Seating depth terminology

[oldduc]

It is often hard to determine what folks are talking about when the subject is bullet seating depth. Many reports use "+" and "-" designations for seating depth. Others use "jump" or "jam" or "in" or "out" or "off" or "from" or some other terminology. The problem is that, particularly with "+/-", some people reverse them. "+" is sometimes used to mean into/jammed/in the lands and others use "+" to mean away/off/out/jumped to the lands. There are many threads where people ask questions to clarify how the designation is being used. It would be great if some standard terminology could be used when reporting seating depth information. Not sure, however, how that could be accomplished.

 

[Coyotefurharvester]

I guess I always thought of "jump" and "-" the same. Touching 0.0 ( 0.010 jump or - 0.010)

 

[dgeesaman]

It makes sense when you think of It as CBTO touch length with a tolerance. + is longer cartridge and seated into the lands, - is shorter and jumping to the lands.

I don’t love this shorthand myself but that’s how I keep track of it.

 

[jimmymac]

It is often hard to determine what folks are talking about when the subject is bullet seating depth. Many reports use "+" and "-" designations for seating depth. Others use "jump" or "jam" or "in" or "out" or "off" or "from" or some other terminology. The problem is that, particularly with "+/-", some people reverse them. "+" is sometimes used to mean into/jammed/in the lands and others use "+" to mean away/off/out/jumped to the lands. There are many threads where people ask questions to clarify how the designation is being used. It would be great if some standard terminology could be used when reporting seating depth information. Not sure, however, how that could be accomplished.

I think people use different terminology but often mean the same thing. Because of that, I pay little attention when people post their seating depth discoveries. Everything is individualized in my opinion. The main thing is to have your own system and stick with it.

For me, I'll find my jam length. I'll size a case with the bushing I'm planning on working with. I'll then seat the bullet extra long, take the CBTO measurement and record it. Using a stripped bolt, I'll chamber the round. If I've seated the bullet long enough, the CBTO of the extracted round will be less than where I started. I'll repeat this process to be sure of my dimension. Once satisfied, that becomes my jam length dimension for that bullet using the above mentioned bushing. I record that number, then all seating depth references I make in my log book will be minus numbers.

The same can be done from touch length for the same given bullet using the Wheeler method as shown in his video. Once I find touch I record that dimension. From there, minus numbers indicate bullet jump and plus numbers indicate longer seating depth moving towards my jam length described above.

I always find both my touch length dimension and jam length dimension for each bullet I use. It helps me keep things straight in my head.

 

[BoydAllen]

If you are using touch as your reference, longer than touch, or shorter than touch seems simple. Jumping also seems to be pretty clear. The main issue seems to be the use of the word jam, which has been corrupted because most don't know the original definition.

 

[jimmymac]

If you are using touch as your reference, longer than touch, or shorter than touch seems simple. Jumping also seems to be pretty clear. The main issue seems to be the use of the word jam, which has been corrupted because most don't know the original definition.

Do you find my definition above to be the original definition? I believe the method I'm using is the same as what Tony Boyer describes in his book.

 

[RGRobinett]

Do you find my definition above to be the original definition? I believe the method I'm using is the same as what Tony Boyer describes in his book.

When I began, this was referred to as "jam-seat(ing)", which is what I use to this day, recording the seater-stem (Wilson) length: per your comment above, it's merely a reference length/point, from which, there is only one direction to go. Oh, using a barrel-stub, "shoulder bump" gauge, I begin with what, if the bullet did not set-back upon lock-up, would amount to a 0.030" jam. I place five 0.010" shims between the die-cap and the die-top, and, if necessary, remove them to scan for a "better" area. I believe you're pretty close.RG

 

[ShootDots]

This is MY way of thinking and maybe I am a bit too simplistic. If you are measuring your bullet with the "Hornady / old Stony Point" system, then to my way of thinking is that when the bullet just barely touches the lands, it is neither "jammed nor is it OFF the lands". If you go FORWARD, INTO the lands, you have jammed the bullet into the lands. If you go away from the lands you are OFF the lands. I agree this + /- thing or 10 thousandths off "Hard Jam" is very nebulous to me. That is why I use the terms INTO the lands to designate a bullet being jammed into the lands and I also use OFF the lands, as in 15 Thousandths OFF the lands, meaning 15 thousandths from just touching the lands.
How do you define "Hard Jam"? Is hard jam the opposite of "soft jam" or just "jam"? To my way of thinking is that IF you have not entered the lands, you are not jammed. If you have just touched the lands, you know that you either go IN from there or away or OFF from there. Pretty simple to me.. But like I stated, maybe that's just a bit too simplistic. However, it works for me and has for almost 50 years!

 

[mikecr]

I use Off the lands (OTL) or In the lands (ITL) an x.xxx amount (no need for (+/-).
I suppose touching would be TTL, but it never made sense to manage that..

 

[BoydAllen]

My understanding of the original short range group benchrest definition of "jam" is the maximum length that a bullet can be seated to that will not result in its being pushed back into the case by chambering the round. Putting it another way, it is the length to which a bullet will be pushed back to when seated longer than the chamber can accommodate without the bullet being pushed back from chambering the round. This would be at the neck ID condition, and degree of sizing that will be used for loading the ammunition. The handy thing about this method is that if you are loading at the range, all you have to do is seat one long, chamber the round or dummy, remove it from the chamber, confirm that it has been shortened, and you have jam for that bullet, barrel and brass. A shooter might say that he is seating .007 off jam or shorter than jam. There are even cases where someone might seat longer than jam so that he is intentionally finishing his seating of each bullet as he chambers that round. Back in the day, a highpower competitor that I knew referred to this as soft seating. It is not normally done with high neck tension.

 

[rebs]

What does CBTO stand for ?

 

[Lone Hunter]

Cartridge Base To Ogive

 

[Kracken McGraw]

What does CBTO stand for ?

Measurement of cartridge base to ojive of Bullet. Bullet ojive is the widest point of the front part that will engage the barrel rifling first.

 

[BenPerfected]

This is MY way of thinking and maybe I am a bit too simplistic. If you are measuring your bullet with the "Hornady / old Stony Point" system, then to my way of thinking is that when the bullet just barely touches the lands, it is neither "jammed nor is it OFF the lands". If you go FORWARD, INTO the lands, you have jammed the bullet into the lands. If you go away from the lands you are OFF the lands. I agree this + /- thing or 10 thousandths off "Hard Jam" is very nebulous to me. That is why I use the terms INTO the lands to designate a bullet being jammed into the lands and I also use OFF the lands, as in 15 Thousandths OFF the lands, meaning 15 thousandths from just touching the lands.
How do you define "Hard Jam"? Is hard jam the opposite of "soft jam" or just "jam"? To my way of thinking is that IF you have not entered the lands, you are not jammed. If you have just touched the lands, you know that you either go IN from there or away or OFF from there. Pretty simple to me.. But like I stated, maybe that's just a bit too simplistic. However, it works for me and has for almost 50 years!

Agree that finding touch is the 1st step. I stopped jamming or jumping as all the screwing around was a waste of ammo and it accelerated my barrel wear. Now, after about 30-50 rounds my barrel erosion is measurable. Now I just preload my bullets long & then adjust my seating depth about ever 30-40 rounds to keep up with the erosion. As the conditions change, just tweak my tuner.
Ben

 

[cw308]

I use CBTO as Closed Bolt To Ogive , that's why I stopped neck sizing , the thought of a case that was neck sized until it chambered with resistance . Then how could you measure your ogive accurately . Once the case has zero movement in the chamber from bolt face to shoulder then from that point I could see the accurate measurement from bolt face to ogive , having no wiggle room . So for all that neck size is you jump or jam measurements accurate or just in the ballpark . Nothing like opening up a bag of worms .

 

[F Class John]

I use the ‘Wheeler method’ for finding where my lands start but the same would apply if you could accurately find a zero point with the Stoney gauge. That’s 0 point either way. Everything seated back of that is jump or off the lands or -.000. It’s all the same in my book. Anything forward seated of my 0 point is jammed or in the lands or +.0000. That definition is used by nearly everyone I shoot with.

 

[foxguy]

I to now use the wheeler method of finding the lands. Now that I know the touch distance (at the lands-ATL ) I can seat deeper into the lands +0.0XX which is then +0.0xx relative to the lands or -0.0xx off the lands relative to the lands .

In the lands (ITL) +0.0xx
Off the lands (OTL) -0.0xx

That's just how learned it and now read it - relative to the lands.

Thanks to Accurate Shooter members

 

[cw308]

I like to keep it simple . Jam is .002 jump is .002 touching is touching. Or you can be a lawyer and make it two pages long and say the same thing .

 

[Coyotefurharvester]

Always "-" because I hunt, no long range steel,no competition. Only have one rifle I single shot load, early 90's Savage m12 long range varminter ,strictly a prairie dog rifle. So I'm always "working away from touching". Eliminate vertical and just read the wind.

 

[cw308]

Coyote
Reading the wind is a talent only by experience and knowing your rifle . I'm only shooting 308 at 200 yards and shooting from a bench in perfect conditions . Never got into the art of real shooting at long distance. Maybe one day .

Chris