FN Police Shotgun\Winchester 1300 Defender

[Imshootin]

I've got an FN police shotgun\Win 1300 Defender with a 7 rd. magazine tube. I picked up a clearance Winchester 1300 slug barrel for it but it's made for a standard 5 rd. mag tube. Does anybody make a longer magazine cap to make this a workable option or am I going to have to return this. The barrel bracket on the smooth bore is about 5 1/4 inches further forward than the slug barrel. Thanks

[Imshootin]

After talking to a few gunsmiths, I returned the barrel. Too much trouble. Instead, I am considering buying a Winchoke for sabot slugs. I wasn't aware they were available. Does anyone have any experience with this setup? If that short length of rifling will shoot sabot slugs accurately, it definitely seems like the way to go.