S&W 915 Bore diameter?

[43PU]

I just picked up a nice used S&W 915, I just slugged the barrel 2 times and read the slug about 10 times being 5 groove rifling. but it came out to .353 and 350!! has any one seen this in a Smith before? all of the other 30+ 9mms I have read between 356-360! if anyone has seen anything like this can you shed some light?

Thanks
43PU