Determining touch vs jam

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adamsgt

Jerry Adams
I was trying to get some data to set up the Berger 115 in my 30BR. I used the Sinclair seating depth tool to determine touch and got a value of 1.598 on the Davidson gauge. I then used another case to determine jam and came up with a value of 1.660. That's a difference of .062 between touch and jam. Is that reasonable for this case and bullet? Jam is certainly easier to determine but determining "touch" is a little more subjective. Is there a better way of getting an accurate determination of touch?
 
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Here's what I do to find touch. First jam the bullet by seating long and using weak neck tension. Then adjust the seater until the land marks are barely visible under a loop (of course you have to paint or smoke the bullet in between each try). I usually go down in 0.002" increments. Bolt closure should be much easier when you're just kissing the lands.

-Lee
www.singleactons.com
 
Jerry,

if you have a micrometer, measure the shank diameter.

do you know what your freebore diameter is supposed to be in that chamber?
 
I have found

that when I neck size a case, start a bullet in the case and then load it into the chamber the amount of bullet in the lands = from .012" to .015", usually .012. One can cut their cycles of the .002 increments pushes down considerably by seating the bullet in, say .008" or .010 the first whack, even .006" lets say. I use a Stony Point comparator to measure the OAL of the bullet as I go. I keep pushing the bullet in until I can just see a faint touch from the lands. I record that OAL as well as save that dummy case in the batch of bullets I am using. I also keep a dummy of the best seating depth I find for that bullet-powder combination. I am not particularly good at keeping notes and have little memory left to help me out later on. I also draw pictures of the groups from my test results when I can think to do it and measure the groups, when I get back home and indicate which load/ seating depth produces the best results. It's hard to get old :).

Pete
 
One thing that I do is to compare the datum to head measurements of the modified case and one that has been fired, and had the primer removed. For one of my 6PPCs the difference is .006 which I add to the ogive to head measurement that I get using the factory modified case. Without this step my touch measurements would be off by that amount. Also, I use what I believe to be the original, benchrest, definition of jam. To measure it, I use the neck tension that I will be loading with, and of course jam increases with neck tension.
 
Lee Martin said:
Here's what I do to find touch. First jam the bullet by seating long and using weak neck tension. Then adjust the seater until the land marks are barely visible under a loop (of course you have to paint or smoke the bullet in between each try). I usually go down in 0.002" increments. Bolt closure should be much easier when you're just kissing the lands.

-Lee
www.singleactons.com
Click to expand...

At risk of being considered too persnickety, if you're just touching, the bullet won't be marked. By the time the bullet is marked, you're into the lands for some distance. My initial question was as to the validity of .062 between jam and touch being a reasonable number. I was trying to see if the results I got using the Sinclair tool were good enough. I guess the next step is to do what you suggested and compare the results I got with the Sinclair tool. I'd like to see if there is a better/easier way to determine touch besides trial and error. There may not be and I'll find that out. I'd rather do that than watch Obama tonight.
 
If you have the dial micrometer tool Chuck McClure makes its exact if you make one more adapter for it.with the barrel removed determining exact touch is easy. Otherwise determining exact touch can be a pain. You can get close by trial and error by buffing the bullet nose with 0000 steel wool.
 
Pete Wass said:
that when I neck size a case, start a bullet in the case and then load it into the chamber the amount of bullet in the lands = from .012" to .015", usually .012. One can cut their cycles of the .002 increments pushes down considerably by seating the bullet in, say .008" or .010 the first whack, even .006" lets say. I use a Stony Point comparator to measure the OAL of the bullet as I go. I keep pushing the bullet in until I can just see a faint touch from the lands. I record that OAL as well as save that dummy case in the batch of bullets I am using. I also keep a dummy of the best seating depth I find for that bullet-powder combination. I am not particularly good at keeping notes and have little memory left to help me out later on. I also draw pictures of the groups from my test results when I can think to do it and measure the groups, when I get back home and indicate which load/ seating depth produces the best results. It's hard to get old :).

Pete
Click to expand...
Pete, this exercise was that I was trying to work up something with the Berger .30 115 gr FB bullet. When I was setting up the Sinclair Seating depth tool, I measured the length of fifteen bullets and had an extreme spread of .006 nose to base. While this was of no consequence when using the tool to find touch, I didn't want to measure off the nose for anything else. I intended to measure off the ogive using the Davidson tool. Your comments are very helpful and I intend to digest them further after I have digested my leftover dinner.
 
Boyd Allen said:
One thing that I do is to compare the datum to head measurements of the modified case and one that has been fired, and had the primer removed. For one of my 6PPCs the difference is .006 which I add to the ogive to head measurement that I get using the factory modified case. Without this step my touch measurements would be off by that amount. Also, I use what I believe to be the original, benchrest, definition of jam. To measure it, I use the neck tension that I will be loading with, and of course jam increases with neck tension.
Click to expand...

Boyd, I'm unable to create a picture of what you're describing in the first sentence. Is the "modified case" you're referring to the one used with the Stoney Point tool? I'm able to make those cases as I have the required drill and tap but haven't made one yet for this gun. I've mde them for 6PPC and 6 Beggs. So, I guess I need to make one of those cases, as soon as I can find the tap a and drill. Then do the Stoney Point tool, the method Lee suggested and compare the results from all three and see what falls out. Again, sounds like a lot more fun than listening to Obama.
 
JerrySharrett said:
If you have the dial micrometer tool Chuck McClure makes its exact if you make one more adapter for it.with the barrel removed determining exact touch is easy. Otherwise determining exact touch can be a pain. You can get close by trial and error by buffing the bullet nose with 0000 steel wool.
Click to expand...

Well that sound interesting,Jerry. Where can I find out more info on this tool? The term "dial micrometer" is intriguing.
 
Lee Martin said:
Here's what I do to find touch. First jam the bullet by seating long and using weak neck tension. Then adjust the seater until the land marks are barely visible under a loop (of course you have to paint or smoke the bullet in between each try). I usually go down in 0.002" increments. Bolt closure should be much easier when you're just kissing the lands.

-Lee
www.singleactons.com
Click to expand...

smoking the bullet shows the best, works best with no powder or primer ;)
 
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That's exactly what I do George. The matte black on copper gives perfect contrast.

My process is probably similar to most folks'. Using 0000 steel wool and a Zippo lighter, I smoke the bullet and jam it. Marks observed. The bullet is again steel wooled, smoked, and re-seated, this time 0.002" down on the plug. That continues until the land marks really begin to thin. I then switch to 0.001" steps and at some point they become barely visible under a loop. And by barely I mean they're just cutting the carbon. For all intents and purposes, that's touch. I say that because when I go down another thou you see nothing. Is it absolute touch or am I in a hair? Doesn't really matter because the up or down would be tenths....and no micro seater measures to ten-thousandths, nor would a couple of tenths show-up on paper. But as Jerry said, there has to be some visual evidence, otherwise you're guessing on whether it's meeting the lands or jumping.

-Lee
www.singleactions.com
 
I bought my modified case from Stoney Point, (now Hornady) so I knew that there would be a difference in head to shoulder as compared with a fired case. By measuring both, I can add the difference to the measurement that I take using the factory modified case, which gives me the proper dimension for a case that has been fire formed in the barrel/rifle that I am loading for. Different barrels will vary slightly, and rifles may by more. If I were to make my own using a fired case, it would only be correct for the barrel and/or rifle that the case was fired in.
 
Lee Martin said:
That's exactly what I do George. The matte black on copper gives perfect contrast.

My process is probably similar to most folks'. Using 0000 steel wool and a Zippo lighter, I smoke the bullet and jam it. Marks observed. The bullet is again steel wooled, smoked, and re-seated, this time 0.002" down on the plug. That continues until the land marks really begin to thin. I then switch to 0.001" steps and at some point they become barely visible under a loop. And by barely I mean they're just cutting the carbon. For all intents and purposes, that's touch. I say that because when I go down another thou you see nothing. Is it absolute touch or am I in a hair? Doesn't really matter because the up or down would be tenths....and no micro seater measures to ten-thousandths, nor would a couple of tenths show-up on paper. But as Jerry said, there has to be some visual evidence, otherwise you're guessing on whether it's meeting the lands or jumping.

-Lee
www.singleactions.com
Click to expand...

Thank you Lee, that's a much clearer elaboration of your process, Super. Well, maybe I shouldn't put it that way. How bout this. It's just much clearer to this old thick headed Polack. Picture me slapping my flat forehead with my big kielbasa hand saying, DOH.
 
Boyd Allen said:
I bought my modified case from Stoney Point, (now Hornady) so I knew that there would be a difference in head to shoulder as compared with a fired case. By measuring both, I can add the difference to the measurement that I take using the factory modified case, which gives me the proper dimension for a case that has been fire formed in the barrel/rifle that I am loading for. Different barrels will vary slightly, and rifles may by more. If I were to make my own using a fired case, it would only be correct for the barrel and/or rifle that the case was fired in.
Click to expand...

After my leftover dinner, I went to look for the drill bit and tap to make the case. Found them in a parts drawer and right next to them was a 6BR case with a .30 neck and a large threaded hole in the base. Seems I made a case for the gun right after I bought it a tucked it away so I could find it easy. Right. Well, I had a couple of glasses of wine with my dinner, which was excellent, so I'll wait til morning to do the precision work. I was wondering if I had bought a case holder for the 30 BR so I could trim when I make new brass then I remember that was what i used to hold the case in the lathe chuck when I drilled and tapped it. Now I got to find that. You can tell I'm real organised.
 
geo.ulrich said:
smoking the bullet shows the best, works best with no powder or primer ;)
Click to expand...

Now I got to find the carbide lamp I used to smoke my Gold Cup .45 sights when I was shooting bullseye pistol. I know it's round somewhere and I think I've got a bottle of carbide chunks left.
 
With the Berger 115FB and a bushing 0.004 smaller than the loaded round neck diameter used to measure the jam length, and measuring "touch" using the Sinclair tool, the difference in my 30BR is about 0.020.
 
tobybradshaw said:
With the Berger 115FB and a bushing 0.004 smaller than the loaded round neck diameter used to measure the jam length, and measuring "touch" using the Sinclair tool, the difference in my 30BR is about 0.020.
Click to expand...

Thanks for that info Toby. That's the first figure I've got from anyone that I can use for comparison. So I decided to go to my reloading shed this morning and try to visualize. what these numbers looked like. 62 sounds like a big number so I set .062 in my dial caliper. That didn't look real big when looking at the distance between the caliper jaws. .020 looked pretty small. So, for grins I measured the thickness of the paper the instruction sheet for the Sinclair tool is printed on. That came to .006. That was an interesting exercise. Shows that we're working with really small distances here. But, just how small?

Last year I was going through some boxes in my workshop and came across three slides rules I had used in the ancient times. I remember someone saying back then that one of the characteristics of a slide rule is that you had to know where to put the decimal point in the results you obtained from the slide rule. So you had to know just about what the right number was. The slide rule gave you the precision in the numbers to the right of the decimal point.

So, what I've been trying to do is see if I can find some value that gives me some assurance that the results I get from my measuring is "reasonable". Obviously this will vary for different shape bullets. But, it would be nice to have a way to quickly know if my results are out of whack.

Well, we've got at least a couple of days of cold and rainy weather coming at us here so, I'll just crank up the heater in my reloading shed and have some fun pursing this.

Thanks to all the posters who provided so much valuable insight. Gives me a lot to work with. I think my "AHA" moment came last night. Now I just need to put what I've learned to work and experiment and validate.
 
As a practical matter, all that is needed is a starting point that you can reproduce reliably. Once you have that, you can change your seating depth to optimize your results, and return to that setting when you need to compensate for throat wear.
 
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