You all know I'm new to loading shot gun stuff and I'm more than willing to push the envelope on reloading rifles. Well This is what we ended up with. ,BEFORE I START "IN MONTANA WE CAN AND DO USE ALMOST ANY THING TO HUNT WITH" AND BUCK SHOT IS LEGAL AND EXCEPTED" TO SHOOT TURKEY,DEER,AND COYOTES.... OK with that said; We tried a #4buck and 4 shot load with our X-full extended turkey chokes and were very underwhelmed. The mix was inconsistent and it cut down our hits with the buck. What we did end up with was; using new primed Fiocchi brown plastic 3" hulls,BP supper sonic 1 7/8 oz wads,42 grains blue dot,34( 1 5/8 oz) #4 supper buck shot,two scoops buffer and mica slick on the wads,and an over shot card, with a 6 point crimp.The listed speed is 1350 and 13500 psi. We patterned it at 55 yards on a standard shipping pallet covered with plain white newsprint.We put a coyote picture target ( natural size) and aimed at the shoulder.We are using our 870's with just bird ,bead and smooth bore and extended x full rem chocks. Of the 34 #4's all hit the paper with and average of 21 in the coyote. We ( two of us ) tested 5 each and had all the pellets ON PAPER. My Supper express has a 2 inch longer barrel than the other and I looked like I had  a bit better pattern most of the hits were in a 3 foot circle but we both averaged the same on HITS ON TARGET.

The other loads we tried did not seam to do any thing special, We did have one more that we will use for birds ( any thing we can use lead on ).It is same hulls,and wads,mica slick,6 point crimp. It is a 1 7/8 oz load of 5 shot and 7 shot with 44 gr of blue dot. The speed is slower at 1250 and the same PSI.This load with our Full choke at 50 yards was very impressive. I did not count the hits on the paper but it looks like 200?? This is going to spell death to any thing that flies from Doves to sage hens.
The buck shot loads cost me around $1.25 each and the bird shot ones should cost about $.55 each not to bad for a first try. Were going to move on to steel as soon as we can. 

My step dad had on of them WAY back when I was a kid, you HAD to have it put on by a smith. There is tuns of chokes and they range in price from like $20 to over $200. Ours are just X full Rem chokes price around $40. I think there only 2 steps fuller. ( is that a word-Fuller?) Tight .687" constriction

Born-to-Hunt, try the undertaker choke tubes and try different loads in it. Custom choke tubes can get pricey, and I have yet to see an Undertaker that I was not pleased with.  I have had the same Remington Super Extra Full in my 870 for the last 12 years. That thing loves the lead 3.5" Winchester Supremes in #4. Only problem is that the choke is only rated for lead so no new fancy hevi-shot type loads for me. But no worries, when you see what it does to a turkey head/neck target you will understand why I have stayed with it for 12 years!!!!

Ned

My brother Charlie and I bought a Mech 250 with several loading bars when we were kids. One bar was bored out for a 3" (12GA) powder load, for 2 3/4" shells.
We saved left over shot sizes 2,4,5,and 6 shot mixed in a coffee can and loaded it into what we called our Super Loads. The extra heavy powder charge in the 2 3/4" shells with the mixed shot killed ducks at never before experienced distances.
We did have to cut back a tad on the lead shot charge because of the extra room the powder charge took up.
The loads kicked like hell but sure did kill ducks!