No I don't use inserts at the moment, definitely is the stock barrel.
I thought I'd read the only the new Shaft5 backs are available with different bores.
Not that it matters as sounds like it will fit.
Cheers
The shaft series are sized by the back, so you have one size with your standard etha barrel and can add other shaft backs
No issue as shaft 5 backs will for allowing you to add to your set
The issue is that sized backs can only be used with guns with a specific thread. My first autocockers threaded barrel kit wasn't very much use to me as I had tipmanns, spyders, ions etc and at the time i got the kit only one autococker threaded gun. At that time the two big threads were spyder and cocker
Then i got a freak set and could use my set on any gun just by adding the correctly threaded back
I now have many cocker threaded guns, but still an asssortment of others
Eclipse use autococker threads (at the breach) and the shaft thread between front and back. So you get a compatibility among a number of gun brands and if you stick with eclipse then are more likely to have your backs fit the front that came with the gun