Dennis Sir,
GForce Arms explicitly does not recommend using mini-shells with their shotguns, including the GFP3REX. While some retailers list the GFP3REX as compatible with 2- and 3-inch shells, mini-shells are generally unreliable in many pump-action shotguns without a special adapter. The problem with mini-shells in many standard pump-action shotguns is their shorter length, which can lead to cycling issues.
The small size can cause them to not properly feed from the magazine tube and load into the chamber.
To use mini-shells reliably, you would need an adapter, but these are typically specific to certain brands like Mossberg shotguns. There is no indication that an adapter is available or compatible with the GForce GFP3REX. Sorry Bud
Hope the above information helps Sir Dennis. Take care and stay safe 🙏🏻

No sir, they do not work reliably in that firearm. Happy shooting!

Good evening to you!! The best I can tell you is to try it and see. Most pumps won't but you never can tell till you try it. Good luck. Hope this helps. Have a good rest of your day.
🇺🇸🇺🇸 'Merica' 🇺🇸🇺🇸

Hi Dennis and welcome. There will be answers to yay and nay if it is not a Mossberg 500/590 with an adapter. There are more pump shotguns that will fire mini shells than most realize. I would buy a couple of boxes and test in your shotgun to find the answer for yourself. Usually, a quick purposeful pumping action will feed reliably from a good portion of pump shotguns. If they work, they work and if not, just send the rest down range one by one. Cheers, stay safe and enjoy!

You can chamber and fire them one at a time but not cycle them reliably (if at all) from the magazine tube.