Measuring "to the lands"
- Thread starter itchyTF
- Start date
It takes very little effort to stick the bullet in the lands. I drop a small piece of brass tube down the barrel held vertical to unstick. Examination under magnification shows a small line on the bullet, not a "square".
The measurement is relative, anyway. As long as you measure consistently and keep good records of your loads and performance, a few thousandths variance from another shooter's technique does not mean much.
The measurement is relative, anyway. As long as you measure consistently and keep good records of your loads and performance, a few thousandths variance from another shooter's technique does not mean much.
Forum Boss
Administrator
My technique with the Hornady tool has proven pretty repeatable -- I can usually repeat a measurement (with the same bullet), 3 times with .002" or less total spread (e.g.: X.346, X.348, X.347). With practice, it's quite possible to hit the exact same length 2 out of three times (e.g.: X.347, X.345, X.347).
PREP
1. Make sure your chamber is very clean (particularly the shoulder.
2. Make sure the modified case is seated securely.
3. Make sure the rod is not under tension by the lock screw before measuring.
4. Have a wood dowel available to aid extraction.
Measuring
1. When you insert the modified case into the chamber, make sure it is seated tight and flush against the chamber shoulder. You may have to push pretty hard on the back of the Hornady tool (the aluminum collar NOT the push rod) to seat the modified case correctly.
2. With the pad of a finger, TAP the end of the push rod gently 4-5 times. After 4-5 taps, apply a gentle pressure just to make sure the tapping hit the lands. You are NOT trying to push it in further -- just confirm your tapping stop point.
TAPPING Gently is the key to the technique. Tap don't shove.
3. If you have a helper, insert the wood dowel to contact the bullet as you extract the Hornady tool.
4. If you don't have a dowel and the bullet gets stuck, use a drop rod (a short piece of smaller-than-bore diameter brass rod).
REPEAT so you have at least two measurements per bullet.
I try to measure at least THREE bullets per box, and I measure each twice. That will give you six measurements, which will usually cluster around a clear point, give or take a thousandth.
When to re-do the measurement
I remeasure my distance to the lands every 100 rounds or so. This helps keep me in touch with the "point of first jacket to barrel contact" as the throat erodes. NOTE: It is common, with a new barrel, to see the "point of first contact" jump forward .005-.008" after 70-100 rounds, but then stabilize. This occurs as high points or imperfections in the lands burnish off.
PREP
1. Make sure your chamber is very clean (particularly the shoulder.
2. Make sure the modified case is seated securely.
3. Make sure the rod is not under tension by the lock screw before measuring.
4. Have a wood dowel available to aid extraction.
Measuring
1. When you insert the modified case into the chamber, make sure it is seated tight and flush against the chamber shoulder. You may have to push pretty hard on the back of the Hornady tool (the aluminum collar NOT the push rod) to seat the modified case correctly.
2. With the pad of a finger, TAP the end of the push rod gently 4-5 times. After 4-5 taps, apply a gentle pressure just to make sure the tapping hit the lands. You are NOT trying to push it in further -- just confirm your tapping stop point.
TAPPING Gently is the key to the technique. Tap don't shove.
3. If you have a helper, insert the wood dowel to contact the bullet as you extract the Hornady tool.
4. If you don't have a dowel and the bullet gets stuck, use a drop rod (a short piece of smaller-than-bore diameter brass rod).
REPEAT so you have at least two measurements per bullet.
I try to measure at least THREE bullets per box, and I measure each twice. That will give you six measurements, which will usually cluster around a clear point, give or take a thousandth.
When to re-do the measurement
I remeasure my distance to the lands every 100 rounds or so. This helps keep me in touch with the "point of first jacket to barrel contact" as the throat erodes. NOTE: It is common, with a new barrel, to see the "point of first contact" jump forward .005-.008" after 70-100 rounds, but then stabilize. This occurs as high points or imperfections in the lands burnish off.
Seems something important may be missing here:
The guage case may be shorter than the chamber, if so your measurement will be short by the amount of excess headspace.
What I do is stick bits of scotch tape onto the back of the guage case then try to close the bolt on it. I keep adding tape until I get resistance to closing the bolt. I then peel this mass off the back of the bolt and measure it.
The guage case is then lightly abraded with a scotch brite and a sharpy is used to mark ".00X short" so that I won't forget in the future.
The guage case may be shorter than the chamber, if so your measurement will be short by the amount of excess headspace.
What I do is stick bits of scotch tape onto the back of the guage case then try to close the bolt on it. I keep adding tape until I get resistance to closing the bolt. I then peel this mass off the back of the bolt and measure it.
The guage case is then lightly abraded with a scotch brite and a sharpy is used to mark ".00X short" so that I won't forget in the future.
BoydAllen
Gold $$ Contributor
All that is needed is a starting point that is consistent from measurement to measurement. Once a measurement has been obtained, different lengths that or longer or shorter, will invariably be tried, until the seating depth that gives the best result is found. Once is has been, it needs to be recorded, and the difference between it and the initial measurement noted. for instance, if a rifle bullet combination works best loaded say .020 shorter than the measurement, then as long as the drilled and tapped case is not changed, that relationship can be used. By checking for throat wear from time to time, adjustments may be accurately made to compensate for wear. It matters not that there was a slight difference between "headspace" of the case used to measure and that of the chamber, as long as that difference is constant. It is like measuring with a ruler that is off. As long as all measurements are made with the same ruler, everything should fit just fine. Note, this is not a defense of inaccurate measurement, just an example.
Just a quick note on "drop rods".....Make sure you REMOVE it from the barrel after use. This applies to cleaning rods, dowels or whatever is used to push the bullet back out. I believe that the drop rodss are the easiest to forget, and there have been several serious injuries, some by competitors with decades of experience. A good practice is to look through the bore for obstructions before replacing bolts.
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