I have, I think an early pre ban 121 M1 (ser 22xxxx, Arlington) in need of a new recoil spring.
So far I have not been able to get the oem type spring from Benelli, H&K, Midwest, Numrich, or Wolff.
Tried the currently available M1 spring. It is slightly (1/64th"ish) too large in diameter to function, it binds during recoil cycle.
Benelli USA gunsmith seemed to think the currently available M2 recoil spring would function. I ordered one, albeit skeptically.
Internet search indicates speculation that the recoil tube itself could be swapped for later version M1 tube, and then utilize available springs.
Parts sources show this tube available.
I am hoping that someone might have some incite or experience with this issue that might prove helpful before I start throwing money at it.
Thanks in advance,
KS