Distance to lands question

Warpspasm · May 16, 2017

I've been using a Hornady Bullet Comparator for my seating depths. I just came across something I can't figure out. I'm REALLY tired, so maybe that's it, but it has me stumped. I recently purchased some 168gr Monster Match .308 bullets and measured them in my Swiss rifles and in my French rifle. In my Swiss rifles they measure about .097 longer in the 96/11 and .137 longer in the K31 when compared to Hornady Target Match. But, in my French MAS 36 it measures .074 SHORTER than the same Hornady Match. How can this be possible?

Bountied · May 16, 2017

The ogive of the bullets is different? They hit the rifling at different places based on the angle of the lands in the chamber where the rifling starts? Or the type of rifling and the ogive gives you different seating depths. It makes sense in my head.

Warpspasm · May 17, 2017

Bountied said:
The ogive of the bullets is different? They hit the rifling at different places based on the angle of the lands in the chamber where the rifling starts? Or the type of rifling and the ogive gives you different seating depths. It makes sense in my head.

It seems to me that, if the ogive of the Midsouth bullet allows it to go deeper into the rifling of the Swiss gun, compared to the ogive of Hornady bullet, then that should hold true for any barrel those two bullets go into. Not that the actual distance would be the same, but that specific Midsouth bullet would always go deeper compared to that specific Hornady bullet regardless of the barrel.

Seabee · May 17, 2017

Are the bullet diameters exactly the same and are the land and grooves of the rifles exactly the same? As Bountied said, the angle of the taper from throat into the bore could vary also.

Melnic · May 17, 2017

Just a guess but
Lands
Grooves
Erosion
bullet shape

These all will be a factor, correct?

Biggfoot44 · May 18, 2017

Could be an issue with the exact shape of the leade. Could be side effect of headspacing in the MAS.

Jaybeez · May 18, 2017

Slug the bore of all 3 rifles

Warpspasm · May 18, 2017

I think some of you guys are misunderstanding me. Going back to read what I first wrote I can understand why. I am not comparing the length of the Swiss rounds directly to the length of the MAS rounds. Of course they would be different. I am talking about comparing the ogive length and angle of the two different bullets in the same rifle to the same bullet in different rifles. It seems to me that, regardless of rifle, if the Hornady bullet has a shorter ogive length and sharper angle it will always have to be shorter in COL than another bullet with a longer ogive and softer angle. In the Swiss rifles that was the case, but in the MAS that was the case until I tried the Midsouth bullets.

John from MD · May 18, 2017

MAS rifles had short leads.

Doco Overboard · May 18, 2017

Im not so sure a longer ogive always means a longer C o L or vise versa if thats what your asking.

Bountied · May 18, 2017

Doco Overboard said:
Im not so sure a longer ogive always means a longer C o L or vise versa if thats what your asking.

That was my point. You have a long tapered bullet and a squatter fat one. The lands in the rifles are different and the bullets come in contact at different depths. Think if you have a tangent ogive and a secant ogive and the chambers are stepped the secant ogive will go in deeper then hit while the tangent ogive will hit the larger closer diameter first. I wish I could draw a picture on here.

John from MD · May 18, 2017

Here is a link to a good picture. Something won't let me copy the actual picture.

http://bulletin.accurateshooter.com/2007/07/283/

Doco Overboard · May 18, 2017

There are lots of differences in rifles chambers and plus or minus free bore is due to manufacturing tolerances in reamers and tooling alone, test bolts vs component bolts worn TE gauges lathe run-out barrel non egocentricity crowded or mis-reamed chambers etc not to mention additional free bore that has been added intentionally by throating reamers to lower pressure or reduce recoil or ammo problems. Weatherby and wartime Mausers come to mind. The only way to determine what you need to avoid alot of trial and error in component selection is an accurate cerro- safe chamber cast.

John from MD · May 18, 2017

Doco Overboard said:
There are lots of differences in rifles chambers and plus or minus free bore is due to manufacturing tolerances in reamers and tooling alone, test bolts vs component bolts worn TE gauges lathe run-out barrel non egocentricity crowded or mis-reamed chambers etc not to mention additional free bore that has been added intentionally by throating reamers to lower pressure or reduce recoil or ammo problems. Weatherby and wartime Mausers come to mind. The only way to determine what you need to avoid alot of trial and error in component selection is an accurate cerro- safe chamber cast.

+1 Back in the day when I was into serious shooting, I kept an envelope for each rifle I shot. It contained a chamber cast to include the lead, a cast of 1/2 inch of the rifling in front of the lead and a cast of 1/2 inch of the bore from the muzzle.

For the chamber cast, I used cerrosafe and the other two were made with egg sinkers. From these, I determined which cast bullet I would use in that rifle.

Distance to lands question

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