45acp out of 9mm P320 FCU?

Maybe, but if you modify the ejector you’ll void the warranty. Here’s my thoughts on this subject, the 45 ACP FCU will run All calibers. The 9,357,40 needs small modifications. You’re still gonna need the grip module, mags, slide, barrel and RSA for each different caliber to make a working gun. I put together a p320/M18 in .357 Sig using a M17 FCU and the correct parts I purchased from a Sig Talk member. I purchased a p320 compact in .45 from Buds and a 4.7 complete slide assembly from another member here and my total investment is just under $1600. That includes six 45 mags and four .357/40 mags I bought separately. I might have been able to save a few $$ here or there by modifying one FCU for all calibers but I now have 2 working guns that can fire all four calibers without a FCU mod. I hope Sig makes a 10mm caliber X-Change kit for my .45 ACP gun.