[1tonne]

Try around 420-450mm.
Normally, going off the VSR cylinder to barrel ratios, I would say try a barrel around 370mm (This is allowing for the smaller volume of the L96) with 0.48gm but the L96 does have a slightly different cylinder shape which can effect the way the energy is released and from what I have noticed and other have also said, you can use a longer inner barrel and it gives excellent results.
So my guess is that 363mm is a little too short and 509mm would be a too long.
In my upgrade L96 upgrade thread, I had a stock L96 500mm inner barrel (6.08mm). I tested each bb weight to see what gave the most energy. 0.4gm came out on top. Though you did need a 100% air seal. So for the 500mm inner barrel, I recommended using a 0.36gm but you also need to remember that the inner barrel was a 6.08mm and so if you are going to use a 509mm x 6.03mm, then a 0.4gm would be able right. The 0.48gm is quite a bit heavier and so to get maximum energy, you will need shorter. The 509mm inner barrel may even cause the rifle to be slightly inaccurate with the 0.48gm. The shorter 363mm inner barrel will be accurate but you will not get maximum energy.

 

[1tonne]

oh. I see you said 0.43gm. Not 0.48gm. So try a 470mm inner barrel.

 

[1tonne]

The longest shots made consistently were with an extra tight bore. 5.98mm. I use 6.01mm myself and they are great. Years ago you may have been better off with wider but these days heavy bb's are pretty consistent

 

[1tonne]

BLS are the ones. Way better than bb's used to be.
Less plastic build up on the barrel and less jamming = better accuracy and better feeding.

 

[1tonne]

BLS 0.4gm, 0.43gm, 0.45gm and 0.48gm are great. I have them all.
The longest shots were not with BLS but ceramic bb's and a 5.98mm. BLS are very good though. In my DMR I actually have a 6.00mm barrel and I have never had a jam with 0.4gm BLS.