Well I have just been through the process - I have added a 7x65r insert made by Zimmerman to my Ferlach built 16 / 7x65r combination gun.

I went with the same calibre to give a double rifle for use on wild boar. I thought long and hard about a small calibre, but to be honest the 7x65r is very good on Roe up to Red deer and wild boar and no fox I have shot has so far complained.

Had it out earlier today for a test run. First group from the Insert barrel was an inch, albeit 4 inches and high and to the 3" to the left. It took a few shots and a bit of adjustment on the little screws at the front and I soon had it shooting the top barrel about 3/4" high at 40 yds.

Adding the insert barrel did mean the bottom barrel was shooting about 2" to the left. Its added about 1lb in weigth so not surprised its affected point of impact. It is now better balanced - it needed a bit more weight forward. Photos et al on https://www.thestalkingdirectory.co.uk/s...-my-possession!