I recently got a Tac-14 20 gauge from PSA. The only other shotgun I have is a full length 870 in 12 gauge so I didn't know much about these. The gun looks similar to the 12 gauge Tac-14 and comes with the exact same bird's head grip and Magpul for-end. Since the 20 gauge receiver is smaller they ship the gun with metal plate adapter that allows the 12 gauge "stock" to fit into the smaller receiver. I believe
it is the one from Mesa Tactical.
The magazine tube is also a smaller diameter than what the Magpul for-end was designed for so they put a plastic tube around it to increase the outer diameter.
I bought a 12 gauge ribbed wooden fore-end from Boyd's and fit it to my gun. Out of the box it did not fit properly (the fore-end would slide off past the locking nut). It took some length trimming of the plastic tube that increases the magazine diameter and I also had to use some 1" internal locking rings with the lugs cut off to allow the fore-end nut to have adequate purchase on the wood.
For the grip I used the supplied bird's head grip as a template and cut down a wood 870 stock:
I used hand rasps and files to shape the contour to approximately what the supplied grip has. The end that fits into the stock adapter needed a small radius as well.
Here it is after sanding and staining. Still need to apply some BLO and I might increase the radius on the back to match the polymer grip but this feels pretty comfortable as is:
Sadly it is only a 4+1 capacity and I can't find any +1 magazine extensions for 20 gauge even though numerous options exist for 12 gauge. Anyone know of a +1 20 gauge extension?