CT KID over on cmp and m14 forums had a left lug sheared off on his .308 M1 .He sent it to me and I did a detailed inspection of the bolt and found all mechanical specs well within blueprint tolerances .
The surface hardness was right at max spec of 61 HRC but the core was near dead soft at 15 HRC. The issue and cause I found was the case depth exeded the max thickness by over three times blueprint specs and was at .060'' in places.
Left lug contact as also more previlient than the right lug so coupled with max hardness,case too thick,core to soft, improper lug contact resulted in failure to this bolt .Luckily there were no injuries and no apparant damage ti rifle.
If you have one of these bolts in a frequent shooter I strongly advise detail clean and inspect lug contact , check for damage or cracks around locking lugs just to be safe .
Bolt were made and heat treated in lots so its a good bet more of these are out there ,I know of no other failures or documentation any were discovered by inspectors . UNDERWOOD did have M1 Carbine bolt failures .
The surface hardness was right at max spec of 61 HRC but the core was near dead soft at 15 HRC. The issue and cause I found was the case depth exeded the max thickness by over three times blueprint specs and was at .060'' in places.
Left lug contact as also more previlient than the right lug so coupled with max hardness,case too thick,core to soft, improper lug contact resulted in failure to this bolt .Luckily there were no injuries and no apparant damage ti rifle.
If you have one of these bolts in a frequent shooter I strongly advise detail clean and inspect lug contact , check for damage or cracks around locking lugs just to be safe .
Bolt were made and heat treated in lots so its a good bet more of these are out there ,I know of no other failures or documentation any were discovered by inspectors . UNDERWOOD did have M1 Carbine bolt failures .
Comment