Doverham:
H&H still does as a matter of course; they have their own barrel/choke regulator, Steve Cranston. I think the others will by request. I honestly don't think the typical best-gun buyer nowadays does request it. H&H builds so many double-rifles having a regulator aboard makes sense, and a shotgun is easy by comparison.
In the old days makers loaded their own shells and could regulate a gun to the 'house' brand, and a specific load, which the client faithfully used. This is no longer the case.
If you p.m. me with your e-mail I will be happy to send you (or anyone) a chapter I did on the topic, and on Steve Cranston.
