I think he will find that his smith installed a break after threading and crowning and turned it down to look finished. No way could he crown the barrel any other way. My smith put a break on my 270WSM and i wanted it the same diameter. He did a perfect job on it. He didn’t recommend removing it for any reason. Neither do I. Weaver Rifles.If he got the crown inside correct, it shouldn't take away from its accuracy potential. Some times adding or taking away weight from the muzzle end will effect the tune of a load & harmonics of the barrel but not necessarily accuracy potential. As far as velocity loss, I think the most you would likely see would be 80fps from 2" of barrel loss, but it may only be 30-40 fps loss. Its any ones guess until you chronograph what it does now compared to how fast it was before. Velocity loss some what depends on powder burn rate & bullet weight of the loaded round you were shooting or will be shooting. As far as hunting in the rain, I always keep a plastic bag over my muzzle until I'm ready to shoot whether it has a brake or not and whether its stainless or blued because any manner of rust or corrosion in the muzzle is not good. Being ported as such just makes it a little less convenient for drying & cleaning it out. If you were shooting a load or factory ammo that shot good before, It may very well shoot just as good now. If it doesn't, then that doesn't necesarily mean theres anything wrong with the work done to the muzzle, the load may just be out of node(tune) with the rifle now. You may have to try something different. Then on the other hand, it may even shoot better now. As far as drawbacks to being ported, the only draw back i see is it being less convenient to clean and keep it dry.