I ordered a 5 cavity aluminum mold from Arsenal (mostly because they were immediately available) for 9mm. A 358-130-RF-PC, https://arsenalmolds.com/products?product_id=195
My as cast with my personally processed COWW plus 1.5% pewter/tin is only .355"-.3555" (measured with analog and digital micrometers). My normal casting temp is 700-720 degrees but I did try at a low of 660 and high of 770 and saw little to no difference in size.
I have been using a Lee TL356-124-2R, but have had to beagle the mold and then bump them to consistently hit my PC'd target diameter of .358". That's a good bit of fiddling hence the reason for ordering a .358" mold. I have a new Sig P320 M18 and the barrel slugs at .356". I was still getting some fouling until I realized my unsorted mixed brass was swaging down some of my bullets. Since then I have sorted and pin gauged my selected/sized brass and have run a couple hundred rounds with great results.
An FYI, I found that a .351" minus pin gauge that will slip into the case to or nearly where the bullet's bottom will be ensures all loaded rounds with those fat .358" bullets plunk every time.
For some reason Jared at Arsenal has not responded to my call/email from last week so I sent another email and called this evening, but now his voice mail is full. I am assuming he has something personal going on and will get back to me soon.
All that said, the .355" as cast from a .358" mold seems WAY off and with the radiused base I do not have the required tools to measure the diameter (although while typing this I just realized I should be able to get a close measurement from an open half).
Any ideas if I'm doing something wrong and thinking wrong?
Edit added: I tried to measure the mold cavity using pin gauges held on an angle to try and get the end of the pin down in there. It is not accurate because a .354" and .355" were both close but the .354" (.3538" actual) seemed to block the light best.