If I've not done so previously, Welcome to the T&TH forum.
I just saw your post about choke tubes. I apologize for not getting back to you more quickly.
Yes, the subject of turkey chokes can be a pretty hot topic. I have tried to shoot all the commercially available chokes and as many of the different sizes of those chokes (exit diameters) as possible, with as many of the popular shotshells and through as many of the shotgun makes as possible.
I've done a lot of shootiing in the last 10 years especially. It's been a very interesting time with many new shells on the market and many new chokes. In many ways, it's the golden age of turkey hunting. It also gets pretty complicated at times.
I shoot 870s in both 12 gauge and 20 gauge shotguns in competition, in my work and for hunting. I have some that have thousands of rounds through them and they're still going strong.
The good news is that there are several good chokes on the market today. Some will work better than others and there is a pretty wide range in the prices of those chokes. The good news is that you can invest in a premium quality turkey choke, without breaking the bank.
The SSX http://allaboutshooting.com/product_info.php?cPath=23&products_id=74
is truly a premium quality turkey choke, rated for all lead and tungsten-based shot (Hevi-13, Winchester Xtended Range Hi-Density, Remington Wingmaster HD, etc.), it has great internal geometry, throws great hunting patterns and is very reasonably priced.
The SSX Turkey Choke in your gun with a "deep cleaned" barrel and one of the tungsten-based or HV lead loads will allow you to do what you need to do to cleanly kill turkeys at 40 yards.
I hope that helps. Just let me know if I can be of help.