunfighter or “B” Western Category must wear two standard holsters, one on each side of the body. Cross draw, shoulder, or butt forward holsters are not allowed within these two categories. It is also necessary to note that during the course of fire, the shooter must be given the ability to draw and holster revolvers from “straight hang” holsters and the ability to retrieve and return vertically staged double-barreled shotguns without penalty.
As you can see, the term "standard holsters" is elaborated in the sentence following its appearance. I.E. Cross draw, shoulder, or butt forward holsters are NON-STANDARD.
If you want to spend your life arguing the syntactics of the verbage in SASS manuals, you'd certainly find a lot to keep you occupied. However, the symantics of "standard holster" seems pretty clear in this paragraph -- at least to me.
You're right, there are no holster limitations in other categories. I overstated the rule because it appears under gunfighter and is also a part of the Wild Bunch rules. I got carried away. You could use butt forward rigs in other categories. BUT, and it's a really big one, you cannot break the 170 rule when using non-standard holsters. You do have the latitude to reholster while using a standard, strong side rig -- regardless of your orientation to up-down range. This is a convention afforded users of standard holsters as long as they keep their barrels pointed down while holstering.
A butt forward rig, which is usually canted as well as being backwards, allows for no margin of error in getting the gun deployed. If you draw the gun at the angle that it rests in the holster, you've broken the 170 and have a stage DQ for your efforts. No allowance for deploying or reholstering is extended to the butt forward rig.
So, de facto, you would be hard pressed to actually use a butt forward rig in any category. At the very least, you would draw the scrutiny of every rule litigator on the posse. This sort of thing can really ruin a match.
Just say no to non standard holsters. I suppose they get style points, but the safety and performance issues that attend them makes in a high price to pay for playing Wild Bill Hickock.