Food for thought. The CID between a .040 over 340 and a .060 over 340 is about 3 1/2 CID. So, a mild 340 build would be lucky to make 1 hp per CID. So why would anyone risk boring further than needed for 3 1/2 hp. Just saying. Mark:)
^^Yup.
Ring seal makes more power than bigger bores. Period. You need a stable wall long before you need that extra .030". Boring is needed - to re-establish the geometry of a factory machined and worn block and provide the best up-to-date technology for maximum efficiency and power.
If you want to buy a sonic tester, buy a good one that is certified. That means over $1000 for it, and it should be one that can be calibrated on your material - not preset for various materials. You also need the right transducer - those are $250 each. The wrong radius there will skew the results.
As far as "pass" vs "fail", it's just as they say - depends on what you plan to do with it. I get nervous with anything on either thrust under .150, minor thrust under .110". That being said - I have built an engine with less because the owner took responsibility for that decision. It's his money so it's up to him. I can only report what I find and give my recommendation. I'll also add - that engine (big block) is making 1.2hp/inch and has had no cooling or strength issues.