How much tension when determining the "jam"

M

marellaj

New member
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 am not answering your question for the reason you listed, sort of.
varying neck tension will vary how far into the lands a bullet will jam.
how to you measure jam with the necked eye ?
i use touch. i want to see each land just barely mark the bullet.
i keep seating deeper(.001 steps) and polishing the bullet till i loose contact.
then add .001 and look for all lands
that is touch
 
Start with quite a bit of neck tension and seat the bullet such that the bolt won't close easily. Reduce the length of the round .001 at a time and see what it does. At some point, you'll be able to close the bolt rather easily and that's a good starting point right there....if not the best point of all. Good to have a click-stop seater die when doing this.
 
"use a Stoney Point tool and caliper to measure the OAL"

With the proper tools, no tension is needed to find the jam.
And when you find it, write it down and refer back to those measurements cause it WILL CHANGE, sometimes sooner than you expect.
 
When changing bullets or barrels I use a dummy round with a small split in the neck to get started. The split doesn't allow for much tension so I make sure measurement is repeatable. That's my starting COL and I finish using Wilbur's method.

Mort

PS I also use a touch of Dykem to see how much contact I'm making. A flat marking pen works just as well.
 
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Based on the original old school benchrest definition of jam, the word is in wide misuse. Originally jam was, and is for me still, the maximum length that a bullet can be seated to without being pushed back as the round is chambered. Of course this varies with how much friction there is between the bullet and the inside of the case neck, which varies according to a number of factors: how much the neck is sized under bullet diameter, the hardness and thickness of the neck, and a couple of other things. If you are trying to find out this old school jam, neck tension matters. The tighter the case grips the bullet, the farther that the bullet can be forced into the rifling. I have a question for you. Of what use would the jam length be for a neck tension that you were not going to use for your loads?
 
Boyd Allen said:
Based on the original old school benchrest definition of jam, the word is in wide misuse. Originally jam was, and is for me still, the maximum length that a bullet can be seated to without being pushed back as the round is chambered. Of course this varies with how much friction there is between the bullet and the inside of the case neck, which varies according to a number of factors: how much the neck is sized under bullet diameter, the hardness and thickness of the neck, and a couple of other things. If you are trying to find out this old school jam, neck tension matters. The tighter the case grips the bullet, the farther that the bullet can be forced into the rifling. I have a question for you. Of what use would the jam length be for a neck tension that you were not going to use for your loads?
Click to expand...

Answer: Nil use

It actually doesn't matter how you go about it, as potentially you will end up in the same place. It only matters when you want to direct compare with another competitor or on here.

Whether it be hard jam start with the neck tension you use, touch via Hornady tool, touch via engraving marks with smoked projectile or the method on the Youtube video posted.

All this does is get your starting point, so you can repeat and adjust from there.

From what I have seen of documented seating depth 90% or more (Source here somewhere on a equipment list) shoot into lands to some degree. So it is either push into case from hard jam or push out of case with just touch.

That's the way I see it

Michael
 
but there is no definition of JAM nor OF HARD JAM...none.
and repeatability is what accuracy is all about.
jam with out an optical comparator is just a guess in the wind.

Michael Huebner said:
Answer: Nil use

It actually doesn't matter how you go about it, as potentially you will end up in the same place. It only matters when you want to direct compare with another competitor or on here.

Whether it be hard jam start with the neck tension you use, touch via Hornady tool, touch via engraving marks with smoked projectile or the method on the Youtube video posted.

All this does is get your starting point, so you can repeat and adjust from there.

From what I have seen of documented seating depth 90% or more (Source here somewhere on a equipment list) shoot into lands to some degree. So it is either push into case from hard jam or push out of case with just touch.

That's the way I see it

Michael
Click to expand...
 
Boyd Allen said:
Based on the original old school benchrest definition of jam, the word is in wide misuse. Originally jam was, and is for me still, the maximum length that a bullet can be seated to without being pushed back as the round is chambered. Of course this varies with how much friction there is between the bullet and the inside of the case neck, which varies according to a number of factors: how much the neck is sized under bullet diameter, the hardness and thickness of the neck, and a couple of other things. If you are trying to find out this old school jam, neck tension matters. The tighter the case grips the bullet, the farther that the bullet can be forced into the rifling. I have a question for you. Of what use would the jam length be for a neck tension that you were not going to use for your loads?
Click to expand...

Exactly!
 
retired said:
but there is no definition of JAM nor OF HARD JAM...none.
and repeatability is what accuracy is all about.
jam with out an optical comparator is just a guess in the wind.
Click to expand...

Agreed to definition

That’s why it doesn’t matter as long as you do it the same each time.
Once you have the starting point the adjustments in or out and the target tell you what is working.

And you measure the loaded round, write it down in your records which imo is more important for repeatability than knowing exactly what touch or hard jam or whatever you use is.
 
Michael Huebner said:
Agreed to definitionThat’s why it doesn’t matter as long as you do it the same each time.Once you have the starting point the adjustments in or out and the target tell you what is working.And you measure the loaded round, write it down in your records which imo is more important for repeatability than knowing exactly what touch or hard jam or whatever you use is.
Click to expand...
IMO, there are 2 significant advantages of using "touch" as your datum. First, it is consistent. Variations in case neck lubricity could affect how much resistance it offers to the bullet being jammed into the lands. Secondly, and way more importantly, finding and monitoring touch allows you to chase the lands as the barrel wears.
 
Read carefully, Boyd's post number 11

retired said:
but there is no definition of JAM nor OF HARD JAM...none.
and repeatability is what accuracy is all about.
jam with out an optical comparator is just a guess in the wind.
Click to expand...



Mr Fellow Retiree :cool:

You say "There is no definition of JAM nor of HARD JAM... none."

Boyd Allen described it perfectly in his post number eleven. Any extension beyond touch will cause the bullet to stick in the lands. This can be felt easily during the last bit of opening the bolt when the firing pin assembly is removed. If the bullet is the least bit stuck in the lands, you can feel a slight click as the extractor pulls the bullet out of the lands. Once this is felt, begin lengthening the stem of your seater die in .005 increments until no click is felt when the bolt fully opens.

Maybe I should refer to my pet seating depth as "just off stick" instead of just off the lands. It requires a bit of finesse and a delicate touch on the bolt handle but it is very accurate and no optical comparator is necessary nor do you have to shine up the bullet and use a magnifying glass to look for land marks. The whole process is quick and easy and no tools or other gadgets are required. Try it! You'll like it. :p

Later,

Gene Beggs
 
FBecigneul said:
All you guys who advocate finding "jam" by seating a bullet long and closing the bolt on it fail to mention one other "theory" of mine. If the bullet is pushed further into the neck, what keeps this "jam" from pulling the bullet out again as you open the bolt? This, to me, makes for a failed attempt to find " jam". Second. Why the love affair with jam?
Just set the OAL to a length that has the bullet on the lands and go from that length as determined by the target. After all, isn't that what we're aiming for?
Click to expand...

I actually do both. I use the Hornady tool which probably has it in a couple of thous at touch.

But the hard jam comes from there is only one way to go - push bullet back into case. Pretty sure it is in the Tony Boyer book somewhere. From memory there is also a target example.
The bullet stays put with 3 to 4 thous neck tension which when using 133 isn’t a unusual amount
 
Good Question

FBecigneul said:
All you guys who advocate finding "jam" by seating a bullet long and closing the bolt on it fail to mention one other "theory" of mine. If the bullet is pushed further into the neck, what keeps this "jam" from pulling the bullet out again as you open the bolt? This, to me, makes for a failed attempt to find " jam". Second. Why the love affair with jam?
Just set the OAL to a length that has the bullet on the lands and go from that length as determined by the target. After all, isn't that what we're aiming for?
Click to expand...


Francis, You bring up a good point and back when I used lighter neck tension, I had that happen a number of times. I can thank Mr. Ed Watson for teaching me how to prevent the bullet from being dislodged as you open the bolt. Simply open and close the bolt handle smartly three or four times (all the way up and down) before pulling it back to extract the dummy round. By using this technique and a little more neck tension, (about what N133 likes anyway), I've never had the bullet dislodge when establishing 'JAM.'

'Why the love affair with jam?' It provides a very precise starting point. If you are working with a rifle you are not real familiar with it gives you a good idea of the freebore length and how this will coordinate with the bullets you're using as far as how deep they seat in the case neck. I do a lot of teaching and experimenting with other's rifles in the tunnel and doing a ''Jam Check" tells me exactly where I am to start with. Don't misunderstand; I never shoot with the bullets on "Jam" except to demonstrate what happens to a trainee. I've never seen a benchrest rifle yet that would shoot with the bullets seated on 'Jam.' It always takes 15 or 20 thousandths off of 'Jam' for the bullets to quit sticking in the leade as evidenced by the subtle little click at the top when the dummy round is extracted. This can be quickly and easily demonstrated but a challenge to get across with the written word. Hope this helps.

Best regards

Gene Beggs
 
Gene
My best 100 yd groups with my Rem.722/222 were .020 off the lands.Finding the contact point is just the start.

Mort
 
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