Gentlemen, I have an inland serial number 68,xxx with a flat bolt. Should I get a round one and have it headspaced? I have heard of flat bolts cracking. If so what do I need to know about finding the proper round bolt. Can I check headspace myself. If tool is needed I will buy one.
A flat bolt is no more likely to crack than a round one. Perhaps you heard of the early bolts without the web of metal behind the extractor. They were the very first design and only a few found their way into production. They were quickly replaced when cracking was reported and are extremely rare to find. If you do choose to replace your flat bolt, definitely have the headspace checked.
The only thing I have every read about or experienced concerning flat-bolts is don't trust an N14 (National Postal Meter). I have had one crack and you can search-out plenty of discussion about the N14 and it's problems. I have never had any other flat bolt to fail.
The round bolt was to help stop bolt breakage as well as to improve bolt performance. Both types of flat bolts can break in the web area where the extractor sits. The type one bolt was replaced very early in production because of breakage. The type two lasted till early 1944 and has been used in rebuilds into the Viet Nam era. The type 3 round bolt became the final standard but if your type 2 bolt is working fine then there really is no need to replace it.
Yup like hens teeth they are that rare. Only used at the very most on up to maybe the first 5000 carbines out of Inland if that many. Winchester even a lot less. Most if not all have been replaced by Inland and Winchester and during a rebuild. You would have better luck hitting the lottery then having a type 1 bolt in your carbine.