A friend had one of the H&R 10 gauge single shot slug guns. This was 30 years ago so your results may be completely different but ours were memorable. It was an open choked version with rifle sights and would recoil hard enough to pop the forearm off and unlatch the barrel. With no forearm the barrel would then fall off leaving the shooter with the stock in one hand, the forearm in the other and the barrel in the dirt. I think the later H&R versions used a screw to attach the forearm rather than a latch. This would keep the forearm attached and the barrel from falling off after the automatic opening and empty shell ejection feature was activated. Hoping your results are more favorable.
An insider tip, is to keep the action dry too prevent the gun from opening. I suspect Remington was not aware of this when they purchased H&R. The 10ga must have been too much for the fore arm. I always assumed the change was to save mfg cost.
