Measuring Jam, Sierra vs Berger. Surprised me!

[NC/Br Shooter]

As the title suggests, I went at it again measuring Jam with Sierra 107s. I'm doing so by seating the bullet long and clambering it,then measuring using the Hornady tool pictured. I did this with 20 pieces. After I measured 5, I thought hey! All measured within 2 thou. Then 10 pieces. All within 3 thou. Man, I measured 20 pieces. All within 3 thousandth of each other.
Now, all the bass is 3x fired,,6bra and a new box of 107s.
I've used this method on my other bullets in the past but never get that level of consistency.
Is Sierra just that consistent ?
Is it just maybe a good lot?
I'm comparing them to berger 108s that I have.
This measuring method isn't new to me. I've just never found a bullet that gave me that level of measure one right after the other. I know it's where the ojive hits the chamber. I'm guessing maybe the 108s have move slope at that particular spot throwing the readings off. Any thoughts welcome. I'd just like to hear what yall think about it.
Thanks

 

[AlNyhus]

Keep in mind that with the Hornady comparator, your measurements are at a single 'line point' on the bullet. That's not necessarily bad...just that it's a single point of measurement across the interface of two different angles.

Good shootin' -Al

 

[Straightshooter1]

As the title suggests, I went at it again measuring Jam with Sierra 107s. I'm doing so by seating the bullet long and clambering it,then measuring using the Hornady tool pictured. I did this with 20 pieces. After I measured 5, I thought hey! All measured within 2 thou. Then 10 pieces. All within 3 thou. Man, I measured 20 pieces. All within 3 thousandth of each other.
Now, all the bass is 3x fired,,6bra and a new box of 107s.
I've used this method on my other bullets in the past but never get that level of consistency.
Is Sierra just that consistent ?
Is it just maybe a good lot?
I'm comparing them to berger 108s that I have.
This measuring method isn't new to me. I've just never found a bullet that gave me that level of measure one right after the other. I know it's where the ojive hits the chamber. I'm guessing maybe the 108s have move slope at that particular spot throwing the readings off. Any thoughts welcome. I'd just like to hear what yall think about it.
Thanks

The method you describe for your measurement has little or nothing to do with the consistency of the bullet. I'd say it just you doing a more consistent job with your method. If you want to know the consistency of the lot of bullets, you'd need to measure the bullet's BTO's. Now, if the BTO's are staying in within .003", that's a good lot and not usual.

 

[NC/Br Shooter]

Your both correct. It's just that I've done this thousands of times and never came up with results this good. The only thing I can come up with is bullet consistency. The burgers, they stick in the chamber, come out long, short, fall out. Same brass.

 

[Ned Ludd]

The longitudinal distance between the points on the bullet ogive where it first touches/pushes into the lands and the point where your caliper insert seats should be very small. If you're not obtaining consistent CBTO measurements with almost any bullet you try, something is wrong. It could be diametral inconsistency of a specific brand of bullet, or it could be measurement error due to some other cause. I wouldn't go too far out on a limb in terms of attempting to interpret this result as a definitive measure of bullet consistency.

 

[NC/Br Shooter]

The longitudinal distance between the points on the bullet ogive where it first touches/pushes into the lands and the point where your caliper insert seats should be very small. If you're not obtaining consistent CBTO measurements with almost any bullet you try, something is wrong. It could be diametral inconsistency of a specific brand of bullet, or it could be measurement error due to some other cause. I wouldn't go too far out on a limb in terms of attempting to interpret this result as a definitive measure of bullet consistency.

I mean you could be right. It's just I've never gotten those measurements with the bergers. I've done thousands of them and this morning, I chambered those 107s and basically got the same reading for 20 straight. I've never seen that with any other projectile using this method. This is whole reason I posted the thread. I just thought it was "something "! But yall all right too

 

[JEFFPPC]

This ongoing facination with jam amazes me. The term jam itself to me leaves much to be desired. How about touch, mark on bullet from the lands. You can see and verify it. But in reality neither is need. Seat a bullet in a dummy round. Now seat plus and minus till you find a sweet spot. Jam, touch, whatever, not really an absolute must. All you need is a starting point and a process to tune. No fancy terms needed. Come up with a repeatable process that works for you. Now, once you feel you have refined your load to perfection, if you have a tuner go a bump or two bot ways and see if you can refine it. Best case is you can not improve it, your process has found the best tune. Now as conditions change and the barrel wears use the tuner to get back on point with minimal additional rounds down the barrel. I hate to waste on tune rounds on anything but a match target.

 

[dgeesaman]

I think a lot of recent conversation about jam came from Alex Wheeler, who was providing his customers guidance on seating depth tuning, which required a reference measurement that any reloader could follow and produce consistent results. Of course, that specifically means stripping the bolt and finding a touch point. Jam is anything seated longer. This method is probably the best way to make jam measurements transferable.

I agree that its one way to do it. In my experience it’s not the fastest way and in my reloading practices, I prefer a different way (Hornady tool). I understand that still others prefer imprinted square marks on the bullet. But my method isn’t as transferable.

 

[BoydAllen]

I have to resist the temptation to be irritated in discussions like this. The reason is that the term jam, as applied to seating depth has become so corrupted from its origin, which I believe was in short range group, many years back. The original meaning was the specific length to which a bullet would be pushed back, when loaded long chambered and then removed for measurement, The key issues are that the condition of the neck should be the same as it will be for the loads that will be fired, same neck tension (difference between sized neck OD and loaded, measured over the seated bullet's pressure ring if there is one) neck ID fouling, and these days, state of anneal. The original use would have shooters referring to how much shorter than jam they were seating bullets. Shooters would say that they were seating a certain number of thousandths "off jam" meaning shorter than. So under that convention one would either be jumping ( seating shorter than touch, by a specified amount), at touch, or, in the short range game, seating a specified amount off, meaning shorter than jam. In later years I have found it interesting to determine the distance between jam and touch, which tends to vary with the shape of the ogive. This tells you how far you can seat longer than touch without the bullet being pushed back. It gives you the range that you have available. For touch, I have adopted the Wheeler method when making this calculation.

I believe that the reason that short range shooters have used jam as a starting point is that it is so quick to find when you are loading at the range. You load one long, take it to the firing line when the range is hot and chamber, and then unchambering it. The key is to measure before and after to make sure that the bullet has been pushed back by the round being chambered. The amount of shortening is the key. As an example, if the bullet is pushed back .007, and I want to be seated .003 off jam, I can adjust my seater to reduce the ogive to head measurement by .010 and I should be right where I want to be.

 

[SweaterDood]

To attempt to answer the OPs question as to why Sierras are pushed back to a more uniform location in the case:

This likely comes down to the nose shape differences between bullets. The fact that Bergers seem to have inconsistency and also tend to get stuck in the barrels indicates a shallower nose angle at the point of contact with the rifling. The inconsistency may well stem from the fact that when Bergers don’t stock in the barrel, they may be pulled back out on occasion by the rifling. Sierras on the other hand are likely more blunt at the point of contact, and push to a consistent location, and allowing for a clean release from the rifling when extracted.

In agreement with the other responses:

This particular measurement is relatively fruitless, aside from a slightly more precise base measurement for Base to Ogive when starting seating depth testing. In the end the tunes seating depth will be what it is. The distance from the arbitrary starting location means little to nothing.

 

[NC/Br Shooter]

To attempt to answer the OPs question as to why Sierras are pushed back to a more uniform location in the case:

This likely comes down to the nose shape differences between bullets. The fact that Bergers seem to have inconsistency and also tend to get stuck in the barrels indicates a shallower nose angle at the point of contact with the rifling. The inconsistency may well stem from the fact that when Bergers don’t stock in the barrel, they may be pulled back out on occasion by the rifling. Sierras on the other hand are likely more blunt at the point of contact, and push to a consistent location, and allowing for a clean release from the rifling when extracted.

In agreement with the other responses:

This particular measurement is relatively fruitless, aside from a slightly more precise base measurement for Base to Ogive when starting seating depth testing. In the end the tunes seating depth will be what it is. The distance from the arbitrary starting location means little to nothing.

Yes, . I THINK your right. I think I understand what you

 

[sqrlgtr]

I have to resist the temptation to be irritated in discussions like this. The reason is that the term jam, as applied to seating depth has become so corrupted from its origin, which I believe was in short range group, many years back. The original meaning was the specific length to which a bullet would be pushed back, when loaded long chambered and then removed for measurement, The key issues are that the condition of the neck should be the same as it will be for the loads that will be fired, same neck tension (difference between sized neck OD and loaded, measured over the seated bullet's pressure ring if there is one) neck ID fouling, and these days, state of anneal. The original use would have shooters referring to how much shorter than jam they were seating bullets. Shooters would say that they were seating a certain number of thousandths "off jam" meaning shorter than. So under that convention one would either be jumping ( seating shorter than touch, by a specified amount), at touch, or, in the short range game, seating a specified amount off, meaning shorter than jam. In later years I have found it interesting to determine the distance between jam and touch, which tends to vary with the shape of the ogive. This tells you how far you can seat longer than touch without the bullet being pushed back. It gives you the range that you have available. For touch, I have adopted the Wheeler method when making this calculation.

I believe that the reason that short range shooters have used jam as a starting point is that it is so quick to find when you are loading at the range. You load one long, take it to the firing line when the range is hot and chamber, and then unchambering it. The key is to measure before and after to make sure that the bullet has been pushed back by the round being chambered. The amount of shortening is the key. As an example, if the bullet is pushed back .007, and I want to be seated .003 off jam, I can adjust my seater to reduce the ogive to head measurement by .010 and I should be right where I want to be.

great explanation and this is what I always thought of the term "jam" as it pertains to our sport....

 

[AlNyhus]

To me, the term 'jam' shouldn't even be used. It's Halloween...put a stake in the heart of that term. The 'jam' method is why a vast majority simply don't get their seating depth correct.

A better, more reliable and more repeatable method is to simply find out where the 'touch point' is with a specific bullet in a specific barrel.

Do this for each bullet you're going to use and simply record the seating stem length to the 'touch point' of each particular bullet in each particular barrel. Now you have a standard to go by and get back to. This method also allows you to better monitor the leading edge of the rifling as it moves forward.

Once you know the 'touch point', simply adjust the seating stem to move the bullet in or out when you tune the seating depth. Start with the bullet long...then you only have one way to go with it.

When the bullet is seated longer than the 'touch point', many of us refer to this as the 'jam/seat number'....which is exactly what it is....even though it's different that the traditional meaning of 'jam'.

This won't be a popular opinion. But it's true.

Ducking the slings and arrows headed this direction....... -Al

 

[BoydAllen]

To me, the term 'jam' shouldn't even be used. It's Halloween...put a stake in the heart of that term. The 'jam' method is why a vast majority simply don't get their seating depth correct.

A better, more reliable and more repeatable method is to simply find out where the 'touch point' is with a specific bullet in a specific barrel.

Do this for each bullet you're going to use and simply record the seating stem length to the 'touch point' of each particular bullet in each particular barrel. Now you have a standard to go by and get back to. This method also allows you to better monitor the leading edge of the rifling as it moves forward.

Once you know the 'touch point', simply adjust the seating stem to move the bullet in or out when you tune the seating depth. Start with the bullet long...then you only have one way to go with it.

When the bullet is seated longer than the 'touch point', many of us refer to this as the 'jam/seat number'....which is exactly what it is....even though it's different that the traditional meaning of 'jam'.

This won't be a popular opinion. But it's true.

Ducking the slings and arrows headed this direction....... -Al

Al, I was not recommending just explaining the original definition and associated procedure. I work from touch, but I want to know how far into the rifling I can seat before the bullet is pushed back, and where it may be likely to cause a bullet to stick and be pulled if the round is unloaded instead of being fired. Typically, I seat into the rifling and would refer to a particular seating depth as being a specific distance into the rifling. One exception is my procedure for doing an initial powder charge test. For that I set my seater so that I have marks that are about half as long as wide and that has worked well over the years, for that purpose. For others that may be reading this, I firmly grasp the seated bullet with a wad of 0000 steel wool and turn the round a few times with my right hand to put tiny striations around the bullet that make rifling marks a lot easier to see. The marks do no harm to the bullet as far as accuracy or anything else is concerned. I prefer precise terminology, which is why I mentioned the method that I use to find where a bullet just touches the rifling. I do this because different methods can yield slightly different results.

 

[Martin52]

I recently put a few 200.20x's in a barrel with uncertain freebore to find the distance to the lands and COAL.

Referring to Boyd's post and definitions, jam produced a COAL of 3.044 and bolt closure required a little pressure. The bolt did not drop freely without pressure until seating was pushed back from jam by 0.040 to a COAL of 3.004 - so touch at 3.004.

Unlike the lighter projectiles I usually use (155.5's) the 0.040 variance between touch and jam for these 200.20x's seems to be related to their longer bearing surface.

 

[boltfluter]

I recently put a few 200.20x's in a barrel with uncertain freebore to find the distance to the lands and COAL.

Referring to Boyd's post and definitions, jam produced a COAL of 3.044 and bolt closure required a little pressure. The bolt did not drop freely without pressure until seating was pushed back from jam by 0.040 to a COAL of 3.004 - so touch at 3.004.

Unlike the lighter projectiles I usually use (155.5's) the 0.040 variance between touch and jam for these 200.20x's seems to be related to their longer bearing surface.

That sounds about right, when compared to the square marks I get on a bullet when seated long. My favorite is Huckleberry jam!

Paul

 

[AlNyhus]

......jam produced a COAL of 3.044 and bolt closure required a little pressure. The bolt did not drop freely without pressure until seating was pushed back from jam by 0.040 to a COAL of 3.004 - so touch at 3.004.

Lacking a visual inspection of the bullet, 3.004 may not be the actual 'touch' point.

Good shootin' -Al

 

[AlNyhus]

That sounds about right, when compared to the square marks I get on a bullet when seated long.

Paul, those marks are another area that veers people off the correct path to seating depth. Using a certain 'mark' as a seating depth indicator is valid only for a specific barrel from that mfg. with the same lands/groove dimensions and chambered with the same reamer throat leade angle.

As an example, with the same bullet seated .020 longer than the 'touch point' (ie: a .020 jam/seat), the marks are completely different between my Liljas, Kreigers, Bartlien, Rock and Shilen .30 cal. barrels that have been done with the same reamer.

Good shootin' -Al

 

[Dusty Stevens]

I think if you actually get a fist full of sierra 107 bullets and shoot them youll be pleasantly surprised. Dont play with them, dont study them, just load them at touch and shoot them. Youll probably keep shooting them at that point.

 

[JEFFPPC]

Paul, those marks are another area that veers people off the correct path to seating depth. Using a certain 'mark' as a seating depth indicator is valid only for a specific barrel from that mfg. with the same lands/groove dimensions and chambered with the same reamer throat leade angle.

As an example, with the same bullet seated .020 longer than the 'touch point' (ie: a .020 jam/seat), the marks are completely different between my Liljas, Kreigers, Bartlien, Rock and Shilen .30 cal. barrels that have been done with the same reamer.

Good shootin' -Al

How can it steer you wrong. Your tuning a specific bullet to a specific barrel. Accurate Shooting, your not looking for a place to seat mass produced ammunition. Lack of common sense in folks gives me a headache. Your looking for a repeatable starting point. The square mark is not to give you that point. The idea of a square mark is the bullet just might like to shoot well with a lot of land engagement.