Bullet seating into the lands.

[std7mag]

So i've been reading some posts about seating a bullets so that it is "X" distance into the lands.
And i'm trying to wrap my head around this.
The lands being part of the "immovable" steel barrel.
The bullet, while having an interference grip with the neck, is still the movable part.
You already proved this by seating the bullet into the casing past this interference.

Wouldn't it then be that it was loaded slightly long, and the lands finished seating it, making sure of a contact with the lands?

 

[dolek]

Have you ever tried the "Stripped Bolt" method ? If not,give it a try. It will answer your question easier than words.

 

[David Christian]

So i've been reading some posts about seating a bullets so that it is "X" distance into the lands.
And i'm trying to wrap my head around this.
The lands being part of the "immovable" steel barrel.
The bullet, while having an interference grip with the neck, is still the movable part.
You already proved this by seating the bullet into the casing past this interference.

Wouldn't it then be that it was loaded slightly long, and the lands finished seating it, making sure of a contact with the lands?

The copper jacket is malleable, therefore there will be a certain jam distance that does not seat the bullet deeper when the round is chambered.

 

[dannyjbiggs]

So i've been reading some posts about seating a bullets so that it is "X" distance into the lands.
And i'm trying to wrap my head around this.
The lands being part of the "immovable" steel barrel.
The bullet, while having an interference grip with the neck, is still the movable part.
You already proved this by seating the bullet into the casing past this interference.

Wouldn't it then be that it was loaded slightly long, and the lands finished seating it, making sure of a contact with the lands?

Yes...what you have when the jam-into-the-lans finally fully seats your bullet into the case neck at bolt closure is the classic "soft seat". However, depending on your case neck tension, it could easily be the classic "hard seat"!! (There is the opportunity for a lot of work in this area, experimenting, etc., to get it worked out properly.)

Dan

 

[243winxb]

I jammed back in the 70s, till i had to unload without firing the round.

Bullet stuck in rifling & powder dumped in the action.

Interesting question , that i dont know the answer too.

Wouldn't it then be that it was loaded slightly long, and the lands finished seating it, making sure of a contact with the lands?

I guess, yes. Neck tension of .001" lets the barrel seat the bullets.

But when the barrel gets dirty, the COL may change?

 

[RegionRat]

Yes, Dan is correct. At some point the neck tension and case friction is high enough to force the bullet to engrave, and sometimes the neck tension is low enough that the bullet gets forced back into the case part way as well as wedging into the lands part way.

It takes some trial and error to learn how much is really going on. Tapping backward with a cleaning rod while opening the bolt, ink marking the bullet and case, measuring the CBTO before and after, etc., are all ways to learn if you are really jammed or pushing the bullet back into the case.

ETA: there is also a difference between a brand new rig, versus one part way through life with erosion in the throat. A reamer can also have a shallow or steep angle cut that changes this experience depending on the design of the ogive and how steep that initial contact angle runs.

 

[rsmithsr50]

angle of the lands(throat), neck tension, softness of the copper jacket all determine how far into the lands you can jam.
as a rule, I don't, maybe .005, all else is AT THE LANDS, or jumping.

 

[swd]

Full jam is the point where the lands push the bullet further into the case. Anything short of that is just “in”. Neck tension will change the full jam OAL, and also when and if the bullet will stick in the barrel if you try to extract an unfired round.

 

[dgeesaman]

So i've been reading some posts about seating a bullets so that it is "X" distance into the lands.
And i'm trying to wrap my head around this.
The lands being part of the "immovable" steel barrel.
The bullet, while having an interference grip with the neck, is still the movable part.
You already proved this by seating the bullet into the casing past this interference.

Wouldn't it then be that it was loaded slightly long, and the lands finished seating it, making sure of a contact with the lands?

True the lands don’t move. When you close the bolt the bullet probably moves.

But if you test at varying depth of jam you will find they don’t shoot the same. I can’t say how much of that jam is preload vs bullet deforming vs reseating but up to about .015 jam behaves differently.

David

 

[carlsbad]

generally you have too much neck tension to move the bullet.

the land angle is 1.5 deg so jamming deforms the bullet by the amount jammed x tan 1.5 degs. so for jamming .020, the lands push into the bullet .0005"

Jerry

 

[Ccrider]

Load one (without powder and primer) long, measure it and see how much it moves. I promise it will move. Not as much depending on neck tension. Also, you may need a rod to lightly push it out.

 

[Whisky Tahoe Foxtrot]

Finding where your lands are is relatively easy provided you have the tools to strip your bolt.
The Sinclair & Hornady tools push the bullet being tested into the lands just enough to throw off the readings.

Wheeler Accuracy has posted a very nice video:

 

[carlsbad]

lots of people laugh at Mathematics.

 

[rsmithsr50]

while alex's method is great, it does not work well with ar's. ( not bolt handle, no lug cams) the Hornady tool is a tool and works VERY WELL with some attention. I go for TOUCH not jam not jump. it requires a magnifying glass .

Finding where your lands are is relatively easy provided you have the tools to strip your bolt.
The Sinclair & Hornady tools push the bullet being tested into the lands just enough to throw off the readings.

Wheeler Accuracy has posted a very nice video:

 

[dolek]

lots of people laugh at Mathematics.

Especially those that do not understand... I think it's nervous laughter mostly.

 

[Drop Port]

lots of people laugh at Mathematics.

Like the saying goes you have the right to your own opinion, not the facts. Hard to argue with math.

 

[JMayo]

Mixture of hunters,
that send the bolt home with rifle angled down and palm on bolt handle...
Simi autos that slam.

Brench rest that push bolt just enough so not to upset rifle. (Unless jam requires a little shove)

So....

 

[carlsbad]

Load one (without powder and primer) long, measure it and see how much it moves. I promise it will move. Not as much depending on neck tension. Also, you may need a rod to lightly push it out.

It'll move if you jam it a quarter inch. I run very light neck tension (.001") and .020 jam and they don't move. Most people run more neck tension than I do and nobody that I know jambs much beyond .040.

So sure you can move it if you try. But what will happen more likely is you jam it, it doesn't move but bullet gets stuck in the lands. You have to pull hard to open bolt, extracting bullet and dropping powder in the action....why a lot of people don't like to jam.

--Jerry

 

[carlsbad]

your math is not hard to laugh at.
it does not match real world plain and simple.
20 thou jam is only a 1/2 thou engagement...not in the real world.

Answer me one thing: Is the world round or flat?

 

[Zero333]

There is the thing where the bullet is in the lands, and there is the thing where the bullet is JAMMED in the lands.

Sometimes depending on leade angle and bullet ogive, you can sit the bullet 0.020" in the lands and still not have it jammed in the lands. Meaning you can extract a live round and feel no different than one with the bullet away from the lands.