Finding Jam - I thought I knew how

[QuietTexan]

In general case length shouldn't matter as long as you are in the trim range, generally speaking 0.015" less than SAAMI max length, up to the max length. If the case isn't over length, it shouldn't matter for measuring purposes. But you aren't using a cut in the neck though... so in your particular case it might cause a different in seating pressure as the bullet engages the lands and create an inconsistency. Have you tried measuring with the relief cut?

You said you were using sized cases so the base to shoulder should be consistent, so there shouldn't be a variance from headspace.

Overall cartridge length variance is more a product of inconsistent meplat or ballitic tip shape/length than inconsistent BTO in my experience. I don't typically even measure it. I do check bullet base to ogive for a couple bullets out of each box, but generally they're the same (inside a given lot) from a good manufacturer.

I only measure using one bullet, I save that bullet for later, and never shoot it.

 

[antelopedundee]

My wife makes jam every year just before Christmas. If I open the fridge I can usually find it. If its not in the fridge then its in the basement-- peach, apple,, plum, and strawberry ---always in Mason jars

Jam jam thank you ma'am.

 

[Les in Wyoming]

Case length shouldn't matter as long as you are in the trim range, generally speaking 0.015" less than SAAMI max length, up to the max length. If the case isn't over length, it shouldn't matter for measuring purposes.

You said you were using sized cases so the base to shoulder should be consistent, so there shouldn't be a variance from headspace.

Overall cartridge length variance is more a product of inconsistent meplat or ballitic tip shape/length than inconsistent BTO in my experience. I don't typically even measure it. I do check bullet base to ogive for a couple bullets out of each box, but generally they're the same (inside a given lot) from a good manufacturer.

I don't understand why the bullet jam measurement (at the ogive) is different with different cases. My bullet jam measurements are all too different for me to get an idea where to start these Berger bullets. If I want to start with a .010 jump, some will be jammed in the rifling and some way out - depending on the figure I use. They won't be the same. I wonder if I should do the same test with several new unfired cases to see if I get the same measurement? If so, that means that case length somehow affects CBTO - which doesn't make sense to me.

 

[orkan]

I've been using a hornady oal length gauge and tool a few years and found a few inconsistencies. I switched to the method shown above from Greg with primal rights (which I believe is the same as Alex wheeler if I recall). I have since decided to try Erik Cortina's method for my latest load development and the next one to come and so far it's proving to be very accurate loads and I like the idea of his method but less focused on the actual length it self which was an odd concept lol

I would definitely call it the Wheeler method. I'm willing to bet he did it before I did. I had been doing it for a decade before I uploaded that video, but I'm betting others were doing it far longer than I. I didn't know there was a prior video outlining it when I uploaded mine. I was going to remove mine, but a few folks said they liked my presentation and encouraged me to leave it up.

that means that case length somehow affects CBTO - which doesn't make sense to me.

This has to do with the various neck thickness and metallurgical structure of the different brands of brass. Even among the same brand, cases which have different numbers of firings or are treated differently will produce different measurements at the same seating die setting. The amount of force required to overcome the varying degrees of compression will show up as different lengths. That seating force variance requires different adjustments to the micrometer on the seating die.

If you are setting up a case as defined in the Wheeler method, then you will achieve a precise measurement that will be independent of brass. That measurement will be good with that bullet, regardless of brass manufacturer. However, the adjustment that you need to have in your seating die will be very component specific, right down to the number of firings on the case. They must be identical and uniform for the seating force to remain static and thus produce bullets seating at the correct measurement. Adjustments to the seating die will be needed as you move from lot to lot, in order to stay on top of your desired measurement.

The same thing can be seen when moving into compressed loads. You'll have to run the seating stem deeper to overcome the extra force resisting your efforts, despite the fact you're working with the same components.

 

[Pdvdh]

I would definitely call it the Wheeler method. I'm willing to bet he did it before I did. I had been doing it for a decade before I uploaded that video, but I'm betting others were doing it far longer than I. I didn't know there was a prior video outlining it when I uploaded mine. I was going to remove mine, but a few folks said they liked my presentation and encouraged me to leave it up.



This has to do with the various neck thickness and metallurgical structure of the different brands of brass. Even among the same brand, cases which have different numbers of firings or are treated differently will produce different measurements at the same seating die setting. The amount of force required to overcome the varying degrees of compression will show up as different lengths. That seating force variance requires different adjustments to the micrometer on the seating die.

If you are setting up a case as defined in the Wheeler method, then you will achieve a precise measurement that will be independent of brass. That measurement will be good with that bullet, regardless of brass manufacturer. However, the adjustment that you need to have in your seating die will be very component specific, right down to the number of firings on the case. They must be identical and uniform for the seating force to remain static and thus produce bullets seating at the correct measurement. Adjustments to the seating die will be needed as you move from lot to lot, in order to stay on top of your desired measurement.

The same thing can be seen when moving into compressed loads. You'll have to run the seating stem deeper to overcome the extra force resisting your efforts, despite the fact you're working with the same components.

After establishing the CBTO length, you are stating the bullet seating depth will vary with different case neck tensions on the bullet, correct?
So any variance in case neck tension will result in a differing bullet seating depth... In the bullet seating die?
Higher neck tension results in longer CBTO measured lengths. Lesser neck tension results in shorter CBTO measured lengths?

 

[capona]

would there, or could there be some brass bounce back here if you are jamming it that could lead to inconsistent readings? That bolt has a lot of torque potential to compress.m when neck tension is tight.

 

[orkan]

After establishing the CBTO length, you are stating the bullet seating depth will vary with different case neck tensions on the bullet, correct?
So any variance in case neck tension will result in a differing bullet seating depth... In the bullet seating die?
Higher neck tension results in longer CBTO measured lengths. Lesser neck tension results in shorter CBTO measured lengths?

That's the general idea, yes. Where the rubber really meets the road is that those bullet seating force variations translate directly to variations in bullet release, which can/will alter the timing and have undesirable effects down range.

This is what is behind the practice of culling into lots during bullet seating. Some rounds that you feel seat hard, should be put into a separate bin... as should those you feel seat soft. Anything that strays from the median should be held aside... as they will inexorably shoot different.

This entire ecosystem of equipment and technique such as force gauge seaters, annealing, neck turning, and tumbling techniques is all either designed specifically to that end, or has the additional byproduct of ensuring consistent bullet seating force and thereby uniform release.

 

[SSG Graybush]

OK, the way I used to do it is by resizing a cartridge and barely seating a bullet. Then slowly closing the bolt and locking down. This pushes the bullet to "Jam." Then I got a fancy cartridge seating depth gage. I have had a horrible time finding a seating depth for Nosler bullets. None were accurate. Then I compared my old "jam" method and found there to be a big difference in COAL measurement. As much as .032. Now I am confused. But wait, there's more. I was trying to find jam with Berger bullets. They are also different from the cartridge seating depth gauge, but unlike the Noslers, they vary among themselves. Doing 7 empty cases with long seated bullets, the Bergers vary as much as .050. The Noslers vary only .005 and I got a couple that were the same.

I measure with CBTO gauge and COAL with calipers. Every one of those bullets has marks showing they engaged the lands. How in the world can you know which is right? What am I doing wrong? I sure would appreciate input. Thanks.

Take a full length sized pc of brass trimmed to spec. Load a bullet long. Shove it in the chamber with your finger. The bullet ogive hangs in the rifling. Remove thr bullet and shorten it by 2 thou and repeat till you can shove the round in the chamber and get the shoulder or belt to make contact without the ogive hanging in the lands. This is my way to find zero jump. Do it once more to confirm. This way is more repeatable/accurate for me then the Hornady coal tool or any method to find zero jump.
And measuring bto is much more accurate then measuring coal. The meplate on most bullets can vary by 3 to 5 thou. Measuring bto gets you down to 1 to 3 thou. And the bto is what matters.
To answer your question the trim length of brass doesn't effect your coal or bto. Coal and bto are only affected by your seating stem height.

 

[Brush4646]

I used Eric Cortina's method, which is what I always used to do. He said it doesn't matter if you get different readings, but if I have a large difference from different shells, how do I know if I my load is going to be .010 off jam or .020 into the rifling?

I used 3 different de-primed cartridges and they were all different. So I did them over and over again. It looks like each cartridge comes out the same each time - but each are different. Hmmmm. So I checked cartridge length. Each are different. In my pea brain, it seems to me it would not matter what the cartridge length is, because we are going for base of cartridge to ogive. That figure should be the same and the bullet jump should therefore be the same when you measure the OAL. Am I right?

It looks like my fired cases measure differently. I have a Lee case hand sizer. It sticks into the primer hole as a pilot and you spin it which cuts to size. But it looks like the length is different.

So, it could be that I am going to reveal some ignorance here, but I am here to learn. Does the actual case length make a difference in how deep the bullet sits from the lands when you measure CBTO?

Secondly, does cartridge length make a difference in accuracy if they are all seated the same CBTO? If so, what would the tolerance be? within .001? .002? or .009? etc. I will appreciate any input. Thanks

 

[antelopedundee]

I don't understand why the bullet jam measurement (at the ogive) is different with different cases. My bullet jam measurements are all too different for me to get an idea where to start these Berger bullets. If I want to start with a .010 jump, some will be jammed in the rifling and some way out - depending on the figure I use. They won't be the same. I wonder if I should do the same test with several new unfired cases to see if I get the same measurement? If so, that means that case length somehow affects CBTO - which doesn't make sense to me.

I would suggest that you invest in a decent caliper and one of these Sinclair bullet comparators. Before you do anything you should sort through a box of bullets and find 10 or so that have the same bullet length and the same distance from base to ogive as determined with the Sinclair comparator. Next you should turn [or find a friend to do it for you] some case necks to uniform wall thickness. Your case necks should be just tight enough to hold a bullet. Seat a bullet that's longer than COAL plus some extra. Chamber it in your rifle until you can feel it touch the lands. Save this as a reference dummy, assuming that your chamber is relatively new. Turn the seater stem in until you reach the amount of "off the lands" distance [say 0.020 inches] and seat some bullets using cases sized to however much neck tension that you want. Your 10 sorted bullets should all measure the same COAL with the Sinclair comparator. Maybe randomly pick 10 bullets out of the 90 left in the box and see how COAL measures. Many times there are differences in bullets from the same box.

You will not be able to accomplish much of this with just a standard set of dies. You will need either the neck size bushing approach or a set of expander mandrels which you use to set neck diameter AFTER you FL size your cases WITHOUT the expander stem assembly in there.
GOOD LUCK.

 

[LaHunter]

You got your answer in posts #7 & #8.

 

[misterc01]

My wife makes jam every year just before Christmas. If I open the fridge I can usually find it. If its not in the fridge then its in the basement-- peach, apple,, plum, and strawberry ---always in Mason jars

I just look on the shelf at the store - all sorts there.

 

[misterc01]

IF you are using either the Hornady pre-prepped case, or etter yet - you have had one threaded from a once-fired case, you eliminate the case from equation and it is all the bullet. I use BOTH the Horandy and Sinclair Comparators, and that gives me two sets of data to work from. I get consistent feadings from each - one set Horndady, one set Sinclair, that gives me the seating depth answer. As for Berger's - they seat either deeper into the lands, or rather far out for the seating depth that give the best accuracy. IF you use the wheelr.Cortin mehtod, then the extraor and ejector need to be removed for the best results.

 

[rammac]

Maybe somebody said something about ogive shape/taper but I didn't see it.

When you measure to the ogive you have to remember that the ogive is a taper (imagine cutting the bullet in half along it's length) and different brand bullets, regardless of weight or overall length, will have different tapers.

You measure to the ogive using a tool that has a hole equal to the diameter of the place on the bullet that you want to measure. If your bore is (at the top of the lands) is .30" then the place on the ogive that you want to measure is where the bullet's diameter is .30".

If the tool you are using to measure the base-to-ogive dimension has a hole that is the wrong size then you will not get a good number for your bullet seating depth. If your tool has a tapered hole it must be tapered correctly, too sharp of a taper and the tool will not touch at the proper ogive diameter.

Regardless of what method you use to find the cartridges overall length (COAL) you have to recognize that the length is only good for that bullet. Your numbers will vary if you change anything about the bullets; brand, weight, style, etc.. Even within the same brand and lot number you will have some variances but not enough to worry about.