Bullet comparators - Which one is correct?
- Thread starter Easternncnative
- Start date
It does matter . Depending on the internal measurement of your comparator the measurement can change based on where the Comparator meets the Ogive of the bullet. If internal dimensions of your Comparator are not the same as your bore diameter in your rifle barrel, then your measurement will be wrong . Let’s say your rifle has a .298 bore diameter, but your comparators internal diameter is .304 your bullet will contact the Ogive in different places, giving you two different measurements.
There is one advantage of having a set of Hornaday OAL gage comparators and also Headspace Comparators in your tool box. There comes a time when I want to measure the base to datum of a shot cartridge case for sizing purposes, and doing this with a spent primer in the pocket is problematic due to induced errors from primer cratering.
Using an OAL comparator on one blade of your caliper, and a Headspace comparator on the other eliminates the error from the primer and makes this measurement quick and easy with a digital caliper.
Using an OAL comparator on one blade of your caliper, and a Headspace comparator on the other eliminates the error from the primer and makes this measurement quick and easy with a digital caliper.
You're writing theoretically, of course, as measuring the blended curve between the bearing surface and the start of the ogive would present some big problems. For starters, because of the extremely flat curve at that juncture the very, very small changes in bullet diameter, not to mention pressure exerted on the tool and temperature changes would yield large changes in dimensional length from bullet to bullet.
For the most part though, using a tool with a hole diameter that is close, but not too close is probably better than using one that is much different in size, in case you're planning on making your own.
In that case, as long as you pick a datum point along the ogive that is consistent from bullet to bullet, all you're doing is taking a relative measurement, not an absolute one for the purpose of establishing an amount of jump or jamb.
If you want to make you own tool, using the method described above by seating a bullet long and chambering it to visually determine land engagement would be a good start to determine hole size. Conversely, if you have a drawing of the reamer used to chamber your barrel, you could do the math to determine the hole size.
This of course leaves out the problems of actually boring a hole on a lathe and holding it to +/- .0001 and then radius the edge to an even closer tolerance. IMOP, all of this would be perhaps an academic endeavor more than a practical one.
As stated a comparator is just that. It makes comparisons between two or more objects. Not only are there differences in readings between comparator manufacturers, but between any two comparators from the same manufacturer.
This is a result of tolerances or allowables in the manufacturing process and between different CNC machines.
For this reason it is important to use the same bushing each and every time. If you have more than one bushing for doing other types of comparisons, it is critical to mark them to ensure you don't use the wrong one and produce false comparisons.
This is a result of tolerances or allowables in the manufacturing process and between different CNC machines.
For this reason it is important to use the same bushing each and every time. If you have more than one bushing for doing other types of comparisons, it is critical to mark them to ensure you don't use the wrong one and produce false comparisons.
XTR
F-TR obssessed shooting junkie
Dude, this thread is 5 yrs old.
And it doesn't matter as long as you do it the same way with a case in the chamber (whether you use something like the Sinclair or Alex Wheeler's method) and with the bullets that you load.
PatMiles
Silver $$ Contributor
BINGO!!
I use the hornady overall length gauge and it is definitely pressure sensitive I try to be as accurate as possible but what I do is I measure 10 times then figure out an average number and go from there
As with any measuring tool, it requires a learned skill to be accurate and repeatable. This come with practice and time. This is even more evident when measuring a sloped surface. A little more or less pressure can provide large variations in the readings.
It does matter. I can not make it any clearer.
PatMiles
Silver $$ Contributor
I will agree with you.
What does one do when the lands as well as the bore when the throat starts eroding due to rounds shot.
Ned Ludd
Silver $$ Contributor
The answer to the original question is simple: the Hornady comparator insert has a noticeably smaller diameter hole for a given caliber than does a Sinclair gauge. Does it matter? That's a slightly more complex question and may largely depend on whether you're a glass half full or glass half empty type of person.
As shown in the cartoon below, the two critical contact points (shown in red and blue, with the critical distance in between shown in green) on the bullet ogive for uniform seating depth are 1) the point at which the seater die stem contacts the nose and "pushes" the bullet into the case, and 2) the point at which the bullet first contacts the rifling. If there is bullet length variance between these two points, there will also be seating depth variance unless the seater die micrometer is adjusted to account for it.
We typically use the comparator insert contact point on the bullet ogive as though it were identical to the actual point at which the bullet ogive first contacts the rifling. This may, or may not, actually be true. The Sinclair comparator insert holes are specifically designed to seat on the bullet ogive jat, or ever so slightly above the bearing surface/ogive junction. Presumably, this point is very close, if not identical, to the point on the bullet ogive that first contacts the rifling.
In contrast, the Hornady comparator insert with its smaller hole seats noticeably farther out from the bearing surface junction on the bullet ogive. This means that you are not measuring the true distance from the base of the case to the point on the seated bullet ogive that will first contact the rifling. The Sinclair comparator insert give a truer measurement in this particular instance. However, because bullet length variance between the two critical points (seater die stem contact and comparator insert contact) can lead to seating depth variance, the closer the comparator insert seats on the bullet ogive to where the seating die stem contacts it, the less opportunity there is for bullet nose length variance, and therefore, the less opportunity there is for seating depth error to be induced by bullet nose length variance. So the real question is which (if either one) is the more critical aspect? For the most part, that's largely a personal preference issue and rather difficult and laborious to prove one way or the other in a statistically significant manner.
The real key to CBTO measurements are that you use the same comparator insert every time. As long as you do that, you will be measuring the actual loaded rounds you will ultimately shoot at a target to determine what seating depth gives you the tightest and most consistent grouping. Whichever caliper insert you choose can easily reproduce the same CBTO measurement to about +/- .0005" with reasonable care in its use. In other words, you only have to produce a given seating depth, then be able to consistently reproduce the one that gave you the best results. Either comparator insert can do that. Like the measurements we take to determine the distance to "touching" the lands, CBTO measurements are largely "relative", meaning the value obtained with either brand caliper insert may not be the actual "true" value. However, accuracy is less critical in the case of this and many other "relative" measurements for most of us. What really matters is that we can consistently reproduce whatever measurement we need.
So does the brand of caliper insert you choose really matter? Lots of things matter "in theory". Whether a given individual, their rifle, and their load can shoot well enough to distinguish certain very minute theoretical differences is another story. Only the individual can ultimately answer that question, and it's usually a ton of work and rigorous statistical analysis to do so. I own and have used both the Sinclair and Hornady caliper inserts. For a variety of reasons, I now routinely use the Hornady inserts, and they have performed adequately for my needs.
As shown in the cartoon below, the two critical contact points (shown in red and blue, with the critical distance in between shown in green) on the bullet ogive for uniform seating depth are 1) the point at which the seater die stem contacts the nose and "pushes" the bullet into the case, and 2) the point at which the bullet first contacts the rifling. If there is bullet length variance between these two points, there will also be seating depth variance unless the seater die micrometer is adjusted to account for it.
We typically use the comparator insert contact point on the bullet ogive as though it were identical to the actual point at which the bullet ogive first contacts the rifling. This may, or may not, actually be true. The Sinclair comparator insert holes are specifically designed to seat on the bullet ogive jat, or ever so slightly above the bearing surface/ogive junction. Presumably, this point is very close, if not identical, to the point on the bullet ogive that first contacts the rifling.
In contrast, the Hornady comparator insert with its smaller hole seats noticeably farther out from the bearing surface junction on the bullet ogive. This means that you are not measuring the true distance from the base of the case to the point on the seated bullet ogive that will first contact the rifling. The Sinclair comparator insert give a truer measurement in this particular instance. However, because bullet length variance between the two critical points (seater die stem contact and comparator insert contact) can lead to seating depth variance, the closer the comparator insert seats on the bullet ogive to where the seating die stem contacts it, the less opportunity there is for bullet nose length variance, and therefore, the less opportunity there is for seating depth error to be induced by bullet nose length variance. So the real question is which (if either one) is the more critical aspect? For the most part, that's largely a personal preference issue and rather difficult and laborious to prove one way or the other in a statistically significant manner.
The real key to CBTO measurements are that you use the same comparator insert every time. As long as you do that, you will be measuring the actual loaded rounds you will ultimately shoot at a target to determine what seating depth gives you the tightest and most consistent grouping. Whichever caliper insert you choose can easily reproduce the same CBTO measurement to about +/- .0005" with reasonable care in its use. In other words, you only have to produce a given seating depth, then be able to consistently reproduce the one that gave you the best results. Either comparator insert can do that. Like the measurements we take to determine the distance to "touching" the lands, CBTO measurements are largely "relative", meaning the value obtained with either brand caliper insert may not be the actual "true" value. However, accuracy is less critical in the case of this and many other "relative" measurements for most of us. What really matters is that we can consistently reproduce whatever measurement we need.
So does the brand of caliper insert you choose really matter? Lots of things matter "in theory". Whether a given individual, their rifle, and their load can shoot well enough to distinguish certain very minute theoretical differences is another story. Only the individual can ultimately answer that question, and it's usually a ton of work and rigorous statistical analysis to do so. I own and have used both the Sinclair and Hornady caliper inserts. For a variety of reasons, I now routinely use the Hornady inserts, and they have performed adequately for my needs.
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Nedd, I'm going to bet that you bed your seating dies to the bullet. Yes?
The problem I've seen in seating stems that contact much further down the bullet ogive and closer to the bearing surface is that the radius of bullet profile is very flat, and therefore has a tendency to slide up into the stem as seating pressure increases. I recently experienced this with the new Hornaday A-tip and the "special" seating stem sold to work with these bullets.
Thin copper jackets combined with soft lead cores result in deformation at the stem contact area. Very slight changes in seating pressure will cause significant changes in measured seating depth. My guess is that only by bedding and therefore vastly increasing the stem contact area with the bullet jacket of a particular bullet model, is consistency improved to the point of .0005 accuracy. This assumes that neck tension, neck inside finish and coating, wall thickness is evenly turned, and brass hardness is all addressed. As Vergil King noted, brass preparation is the key, with charge wt, propellant lot, bullet lot all placing well down the list of important variables.
Another problem is the gage contacting the bullet ogive at the same location where seating pressure was applied. Any slight deformation in the jacket will case errors in measurement. Another argument favoring bedding the stem.
What has been your experience with regard to these issues?
Have you tried bedding your comparator to the bullet by increasing hole diameter and closing the critical distance in your cartoon?
Inquiring minds may find this very interesting.
The problem I've seen in seating stems that contact much further down the bullet ogive and closer to the bearing surface is that the radius of bullet profile is very flat, and therefore has a tendency to slide up into the stem as seating pressure increases. I recently experienced this with the new Hornaday A-tip and the "special" seating stem sold to work with these bullets.
Thin copper jackets combined with soft lead cores result in deformation at the stem contact area. Very slight changes in seating pressure will cause significant changes in measured seating depth. My guess is that only by bedding and therefore vastly increasing the stem contact area with the bullet jacket of a particular bullet model, is consistency improved to the point of .0005 accuracy. This assumes that neck tension, neck inside finish and coating, wall thickness is evenly turned, and brass hardness is all addressed. As Vergil King noted, brass preparation is the key, with charge wt, propellant lot, bullet lot all placing well down the list of important variables.
Another problem is the gage contacting the bullet ogive at the same location where seating pressure was applied. Any slight deformation in the jacket will case errors in measurement. Another argument favoring bedding the stem.
What has been your experience with regard to these issues?
Have you tried bedding your comparator to the bullet by increasing hole diameter and closing the critical distance in your cartoon?
Inquiring minds may find this very interesting.
Dusty Stevens
Shiner
Make an insert with your reamer. Cant get any better than your actual freebore dia and angle
Ned Ludd
Silver $$ Contributor
I do not "bed" my seating die stems. Although it's certainly possible to do that; I am aware of people that have used a hot glue gun to fill the stem and then push the bullet tip in before it cools, but I have never found it necessary to do that. For my .308s Win rifles, I have a couple seater dies, one with a standard stem, the other with a VLD stem. I have used the VLD stem with bullets as long and pointy as the Warner Flatlines, but more often with Berger 200s. The standard stem is used for bullets like 168s, 175s, and 185s. For my .223s, I only shoot ~90 gr bullets, so all the dies have a VLD stem.
I do not find it difficult to maintain better than 95% of my loaded rounds within .0005" seating depth with any of my seating dies. On the rare occasion that I do get a loaded out by .001", I'll set it aside and use it as a fouler/sighter.
I do not find it difficult to maintain better than 95% of my loaded rounds within .0005" seating depth with any of my seating dies. On the rare occasion that I do get a loaded out by .001", I'll set it aside and use it as a fouler/sighter.
This here!
It is a way to give yourself a reference to adjust the shoulder bump or seating depth by off the ogive of bullet. It is for you only, no two are alike so treat each one like that. Once you use one, never mix with another unless you know for sure they measure exactly identical.
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