I hunt a lot of prairie grouse and huns each year, the experience should apply to your logging road ruffies.
1. pace off the distance of your next few shots. Many people have trouble estimating range, it may be the birds are just too far. More than 50 yards IS too far.
2. pattern your gun. Does it shoot where you look? how big are the holes in the pattern at 50 yards? A bird should be hit solidly with 2-3 pellets, not one "magic BB" If you can't get three pellets in the body every shot it is too far, or your gun is not up to the task,(choke, barrel patterning ability etc.) or it does not fit you and the center of the pattern is simply missing what you are aiming at.
3. From extensive patterning and hunting experience, I found that there is no advantage to going bigger than #5 on grouse, and #6 patterns so much better in most guns that bigger shot is a mistake. No 4's are too large for most upland bird shooting IMHO. There is also a big difference in penetration between 6 and 7-1/2, try it on 3/8" spruce plywood at 40 - 50 yards some time. 6's will penetrate right through, 7-1/2 will stick in the first layer at that range. #5's pattern OK in many guns, but are hard to find in most stores. So #6 gets my vote for your situation, unless you have access to hand loaded #7 nickel plate, that stuff penetrates very very well because of the slick plating it does not catch on feathers, but slips between the fibers.
4. "Magnum" lead loads look good on paper, but do not deliver the goods in the field unless you need turkey loads. The long shot column strings out, the pattern generally has holes in it because the pellets are deformed from the high pressure and crowded condition at the forcing cone and choke. Specialty tungsten pellet long range waterfowl loads will work, but are kinda silly to use!
If you do your homework, I think you'll solve the mystery of the armour plated grouse! good hunting!