I received an email asking how to measure that the bullet is 30 thou off the rifling when laoding for a M14.
I will share the answer. There are a variety of ways to do this. This is an easy way involving nothing more elborate than a caliper.
This is best done with rounds made with no powder.
Take a case that is sized and ready for loading in all respects and seat a bullet long. Say 2.900 OAL.
Put it in the chamber and let the bolt slam closed on it. If the bullet is seated too long, it should engrave in the rifling. You will see four, five or six grooves in the front shoulder of the bullet, where it hit the rifling. The length of these marks will give you a hint of how much you have to turn the seater down. If there are no marks, then you have to back it out a full revolution and try again.
Assuming there are marks on the bullet, turn the seater stem down, say, a half revolution, and seat another bullet in an another case. Measure the OAL of this round and note how much shorter it is. This will tell you how much a half turn of your seater moves the bullet. You need to know this. My seater moves the bullet 12 thou per quarter turn. It will depend on the thread pitch of your seater die.
Chamber this round, drop the bolt and see if the bullet has rifling marks. Keep doing this until you get a round with an unmarked bullet. Note that OAL (with that particular brand/weight of bullet) and call that “just barely off the rifling”. Make a note of that in your loading logbook.
Now, to answer your question of how do you get the bullet 30 thou off the rifling, turn the seater die in enough more to give 30 thou. On my seater, that would be just over a half revolution. Make a note of that OAL for your log.
Why 30 thou? Bullets have a lot of variation in the location of the ogive where the bullet touches the rifling. In a give box there can easily a 20 thou variation between bullet tip and bullet ogive. You don’t want to have some rounds with the bullet touching the rifling and others with it not touching. So back off 30 thou.
I will share the answer. There are a variety of ways to do this. This is an easy way involving nothing more elborate than a caliper.
This is best done with rounds made with no powder.
Take a case that is sized and ready for loading in all respects and seat a bullet long. Say 2.900 OAL.
Put it in the chamber and let the bolt slam closed on it. If the bullet is seated too long, it should engrave in the rifling. You will see four, five or six grooves in the front shoulder of the bullet, where it hit the rifling. The length of these marks will give you a hint of how much you have to turn the seater down. If there are no marks, then you have to back it out a full revolution and try again.
Assuming there are marks on the bullet, turn the seater stem down, say, a half revolution, and seat another bullet in an another case. Measure the OAL of this round and note how much shorter it is. This will tell you how much a half turn of your seater moves the bullet. You need to know this. My seater moves the bullet 12 thou per quarter turn. It will depend on the thread pitch of your seater die.
Chamber this round, drop the bolt and see if the bullet has rifling marks. Keep doing this until you get a round with an unmarked bullet. Note that OAL (with that particular brand/weight of bullet) and call that “just barely off the rifling”. Make a note of that in your loading logbook.
Now, to answer your question of how do you get the bullet 30 thou off the rifling, turn the seater die in enough more to give 30 thou. On my seater, that would be just over a half revolution. Make a note of that OAL for your log.
Why 30 thou? Bullets have a lot of variation in the location of the ogive where the bullet touches the rifling. In a give box there can easily a 20 thou variation between bullet tip and bullet ogive. You don’t want to have some rounds with the bullet touching the rifling and others with it not touching. So back off 30 thou.
