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?

I like it. You need to rough up the forearm.  It's to shiny compared to the grip.

I put some BLO on the grip since taking the pics and it will hopefully give a bit of luster to it.

Nice.

Now for your next trick, hang cut some checkering in there!

Pretty cool.  Just curious though, wouldn't it have been easier to just buy a 20ga stock and forend?  Then you wouldn't have to monkey around with the forend sleeve, and you could leave off the Lucy adapter for the stock.

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Not that there's anything wrong with the Lucy, mind you, but starting with a 20 ga. stock would be .... well, prettier.  

Had a 12 ga. set laying around, maybe?

Yeah I had a spare 12 ga stock and I couldn't find a 20 ga for-end in the style I wanted.