Ebay has two auctions by Northridge International for IBM flat bolts. I am not recommending or wanting to purchase these bolts but I am curious about the description. Both are Type 2 and are marked "AOB". One is described as a 1942 model with an "SVB" firing pin and "IB" extractor. The other is a 1943-1944 model with a "B-EB" firing pin and "US-B" extractor.
My questions is, what characteristic(s) enable one to identify the particular year or period of production of these Type 2 bolts?
They really can't. At best they are going on what is in the bolt like a type 1 firing pin in one bolt and a type 3 in the other. Or the extractor type in one and a different one in the other. But a type 2 bolt is the same no matter when it was made and that was the first bolt IBM made and used.
That might not be entirely correct Tuna. I'm not that familiar with IBM bolts, but I'm sure they went thru some of the same modifications that other bolts went thru. The angle cuts on the lug might be different between earlier and later IBM bolts. I'd have to do some study to know one way or the other. Brian Q might know the answer to that one.
OGCA Lifer,NRA Life member, son of a 325th GIR Glider Rider
Jim, IBM only used the type 2 bolt and later the type 3. I don't think that any modifications made during production would be visible to the naked eye and I doubt anyone took the time to measure the differences between bolts if any at Northridge. lol
Use of the type 1 bolt was during the summer of 1942 and was dropped for the type 2 bolt in the fall of 1942. The area of the extractor is the weak point on a carbine bolt. The type 2 had more metal left in this area when machined to give the bolt more strength but bolts did continue to break off and on.