IMHO length of a barel has little to do with anything and getting a good fit bore is the key, sterling shield I have found is big paint and I have sized my batch at .693; this paint shoots really well out of stock barrels that generally are overbored.
Try shooting a box of shield through it and see. It's shortness shouldn't make much difference if the bore fits.
The standard Axe Barrel is fine. In our team when we first had these in 2011 we had approx 16 guns and 10 players used the standard barrel whilst the other tarts in the team bought barrel kits, both worked fine with the gun.
Barrel kits are good but sometimes the standard barrel for the gun is fine.