Hello Paroxsym, welcome to the boards, and thank you for your service to our country.
I have little experience with multi pump guns, but I'll offer this opinion. It is only the opinion of one, and worth exactly what you've paid for it.
The 880 series from Daisy is a budget rifle designed and built to a price point, with the intended use of plinking for fun. "60 foot plinker" if you will. To build an air gun to the price of $60.00 MSRP or less, that shoots both pellets and BB's there have to be certain compromises. One of these is the barrel. It has to be loose enough to pass a steel BB without damage. Something a higher grade rifle is just not built to do, a BB will destroy a "springer" and will damage a pcp rifle to the point of hopeless inaccuracy. So to fire a pellet accurately the skirt has to flare more than normally needed, but the head of the pellet is not able to ride atop the lands of the rifling squarely along the bore. As a result the pellet leaves the bore at a slightly different angle each time it is fired, and therefore sprays a pattern instead of a tight group.
Now for a solution, there are two different size .177 pellets manufactured these days. European sized, and German sized. I forget now which is the larger, but you are using one try the other. Also try to add a slight bit of light grease or heavy oil to the head of a few pellets. Just a very slight coating at the bearing surfaces to see if this improves things for you. If this fails having the barrel re-crowned may also help. The 880 will likely never be a 50 yard gun, but 30 yards should certainly be within reach.
Best of luck in your search
Keith