understanding the lands

[Tim Singleton]

I'm still not seeing the point in knowing the location of the lands with such precision. Are you BR guys not testing your changes and making seating adjustments based purely on the measurements? If you are testing, then why does it matter exactly where the lands are? Seems like being within a couple thous is plenty.

With the ogive Bullets a lot of us use it is fairly critical to begin testing at the touch point or as close as you can. YES a few thousandths make a difference from placing in the top 5-10 or shooting for middle of the pack.
All I am saying is the Stoney point tool can't get you even in the ball part of what your actual touch point. Being off from where the gun is in tune can be as little as .005" that will take you from contention to wondering what happened
This is Accurateshooter if any of you don't want to take the free knowledge that has came with great cost and time spent in competition that's up to you. None of us have to share
That said I'm going out the door testing a new barrel today

 

[dcali]

The point is that you don't need to know where the lands are to test down to the thousandth. You just need a reference datum, and it's convenient if that datum coincides with the lands. But what is the big deal if it's off by 3 thous? I get wanting to know, but at the end of the day, do you not test your loads based on CBTO, whatever the lands might be doing?

Suppose you have a perfectly tuned load with a CBTO of 2.000". You think this is right at the lands. But it they could be off by .002" either way.

Now, you shoot a bunch and decide to check the lands again. You find them to be at 2.005" (again plus or minus .002"). Now if it's me, if it's not still shooting well, I'm going to start a new round of testing at 2.005" CBTO on the hypothesis that just touching the lands is the right way to go (based on my previous tune). Why do I care where the lands are *exactly*? What do you do that's different from what I described?

 

[Tim Singleton]

The point is that you don't need to know where the lands are to test down to the thousandth. You just need a reference datum, and it's convenient if that datum coincides with the lands. But what is the big deal if it's off by 3 thous? I get wanting to know, but at the end of the day, do you not test your loads based on CBTO, whatever the lands might be doing?

Suppose you have a perfectly tuned load with a CBTO of 2.000". You think this is right at the lands. But it they could be off by .002" either way.

Now, you shoot a bunch and decide to check the lands again. You find them to be at 2.005" (again plus or minus .002"). Now if it's me, if it's not still shooting well, I'm going to start a new round of testing at 2.005" CBTO on the hypothesis that just touching the lands is the right way to go (based on my previous tune). Why do I care where the lands are *exactly*? What do you do that's different from what I described?

A lot I imagine.

I don't know what you shoot or what your shooting system is. It may very well be that you can't see the difference. So you wouldn't care to much

 

[Toby Bradshaw]

The point is that you don't need to know where the lands are to test down to the thousandth. You just need a reference datum, and it's convenient if that datum coincides with the lands. But what is the big deal if it's off by 3 thous? I get wanting to know, but at the end of the day, do you not test your loads based on CBTO, whatever the lands might be doing?

A short-range BR barrel has a competitive life of approximately 700 rounds -- maybe 10-12 grand aggs. For a new barrel it takes 40-50 shots to test powder charges and seating depths if you use just 1 powder and 1 bullet and 1 neck tension. Re-doing load development even one more time during the life of the barrel takes roughly 1 grand agg out of the barrel's life.

In my experience, once you have the right seating depth in relation to the lands, you can tune for changing conditions with powder charge (and, maybe, neck tension). It's common to go to the line with 2 or 3 different charges to test on the sighter during a match.

Periodically you measure throat advancement and adjust seating depth accordingly, especially if you are seeing a problem on the target. No way would I do a whole load development AGAIN -- it's a waste of precious barrel life.

And, if you can measure the relevant variable exactly -- the seating depth where the bullet is touching the lands -- why would you use a less precise/approximate method that takes just as long and requires another tool?

Probably the most common reference point for the lands in short-range BR is the jam, and this certainly works. The advantage of Alex's method is that the measurement to the lands is repeatable and can be communicated to other shooters, whereas jam length depends on neck tension, which can be quite different between different shooters and can even change for the same set of cases as they work-harden.

 

[spife7980]

I'm still not seeing the point in knowing the location of the lands with such precision. Are you BR guys not testing your changes and making seating adjustments based purely on the measurements? If you are testing, then why does it matter exactly where the lands are? Seems like being within a couple thous is plenty.

So you would rather use some arbitrary point in space? How could having an exacting measurement not be entirely better than not having it?

I guess for some ignorance is bliss

 

[fyrewall]

I am not a bench rest shooter, don't use custom bullets and load bullets just out of the box. I usually can buy on sale 87 Hornady V max at under $20 per box and 105 hpbt for a little more. I just bought a bunch of 87's at Cabello's for a real good price.

I think measuring an ogive by feel to .0005 (tiny) really does not mean much because the ogives might vary much more than that for each bullet. My Rem700 .243 W is over 20 years old and has about 2500 rounds through it. For some reason the rifling at the bottom of the throat has been eroded away but the top at like 10 - 2 o'clock looks much better. My other .243 W is a Ruger M77 MKII, control feed, and has less than 200 rounds.

Loading the 87 grain Hornady V Max, 2 different seating depths are used. For the R700 the bullets are seated so they touch the rifling (3 out of 6, 6 L&G). For the Ruger I seat the bullets at .01, determined by actual shooting, back from where 1 of the 5 dummy round contacted. I do this by sight, using engraving marks on a ink covered surface.

My .01 set back is done by using my seating die as a gauge. I remove the die from the press, put the dummy round that shows an ink coated bullet that barely contacts the rifling in the die and measure, using my caliper from the cartridge base to the top of the knurled knob when twisted adjusts seating depth and record that measurement, for reference, for Rem. & Ruger .243's and 6mm AI. Then the die is placed back in the press and height of the knob from the lock ring of the seating stem adjust is measured by using the tab on the tail of the caliper. The desired seating depth for the Ruger is done by subtracting .01 from that measurement, locking the caliper, then screwing in the adjust stem in by .01 inch. The total measurement from the base of the cartridge to top of adjust is recorded for each rifle and kept with the seating die. I use Hornady seating dies and the same 6mm die is used for the .243's and 6mm AI.

I don't really know how much variance exists for ogives in my bargain bullets. I can determine where the ogives do barely contact by sampling 5 bullets and either leave my seating depth there (3 out of 6, R700) or seat deeper .01 for the new control feed Ruger. My easy & casual standards are not of BR quality but I load many rounds. I am concerned with neck tension to hold bullets because at times rounds are fed from the magazine of the Ruger into the chamber for a fast 2nd shot or even a 3rd to jam some fleeing varmint that has just jumped.

I always try to learn new stuff and avoid defending the indefensible. Lacking specialized tools it would take me almost 30 minutes to remove and replace the ejector of my Rem 700, my seat by sight method allows compression of the ejector. Possibly, I will get specialized stuff to allow removal and replacement of the ejector but about 5 minutes vs. 10 seconds seems realistic for my abilities and would allow inspection and cleaning.

Should I actually measure ogive position and determine locations to .001 and want to determine extremes I would measure 15-20 ogive positions then subject this to a 95 % normal distribution confidence level test and look for those that would fall into the 2.5 % on each end of the distribution (short or long). This would provide an idea what could be expected for a larger ammo production of 500 or more rounds, like for a entire season of shooting. This would also provide some idea of the difference between buckets of $20 and $37 per box bullets. How far away would the extremes be from my .01 departure from land contact? I might buy the needed stuff and do this; would I be disappointed after comparing $20 to $37 per box bullets? Should the ogives of all these bullets vary, any expectation of an meaningful exact measurement would not happen and true references would vary with ogive position. Any info out there on the PTG ogive gauge that looks like a hex nut with holes drilled in it - $27.

 

[dmoran]

@damoncali -
I can agree, the point of contact is kind of a hypothetical.
But the repeatability and accuracy of the method used, is what is vital to me.
The "stripped bolt method" is by far the best method that I've ever used.
Within a 1/2-thousandths is what I myself feel I can repeat.
It being a true reference of the bullet to the lands is icing on the cake
Donovan

 

[spife7980]

Lacking specialized tools it would take me almost 30 minutes to remove and replace the ejector of my Rem 700, my seat by sight method allows compression of the ejector. Possibly, I will get specialized stuff to allow removal and replacement of the ejector but about 5 minutes vs. 10 seconds seems realistic for my abilities and would allow inspection and cleaning.

Should I actually measure ogive position and determine locations to .001 and want to determine extremes I would measure 15-20 ogive positions then subject this to a 95 % normal distribution confidence level test and look for those that would fall into the 2.5 % on each end of the distribution (short or long).

Well it takes me all of 45 seconds to remove the ejector with a finishing nail and a hammer...
It takes me about 45 seconds to remove the firing pin as I have to put on an old sneaker that has shoe laces...
No special tool needed. Its only pushing one 1/2" pin out and unscrewing.

Leave the 20 ogives and confidence intervals at home, nerd. Test three bullets and youll find that you get the same number each time. And a thousandth (or half of that which is what people are referencing) isnt a big deal here but knowing that the loose neck and jam method is actually .015 jammed and not the point where you first touch the lands is useful information.

 

[kvd]

@damoncali -
I can agree, the point of contact is kind of a hypothetical.
But the repeatability and accuracy of the method used, is what is vital to me.
The "stripped bolt method" is by far the best method that I've ever used.
Within a 1/2-thousandths is what I myself feel I can repeat.
It being a true reference of the bullet to the lands is icing on the cake
Donovan

Bullet comparators like the Bob Green tool and Sinclair/Wilson seating dies with 0.0005 click adjustments in conjunction with the stripped bolt method of finding the lands enhance the repeatability and accuracy of bullet seating as well.

 

[dmoran]

@kvd -
Agree 100%...... which I do...... (not a Bob Green, but my own).
Donovan

 

[Richard Coody]

so what you guys are saying is that your seating depth accuracy node with these competition rifles is only .001 or even .0005 wide?

is that standard? i find my seating depth nodes are much more forgiving than that. no wonder jams are so popular in benchrest. chasing the lands with only .0005 to play with would get kind of tedious.

 

[dmoran]

Wow... ^^^^^ ..... now that's being silly

 

[Toby Bradshaw]

so what you guys are saying is that your seating depth accuracy node with these competition rifles is only .001 or even .0005 wide?

No. But the window is only a few thousandths wide, and you need to know where you are since the throat is eroding (lengthening) with every shot.

I've already (re)posted a charge/depth test for my 30BR, with 0.005" difference in seating depth between groups. The effect of seating depth is obvious. Maybe Tim will repost a 6PPC charge/depth test that shows the width of the seating depth window for one of his barrels.

You could also read Tony Boyer's book.

 

[fyrewall]

Well it takes me all of 45 seconds to remove the ejector with a finishing nail and a hammer...
It takes me about 45 seconds to remove the firing pin as I have to put on an old sneaker that has shoe laces...
No special tool needed. Its only pushing one 1/2" pin out and unscrewing.

Leave the 20 ogives and confidence intervals at home, nerd. Test three bullets and youll find that you get the same number each time. And a thousandth (or half of that which is what people are referencing) isnt a big deal here but knowing that the loose neck and jam method is actually .015 jammed and not the point where you first touch the lands is useful information.

I am sorry that my post annoyed you.

By any chance would you happen to have any valuable info to share on the validity of the various ogive comparator tools that have been sold for some time which in most instances would be used to sample more than 3 rounds of ammo. Statistically a sample size of 3 is inadequate for most sampling and measuring 100's of rounds of ammo or more.to determine ogives would be a waste of time - thus a reasonable number of 20 was suggested to get some idea of what would be expected for values on each side of the 95 % confidence distribution. Playing around with this stuff would not be needed if the ogives of these 3 bullets were the same as every bullet in the box but seeing a variation on first contact positions I doubt this is true. We appear to be into a discussion where tolerances of .001 are considered. Could I guess some standard penetration (jam) of .015 inches into some chamber throat to reach some standard might not work for every chamber due to less than fine BR gun-smithing, uneven wear or variations in leade angles.

Thank-you for the info on pin removal. 45 seconds is 4.5 times longer than 10 seconds and nails are real cheap - the time interval is growing.

This stuff is real educational and I am sucking up info like a sponge - so far I have read that assumptions are made that ogive positions are equal using a sample of 3, seating depths of down to .0005 can be done by feel, .015 inch (jammed?) is sort of a standard, tolerances down to .0002 between bullet and chamber are considered, a wide range of opinions like "touch point" and "jammed" are presented, measuring chamber dimensions down to .0005 to .0002, and lots of other mega precise stuff..

All of this began with an inquiry concerning COAL using the non-bench rest 87 grain Hornady VMax bullet and quickly morphed into a real esoteric exchange, unfortunately including my quickly dismissed statistical stuff that approached social unacceptability. I hope the OP gets good results with his 6 BR & 87 Vmaxes.

My plans now are to acquire a Magneto speed and a PTG comparator. Selecting my .20 Practical rodent rifle I will experiment with Alliant AR comp and IMR 8208 and the 40 grain H VMax bullet. I will record velocities to determine average max (up) and min (down) using a 95 % distribution with a number of cases (not of the brass type) ranging from 50 to 1000 expecting the differences between max (up) and min (down) to be less upon increasing the number of cases (not of the brass type). This should give me an idea of what I could expect upon actual shooting. Striving for some aggregate in the "ones" at 100 yards would be a foolish and impossible consideration, possibly resulting in social ostracizing out on the prairie, but some of the BR techniques would be of value. Taking multiple shots at tiny targets at extended ranges and maintaining a good "batting" average (frequency of hits) would make velocity variations resulting in drop values a consideration. The 95 % confidence level should prove to be useful in selecting a powder and load to provide optimum results for practical extended range rodent shooting. Why not?; some of this stat stuff is in the Berger manual. Supplied chrony software usually includes the socially acceptable S.D. (standard deviation); the S.D. is a required calculation for confidence distributions.

The PTG bullet comparator, should provide an idea of the ogive quality of the 40 gr. VMax and other bullets. Not being OCD, I don't intend to measure all the 1800 bullets including .20's, .22's, .24's, and .26's or play around with .0005 seating depths but I will sample 20 of each type and using a 95 % confidence level see what might be expected for the rest of the 800 to 200 of a certain type looking at variations within each lot. Possibly limited accuracy testing might show differences. I would expect some microns of erosion to occur every time I pulled the trigger.

This thread is 3 pages long!; it was kicked off by a simple inquiry about COAL with 87 VMax bullets using a 6mm BR. Hopefully, my planned thread where I play around with some simple stats will result in the same interest - if not I will a have a useful tool somewhat like the discussion in the Berger manual.

 

[Toby Bradshaw]

Thank-you for the info on pin removal. 45 seconds is 4.5 times longer than 10 seconds and nails are real cheap - the time interval is growing.

Watch this, and count. Less than 10 seconds.

All of this began with an inquiry concerning COAL using the non-bench rest 87 grain Hornady VMax bullet and quickly morphed into a real esoteric exchange ...

The OP got the right answer from Donovan in the second post in this thread. Since then it's been mostly pig wrestling.

My plans now are to acquire a Magneto speed and a PTG comparator.

And yet you can't afford the tools to strip a bolt?

For field shooting you'd be better off to skip the chrono, learn to find the lands, and let the targets tell you what you need to know.

I'm out.

 

[LHSmith]

i really would like to have a quality 6ppc and learn how to shoot short range benchrest. getting close to retirement. maybe then i will have the time to try a few matches. which is more fun score or group

Score shooting is my passion.........the 30 BR and its variants have a much longer competitive barrel life and from my neck of the woods I could find a registered tournament virtually every week-end from March through November.
I bet Alex's vid has sold a lot of Sinclair bolt disassembly tools. I gave in-got tired of jerry-rigging homemade tooling (including using nails where a proper roll pin punch is called for) for the task.

 

[UltraBR30]

Shortly after Alex made the video I tried it out. after a few goes at it could see how it was consistently more accurate then the stoney point method I had been using for years and switched to it instead. Ended up all my stoney point measurements that I had been using were .012 to .016 different of Alex's way and actual touch. went from figuring I was .010 to .020 off the lands to actually being slightly into or near the lands. what a wake up it was for me. Thanks Alex for that video.
Phil

 

[Richard Coody]

i have often wished my borescope was long enough to see a bullet and its relationship with the lands.

 

[Ledd Slinger]

so what you guys are saying is that your seating depth accuracy node with these competition rifles is only .001 or even .0005 wide?

is that standard? i find my seating depth nodes are much more forgiving than that. no wonder jams are so popular in benchrest. chasing the lands with only .0005 to play with would get kind of tedious.

People who compete want to win. Groups are measured in thousandths of an inch. In the BR world, these guys are pushing rifle building, load testing and other methods of conquering world records to the next level all the time. IF you want to win, you better have your ducks in a row and pay close attention to every little detail because you can bet the guys who are consistently at the top of the pack are surely doing so. Every .001" in that group size matters for BR.

Unfortunately, I can't devote the time and effort into the testing and development at this point in my life like these guys do so I don't compete. If I can't get to the level where I know I will win, I see no point in spending the time on it. Perhaps later in life I will re-visit competition shooting. For now, I just stick to my hunting and varmint shooting. However, I still watch, read, and learn from the best shooters and gunsmiths all the time and employ their methods in my hunting and varmint rigs to achieve the highest levels of accuracy my rifles are capable of. I know first hand that these methods work and will improve accuracy with any rifle if done correctly.

 

[lpreddick]

Shortly after Alex made the video I tried it out. after a few goes at it could see how it was consistently more accurate then the stoney point method I had been using for years and switched to it instead. Ended up all my stoney point measurements that I had been using were .012 to .016 different of Alex's way and actual touch. went from figuring I was .010 to .020 off the lands to actually being slightly into or near the lands. what a wake up it was for me. Thanks Alex for that video.
Phil

I came across a problem using Alex's procedure. The first few bolt lifts after seating the bullet were easier as the bullet was backing out of the lands, then lift had a slight hesitation and did not quit even as I seated the bullet's pressure ring thru the neck-shoulder junction??? I was well off the lands and I still felt slight resistance to bolt closure as if the bullet was going into the lands. Problem solved: my chamber is tight and i didn't turn the necks if these cases. This bullet was longer than ones previously sucessfully measured. The pressure ring in the lowest part of the neck was measured slightly over chamber diameter and was jamming in this part of the chamber. Turn this neck and remeasured per his video and all is well.