I'm not saying I wouldn't keep the rifle, and if I couldn't afford a new receiver I would likely continue to shoot it. But I'm also don't like to gamble on possibly injuring myself (or god forbid someone else) if I don't need to.can we keep things closer to Realityville?
the "heel" of the receiver does TWO things (when shooting "normal" ammo anyway):
1. GUIDES the bolt backward and SLIGHTLY downward.
2. PROTECTS the bolt from mud, dust, etc.
When fired with normal ammo, the BOLT DOES NOT GO ALL THE WAY BACK. It (should) actually STOP before it whacks into the inside of the heel.
Likewise the whole M1 Garand system is like a small TEETER-TOTTER. The mainspring is only 17 pounds of pressure and if you added just a few more pounds (say 5-7 pounds) of spring pressure, the rifle bolt would NOT MOVE backwards at all. You can EASILY hold the M1 bolt SHUT while firing with your hand (use gloves in case of gas spitting).
Also, get out your rifle, remove the action from the stock and (carefully) pull back the bolt (yes, with the mainspring in it). You can easily see (feel too) how the rifle is designed to eject and feed without the bolt going all the way back.
OK, so, what if you fire a "hot" round and the bolt does go all the way back and cracks the receiver heel COMPLETELY off. Hello, you don't need a physics lesson to figure out that at the END of the gas cycle, the bolt is already FIGHTING a 17 pound force trying to PULL IT BACK/AWAY. So, how much energy is LEFT to whack the heel into your face? Not bloody much.
So, bottom line, even if the heel came off completely, as long as it didn't hit your unprotected eyeball, it would not have enough energy to do much (any?) harm to your face.
Under NORMAL operation, you are correct, the heel is a low stress area. And may be fine. But as the heel is not designed to crack under normal operation, obviously this receiver was part of a rifle which did not operate normally on atleast one occasion.
It may have been worn out spring, may have been a hot load, high primer, who knows. But obviously it wasn't something designed to happen.
But all it takes is for Murphy to pop his head up and say "F you very much" to make a fun day at the range a disaster.
As for anything else, I'll reference a post Gus Fisher made awhile back in reference to receiver failures. I feel fairly confident in saying he knows a lot more than either of us do when it comes to the operation of the M1/M14, with the experience to backup that knowledge.
(Underline for emphasis)I have been "on the spot" only one time when a receiver failed catastrophically to a point the shooter was seriously injured. It was a REAL US GI M14 receiver built into a NM rifle for THE Marine Corps Rifle Team in 1975. I was "walking the line" as a NM Armorer on the OTHER side of the center of the line when it blew, but ran to give assistance when I heard it blow and the shooter scream. The barrel expanded hugely on both ends and opened up like a banana on both ends. A large chunk of the barrel ring sheered off and went flying and there were other cracks in the barrel ring. Pieces of the receiver were laying around. The heel of the receiver had come off and plowed a shallow furrow through the shooters cheek. The shooter had bits and pieces of metal stuck in his face and THANK GOD he was wearing shooting glasses as pieces of metal were embedded into them and more cracks were in them from other things hitting them. Those shooting glasses saved one or both eyeballs. The stock was a huge Walnut Bishop stock and it shattered sideways and a good size piece embedded into the shooter's forearm needing a fair number of stitches He had other small slivers stuck in his hands.
Pictures were taken as part of the Official Investigation, BUT were never released. We were ordered NOT to talk about it at the time outside the Team or RTE Shop. H.P White Laboratory did the Engineering Analysis and concluded the BARREL STEEL was made out of an INFERIOR steel containing sulphur stringers RATHER than good quality barrel steel. So we contacted the Barrel Maker and PULLED every one of his barrels from that lot of barrels we had purchased from him so it would not happen again. After the Investigation was concluded, we wired all the bits and pieces of the rifle and magazine together on a board back "close" to where the parts were on a complete rifle. We hung that board in the RTE Shop for years as a reminder of what could happen and New Shooters were shown that board to give the severest reason why it was mandatory to wear some kind of shooting glasses. Needless to say it has left a DEEP and LASTING impression on me.
I want to reiterate the cause of the failure was NOT the receiver, but rather
improper barrel steel. The pulled barrels and other barrels that had not yet been mountd were kept for years as "evidence" for the Investigation and any follow up the Government may have determinded necessary. In the mid 90's while I was the RTE Shop Chief, my Master Sergeant who ran the Shop procurement and supply found a few of the barrels stuck away in a corner. He did not know why we had "new barrels" we had never used. When he showed me a couple of them, I KNEW what they were and ordered the barrels cut up right away so they would never be mistakenly used on another rifle and told him about the incident. The incident had happened before he became an RTE Armorer. Had we NOT pulled all those barrels, there is no telling how many more of them would have failed catestrophically and when and how much personal injury would have resulted.
Now the REST of the US GI receiver failures I have personally seen or had true knowledge of, did not result in catastrophic failure or injury to a shooter. OF COURSE NOT as we condemned the receivers BEFORE it happened, thanks to frequent techical/safety inspections we did.
I have also mentioned in 1975 on THE Marine Corps Rifle Team, they developed a handload for long range shooting that was WAY TOO HOT and they would not listen to us Armorers and back down the load UNTIL within the next year or two, that too hot ammo had battered the receiver lugs and receiver heels so much we condemned a bunch of those receivers. I was transferred from the RTE Shop before all of those damaged receivers were condemned, so I don't know the exact number of them. The best I can remember it was around two to three dozen receivers, BUT it has been almost 40 years since then and it was not any sort of priority to remember exactly how many of the receivers had to be condemned.
ALL Infantry Weapons Armorers and NM Armorers were taught to pay special attention to the receiver heel when inspecting M1 Garands and M14's. The REASON for that was the bolt hits the inside of the receiver heel EVERY time the rifle is fired. Now, replacing the operating rod springs when they got too short, kept such damage to an absolute minimum, BUT even a properly made and surface hardened receiver is going to fail there when enough rounds are fired due to metal fatigue. If the metal had not been surface hardened correctly, there was no way of knowing UNTIL a crack or cracks started to form. IF you spot a crack on the sides of a receiver near the receiver heel then STOP firing the receiver and condemn it so you won't have a catastophic failure. If you IGNORE a crack there and keep firing it, sooner or later a chunk of the receiver heel is going to come back into your face. Thank Heaven that MOST people are not so stupid as to continue to shoot a cracked receiver.
I have never seen a Commercially made M14 receiver fail catastrophically, BUT a huge part of the reason for that is when NM Armorers or Gunsmiths found problems that could or would lead to catastrophic failure, they returned or had the owners return the receivers to the manufacturer or someone else for surface hardening or condemned the receivers and USUALLY the shooter had us replace the receiver. Then the shooter/owner KEPT or junked the receiver. So there is no "documented evidence" of it happening.
OK, I'm getting tired, so I will end this post for now and come back later for things I have personally found that would cause a receiver to fail and other things I have true knowledge of