I'm planning of buying my friend's Remington 870 police magnum, cost is around US$540. The barrel is 14.5 inches, blued, with 4 shot capacity. The stock and pump handle is made of wood. The condition of the gun is around 80-85%

I plan to use it primarily as my house gun for security/home defense purpose.
From what I've read, Remingtons are used by almost all of the police organizations in the US. I think its one of the most durable and reliable shotguns out there.

Is this a good deal?
Also, does anyone know how much would a replacement (longer) barrel and extension tube for increasing the capacity of shells cost?
Thanks

A shotgun with 14.5" barrel would fall under the NFA (meaning that you'd have to have it licensed and it would have to be transferable), as for replacement barrel you can probably find one for about $100-200. I kinda doubt he got the shotgun that way; or he bought it from somebody like that. Either way, you would be inviting trouble if you carried it around in that configuration.

As for the price, that seems kinda high. I just bought an 870 super mag for about half that brand new.

thanks for the info, will check with the local police regarding the legality issue. Maybe he was selling it at that price because the 870 came in that original configuration

buy the shotgun without the barrel, and then just get a new barrel