I bought two cases of Cabelas Estate Buckshot and had nothing but problems with it. The spents would not clear the gun resulting in a jam almost every time I shot. Is this possibly the result of a gasket that needs replacing or some crappy ammo?
If it is an A5 and is made to handle magnum shells, which it sounds like it is, you may have to mess with the spring(s) and the spacer (probably not what it's called) that surround the magazine tube. I think that spacer ring has a bevel on one side and is flat on the other - you turn it one way for magnum shells and the other for 2 3/4" light loads. I was messing with one recently and had to remove one of the two recoil springs so it would cycle standard dove loads. Mine is a "Light Twelve" so it will only handle 2 3/4" but I've had to use high brass to get it to cycle when hunting in Kansas in January.
Anyway, you may need to mess with the spring/spacer deal to get it to run properly.
It's the Light Twelve, which I assume is a sub model of the A5. It has "Special Steel shot" noted on the base of the barrel where it marries into the forward stock.
The bit on page 12 about oil on the magazine tube is interesting, as well. This is consistent with what we experienced hunting in the cold in Kansas. Back then we used to use wd-40 which is known to gum up with age and probably extreme cold. Only high brass shells would cycle.
Moral of the story - Don't blame the great John Moses Browning, blame your own dumb ass for not reading the owner's manual.