Our sponsor sells the 4.4s Matt,, JS Ramsbottom. I use H&N Excite Smart Shot BBs in my fairground rifles as the rifles are 4.4mm, They know it says 4.5 on the tin but are quite a bit smaller.. Odd calibres, Maybe they have something for your rifle, Col.
Have a look at this article even though they are pellets as it has a few interesting bits on how much of a variation there is in batches.. Col.
https://www.gatewaytoairguns.org/GTA...topic=151990.0