Every gun has a sweet load that it shoots better than others. You may be shooting a load that the 870 "likes" and that the 835 doesnt care for. My 835 is partial to Winchester 3.5 or 3 inch HV #6's and Federal #5's coming in a close second. There is also another thread that i posted some instructions to polish the barrel on your 835 for just a few bucks, this will help the pattern greatly.

Hope this helps

AH