I have a chance to buy a O/U that has a set of Briley inserts for the 3 sub gauges. Does anyone have any experience with these and what do I need to be looking for? I have not inspected the shotgun so not sure if these are sidekicks or full inserts.

Yes, have had Briley full length inserts. They work well, but naturally add front end weight. Have to be careful lining them up when inserting or you will ruin an ejector when closing. Can be fixed, but who wants to have to. I think they now make LW-or lighter weight-sets. A full set of three is an expensive addition. Sometimes used you can get them much less so.

Sidekikck? Some like them, I don't, nor would I pay extra for them.

What kind of gun? Subgauge tubes are either good or a busted pos. They simply knock in and out.
I have owned Briley and Kolar in both std weight and lightweight and much prefer the lightweight tubes as I shoot 30 inch barrels at a minimum. Are the tubes fitted to the 12 gauge barrels or carrier barrels?

Thank you all for the information. It is a Rem 3200 Skeet. I am being told, 28" tubes. I will not put my hands on it for another day or two.

Make sure the updates have been done. Based on the age of the gun I would think it’s got std weight tubes and she’s a handful as the bare gun is heavy.

The only caveat is one will need to use smooth Win Aa or Rem STS type hulls for best results. These smooth sided hulls do not stick in the chambers like the ribbed type (Federal/Estate, Winchester, Remington, Fiocchi, et al) will often do. The AA and STS will also have the brass heads which again are "slicker" and more resilient than the zinc/steel heads of the less expensive lines.

In my small sample size of two I found the 410 tubes to be less sensitive to hull type but others have had dismal results with anything ribbed. The Remington STS in 410 are ribbed and would stick occasionally in the tubes. PMC and Nobel were as reliable as Win AA until the third or fourth loading were they began to stick. Federal and Remington's field line stuck pretty regularly from the start as did Fiocchi.

The 20 and 28 tubes stuck everything except AA and STS on a regular basis.

My findings mirror woodsmaster except the only hull extraction issue I have had is with cheap 20 gauge. Still something to factor in, you need to run good hulls be it factory or reloads for smooth extraction