The thumb release mechanism was a relatively early interim-era feature of the Remington Model 14 breech block. They were considered a collector variation worth a premium. I had opportunities to acquire them periodically. But as noted, they weren't practical and I bypassed for that reason. So the good news, your specimen is probably more valuable... If less convenient! smile As I've "opined" before. The Rem Models 14 & 141 are the Swiss Watches of gunmaking art! The downside was bit of clumsiness & inconvenience!

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RE REMINGTON FORUM.
!. Perhaps someone with sufficient stripes to poll in each of the the various Forums concerning Members' interest/participation in such an endeavour. Recruit from our own! Beyond, either to make the venture happen & and see who comes, or just abandon ship!

2. We'd need modern Remington Bolt Gun expertise, Rifles from 700 series forward. 'Perhaps', Rem shotguns too! 4. Legitimate questions should never go unanswered. It is OK to say I don't know, but there shouldn't be a void of silence.

3. Last, the delicate matter of Fire Forums "decorum". Very much of Administrators who condone rough and tumble including personal character attacks. One matter to accept "personal attacks" here as the 'Toll' for participation. I can do that. Yet, quite another to recruit outside experts. "Gentlemen" of whom I'd feel wouldn't be willing to subject themselves to attack for sake of participation.
Just my take
Good Luck!
John