Barrel heat lot question?

I started out on 1903's and they bear heat lots, when I started playing with garands I noted the barrel markings. I'm assuming they are carrying heat lots as well, I've been keeping track of as many markings as I can. Someone tell me if I'm way off base here.

LMR used A(#) as heat lots
HRA used RS(#) as heat lots
SA Post WWII used A(#)(letter), BU(#), MD(#), Y(#)

If this information is correct then LMR and HRA had only one supplier for their barrels/barrel steel where as Springfield used four suppliers based on the above? This is my understanding of the bolt heat lot theory as being identifyable to steel producers.

I'm also under the impression that the barrel dates were added when assembled rather than when produced? If this isn't correct then when were they added? I've seen barrels with what is the same heat lot (as described above) dated sometimes 11 years apart. All of the other markings are the same but the dates are over a decade different. Most of the "heat lots" vary from a few months to a few years in date but some of the spread is too extreme.

Or am I completely incorrect? All of the information I've gathered from my own personal observations, I've physically held each barrel so I do not feel it is recording errors. I do most certainly thank you for your time.

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Originally Posted by geberl

I started out on 1903's and they bear heat lots, when I started playing with garands I noted the barrel markings. I'm assuming they are carrying heat lots as well, I've been keeping track of as many markings as I can. Someone tell me if I'm way off base here.

LMR used A(#) as heat lots
HRA used RS(#) as heat lots
SA Post WWII used A(#)(letter), BU(#), MD(#), Y(#)

There are others such as B, Z, US, YO for SA.

If this information is correct then LMR and HRA had only one supplier for their barrels/barrel steel where as Springfield used four suppliers based on the above?

That's what it looks like except there were more steel suppliers than four for post war SA.

This is my understanding of the bolt heat lot theory as being identifyable to steel producers.

Correct. It had to be traceable to a supplier.

I'm also under the impression that the barrel dates were added when assembled rather than when produced? If this isn't correct then when were they added?

Barrel dates were marked near the end of manufacture and before phosphate finishing, not at assembly. If marked at assembly then there would be no barrel date to receiver discrepancy. Many barrels of all dates were used years later during rebuild.

I've seen barrels with what is the same heat lot (as described above) dated sometimes 11 years apart.

Examples? This is possible because steel was left over from WW2, stored and resurrected for Korea. It's quite commonly seen on post war receiver production.

All of the other markings are the same but the dates are over a decade different. Most of the "heat lots" vary from a few months to a few years in date but some of the spread is too extreme.

Or am I completely incorrect? All of the information I've gathered from my own personal observations, I've physically held each barrel so I do not feel it is recording errors. I do most certainly thank you for your time.

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I don't have all the data into softcopy so I knew there were more steel suppliers, the above was just what I'd input to the spreadsheet.

A good example of date spread is SA MD51 5/55, 6/55, 7/55, 4/56, 4/63, 7/64, 11/65

There are others that I've seen in the SA barrels from multiple supplier designators and most appear late in each series. A216B onward, MD 43 onward, and so on, With dating after phosphating I believe these might have been blanks that just weren't finished until later. These later heat lots could very easily have been in stock the summer of 56 and kept being used through the 60's. My biggest problem was trying to decipher when the dates were put on and the manufacturing process. I believe I understand this now, I do most certianly thank you for your help sir.

"With dating after phosphating I believe these might have been blanks that just weren't finished until later."

As Ramboueille said. the marking and dating was certainly done before phosphating. I don't think the dating and drawing/heat lot numbering were done at the same time. I do think the dating was probally close to the last operation prior to phosphating.

Yes, mind and fingers weren't working at the same speed. I understood what he was refering to, simply didn't output correctly.

My initial assumptions with my study would be to find what barrel date corresponded to which heat lot. Early on I noted multiple dates for each heat lot and realized there was something going on to create this variation. The above post helped me to realized I was closing on the answers and Ramboueille finalized this for me. I've added less and less to my ledger each year and recently have started to input everything from my books into computer spreadsheets. The computer makes everything easier to access and crossreferene but inputting is a time consuming process.