Per the AQHA rule book:
Should I try a different bit? If so, which one? (and if so, what about one legal in AQHA and 4H?)
Specific bit descriptions:
SHW305.8 In all western classes except for speed events, team-penning, ranch sorting, roping and cowboy mounted shooting, horses will be shown in a western saddle and appropriate bridle, snaffle bit or hackamore for the duration of the class. A western saddle is a common type of saddle distinguished by a large noticeable fork on which there is some form of horn, a high cantle and large skirts. Silver equipment will not count over a good working outfit. Horses 5-years-old and younger may be shown in a snaffle bit, hackamore, curb bit, half-breed or spade bit. Horses 6-years-old and older may only be shown in a curb bit, half-breed or spade bit. Any horse of any age shown in any Rookie/Level 1 (Novice) youth or Rookie/Level 1 (Novice) amateur class may be shown two handed with a snaffle bit/hackamore. When a curb bit is used, a curb strap or curb chain is required, but must meet the approval of the judge, be at least one-half inch in width and lie flat against the jaw of the horse. Curb chains cannot be tied to the bit with string or cord. A broken strap or chain is not necessarily cause for disqualification.
SHW305.1 Hackamore means the use of a flexible, braided rawhide, leather or rope bosal, the core of which must be flexible. A hackamore must use a complete mecate rein, which must include a tie-rein. Absolutely no rigid material will be permitted under the jaws, regardless of how padded or covered. Horse hair bosals are prohibited. This rule does not refer to a mechanical hackamore.
SHW305.2 Snaffle bits in western performance classes mean the conventional O-ring, egg-butt or D-ring with a ring no larger than 4" in diameter (100 mm). The inside circumference of the ring must be free of rein, curb or headstall attachments which would provide leverage. The mouthpiece should be round, oval or egg-shaped, smooth and unwrapped metal. It may be inlaid, but smooth or latex-wrapped. The bars must be a minimum of 5/16" (8 mm) in diameter, measured one inch (25 mm) in from the cheek with a gradual decrease to center of the snaffle. The mouthpiece may be two or three pieces. A three-piece, connecting ring of 1 1/4" (32 mm) or less in diameter, or a connecting flat bar of 3/8" to 3/4"(10 mm to 20 mm) measured top to bottom, with a maximum length of 2" (50 mm), which lies flat in the horse’s mouth, is acceptable. Optional leather strap attached below the reins on a snaffle bit is acceptable.
SHW305.3 Bit in western performance classes means the use of a curb bit that has a solid or broken mouthpiece, has shanks and acts with leverage. All curb bits must be free of mechanical device and should be considered a standard western bit.
AQHA Handbook link is here: AQHA: AQHA Handbook
SHW305.4 The description of a legal, standard western bit includes:
SHW305.4.1 8 1/2" (215 mm) maximum length shank to be measured as indicated in the diagram on the previous page. Shanks may be fixed or loose;
SHW305.4.2 concerning mouthpieces, bars must be round, oval or egg shaped, smooth and unwrapped metal of 5/16" to 3/4" (8 mm to 20 mm) in diameter, measured 1" (25 mm) from the cheek. However, wire on the sway bars (above the bars and attaching to the spade) of a traditional spade bit is acceptable. They may be inlaid, but must be smooth or latex wrapped. Nothing may protrude below the mouthpiece (bar), such as extensions or prongs, including upward prongs on solid mouthpieces. The mouthpiece may be two or three pieces. A three-piece, connecting ring of 1 1/4" (32 mm) or less in diameter, or a connecting flat bar of 3/8" to 3/4" (10mm to 20 mm) measured top to bottom with a maximum length of 2" (50 mm), which lies flat in the horse’s mouth, is acceptable;
SHW305.4.3 the port must be no higher than 3 1/2" (90 mm) maximum, with rollers and covers acceptable. Broken mouthpieces, halfbreeds and spades are standard;
SHW305.4.4 donut and flat polo mouthpieces are not acceptable;
SHW305.4.5 a curb bit must be used with a curb strap or curb chain properly attached so as to make contact with horse’s chin;
SHW305.4.6 slip or gag bit is permitted in speed events
SHW305.5 Except for hackamore/snaffle bit classes or junior horses shown with hackamore/snaffle bit, only one hand may be used on the reins, and the hand must not be changed. The hand is to be around the reins; index finger only between split reins is permitted. In trail, it is permissible to change hands to work an obstacle. Violation of this rule is an automatic disqualification.