I recently FL re-sized 171 pieces of DA64/65/66 twice fired brass with their last firing in an M14 with a 1.635 chamber. Brass was re-sized to fit a 7.62mm Garand with a 1.635 chamber. To set my re-sizing die I used the rifle and stripped bolt as a gauge with the die being adjusted to a point where resized brass would allow the stripped bolt to fully close w/o resistance. The die was then turned down another 1/8 turn and locked.
All brass was then FL resized, wiped dry and trial fitted in the rifle with the following results;
- 125 pcs allowed the bolt to close fully with no felt resistance and full metal to metal contact between the bottom of the right locking lug and the receiver
- 46 pcs would not allow the bolt to fully close. Of these, 5 cases allowed the right lug to close about half-way down and 1 case would not allow the bolt lug to engage the vertical lug seat in the receiver at all. In some cases it was evident that an overly large radial dimension was the problem, rather than just insufficient shoulder set-back.
- I then ran all 46 pcs thru the FL re-sizing die and found that 5 would still not allow the bolt to close fully. After a third resizing these 5 cases allowed the bolt to close fully.
This exercise illustrates that "springback" does occur in FL resizing brass to one extent or another as some brass wants to "remember" where it was before being FL resized. This is a caution for folks reloading for Garand and M14 types as insufficiently sized brass can lead to an out of battery detonation, especially in combination with other factors incl high primers, overly sensitive primers, and a firing pin which might be at or exceed protrusion limits.
It is generally believed that brass will have the shoulder set back .001 as a result of the "drive-in" factor when being chambered in a FA or SA firearm. The hammer fall when the trigger is released would also assist the bolt to fully close on some insufficiently resized rounds. No doubt this would have assisted a high percentage of the initial lot of 46 pcs of "no go" resized brass to fully chamber and fire w/o any difficulty.
If the bolt won't fully rotate closed on a chambered round in a Garand/M14, the safety feature of the action, which has the receiver bridge engage the tang at the rear of the firing pin and prevent the firing pin from going foreword until the bolt has rotated to a 90/95% closed position, would have theoretically prevented a number of these insufficiently sized rounds from being fired. But the degree of wear on the receiver safety bridge and the firing pin tang are always unknown.
My assessment is that I may have had an issue ranging from a possible failure to fire with 5 pcs of FL resized brass, or a possible out of battery detonation with 1 case out of the initial batch of 171 pcs of FL resized brass, even after the brass had been FL resized with the resizing die set to allow the brass to fully chamber in the rifle plus a safety margin. All cases needed trimming after resizing, but there was enough freebore in the barrel throat to accommodate this as all cases chambered freely after final resizing.
"Springback" of resized brass is a factor that folks should bear in mind when reloading for Garand/M14 types. This is much more of a concern than in a bolt gun where the powerful camming action of the bolt lugs will most often let you get away with chambering an insufficiently resized case. My recommendation is that Garand/M14 reloaders always trial fit their resized cases in the rifle with the stripped bolt to ensure full chambering before reloading their brass. This is in addition to whatever other checks are done with case length gauges, etc. This is especially important for reloaders who are using surplus military 7.62 brass in .308 Win dimension chambers as 7.62 chambers are nominally larger than .308 Win chambers, and a lot of surplus 7.62 brass has been fired in MGs which can be quite generous in chamber dimensions.
All brass was then FL resized, wiped dry and trial fitted in the rifle with the following results;
- 125 pcs allowed the bolt to close fully with no felt resistance and full metal to metal contact between the bottom of the right locking lug and the receiver
- 46 pcs would not allow the bolt to fully close. Of these, 5 cases allowed the right lug to close about half-way down and 1 case would not allow the bolt lug to engage the vertical lug seat in the receiver at all. In some cases it was evident that an overly large radial dimension was the problem, rather than just insufficient shoulder set-back.
- I then ran all 46 pcs thru the FL re-sizing die and found that 5 would still not allow the bolt to close fully. After a third resizing these 5 cases allowed the bolt to close fully.
This exercise illustrates that "springback" does occur in FL resizing brass to one extent or another as some brass wants to "remember" where it was before being FL resized. This is a caution for folks reloading for Garand and M14 types as insufficiently sized brass can lead to an out of battery detonation, especially in combination with other factors incl high primers, overly sensitive primers, and a firing pin which might be at or exceed protrusion limits.
It is generally believed that brass will have the shoulder set back .001 as a result of the "drive-in" factor when being chambered in a FA or SA firearm. The hammer fall when the trigger is released would also assist the bolt to fully close on some insufficiently resized rounds. No doubt this would have assisted a high percentage of the initial lot of 46 pcs of "no go" resized brass to fully chamber and fire w/o any difficulty.
If the bolt won't fully rotate closed on a chambered round in a Garand/M14, the safety feature of the action, which has the receiver bridge engage the tang at the rear of the firing pin and prevent the firing pin from going foreword until the bolt has rotated to a 90/95% closed position, would have theoretically prevented a number of these insufficiently sized rounds from being fired. But the degree of wear on the receiver safety bridge and the firing pin tang are always unknown.
My assessment is that I may have had an issue ranging from a possible failure to fire with 5 pcs of FL resized brass, or a possible out of battery detonation with 1 case out of the initial batch of 171 pcs of FL resized brass, even after the brass had been FL resized with the resizing die set to allow the brass to fully chamber in the rifle plus a safety margin. All cases needed trimming after resizing, but there was enough freebore in the barrel throat to accommodate this as all cases chambered freely after final resizing.
"Springback" of resized brass is a factor that folks should bear in mind when reloading for Garand/M14 types. This is much more of a concern than in a bolt gun where the powerful camming action of the bolt lugs will most often let you get away with chambering an insufficiently resized case. My recommendation is that Garand/M14 reloaders always trial fit their resized cases in the rifle with the stripped bolt to ensure full chambering before reloading their brass. This is in addition to whatever other checks are done with case length gauges, etc. This is especially important for reloaders who are using surplus military 7.62 brass in .308 Win dimension chambers as 7.62 chambers are nominally larger than .308 Win chambers, and a lot of surplus 7.62 brass has been fired in MGs which can be quite generous in chamber dimensions.
