Remington 1187 not cycling

[trappy]

I converted by 1187 with a rifled slug barrel to smooth bore slug barrel
and then added an extention mag tube. My question is why can I only use high brass shells for it to cycle properly. If I shoot a trap load it will not cycle.
What can I do for this to cycle trap loads?....thanks

 

[rantingredneck]

11-87 short barrels (less than 26-28") are not intended for light loads.

It's a gas operated gun, so the action is cycled by the gas bleed off from the barrel through the gas ports at the barrel ring. There's not enough barrel past the gas ports on the 18-21" barrels to allow time for the pressure in the barrel to cycle the action, when using light loads. Heavier loads have more oopmh and can work the action in a short barrel.

Some folks, I believe, have modified their gas ports to some extent to allow cycling of lighter loads. I just run a longer barrel on mine when I want to shoot low-brass birdshot.