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Topic: Where are the lands? A measurement technique comparison  (Read 3713 times) previous topic - next topic

Where are the lands? A measurement technique comparison

I finally got over my fear of pulling apart the bolt from my Browning X-bolt in order to measure my distance to lands using what I'll call the bolt technique.

The technique was brought up in another thread by @jvw2008 and may be seen here:

https://youtu.be/TWmIwPwLyyg

It requires removing the ejector and firing pin from the bolt so that there is no tension when closing and opening  it.

The other technique is one we all probably use or have tried; the Hornady OAL gauge, aka the Stoney Point gauge. I won;t go into the details of this technique as it's so widely used.

The bullet used here is a random sample Hornady 140 gr Match BTHP. The rifle is a broken in Browning X-bolt Target.

I measured CBTO with the Hornady gauge 10 times, the results appear in the chart below. Frankly, I was surprised at the spread over these measurements as I consider myself an accomplished OAL gauger, lol, guess I know better now. I included an 0.006 adjustment factor derived by considering the generic Hornday case base-to-shoulder versus the actual case base-to-shoulder.

For the bolt technique I followed the video, seating the bullet down by 0001 until there was absolutely no "feel" or click when lifting the bolt. For CBTO I used 0.001 above this point because that's precisely where the bullet contacts the rifling.



The yellow rows on the spreadsheet show the difference between the two techniques for average, median and mode numbers using the Hornady gauge.

The best case, using the mode, is 0.013 difference versus the bolt method. If we use the average there's a 0.020 difference.

Looking back in my notes I've been using a Hornday gauge measurement for this rifle/bullet of 2.202, how's that for throat erosion?

If I believe the bolt technique is accurate, and I do, that means when I say my rifle likes these bullets seated 0.013 OTL, what I'm most likely saying is it likes 0.000 OTL or jam. That's best case, maybe it likes +0.007 jam.  :o

Here's an interesting side note: I could not use Alpha brass for the bolt technique. Even when body and neck sized they fit sufficiently tight in the chamber that there's always bolt lift click, even without a bullet. I had to use some Starline brass which worked just fine.

Chris

Re: Where are the lands? A measurement technique comparison

Reply #1
No matter what method is used, the number is a baseline number unique only to that rifle/bullet combo.  All load development is then based on that baseline.  With the seated bullet in a case an accurate measurement of CBTO can be used as a comparison using the same comparator tools on all loaded ammo. I try to always load a dummy with my test bullet ATL and color it with a Sharpie to double check for lands just touching my mark.  But I expect them because of ejector/extractor pressure. I also measure the dummy for a CBTO baseline.
My method uses a measurement from bolt face to bullet tip on three or more bullets at jam (feel) using a brass rod from the muzzle. The rod has two "sliding" blocks with thumb screws, one is removed while the muzzle to bolt face is found and locked. The second block is reinstalled between the set block.  A bullet is gently pushed into the lands, the rod slid up to its tip, the sliding block slid to the muzzle and locked.  The sliding block is exactly 1.000 inch, i measure between the 2 blocks with a caliper and add 1" to achieve COAL. Simply subtract the tip to ogive for CBTO.  This is averaged and the average  bullet tip to ogive is subtracted from the oal average....again the number serves only as a baseline....and can be used to determine throat wear as long as the "original" test bullets are saved.
I don't know how exactly the Hornady & Stoney point gauges work but assume similar to my method.
I can measure up 4 or 5 different  bullets just a few minutes.  Usually when I install a barrel I will do 3 or 4 from every box of bullets I might use in that barrel.

My baseline, my method and my.02 ; right or wrong!
11X Grandfather
Part time Savagesmith

Re: Where are the lands? A measurement technique comparison

Reply #2
I'd like to add a note:

With the Hornady gauge it was hit or miss if the bullet came out with the tool, or I had to bump the rifle stock on the floor, or I had to use a rod to tap it out. I can't say I observed any correlation between how easy or hard the bullets were retrieved with the measured CBTO, in all fairness I wasn't looking for that. I do recall with certainty the first 4 bullets came out with the gauge, still, the spread for those four is obvious from the numbers.


Chris

Re: Where are the lands? A measurement technique comparison

Reply #3
Homemade...story of my life!

An old bolt body serves as a starter tube for the bullets.  Push the bullets up to the lands with a straight section of a plastic coat hanger.  By pushing back with the brass rod and the bullet between the two, the "feel" of the lands can be found. (The brass cleaning rod also as a flat plastic tip fashioned from an old jag.).
Also once the measurement is made the bullet is then tapped back into the "feed" tube.  The tube then is extracted and the bullet dumped into your hand.  Before I added this feature you sometimes ended up having to turn the gun upside to retrieve the bullet, this is way faster leaving it in the gun vise.
11X Grandfather
Part time Savagesmith

Re: Where are the lands? A measurement technique comparison

Reply #4
Definitely agree on the differences in measurement.  The "feel" is all important.  Having control of Both sides of the bullet let's you adjust this some what.
11X Grandfather
Part time Savagesmith

Re: Where are the lands? A measurement technique comparison

Reply #5
Either way is correct because it's a number only good to you.
If you think it's .02 off and you work a good shooting load using that number
or adjust either way from it, then you just keep measuring from the same number even if it's
not the "actual" number from the lands.
Doesn't matter if it's .02 or really .05
as long as the load groups well for you.




Re: Where are the lands? A measurement technique comparison

Reply #6
I have to do some research on how the Hornady tool works.  My method is based on something similar I read about years ago.
11X Grandfather
Part time Savagesmith

Re: Where are the lands? A measurement technique comparison

Reply #7
Either way is correct because it's a number only good to you.
If you think it's .02 off and you work a good shooting load using that number
or adjust either way from it, then you just keep measuring from the same number even if it's
not the "actual" number from the lands.
Doesn't matter if it's .02 or really .05
as long as the load groups well for you.

True and that’s “good enough” , unless you also need an accurate measurement of lands erosion.





Re: Where are the lands? A measurement technique comparison

Reply #8
Just watched a video of the Hornady tool...the modified case may be shorter than the actual headspace of the rifle.  That may account for some of the discrepancy between the You-tube method and the Hornady.
11X Grandfather
Part time Savagesmith

Re: Where are the lands? A measurement technique comparison

Reply #9
You will definitely get a more uniform reading using a modified case made from a case fired in your chamber. With the right drill bit and tap it’s easy to make your own but I don’t recommended it unless you have a lathe or mill to get a concentric attachment with the Stoney Point (Hornady OAL) rod.

Note: even when you use a chamber compatible case, Bullets with a shallow transition to the ogive (VLD,Hybrids) will not be sensitive enough to your touch to determine the “kiss” of the lands.

Re: Where are the lands? A measurement technique comparison

Reply #10
I use the hornady tool. The one thats curved.. its got a flexible cable in it.. i push the bullet up in the lands till the cable starts to flex.. lock it in place and take a woden dowel in the muzzel end and tap the hornady tool and bullet out.. can get pretty repetitive results doing this.. i have no doubt im jaming the lands a little since i have to tap the bullet out to remove it but like has been said its just a number for me and only me..
Grant

Re: Where are the lands? A measurement technique comparison

Reply #11
I use the "Wheeler" method exclusively on my benchguns and the Hornady tool is good enough for everything else.

.025" jam seems 😲 like a lot but we tend to forget we are talking about 25/1000ths of ONE inch sometimes. When I'm doing the Wheeler method I  seat the bullet at least .050" long in a fairly light neck tension lubed neck the first time and chamber the dummy round letting the lands push the bullet into the neck as far as it can then eject it. This gives you your "jam length" or seated to jammed number. After getting my "touch and off the lands numbers" ive never had one jammed over .025" and  I've never stuck a bullet in the lands using this method.

A jam of .006 - .010 is nothing in the grand scheme of things but it sure makes a huge difference on the target if your gun likes it.

I have stuck the bullet using the Hornady method, enough times that I always have a cleaning rod with a blunt tip in the bore and hold the bullet between it and the Hornady plunger and always get more consistent numbers with much tighter short and long numbers.

Dave

Re: Where are the lands? A measurement technique comparison

Reply #12
The sensitivity of the bolt technique is something I cannot overstate; its so obvious it's ridiculous, in a good way.

Now that I know how to remove the ejector and the firing pin from an X-bolt, I have no reason to use another method with this particular rifle.

Chris

Re: Where are the lands? A measurement technique comparison

Reply #13
Chris knowing what you know now will you keep seating your bullet the same.. knowing its jammed
Grant

Re: Where are the lands? A measurement technique comparison

Reply #14
Chris knowing what you know now will you keep seating your bullet the same.. knowing its jammed

That's a good question Grant. I don't think it's jammed right now since I've been seating to 2.195 CBTO and the bolt technique says 0.000 jam is 2.213 CBTO. Technically I'm 0.018 OTL.

Part of this is I think is me conflating CBTO with OTL. CBTO is what it is; it's a repeatable measurement. Off-the-Lands only means something if we know where the lands are. If I say I seat 0.013 OTL that means something to most people, if I say CBTO 2.195 it means nothing to anyone but me.

I need to be more careful when I believe, and state, a number as real when it's based on another number that may or may not be real.

But to answer your question, I'm gonna keep seating with the same CBTO until the rifle tells me otherwise, which for the time being is .018 OTL :)
Chris