Check this out - a Mosin Nagant styled bolt in 12 gauge! I say "styled" because the description indicates it used the Mosin design for some signalling/launching device but doesn't give particulars.
I suppose the question is would a Mosin receiver have the strength to hanlde 12GFH? Since the 7.62x54R is published to pressures of 50,000 CUP I would think it is, considering the other bolt actions that have been converted?
Mosin Nagant 12 Ga. Shotshell Bolt Assembly | e-GunParts.comThis bolt was used in a European mounted type device that used a 12 Ga. shotshell to propel weather balloons. Although the device uses a Mosin Nagant style bolt, it is not related in any way to the standard Mosin Nagant series rifles. Quantities are very limited.