Gentlemen:
If I may offer some advice. I to went through the same situation you are in and leaned a few things.
Fist in my opinion, believe there is no better first shot gun then an 870 Wingmaster. This is also a great gun to get started in Trap with. It the type of gun that can grow with you, as you grow in experience. There are so many parts and options that you can configure the gun to whatever you want.
Further, a lot of guys get hung up on “NEEDING” to have one with a 3" chamber, but to date 99% of my shooting has been with 2.75 shells, and I have owned both chamber sizes. Further, if cost is and issue, one can generally pick up a good used WM with 2.75 chamber for around $250 to 300. These guns are usually miles ahead of the express in terms of machining and smoothness of action.
When I started trap, I used a standard 12 gauge 870 Wingmaster with a 2.75 chamber and a 30" fixed modified choke. I shot that for about a year. Then I reached a plateau in my shooting level, and thought that a proper Trap butt stock would help. (They have a higher comb for a better cheek weld). So I got one, and I picked up another bird or two consistently. I started shooting handi-cap and wanted more choke flexibility. So I sold my barrel and picked up a 30" vent rib barrel, with front & mid beads and Rem chokes (read screw-in choke tubes)in full, modified and improved cylinder. Now I could use a more open choke for 16 yards, and a tighter one for further back.
I found my concentration was wandering, and needed to focus better. So I bought an extra full turkey choke tube, here on the board, and used it @ 16 yards for training purposes. With this choke you really have to concentrate, because just a minor lapse will cause a miss.
I wanted to shoot doubles and had some success. I decided I wanted a Fatter and longer pump grip that would allow more flexibility where to position my front hand, and fill the hand better. So I looked and bought one off the board. I got to a point where I was shooing 41 out of 50 with that gun.
Further, there are a lot of top trap shooters using “release triggers”. These are triggers that fire not when you pull the trigger, but when you release it. Many shooters that have developed a bad flinch find this type of trigger helpful in curing it. Well I got nosing around, an low and behold, I found a release trigger group for my 870 as well.
In certain light conditions, I was haveing issues seeing my front bead, so I just picked up one of those fiber optic beads that are held to the rib magnetically, and off to the races I went
So as you see, the 870 is defiantly a flexible, durable shotgun.
I hope this helps, and if I can be of further assistance, please let me know.
Regards and all the best
R