They don't need to be gun savvy, just competent NDI specialists. You, the customer tell them what you want done, i.e. MPI of your steel bolt and bolt carrier to determine if there are any cracks or material flaws.
The technician will inspect the parts in accordance with their procedures which are developed from industry standards. He will note the results of the inspection on the company form and route it to the Quality Control person, he will insure everything was done correctly, initial the form and someone will call you to come pick your parts up.
They don't care if it is a gun part, a car part or a part from the next moon rocket, they just do an inspection and generate a report.
What do you want to find out about your bolt? That will determine which non destructive testing (NDT) method is appropriate. While in the USAF I Magnafluxed several hundred M1 Carbine bolts as part of a Time Compliance Technical Order (TCTO).
Magnaflux testing will only help make cracks more visible.
Other options include:
Careful visual inspection under magnification.
Dye penetrant inspection.
Fluorescent dye penetrant inspection.
There is a distributor of NDT supplies in Temple Hills MD you might try giving them a call and see if they can recommend someone for small jobs. Or buy some dye penetrant and DIY. http://www.detek.com/about-us-.html