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I have heard about a Garand situation called the 7th round modification. What was the problem ? How was it cured ? Can it be recognized by examining the receiver ? And lastly, I heard that this problem only occured in early Springfields ? Does anyone know the specific serial ranges involved ?
Lots of questions here. But maybe we can all learn more about this early problem. Thanks
Now, pls forgive me, I'm going on memory here, but the seventh round modification was to repair receivers that had a mistake made during their production. At some step (cutting the hole for the barrel?), a milling operation was allowed to proceed too far into the receiver, and some of the front left guide rib was milled away. This mistake allowed the rounds to move more than they should during the loading sequence. The rifle often jammed on the seventh round, as the clip emptied and the spring pressure on the follower decreased. Once the problem was discovered and positively identified, receivers were "repaired" by welding the area where the rib material had been removed, and then was reshaped to provide the necessary guide to the round as it moved into the chamber. This repair can be identified by discoloration in the parkerized finish. Again, this is from memory, and if I'm wrong, someone pls correct my mistakes. I know that these receivers were early, but I don't remember the serial number ranges in which they were located. HTH, Karl
Karl has covered the bases quite well.
The first ~40,000 receivers exibited this issue. The attached photo shows an original unmodified 1939 receiver (on top) compared to a 1961 National Match Receiver.
Also note the rear sight cover, the follower shape, op-rod catch shape and the square cut at the rear of the bolt cut on the early receiver.....
From my information, all revision 1 receivers had the low guide ribs, most had the correction during rebuild. The revision 2 receivers had the high guide ribs. Both late gas trap and the early gas port rifles had the revision 2 receiver.
A few Winchester receivers were found with low guide ribs too
RCS do you know the approximate serial number break? I think I'm close but I would like to know more.
D-
As stated above,on early gas trap receivers and some early WRA gas port receivers(RCS),when the hole was being bored for the barrel the bit went in too far and took a little "bite" off the top of the front guide ribs inside the receiver. This caused problems with the follower and often jammed on the 7th round. The "modification" was to weld a small bead back onto the top of the damaged ribs and grind/file/mill the top of the rib back into shape,eliminating the 7th round jam issue. This is known as a "7th round modification". Early receivers that have not had the 7th round modification are much more desirable for restorations and will easily outprice a modified receiver. Below is SA 41556 which is an original M1D. Pics show the modification to both sides of the ribs.
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