Seating Depth Bolt Action Rifle?


May 25, 2006, 08:57 PM
My question is, there are 2 places on a bullet that make contact when seating and chambering.

1 - The place on your bullet that your seating die (seating stem) contacts.
2 - The part of your bullet that makes contact with the lands.

Some people believe that since bullets are not perfect and can be different lengths, that because of this when seating to just touch the lands there will be differences that will make some bullets in the lands some out of the lands and others just touching. I believe that there could be or is a difference in the amount of contact with the lands due to bullet variances. I believe that the difference between bullets that could effect this is the difference between where your seating stem seats from and where your bullet actually makes contact with the lands. To see if this is right I did a small check on some bullets I have 30-caliber (175gr SMK’s moly). I have a Sinclair comparator nut, which has different size holes for making measurements. I first measured the bullets using the comparator in the 30-caliber hole then I measured using the 22-caliber hole. The 30-caliber hole represents the part of the bullet that would contact the lands and the 22-caliber hole represents the seating stem for my test. If I understand this right for all the bullets to be seated to just touch the lands the distance between these measurements would have to be the same? What I found was that there was as much as .004 difference between these measurements only measuring 5 bullets. So how do you seat bullets to just touch the lands or be off the lands by a set amount if there is a variance in the bullets between where the seating die seats to and where the bullet actually contacts the lands? Hope this makes sense and hope I used correct terms.

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May 25, 2006, 09:10 PM
I just simply don't seat bullets close to the lands, .030 is as close as I go EVER. I firmly believe that the whole "just off the land's" is just some good ol handloading bugaboo superstition. I've seen too many rifles with such deep throats that you can have the bullets outside of the case and still not touch the lands, shoot too many great groups to believe otherwize.

May 25, 2006, 09:51 PM
I suppose you could cut the throat out of the chamber, mount it to a seating stem, and lathe it down so it's thin enough to fit in a seating die. Then you'd have a custom seating stem that would always contact the bullet exactly where the lands would. :D

May 25, 2006, 10:31 PM
You are right in that slightly longer or shorter bullets will affect the actual measurement, and in my opinion, some rifles do best touching the lands while others do better seated back up to .030, .22-250s are somewhat notorious for likeing the bullet set WAY back, as was mentioned above, the throat in some rifles, also called freebore, weatherby rifles normally have a substancial amount of freebore and even the round nose bullets will not usually reach the lands. Its much more important in varmit/benchrest rifles as .0010 is a substancial amount in those rifles, most hunting rifles that are repeaters are limited by the length of the magazine and seating to touch the lands is not practical because it would render said rifle a single shot.
One way around this problem is useing a bushing sizer die that will close the neck just enough to lightly grip the bullet, (for bolt action single shots only) then you barely start the bullet and seat it with the forward push and camming action of the bolt, the problem with this method is haveing to extract a live unfired round, sometimes it leaves the bullet stuck in the lands and spills powder in your chamber when the bolt is withdrawn. It must be cleaned before fireing. I have used this method with a custom barrel with a reduced chamber neck diameter. The case necks must be turned normally .001 smaller than the chamber neck size with a bullet seated. This gives room for the neck to expand enough to release the bullet on fireing. This would never be used for a hunting rifle.

Ol` Joe
May 26, 2006, 02:00 AM
I`ve never tried your test, but I have measured a lot of loaded cartridge OALs over the years with a Stoney point comparator. The measurements I get on loaded ammo never in memory has shown more then ~0.001" variation, which tells me my distance from the lands must be quite consistant. I use Redding, RCBS, and Forster dies so I am "assuming" they all seat very similarly.

I have though measured bullets with the comparator from bullet base to contact on the ogive and found variation. The difference isn`t as much though as from base of bullet to tip which will drive one to drink. This translates into the bullet being seated deeper in some cases then in others if the depth from leade to the ogive is the same.

May 26, 2006, 03:13 AM
Ol` Joe

I’m new to measuring bullets, but I believe there are differences in total length (measured from the base to tip), there are differences from the base to the Ogive, and there might be differences from the point at which the bullet contacts the lands to where the seating stem seats the bullet. If there are differences from the point at which the bullet contacts the lands to where the seating stem seats the bullet I would think that difference would show when measuring the CARTRIDGE from the base to the Ogive. Think I’ll do some more measuring.

May 26, 2006, 05:49 PM
Well I did some more measuring today and the difference between the 30-caliber and 22-caliber holes on my comparator was within .001 variation. I also measured some loaded rounds from the base to the Ogive using my comparator and the variation was .001. This was right inline with Ol` Joe’s findings. Looks like this is about as good as it gets. I’m done measuring bullets. Just load’em and shoot’em.

May 26, 2006, 11:30 PM
I found that if I seat long so that the bolt jams the bullet deep in the lands, I noticed some trends:
1) More accuracy
2) a spike in pressure
3) pulling the cartridge out unfired may result in a bullet stuck in the chamner and powder spilled in the chamber and action.

I just got back from shooting hundreds of rounds of long seated .223, and I carried a cleaning rod into the field in case I forgot and got a bullet stuck.

May 27, 2006, 03:01 PM
My centerfire bolt guns prefer bullets seated .020-.030" off the lands.

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