How much tension when determining the "Jam"

[Joe Marella]

I would be interested in hearing your thoughts on how much tension to use when determining the "Jam" seating depth. It seems if you use to much tension the bullet will resist jamming and just scratch the bullet making light tension better as the bullet will be able to move to the the jam seating depth.
JPM

 

[Bart B.]

I've seated 30 caliber bullets that need about 2 pounds of force to pull them seated a few thousandths long to set back a couple thousandths when chambered. They came out in the case neck when live round was ejected.

Once, a bullet struck in the throat, evidence I needed to get a cleaning rod ready to push it back out. Ejected the case less the bullet. Did so then barely seated the bullet in the case mouth, chambered it, then shot it to call.

Do tests without primer and powder to determine what's best for your stuff.

 

[AJC]

I would be interested in hearing your thoughts on how much tension to use when determining the "Jam" seating depth. It seems if you use to much tension the bullet will resist jamming and just scratch the bullet making light tension better as the bullet will be able to move to the the jam seating depth.
JPM

Depending on the method you are using, i would say it would not matter. If your smoking the tip and looking for marks, i would not expect you to cam the bullet in the lands. I prefer to measure with the lock n load seating tester, where the bullet is loose to float. If you are cycling the bolt, the ejector spring and button should be removed so the bolt handle should just fall in place. Maybe you should clarify which method you are using for more clear guidance.

 

[Mikemci]

Search for "Finding the lands Alex Wheeler"
You're welcome.

 

[Dusty Stevens]

Search for "Finding the lands Alex Wheeler"
You're welcome.

Finding jam is a whole different ball game than touch. You have to have enough tension to push the bullet into the lands but not gall the lugs. I use .004. Any less and the bullet sticks and is not repeatable even if the bullet comes back out. May even take .005 on thinner necks

 

[farmerjohn]

Given the amount of variables that can come into play, I want to see how this thread comes out.....
Farmer

 

[AJC]

Finding jam is a whole different ball game than touch. You have to have enough tension to push the bullet into the lands but not gall the lugs. I use .004. Any less and the bullet sticks and is not repeatable even if the bullet comes back out. May even take .005 on thinner necks

So very intrested in this. So if your seating with .002 tension how much jam can you get? On unturned necks can you get .010 jam with .002 tension??? If it matters we will say on 223 or 6mmbr. I also assume bullet shape matters a bunch.

 

[abersfelderami]

The tension you should use is the same as the neck tension you are using for that load. The hard jam distance is dependent on the neck tension and the throat angle. It is just a reference point.

 

[Alex Wheeler]

Use what you think you will be using in your rifle. If you use new cases with no carbon in the necks you will get a very long jam, if you lube the neck with something like graphite you will get a short jam, the neck bushing will have less effect than the surface of the neck. Bullet seating force is mostly friction caused by the necks surface not the amount of tension. So use a case thats been fired a couple times and prepped like you will prep you cases (nylon bush in the the neck, ext.) And use a bushing that you expect to use. If you change anything you jam length can change. I like to use touch as a baseline but I also want to know jam so I know how deep I can go before Im soft seating.

 

[243winxb]

Hold the muzzle up when extracting an unfired jammed round/bullet. Less powder to clean out of the action.

 

[dcali]

I’m curious to know how people define “Jam”.

 

[Bart B.]

I’m curious to know how people define “Jam”.

Mine: When the throat lands start engraving into bullet jackets.

Touch is at first contact without engraving.

Throat angle and land width comes into play along with bullet release (pull) force for amount of jam.

 

[AJC]

I’m curious to know how people define “Jam”.

Any amount past the transitional touch point. Includes a + when showing seating depth info.

 

[Alex Wheeler]

Jam is the longest you can load a round before the rifling pushes the bullet into the case. Often we misuse the term to mean anything longer than touch such as .010" jam, really we should say .010" into the lands, but most of us know what we mean.

 

[Intheshop]

I’m curious to know how people define “Jam”.

This took a dz attempts to capture in focus.What I couldn't get was more than one engraving to show up. All lands are represented as this one in both depth AND length. The latter is the acid test.... because of the geometry. R700 ADL 223. Cpl hundred down the factory brrl. This one was ejected because the crow left his death bed in the nick of time @150. Look closely,that isn't a smudge.... it's .001 deep. Also notice line just above first drive band,that's the end of the throat. This and it's buddy's are <.001 runout measured with B&S metrology equipment swiped from our machine shop. Any longer,and the "stick". These are seated with one of our hybrid seaters. It's a Wilson "style" seater with a little bit of std micrometer (Redding,RCBS,etc) thrown in. Works in a std press. Only works for a VERY small range on bullet diameters.... these are .2255,with a "no bump" nose profile. And barely any lube,running @2500 fps.

This is a "med hard jam". Hard means no extracting a live round.

 

[tenring]

I would be interested in hearing your thoughts on how much tension to use when determining the "Jam" seating depth. It seems if you use to much tension the bullet will resist jamming and just scratch the bullet making light tension better as the bullet will be able to move to the the jam seating depth.
JPM

I like to see a light square mark on the bullet where it touches the ogive. I burnish the bullet with 4x steel wool before inserting it in the chamber.I use a 6x jewelers monocular to see it. I make a note of that distance with every new lot of bullets. Seat the bullet long using Wheelers method and work down until bullet does not stick. Always strive for consistency when reloading.