I am thinking of buying my brother-in-law's old Remington Model 17 20 gauge shotgun, but after trying it I found that in a horizontal position (regular shooting position) when I try to pump a shell it moves a bit and then won't go further. If I point the gun straight up or if I roll the gun so that the bottom/top is off vertical by about 30 degrees, it pumps just fine. My question is whether anyone might have any idea what might be wrong and whether it can be relatively easily fixed or whether I should pass on buying it???