I bought the 870 synthetic 7 shot and got a new 26" express barrel and magazine parts online to convert it to a bird gun also. I didn't realize the barrel's are not 100% interchangeable with a magazine cap switch. The problem making the switch is that there is no ball detent on my 26" express field barrel and no dimples on the end cap of the magazine tube of the 7 shot model due to use of the factory mag extension. The plastic retainer of the current 4 shot express model simply turns on the mag spring without the dimples and will not retain a standard factory cap. Can my express barrel be drilled and a spring and ball detent staked into place on the factory barrel lug without much trouble? I was considering drilling the 26" barrel and trying to install the older style retainer system on the new barrel so they will switch over without the problem of the end cap vibrating loose during a hunting trip. I've read about some people using teflon tape. Would that be a better way to solve my problem for a switch barrel system? Thank you for sharing your thoughts. rc