Ok, so you'll be on an ATV, that clears it up a little.
Assuming that you're in an area where it's legal to have a loaded gun on an ATV, I would rig up a gun rack right to the handle bars. That will put the gun in an easily/quickly accessable spot, and you won't have to worry about getting it hung up on anything.
I still say that a laser is a complete waste. Lasers are great when you're inside, or in low light conditions, pointing them at a FLAT PAPER TARGET. Outside, where everything is green and your target is moving quickly, you'd be surprised how hard it is to find them. Especially "from the hip." It takes a ton of practise, and some phenominal hand-eye coordination to get good at shooting from the hip. And even with a pistol grip shotgun it's best to raise it to eye-level & referrence the sights quickly.
I have to agree with Boomer, that you should go with a full stock. A conventionally stocked gun is a lot easier to control than one with a pistol grip. The gun can be fired & brought back on target much more quickly. As recoil is an issue, reduced recoil loads should help, and a recoil pad like Boomer suggested, will help out a lot too. I use a Limb-saver slip-on pad on my slug gun, and I have recommended it to everybody I know. It EATS recoil like you wouldn't believe possible. I would suggest getting either a youth model or a having a normal stock cut down, then putting a limb-saver on it.
If cost isn't an issue, and you do decide to go with a full stock, I would use a semi-auto instead of a pump. Obviously, my choice would be a Remington 1100. Aside from being faster to shoot, semi's absorb some recoil simply by the action cycling. Also because you don't move your arms, they are faster to bring to bear on the target for follow up shots. This is a matter of opinion though, I've seen some people who are pretty fast with a pump. There's no denying though that semi's are a lot of fun!
As for the comments on the Remington 870's reliability, I don't have any trouble with my 870 Express. It's second hand, and since buying it I've fired over 2000 rounds of mixed goose & skeet loads through it. The only problem I've ever had is if I short-stroke the action. That reliability is why I recomend the 870, and why I have 3 of them. I don't reccomend the Mossberg because a gunsmith aquaintence I have constantly complains about fixing broken mossbergs. I am not biased though, and I will admit I have had trouble with a 20ga 870. I bought it for my wife, and although it never had any reliability issues or stoppages, it was nearly impossible to disassemble & reassemble. I still don't know why. New 870s that I've played with (anything with a "J-lock" on the safety) have had a stickier action, but again, nothing that seems to affect reliability.
I don't think you'd have to worry about keeping the magazine under-loaded to reduce stress on the springs. If you were to keep it loaded and stored as a home-defense gun (which we all know is illegal...
) Then yes, it would be wise. However, if the gun stays unloaded for 99.99% of it's life, and is only loaded for several hours or even days at a time, the spring will be fine.
By the way Sixgunner, where are you? I have an 870 that is set up somewhat similar to what I've suggested, and I also have a pistol grip. If you're within a couple hours, we could probably T-up at a range or gravel pit, and you can put a few boxes through the gun in different configurations to get a feel for what you like.
Cheers.
Tim
I use the side saddle to hold five 3 inch slugs for those ferocious neck and face Biters.I'm glad to see I'm not the only one that gets the willies from animals.God bless Shotguns to keep them away.
