Had a chance to shoot our Rem 870 21" youth today with a Sumtoy 562-5 topped with a FF3 using
Federal HW 7s. Was about 50* with a variable breeze. After getting things dialed I backed to 40 yards and fired a few rounds. The circle is 8" and the pattern overall on the large paper was pretty even. I got an average of 80 in the 8" and cleaned with a bore snake between shots. I expected better or am I looking for too much?(http://img.photobucket.com/albums/v638/mq-1/cae8c589-7766-4164-9d28-3748a1694ffb_zps371c1ea0.jpg)
Finally got the pic posted..sorry.
That would correspond to something like 120 in the 10" at 40 yards, assuming all your shots were well centered. I wouldn't hesitate to use that up to 40 yards.
It is funny thing with the Rem 21 inch guns this year. They are shooting big numbers or they are low numbers. Seen a few that we tried few chokes in along with other companies chokes they never did come around. Now you may try a HV13 to see if numbers come up some. I think the Fed HWT is a hot shell and that is why it is giving a fit in some of the pump guns.