First(new)shotgun

[CharlesHarris]

An over-under 12-ga. auto-ejector gun with 28-inch barrels adapted to screw-in choke tubes, and 3" chambers would be ideal.

If you are able to get at least one insert tube or chamber adapter to enable use of other common ammunition for guns you already have, or may come across, that would be good.

The longer barrel insert tubes of 20cm or more, ideal for break-open guns give much better results than the short chamber adapters intended for use in repeating guns. I have one of the German Kepler insert tubes for my Beretta 412 folding shotgun, which fits in a suitcase and has flown with me all over the world back in the day. These are very expensive now, but of the highest quality. http://www.keppeler-te.de/cms/pages/engl...arrels.php

Briley tubes let you use .410, 28-ga. or 20-ga. in 12-ga. guns. They are widely used in the clay target shooting community, are of high quality, but expensive: http://www.briley.com/side-kickchambertubesets.aspx
http://www.gun-tests.com/issues/16_10/fe...196-1.html
http://www.youtube.com/watch?v=q-RtmiZiL0o

A .22LR insert tube makes sense if you will get only one:
http://www.gunadapters.com/12-gauge-to-2...d-adapter/

Some links with the less expensive, (also less effective) chamber adapter examples:
http://shotgunadapter.com/
http://www.gaugemate.com/