Head spacing and seating depth!

[Buccaneerfan]

Could someone please make this simple for me? I have read and read about head spacing and seeating depth and it has only confused me further.
1) How do you decide how far to seat a bullet?

2) What if anything does this have to do with head spacing? From what I gather, head spacing is the scace between the front of the case to the part of the chamber that stops forward movement. The reason I asked is because someone told me to back my headspacing off by .002-.003 for my AR to ensure easy loading etc. I thought this was determined by the chamber on the gun and the length of brass, not how far you seat your bullet.

The stupid part is that last week, I really thought I knew what I was doing until I asked about this damned AR!

 

[boomtube]

Most of us make both things far more difficult to grasp than they should be. OAL and headspace are totally seperate issues.

How and where headspace is measured hardly matters, all it amounts to is the room in the chamber for the cartridge to fit. If our cases are too big in any dimension they won't chamber, usually because a bottleneck shoulder isn't pushed back far enough. If our cartridge is too small it's a sloppy fit and it will have to stretch too much for safety. Forget any definitions of headspace for rimmed or belted cases, if it has a bottle neck just adjust your sizer off the shoulder. Do your own expermentation on how far back to set your AR shoulders, if any at all. Don't 'average' anything, just set your sizer so the longest sized shoulder matches or is just shorter than the longest fired length; anything shorter will obviously fit fine.

Rifle or pistol, the "right" OAL is one that feeds and chambers reliably without jamming the bullet into the rifling (you can't get revolver bullets into the rifling!) AND shoots best in your rig. The OAL in books isn't automatically right for anything but the gun used to develop the listed data, each of us can pick our own OAL. Find the longest length that will fit your magazine and feed, then see if the bullet jams into the lands; if it does just push the bullet deeper until it doesn't. Start your load development close to (but not in) the lands and find the best shooting charge. Then do range testing in groups of maybe two at first, moving back in something like 5 thou steps until you find what seems to shoot well and do more extensive tests around that point, including tweaking the powder charge a couple tenths each way.

The hyperventalating you see on the web about seating deeper running pressures up applies ONLY to the hot small case autoloading hand gun cartridges like the 9 and 10mm/.40 that are high pressure rounds using very fast burning powders. It doesn't apply to rifles and hardly has any meaning for lower pressure autos like the .45 ACP or revolver cartridges.

Good luck!

 

[Buccaneerfan]

Most of us make both things far more difficult to grasp than they should be. OAL and headspace are totally seperate issues.

How and where headspace is measured hardly matters, all it amounts to is the room in the chamber for the cartridge to fit. If our cases are too big in any dimension they won't chamber, usually because a bottleneck shoulder isn't pushed back far enough. If our cartridge is too small it's a sloppy fit and it will have to stretch too much for safety. Forget any definitions of headspace for rimmed or belted cases, if it has a bottle neck just adjust your sizer off the shoulder. Do your own expermentation on how far back to set your AR shoulders, if any at all. Don't 'average' anything, just set your sizer so the longest sized shoulder matches or is just shorter than the longest fired length; anything shorter will obviously fit fine.

Rifle or pistol, the "right" OAL is one that feeds and chambers reliably without jamming the bullet into the rifling (you can't get revolver bullets into the rifling!) AND shoots best in your rig. The OAL in books isn't automatically right for anything but the gun used to develop the listed data, each of us can pick our own OAL. Find the longest length that will fit your magazine and feed, then see if the bullet jams into the lands; if it does just push the bullet deeper until it doesn't. Start your load development close to (but not in) the lands and find the best shooting charge. Then do range testing in groups of maybe two at first, moving back in something like 5 thou steps until you find what seems to shoot well and do more extensive tests around that point, including tweaking the powder charge a couple tenths each way.

The hyperventalating you see on the web about seating deeper running pressures up applies ONLY to the hot small case autoloading hand gun cartridges like the 9 and 10mm/.40 that are high pressure rounds using very fast burning powders. It doesn't apply to rifles and hardly has any meaning for lower pressure autos like the .45 ACP or revolver cartridges.

Good luck!

Thank you! This was very helpful. Is there an easy way to see when you are on the lands or not. That is the part that is confusing.

 

[boomtube]

There are several easy ways to see when you're in or off the lands. They all work but the easiest to explain is to seat a bullet long and paint it with a dark color 'dry erase' marker. Carefully insert it in the chamber (the ink wipes off easily) and close the bolt. Take it back out and see if you can tell where the lands are. If you can't see the lands you aren't there yet, if you do see the land's marks seat deeper and continue painting, testing and seating until you don't see it anymore - then, if it will fit your magazine and feed, that's your MAX OAL.

Most factory rifles shoot best with a jump to the lands of 20 thousanths or more. By developing your load near the lands first and then doing seating tests by moving away from the lands you will be safe and you should find your best load for that powder/bullet combination pretty quickly.

IF your seating ends up long don't worry about the 'conventional wisdom' of seating one caliber deep; a lot of cartridges have necks shorter than one caliber!

 

[Buccaneerfan]

There are several easy ways to see when you're in or off the lands. They all work but the easiest to explain is to seat a bullet long and paint it with a dark color 'dry erase' marker. Carefully insert it in the chamber (the ink wipes off easily) and close the bolt. Take it back out and see if you can tell where the lands are. If you can't see the lands you aren't there yet, if you do see the land's marks seat deeper and continue painting, testing and seating until you don't see it anymore - then, if it will fit your magazine and feed, that's your MAX OAL.

Most factory rifles shoot best with a jump to the lands of 20 thousanths or more. By developing your load near the lands first and then doing seating tests by moving away from the lands you will be safe and you should find your best load for that powder/bullet combination pretty quickly.

IF your seating ends up long don't worry about the 'conventional wisdom' of seating one caliber deep; a lot of cartridges have necks shorter than one caliber!

Thank you! This was the simplest, easiest explanation I have ever heard for this!