Internal mods and aftermarket sights are legal in Production class.
Technically, if your original didn't have an option for an adjustable "reset" screw on the trigger, then you can't add that feature as it's an external mod. Anything that was originally an option is also legal. You cannot disable a safety item, like the FP Interrupt safety.
81 USPSA Handgun Rules, February 2014 Edition
APPENDIX D4 ? Production Division (Cont.)
21.2b Milling of slide ? only as required to insert sights Remains in effect ? a slide may be modified specifically for the purpose of installing sights, and for no other purpose. 21.3 After-market slides and barrels ? provided they are the same length, con- tour and caliber as original factory standard. SLIDES: Current rules remain in effect ? You may replace the slide with an OFM or aftermarket slide which is of the same length, contour and caliber as the original slide for that model of gun. BARRELS: Current rules remain in effect - you may replace the barrel with an OFM or aftermarket barrel which is of the same length, contour and caliber as the original barrel for that model of gun. Special Notes/Clarifications: For purposes of this interpretation, a barrel within +/- 0.1? of OFM is ?the same length?. Barrels of the same length, contour and caliber but with different crown profiles are authorized. 21.4 Grips ? For semi-automatic Production guns, grip tape, grip sleeves, checkering, stippling or other texture may only be applied in the areas shown in appendix E4. Glue and grit is considered the same as stippling. ? Replacement grip panels are allowed provided they do not extend below the butt of the gun to form a make-shift magwell. ? Revolver grips may be replaced with OFM or aftermarket grips of any shape, profile and surface texture. Special Notes/Clarifications: ? See 22.2, below, for specifics with regard to modifications on revolver grips.
82 USPSA Handgun Rules, February 2014 Edition
21.5 Exchange of minor INTERNAL components (strikers, sears, springs, connectors/disconnectors, and other wholly-internal parts) INTERNAL parts: This clause is NOW interpreted to mean that a broad range of INTERNAL parts may be modified or replaced ? either with OFM or aftermarket parts. Special Notes/Clarifications: ? Strikers, sears, springs, connectors/disconnectors, and any other part which is NOT visible when the gun is in battery is considered an INTERNAL part and may be modified or replaced unless otherwise prohibited in these provisions (see section 22 for specific prohibitions).
