Hi Bolthead,
I think you may be misreading the law. As a non-resident you are allowed to possess your rifle and ammunition in MA.
According to Section 129C
The provisions of this section shall not apply to the following exempted persons and uses:
(g) Possession of rifles and shotguns and ammunition therefor by nonresidents while on a firing or shooting range;
(h) Possession of rifles and shotguns and ammunition therefor by nonresidents traveling in or through the commonwealth, providing that any rifles or shotguns are unloaded and enclosed in a case;
(m) The temporary holding, handling or firing of a firearm for examination, trial or instruction in the presence of a holder of a license to carry firearms, or the temporary holding, handling or firing of a rifle or shotgun for examination, trial or instruction in the presence of a holder of a firearm identification card, or where such holding, handling or firing is for a lawful purpose;
Please refer to:
https://malegislature.gov/Laws/GeneralLaws/PartI/TitleXX/Chapter140/Section129cI will let the instructors in that area for that event comment on whether or not they will have loaner rifles available.