Some Help Finding my Lands

[Aaron N]

So I bought a CZ550 in .375, and have been working on loads for it since. Im using 250gr TTSX's, which Barnes recommends starting .050 off the lands. To find the COAL of the cartridge touching the lands, I've been using a brass that i have cut a slit in the neck so the bullet can move freely. This seemed to work good, giving me consistent results every time i chambered the shell. So i made a batch up and tested the loads out at the range. Now I want to fiddle with the seating depth, so double checking my COAL again, it gives me a different length. Has anyone experienced this?

 

[Clayton]

The plug in your seating die may be crushing the exposed lead tip? That and how the plug fits the ogive comes into play.

 

[BRICKBURN]

Do you mean the case is now
Longer after being fired?

 

[Aaron N]

Alright maybe I'm not being clear, my bad. To find where my lands are I use a brass that has been sized with a slit in the neck so the bullet can be pushed in as I chamber it, and stay in place when I eject it, which in theory should give me the COAL of the bullet touching the lands. This seemed like the easier option than buying a tool to find it. This seems to work good. I can do it ten times in a row, and get the same measurement.

My problem is that I loaded 20 cartridges at X length being .050 off the lands. Those were shot, a powder charge decided on, so now I want to try different seating depths. So just to double check, I use this same brass with the slit and now I'm getting a measurement that is close to .030 off the original. This is the third time that I have gotten different measurements after developing some loads then shooting them and coming back later on.

 

[Clayton]

Most all my seating depth problems went away after I started using Forster Seating Dies and these http://www.brownells.com/reloading/...r-hex-style-bullet-comparators-prod83792.aspx Seating Gages. I don't worry about COAL as much as maintaining that 0.050" jump to the lands.

 

[Aaron N]

Most all my seating depth problems went away after I started using Forster Seating Dies and these http://www.brownells.com/reloading/...r-hex-style-bullet-comparators-prod83792.aspx Seating Gages. I don't worry about COAL as much as maintaining that 0.050" jump to the lands.

My Dies give me consistent seating. Its the land depth that seems to be changing after a range session.

 

[Clayton]

Are your loaded rounds Full Length or Neck sized, the same as your "gage" standard you use to measure. If they're not the same, maybe headspace is coming into play. If one headspaces on the shoulder and the other on the belt, you could see a minor difference.

 

[Clayton]

Is the measurement growing or getting shorter? Growing would mean maybe throat erosion and shortened up may be a carbon build up. Either scenario is unlikely and hard to believe would produce changes of any measurable amount in a few rounds fired.

 

[Buckdog]

get the lok n load bullet comparator kit from hornady it used to be stoney pt but you can measure at the ogive of the bullets not the tip trying to measure case overall length at the bullet tip isn't very accurate round to round, make sure you sort your cases at least by the number of times fired. also sometimes on a really compressed load of powder bullets wont seat the same the tip gets smashed more as you crunch down the powder with the bullet. lands depth in your chamber is not changing in one range session that takes thousands of rounds to erode the throat!

 

[lcq]

get the lok n load bullet comparator kit from hornady it used to be stoney pt but you can measure at the ogive of the bullets not the tip trying to measure case overall length at the bullet tip isn't very accurate round to round, make sure you sort your cases at least by the number of times fired. also sometimes on a really compressed load of powder bullets wont seat the same the tip gets smashed more as you crunch down the powder with the bullet. lands depth in your chamber is not changing in one range session that takes thousands of rounds to erode the throat!

+2 easiest and fastest way to accurately know where your lands are

 

[PHOENIX PHIL]

Alright maybe I'm not being clear, my bad. To find where my lands are I use a brass that has been sized with a slit in the neck so the bullet can be pushed in as I chamber it, and stay in place when I eject it, which in theory should give me the COAL of the bullet touching the lands. This seemed like the easier option than buying a tool to find it. This seems to work good. I can do it ten times in a row, and get the same measurement.

My problem is that I loaded 20 cartridges at X length being .050 off the lands. Those were shot, a powder charge decided on, so now I want to try different seating depths. So just to double check, I use this same brass with the slit and now I'm getting a measurement that is close to .030 off the original. This is the third time that I have gotten different measurements after developing some loads then shooting them and coming back later on.

If you're using the same piece of brass that you were previously to do this, I can't help but wonder if the neck tension after repeated use is starting to loosen up just a bit. So now as you "seat" these bullets via contact with the lands, the lands are now able to pull the bullet back out a bit whereas before that wasn't happening.

My trick for doing this is to use a spent piece of brass and seat the bullet may 0.2" long, been awhile so I don't remember off hand. But prior to seating the bullet, I press a portion of the end of the neck of the brass against the table to form a flat spot. This will not be enough tension to keep the bullet from being pulled out, but it's enough that it will keep the bullet from falling into the case.

Once the bullet is at it's starting point. I'll "soot" up the bullet using a match. Then I put the round into the chamber and close the bolt. The bullet will of course be shoved further into the brass. The flat spot will scrape off some of the soot and leave a clean spot. So when the cartridge is removed, if the bullet moves back out of the case by any amount, the clean spot will be revealed.

If that happens and it usually does, you just slowly push the bullet back in using your press up to just when the clean spot is no longer visible. Measure the round and you now have your "max" COAL. Record the value and back off from there to get your desired distance off the lands.

I usually repeat this process a few times and average the results to be little more precise.

 

[Aaron N]

If you're using the same piece of brass that you were previously to do this, I can't help but wonder if the neck tension after repeated use is starting to loosen up just a bit. So now as you "seat" these bullets via contact with the lands, the lands are now able to pull the bullet back out a bit whereas before that wasn't happening.

My trick for doing this is to use a spent piece of brass and seat the bullet may 0.2" long, been awhile so I don't remember off hand. But prior to seating the bullet, I press a portion of the end of the neck of the brass against the table to form a flat spot. This will not be enough tension to keep the bullet from being pulled out, but it's enough that it will keep the bullet from falling into the case.

Once the bullet is at it's starting point. I'll "soot" up the bullet using a match. Then I put the round into the chamber and close the bolt. The bullet will of course be shoved further into the brass. The flat spot will scrape off some of the soot and leave a clean spot. So when the cartridge is removed, if the bullet moves back out of the case by any amount, the clean spot will be revealed.

If that happens and it usually does, you just slowly push the bullet back in using your press up to just when the clean spot is no longer visible. Measure the round and you now have your "max" COAL. Record the value and back off from there to get your desired distance off the lands.

I usually repeat this process a few times and average the results to be little more precise.

This sounds like my next plan. Thanks

 

[Clayton]

Much like Phil, I use a neck sized case and make sure there's no sizing wax left in the neck. Whatever you do, good luck and thanks for making me think for a change.