The military barrels are generally easy. Hacksaw, try square and files are fine, as you discovered. The resulting square crown is usually very accurate, but like any sharp edge, is vulnerable to getting dinged if you bump it into something.
If you find the bolt head didn't do what you wanted, you can download a description of the crowning method I use from my file repository, here
. The advantage is the ball bearing and rotating the barrel and using back and forth motion, like you would lapping an engine valve, tends to self-center and stay even. Most bolt heads are elliptical rather than round in profile, so they have to be kept pointed straight into the muzzle or the barrel constantly rotated to keep the result symmetrical. It often works fairly well, but some bolt heads are more elliptical than others so, YMMV.