If it works at the gunsmiths shop it may be the lot of brass that you are currently using. pick up some range brass and see if that brass is any different in your rifle. There is some brass out there from foreign suppliers as well as US brands that may have head thickness issues. If on the other hand your rifle does this with all brass and it did not do it for the Gunsmith it may be the way you are cycling the bolt.
Jim Briggs
NSS
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