My 16 GA sterlingworth all of a sudden started resetting the safety on after the first shot. There is not a noticeable difference in the force needed to set and unset. Anyone have any ideas?

Sounds like it could be one of two things. You will need to remove the buttstock to get access to the safety. Check to make sure that the safety spring is still in the guide pin on the upper receiver and that the spring is still providing tension to the safety. Second thing and one I have encountered is that the pin in the lower leg of the safety that provides tension to the safety has fallen out if it has you may have to sacrifice a cheap drill bit of the appropriate size to make a replacement pin .

Could be those things but also could be shells with a much stronger recoil impulse.

I can't shoot the Remington black hulled promos anymore. They used to shoot pretty soft but lately they really kick!

As the safety moves back to go on safe & as the gun also recoils back it would seem doubtful recoil would be moving it to safe. That is unless the gun is being allowed to recoil very freely & then brought to a Screeching Halt. I can't really imagine this taking place though.

If I shoot really light loads it doesn't do it. I have shot RGLs and Rio's 1oz 1300FPS before with no problem. I know, pretty heavy. Not a regular diet.

The Fox safety is simple and straight forward with only three parts Since it doesn't occur with light loads that leads me to believe that the safety spring is not exerting enough force to hold the safety securely in the safety detent in the upper receiver. Pull the stock off and see if the spring is broken, is not properly aligned or there is not enough force put on the spring to hold the safety in the detent. There are no other plausible causes I am aware of.

Thanks to all.

Check for firmness of the safety slide and spring itself.

The other variable is the top lever spring. A weak spring COULD cause the situation where the top lever is getting bumped open under recoil some thus resetting the safety. But i find this unlikely on a fox given their use of a pretty stiff coil spring for the top lever.

Is the safety fully going back or jjst enough to cause blockage of the triggers?