understanding the lands

[kvd]

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.

Although the question (the sentence above should end with a question mark) wasn't directed specifically at me, I would be happy to share some insights on comparators with you.

Avoid the type that are like a large nut with six different caliber sized holes drilled on each side. They tend not to be very accurate. Shy away also from caliber sized comparators in general. Why? - because first contact on the bullet ogive will be with the lands and these are sub-caliber to the bore. As an example, 6mm (0.243) lands are 0.236 or 0.237 inch depending on the barrel. Thus, a comparator that measures 0.243 would be off if using CBTO or sorting bullets by BTO. The higher priced comparators take this into consideration.

If you can handle the initial cost, a much more useful tool than a comparator that clamps to the jaws on your calipers and measures from a datum on the bullet ogive rearward, is a bullet comparator that the bullet is inserted into and measures differences in ogive curvature going forward. Now we're getting somewhere because we really want to know where the land diameter will fall on each bullet and make this as consistent as possible. The scale reading on these tools is usually 0.0001 inch.

As an illustration of how this tool is used in practice, the bullet on the dummy around used to find the touch point on the lands is used to zero the dial indicator on the bullet comparator tool. Next, bullets are measured and sorted to some desired value around the zero point. Generally, I use ± 0.0005 inch around the zero point. Bullets greater than ± 0.001 from zero are sorted into groups and the bullet seating die can be adjusted accordingly to seat these bullets at the same depth as the reference bullet. This is how one may eliminate differences in bullet ogive.

 

[daniel brothers]

Great stuff you Guys... because sometimes I feel like I live in No-Man's Lands...LOL.

 

[Tod Hendricks]

Another method I find useful, after testing to No Touch with a stripped bolt, use an ECI or other poker to push that No Touch length cartridge into the chamber, tip the rifle so as to allow the case to free fall out the chamber. You may be surprised by your results.

The case and neck need to be sized to eliminate the possibility of them sticking. Headspace calculations need to be made if you want a precise number.

Freebore diameter and bullet concentricity can come into play as well.

If it doesn’t fall out freely, something is holding/touching it

 

[fyrewall]

Although the question (the sentence above should end with a question mark) wasn't directed specifically at me, I would be happy to share some insights on comparators with you.

Avoid the type that are like a large nut with six different caliber sized holes drilled on each side. They tend not to be very accurate. Shy away also from caliber sized comparators in general. Why? - because first contact on the bullet ogive will be with the lands and these are sub-caliber to the bore. As an example, 6mm (0.243) lands are 0.236 or 0.237 inch depending on the barrel. Thus, a comparator that measures 0.243 would be off if using CBTO or sorting bullets by BTO. The higher priced comparators take this into consideration.

If you can handle the initial cost, a much more useful tool than a comparator that clamps to the jaws on your calipers and measures from a datum on the bullet ogive rearward, is a bullet comparator that the bullet is inserted into and measures differences in ogive curvature going forward. Now we're getting somewhere because we really want to know where the land diameter will fall on each bullet and make this as consistent as possible. The scale reading on these tools is usually 0.0001 inch.

As an illustration of how this tool is used in practice, the bullet on the dummy around used to find the touch point on the lands is used to zero the dial indicator on the bullet comparator tool. Next, bullets are measured and sorted to some desired value around the zero point. Generally, I use ± 0.0005 inch around the zero point. Bullets greater than ± 0.001 from zero are sorted into groups and the bullet seating die can be adjusted accordingly to seat these bullets at the same depth as the reference bullet. This is how one may eliminate differences in bullet ogive.

thank-you for the response & facts

I don't intend to sort because my accuracy requirements are not that fussy and I like to load more than 250 rounds per session - like from box to seating die.

I would like to get some idea of the ogive situation for a whole bunch of bullets for use in multiple calibers. I load ammo for 20 rifles of 10 calibers for 2 shooters that make for about 3000 rounds per year not including rodent events that add another 1000 to 1500. To get some idea of the ogive situation that would occur with a whole bunch of bullets, I plan to sample 20, then determine high and low means for a 95 % confidence range for as many bullets that I might load. Some of these rifles have over 1500 rounds through them and require different CBTO seating than the newer rifles. Should my stats show a predicted high difference between estimated means for ogive locations I would reserve these bullets for the older rifles or consider changing bullets; I would get a good idea of bullet quality considering a whole bunch of bullets. Surprisingly, even the older 1500 plus round rifles can produce acceptable accuracy like 1 moa and in the hands of a better shooter will produce better results than the newer rifles at 300 yards and beyond. These older rifles would not be selected to produce high scores at 600.

Going back to the 6 sided nut shaped comparators having a hole in each side. I don't really know what my land dimensions are, plus or minus .001 inch. Some of the older rifles show extensive erosion and asymmetrical erosion can be seen, like more on the bottom than top. These older rifles still can get 1 moa and are dependable rodent killers even on a 4 inch wide standing rodent @ 300. My thoughts are: the 6 hole comparator would show relative differences on bullet ogives independent of land dimensions and be used to gauge bullet quality.

My alibi for not having the "?" on the sentence that elicited your thoughtful response was that my editor was on the phone.

 

[Ledd Slinger]

Although the question (the sentence above should end with a question mark) wasn't directed specifically at me, I would be happy to share some insights on comparators with you.

Avoid the type that are like a large nut with six different caliber sized holes drilled on each side. They tend not to be very accurate. Shy away also from caliber sized comparators in general. Why? - because first contact on the bullet ogive will be with the lands and these are sub-caliber to the bore. As an example, 6mm (0.243) lands are 0.236 or 0.237 inch depending on the barrel. Thus, a comparator that measures 0.243 would be off if using CBTO or sorting bullets by BTO. The higher priced comparators take this into consideration.

If you can handle the initial cost, a much more useful tool than a comparator that clamps to the jaws on your calipers and measures from a datum on the bullet ogive rearward, is a bullet comparator that the bullet is inserted into and measures differences in ogive curvature going forward. Now we're getting somewhere because we really want to know where the land diameter will fall on each bullet and make this as consistent as possible. The scale reading on these tools is usually 0.0001 inch.

As an illustration of how this tool is used in practice, the bullet on the dummy around used to find the touch point on the lands is used to zero the dial indicator on the bullet comparator tool. Next, bullets are measured and sorted to some desired value around the zero point. Generally, I use ± 0.0005 inch around the zero point. Bullets greater than ± 0.001 from zero are sorted into groups and the bullet seating die can be adjusted accordingly to seat these bullets at the same depth as the reference bullet. This is how one may eliminate differences in bullet ogive.

I understand what you are saying here and it all makes sense. My question is, for the standard comparators, would it really matter if you are measuring EXACTLY where the bullet makes contact with the lands? Say I'm measuring .006" or .007" rearward of the actual contact point with a standard 243 comparator, as long as I've determined where actual contact is using Alex Wheeler's method and providing I use the SAME comparator on the same lot of bullets, the measurement should stay the same as a reference to the seating depth I need. Even if the number is not the actual true contact OAL measurement from base to lands, it would still be a valid 'reference' for knowing the seating depth at which the bullet first contacts the lands. The entire bullet moves when i change the seating depth on my die, so as long as I am measuring at the same point on the ogive all the time (which is actually very close to the lands contact point), I should know how far off or into the lands the bullet is actually sitting.

Another point to consider for my reasoning is that a seating die stem does not place force on the bullet ogive at the lands contact point either.

 

[fyrewall]

I scrounge up whatever bullets of the desired same kind I can find (sort of like going out for a bid not specific to ogive consistency) and lot ID's are usually different. A 6 hole or sided standard comparator should be an unchanging consideration provided I used the same hole for the same diameter bullets. I would then fuss around with the ogive/land distance business for my newer rifles. For the older ones, slightly contacting (for at least 1/2 of the lands) seems to work best.

I have found that some of my seating stems contact the bullet point, especially for the real long pointy ones; to fix this I drill a hole into the bottom of the stem to allow contact with the ogive vs. bullet point. Some seating stems are hard tool steel and I can't drill them deeper and if they contact the point of my pointy bullets I use these stems for bullets like the 87 VMax. I have some Hornady seating stems for intended for their long pointy Amax bullets. I get the point of ogive variances affecting seating depths because the contact point of the seating stem would be above the bullet ogive/rifling contact point.

 

[Ledd Slinger]

While on the subject of lands, bullet seating and ogives...
I always visit the 21st Century Shooting website because John is always coming up with something new to add to his offerings. Noticed he is now making custom arbor style seating dies. Machined specifically to customers supplied fired/sized brass...AND supplied bullets. So not only does he custom ream the die for the case, he also custom reams the seater plug for the bullets you are using. Claims over 1/4" of contact on the ogive while seating and it is adjustable in .0005" increments (1/2 thou). As we all know John's machining is first class. Guessing I'll have to try one of these out

Here's the link if you wanna check the new 21st seaters out
http://www.xxicsi.com/calibrated-bullet-seater.html

 

[kvd]

My question is, for the standard comparators, would it really matter if you are measuring EXACTLY where the bullet makes contact with the lands? Say I'm measuring .006" or .007" rearward of the actual contact point with a standard 243 comparator, as long as I've determined where actual contact is using Alex Wheeler's method and providing I use the SAME comparator on the same lot of bullets, the measurement should stay the same as a reference to the seating depth I need.

What you are saying is true except that the point on the bullet ogive that will contact the lands moves around even in the same lot of bullets. Consequently, if you haven't compared them for this attribute and measure only CBTO with a standard comparator, the distance the contact point is from the lands will be different depending on the bullet. The result is that what one may think the seating depth is may in fact be off by ± 0.003 or more. Does this matter? Each individual shooter must answer this question for themselves.

I plan to sample 20, then determine high and low means for a 95 % confidence range for as many bullets that I might load.

I get that a large volume of fairly accurate ammo is more the goal for some and time constraints preclude large numbers of individual measurements. I would offer this for your consideration. On numerous occasions I've seen bimodal and even trimodal distributions within a box of bullets. Should this be the case in the batch of bullets you are measuring - it would tend to ruin your statistical sample if you were to assume a normal distribution where one does not exist. It really seems to me from what you've said that it would be in your best interest, given your volume and various degrees of wear on your rifles, to simply pick a bullet you like and load it to SAAMI specifications for COAL and rock and roll.

 

[kvd]

As we all know John's machining is first class. Guessing I'll have to try one of these out

Agreed, Mr Perkins' stuff is pretty nice. I really like his neck turning lathe.

 

[kvd]

I have found that some of my seating stems contact the bullet point, especially for the real long pointy ones; to fix this I drill a hole into the bottom of the stem to allow contact with the ogive vs. bullet point. Some seating stems are hard tool steel and I can't drill them deeper and if they contact the point of my pointy bullets I use these stems for bullets like the 87 VMax. I have some Hornady seating stems for intended for their long pointy Amax bullets. I get the point of ogive variances affecting seating depths because the contact point of the seating stem would be above the bullet ogive/rifling contact point.

Some seating die manufacturers have "VLD" seating stem to accommodate the sharper bullet shapes. Clearly the seating stem must make physical contact with the bullet in order to seat it. As long as the seating stem is not damaging the bullet in some way, wherever this contact is will be okay.

 

[Ledd Slinger]

What you are saying is true except that the point on the bullet ogive that will contact the lands moves around even in the same lot of bullets. Consequently, if you haven't compared them for this attribute and measure only CBTO with a standard comparator, the distance the contact point is from the lands will be different depending on the bullet. The result is that what one may think the seating depth is may in fact be off by ± 0.003 or more. Does this matter? Each individual shooter must answer this question for themselves.

I guess the significance of measuring exactly at the point of lands contact would depend on the level of precision with which a certain bullet is produced. ie; Nosler ballistic tips vs. Hornady V-Max vs. Vapor Trail vs. Berger Target Hybrid...

I believe if I sort good quality match bullets with a standard caliber comparator (which is actually smaller than the bullet diameter BTW), then any additional variances that may be found a few thousandths distance up the ogive would be extremely minimal if any at all.

Another bit of food for thought is the angle of the lands vs the angle of the bullet ogive. Being that the area of the lands is a significant length of measurement before full height of the rifling is reached, how would you determine exactly where that lands is first touching the ogive? Marking and jamming the bullet still won't give you an exact point. Marking and touching it with the first point of contact with the Wheeler method may not leave a mark at all. Most would assume that the full height of the rifling is the first point to make contact, but as the lands wears down and develops a more secant shape, this can all change. Perhaps the full rifling height remains the first point of contact, but a larger area of the ogive is now making first contact. So now where is the most significant point to measure on the ogive? Not to mention that no lands will wear perfectly even, but I won't go down that path...

Even with that being said, now I have to research possibly buying some high precision comparators..... hahaha

 

[fyrewall]

KVD - thank-you for the reply

Correct on the numbers game! - is there a normal distribution? - but I really don't know - I don't have an idea of the ogive variations of my multi lot bullet collection - many different boxes of different ages - trades, close out sales, gifts but all of the same kind.

Playing the statistical game would assume a normal distribution would exist but if the bullet ogives only varied by a tiny amount, producing 3 sorted groups, there would be no normal distribution - like a flat line and thus load & shoot. Having never measured bullet ogives I have no idea what the variation would be but should I get a whole bunch of variations having greater magnitudes the possibility of a normal distribution might occur - the only way to find out is to actually check out my bullet collection without measuring 1000's of bullets. Measuring some of my cheaper bullets might show a greater variation than your bullets. I intend to only measure unloaded bullet ogives.

SAAMI COAL's usually don't work, especially loading .22-.250's with pointy bullets that will not fit into to my SAAMI spec Ruger 77 MKII factory magazine boxes that I replaced with a .308 size.

Again, thank you for your astute response about the normal distribution business. If the bullet ogive variations are tiny messing with the statistical stuff will probably be unnecessary (no normal distribution) making your observation valid especially as applied for my purposes but I have no intentions of large volume sampling within lots to find out if sorting would result in 2 or 3 bunches of bullets. Looking at 20 from each lot should be enough and if flat, load & shoot.

Velocity spreads may be a different consideration.

On the seat/point business I can visually inspect hollow point bullets and measure bullet lengths (base to tip) and see differences thus I don't seat the bullets by applying force to the tips; also there are those bullets, with softer than metal, plastic tips that might vary because of deformation prior to seating. I have more confidence in achieving less run-out by seating bullets with no point contact.

 

[fyrewall]

After going through all this I am confident that my batting average on steel targets and tiny rodents can only improve (hit or miss).

 

[dmoran]

... I don't have an idea of the ogive variations of my multi lot bullet collection - many different boxes of different ages - trades, close out sales, gifts but all of the same kind....

Expect the possibility of a lot of variations....
Have seen as much as .060" variation from Lot's that were a few years apart.
Real common to see .010" or more - IME

 

[fyrewall]

Expect the possibility of a lot of variations....
Have seen as much as .060" variation from Lot's that were a few years apart.
Real common to see .010" or more - IME

thank you for your reply

I just had to test stuff out - using Excel I made a routine to find the high average & low average for 20 bullets attempting a meaningful normal distribution with a .95 confidence level. Not knowing what the actual variations were I made them up. My maximum size was .703, minimum size was .690, X spread was .013, average was .701, SD was .003, sample size 20, the one bad bullet was the .690 causing the tiny hiatus (hiccup), the end result was a hi population mean of .702 and a low population mean of .699. Expanding this analysis for a population of 500 or so would reduce the hi & low mean differences.

All the above would go nowhere; but should some .060 extreme variations and common .010 variations occur this stuff might have value for making decisions regarding bulk loadings.

To update: imaginary ogive values for the 20 samples are:

.701, .701, .701, .701, .701, .690, .701, .703, .700, .701, .701, .700, .702, .701, .702, .701, .703, .700, .702, & .701

 

[dmoran]

@fyrewall
I once had a real bad Lot of SMK's, that had 0.025" deviation in BtO. I tested 5 from each the low and high ends, at the same time as one 10-string at 1000yds. The group centers between the two were 27" vertically apart.
Donovan

 

[fyrewall]

@fyrewall
I once had a real bad Lot of SMK's, that had 0.025" deviation in BtO. I tested 5 from each the low and high ends, at the same time as one 10-string at 1000yds. The group centers between the two were 27" vertically apart.
Donovan

Thank-you -- noted

 

[Richard Coody]

thank you for your reply

I just had to test stuff out - using Excel I made a routine to find the high average & low average for 20 bullets attempting a meaningful normal distribution with a .95 confidence level. Not knowing what the actual variations were I made them up. My maximum size was .703, minimum size was .690, X spread was .013, average was .701, SD was .003, sample size 20, the one bad bullet was the .690 causing the tiny hiatus (hiccup), the end result was a hi population mean of .702 and a low population mean of .699. Expanding this analysis for a population of 500 or so would reduce the hi & low mean differences.

All the above would go nowhere; but should some .060 extreme variations and common .010 variations occur this stuff might have value for making decisions regarding bulk loadings.

To update: imaginary ogive values for the 20 samples are:

.701, .701, .701, .701, .701, .690, .701, .703, .700, .701, .701, .700, .702, .701, .702, .701, .703, .700, .702, & .701

one simple question. Are these measured base to tip or base to ogive.

 

[lpreddick]

Expect the possibility of a lot of variations....
Have seen as much as .060" variation from Lot's that were a few years apart.
Real common to see .010" or more - IME

I had a 100 count box of 87 gr factory bullets and none weighed 87 gr. Base to ogive measurements had no more than 12 measuring the same. I received a replacement and they were from the SAME lot, but all weighed 87 gr and B/o measurements were +- .002. Lands do recede as many firings burn the edges first, rounding the engraving surface. One or more land will burn away sooner than others. This could be a problem for those who like to"kiss the lands". I usually seat .020 into the lands and can see a slight difference in engravings in guns with a high round count.....an provacative thread.

 

[fyrewall]

C

one simple question. Are these measured base to tip or base to ogive.

thank-you for your interest

The data are completely fabricated (made up) values to test out my trial process and are just a guess of what some real situation might be.

When I run this thing for real I will measure bullets base to ogive using a caliper with the PTG 6 sided gauge that I plan to buy soon. The fake, made up, values hover around .700 which is a very crude (eyeball) unmeasured approximation of base to ogive for the 123 grain 6.5mm Hornady SST. My one imagined rogue value was .690 and in real life this would not escape Hornady quality control.

This thing needs more work but essentially gives some idea what might be expected. Running a bunch of data having the one rogue made up value of .690, one of 20, puts out a tiny SD of .015 (corrected), meaning running this process with a normal box of high quality bullets would be sort of witless because all the bullets would fall close to each other on the distribution; but if bullets of the same kind but of different lots and ages were considered produced an X spread of .040 and a higher SD it might be of some worth to allow selected mixing of those bullets. I got to admit that after measuring 20 and finding many obvious problems would give enough insight of bullet quality to quit any further number playing. (italics - edit 3570737)

****
I think the process would have much more application with velocity variations - what I first intended. Estimated high and low mean velocities with a realistic confidence level of 95% and their subsequent trajectory effects might be of use in load development and shooting. Velocity values will be placed in a separate column then copied and pasted using Excel when playing around with velocities. Separate columns will be used for each powder and load. A general idea of accuracy will occur before playing with numbers.

It is real cold and snowy here now and measuring ogives is more comfortable than outside accuracy testing and measuring velocities.

Sorry for the verbose response to your simple question but one thing sort of leads into another. We started out with a 3 or 4 line inquiry about COAL with a 6mm BR and 87 Hornady V Max bullets. When I get started with the ogive stuff I will kick off another thread. The velocity stuff will produce another.