I believe this is it.
Standard disclaimer applies, I may be mistaken, but IIRC this was the language.
Protecting The Rights Of Target Shooters
Section 121 of Chapter 140, as appearing in the 2002 Official Edition, is hereby amended by inserting the word “trigger”, in line 107, the following:-
“Single Action Revolver”, any revolver manufactured as a single- action revolver that has at least a 5-cartridge capacity with a barrel length of not less than tree inches, and meets any of the following specifications:
(a) Was originally manufactured prior to 1900 and is a curio or relic, as defined in Section 478.11 of Title 27 of the Code of Federal Regulations.
(b) Has an overall length measured parallel to the barrel of at least 7 ½ inches when the handle, frame or receiver, and barrel are assembled.
(c) Has an overall length measured parallel to the barrel of at least 7 ½ inches when the handle, frame or receiver, and barrel are assembled and this currently approved for importation into the United States pursuant to the provisions of paragraph (3) of subsection (d) of Section 925 of Title 18 of the United States Code.
SECTION 2 Section 123 of Chapter 140 is hereby amended by adding the following paragraph after clause twenty-first:-
“Notwithstanding any general or special law or regulation to the contrary, clause Eighteenth to Twenty-first, inclusive, of said section 123 of Chapter 140, shall not apply to:
(a) any firearm solely designed and sold specifically for formal target shooting competition
(b) any firearm lawfully owned or possessed under a license issued under said Chapter 140 on or before October 21, 1998
(c) any single action revolver