IDPA uses 6 shot revolvers only. I have 66, 686, and 646.
USPSA uses the 8 shot revolvers.
8.1.1 Division Summary
8.1.1.1 IDPA is divided into 8 divisions that are entirely separate from one another in competition. None of the
following divisions compete against any other division:
Stock Service Pistol (SSP)
Enhanced Service Pistol (ESP)
Custom Defensive Pistol (CDP)
Compact Carry Pistol (CCP)
Revolver (REV)*
Backup Gun (BUG)*
Carry Optics (CO)
Pistol Caliber Carbine (PCC)*
*Specialty Division optional division for Tier 1 – Tier 5 Sanctioned matches.
8.1.2 Magazine Loading: All magazines must be loaded to division capacity (or their maximum capacity if smaller) at
the start signal throughout the match except in the following cases:
8.1.2.1 If a magazine is used that holds less than division capacity, the shooter will load all magazines to the capacity
of the lowest magazine throughout the match with the exception of PCC.
8.1.2.2 The stage description may require reduced magazine loading for standard stages and the initial start of a
scenario stage.
8.1.2.3 In the Revolver division, the shooter must load the revolver and all loading devices with the same number of
rounds throughout the match unless the above loading exceptions apply.
8.1.3 Rules for Magazine Division Capacity
8.1.3.1 SSP, 15 rounds*
8.1.3.2 ESP, CO, CCP10 rounds
8.1.3.3 CDP, 8 rounds
8.1.3.4 REV, BUG-S 6 rounds**
8.1.3.5 BUG-R 5 rounds
8.1.3.6 PCC 10 10 rounds
8.1.3.7 PCC 30 rounds*
https://www.idpa.com/wp-content/uploads/2023/12/2024-IDPA-Rulebook-Master-12-14-23.pdf
Read Appendix A5 for specific revolver rules
A.5 Revolver Division (REV)
A.5.1 Revolvers will be categorized into one of the two following sub-categories:
A.5.1.1 Stock Revolver or
A.5.1.2 Enhanced Revolver
A.5.2 Stock Revolver handguns permitted for use must be:
A.5.2.1 Any revolver that uses .38 Special or larger cartridges with a rimmed case and is not loaded with moon
clips.
A.5.2.2 The unloaded firearm must weigh 43.00 oz. or less.
A.5.3 Enhanced Revolver handguns permitted for use must be:
A.5.3.1 Any revolver that uses .357 magnum or larger cartridges with rimmed or rimless cases.
A.5.3.2 The unloaded firearm must weigh 50.00 oz. or less.
A.5.3.3 May be loaded via speed loader or full moon clip.
A.5.4 Stock and Enhanced Revolver requirements:
A.5.4.1 The use of trimmed (shortened) ammunition is not allowed.
A.5.5 Ammunition used must match the cartridge listed on the firearm with the following exceptions:
A.5.5.1 .38 Special in .357 Magnum.
A.5.5.2 .44 Special in .44 Magnum.
A.5.5.3 .45 Auto Rim or .45 GAP in .45 ACP.
A.5.5.4 .45 ACP or .45 GAP in .45 Colt.
A.5.5.5 .40 S&W in 10mm.
A.5.5.6 Barrel length must be 4 ¼” or less.
A.5.5.7 Revolvers must be loaded to the division capacity of 6 rounds in the cylinder. Higher capacity 7 and 8
round revolvers are permitted, but may only load 6 rounds