We own 3 SLP MK1 series shotguns, one for each family member. We chose this series before the new set of barrels were released due the the implied promise of future upgrades and accessories that would make this a formidable all around weapon system that is better than anything competitors could even hope to offer. Now, after the barrels that would bring dreams of clay shooting and better shot control come out, lo and behold they never put in the product descriptions whether these barrels were compatible with the MK1 series of the SLP, just the basic lower capacity SLP models. We were looking at the barrel with the Product #3088929560, and all FN customer service said when we called was they were not sure whether they were compatible or not. it should only be an issue of the length of where the gas block is from the receiver, and nobody seems to know the specs (measuring length from gas block to receiver comes out to about 8 1/16 inches), but there may also be other issues we are unaware of. anybody have any insider info or experience that could help us out?