358win short, what length gas system?

[Lar45]

Hi, quick question for those running the 358 MGP or similar.
What length gas system works best?
I'm getting ready to order a 358 barrel. I'm leaning towards 18.5"
The cartridge will be a 358win x1.66", just a stock reamer run in short.
I've already cut down dies and made some test cartridges.
I'll be limiting myself to 180-200gn bullets to try and get the velocities up.
I have quickload to guesstimate pressures, and a chronograph...
I know a chronograph can't measure pressure, but velocity doesn't come for free. You either raise the pressure or burn more of a slower powder.
I'm planning on trying to keep the pressure around 46k to keep bolt thrust to what other rounds produce.
I have Hornady 200 FTX and Interlock bullets, Speer 180s on order, and will probably try the Lee 358-200 cast bullet.
I just ordered a small pile of Win 308 cases because they are supposed to have more case capacity.
I am open to any thoughts or suggestions..
TIA
Glenn

 

[Lar45]

These are my two options for cartridges. 308 win, or 450bushmaster.
The 308 case holds 45gns of H2O, the Bushmaster is 54gns.
With having to keep the Bushmaster pressures lower, quickload estimates only a 40fps gain. So I'll go with the much more available 308 win cases.
I ordered a Boar Hunter-15 lower from PSA.