The prevalent opinion for the Savage Four Tenner is that it is safe in old shotguns with twist, etc. barrels. This also seemed to be suggested in some of the advertising that accompanied their introduction.
Until a few years ago I would have had no hesitation in using a set in an old sotgun. However, today I am more hesitant after one of the shooters at our trap club was using a set in an old twist barreled double that appeared in good condition had one barrel burst just forward of where the four tenner sub barrel ended.
The cause was not determined but a number of shots were fired in a round of skeet prior to this incident. The ammunition being used was factory loaded.
Today, if I were using barrel inserts in any older shotgun I would prefer full length tubes.
Bill
