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Posted: 9/20/2010 2:12:53 PM EDT
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How does one use the Hornady bullet comparator to set up the seating die? How is the correct COAL determined if the comparator is measuring from the ogive? I understand that the ogive is where the seater actually applies pressure to seat the bullet, but in the reloading manuals, each load is shown with a COAL... not a rim to ogive length... so how do I use he comparator to make sure I am within specs of COAL if the whole point of using the comparator is not measuring COAL because of bullet length variations?
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The bullet comparator is not for setting up your seating die, it for measuring the distance the ogive of the bullet is from the lands of your rifle in conjunction with an OAL gauge and modified case to hold the bullet your checking.
You set your seating die up for mag use using your calipers and the longest bullet(out of say 20 or 30 checked) and then if you want to you can check the consistency of your seating die/bullets by checking the base to ogive length using the comparator and that's about it, good match bullets wont vary at the ogive but cheap plinking bullets will still vary and your wasting your time trying to get them any better than a "good" seating die sets them at. EWP |
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My normal process:
Using the Hornady and their procedure measure the ogive to base for the bullet just touching the grooves. Then decide if you want bullet jump and how much. Set your seating die to achieve that ogive to base dimension for the desired bullet jump. Then measure the OAL from tip to base. If it will fit and cycle reliably using your magazine then that is the OAL you will be using when setting the seating die to the determined ogive to base dimension. If it is too long, then seat deeper until the OAL that will reliably cycle in your magazine is achieved. At that point you are no longer able to set the seating to a specific jump distance. Remember that this process is only good for one type of bullet you are handloading. |
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The LNL OAL gauge determines the Point of Contact of the Specific Bullet's Ogive with lands of your particular chamber. To get a point of reference take several readings and average them.
Now it is basically SENSELESS to try an even get close to the lands with some bullets as you will violate the idea that you need at least one caliber of bullet length in the case length. Most smaller caliber bullets will never come close to the lands and be stable for shooting, unless a chamber is throated specially for them. A lot bullets seated close to the lands will exceed magazine length, so for magazine use this is sort of useless unless you want to shoot single shot. Case in point VLD type bullets in 223, like people trying to seat 75gr Amax at magazine length. Some bullets are meant to jump into the lands case in point the original intent of the 30 cal 168 gr SMK. Yes you can use a bullet comparator to set up a bullet seater to have the same a uniform ogive to base measurement. Bullet seaters are not DEAD LENGTH type of seater as they seat the bullet off of ogive not off the tip so variances in COAL will occur. A person could uniform meplat, and then sort the bullets for base to ogive measurements. |
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When loading to magazine length for an AR, it boils down to this - the length to the ogive is not important.
You're right to be confused, but you worked through only half of the problem, you assumed that length to ogive matters without measuring the rifle's chamber to find out whether the bullet can be seated close to the lands, and whether that dimension or COAL is the controlling dimension. |
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I agree with AeroE. When loading for semi auto military type rifles just load to the max COAL that will reliably fit in the magazine and chamber without forward assist.Don't worry about measuring off the ogive unless you are shooting a bolt gun with brass sized for that gun only. Quoted:
When loading to magazine length for an AR, it boils down to this - the length to the ogive is not important. You're right to be confused, but you worked through only half of the problem, you assumed that length to ogive matters without measuring the rifle's chamber to find out whether the bullet can be seated close to the lands, and whether that dimension or COAL is the controlling dimension. F=ma |
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I have a similar tool and use just the bushing turned around and the bullet going into the wrong end, on purpose.
I find the longest bullet, seat it a shade under mag length, and measure the distance from case head to where the reversed comparator sits. I do it so that I have consistent depth ogives from batch to batch. While the tips may finish off differently the rest of the bullet is fairly identical from bullet to bullet. Of course this only works for that bullet type. I'll be getting the Davidson depth checker off the Sinclair sight soon. |
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Quoted:
When loading to magazine length for an AR, it boils down to this - the length to the ogive is not important. That depends on how you are loading and shooting your AR. I know a few people (including myself) that sometimes choose to insert rounds one at a time into our AR's using a rigid follower in the magazine. I have one magazine that always has that follower in place. We do that in pursuit of accuracy and test for the effect of bullet jump. Please do not assume all readers of this forum are plinkers. A discussion on how much bullet jump affects accuracy and grouping for a given rifle is one for a bench rest forum. |
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Quoted:
Quoted:
When loading to magazine length for an AR, it boils down to this - the length to the ogive is not important. That depends on how you are loading and shooting your AR. I know a few people (including myself) that sometimes choose to insert rounds one at a time into our AR's using a rigid follower in the magazine. I have one magazine that always has that follower in place. We do that in pursuit of accuracy and test for the effect of bullet jump. Please do not assume all readers of this forum are plinkers. A discussion on how much bullet jump affects accuracy and grouping for a given rifle is one for a bench rest forum. "When loading to magazine length ..."; did you miss that part of my comment? Don't assume I don't have a magazine with a single round follower. Or 80 grain bullets seated out for single loading. There's no need to assume someone is a plinker, they're easy to pick out of the crowd. Heck, I don't think plinking is a bad thing, except when it's used as an excuse for sloppy shooting and half-ass reloading. 
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To answer the OP's question it can not be used to set your seating die if you plan on using bullets short enough to be feed from the mag, end of story.
Everything else is simple as well but requires more tools than just a bullet comparator and long match bullets that will not work from your mag more than one at a time, I've been through all this when I first started reloading and it's not rocket science to figure out the tool was made for bolt guns and single fed AR's using very long VLD type match bullets, most bullets even up to a 69gr SMK will just fall out the end of the modified case before you even reach the lands, so seat to mag length and be done with it unless you need more info on loading single shot VLD bullets and how far off the lands you should be and how to figure all that out. EWP |
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What I did for my M1A is I used my Hornady OAL gage to find the max which is a semi-auto exceeds mag length then you can take your comparator insert and see what you have then bump it back .010" at a time to see if it clears the mag (check on several mags as they do vary) you must understand that some like to be seated long and some short, most reloaders I have talked with just seat to 2.800" (.308) which will vary from the ogive depending on the bullet used
Currently I am at 2.260" base to ogive length which puts me .030" off the lands and that's as far as I can go and feed without issue with the bullet I am using |
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Quoted:
Quoted:
Quoted:
When loading to magazine length for an AR, it boils down to this - the length to the ogive is not important. That depends on how you are loading and shooting your AR. I know a few people (including myself) that sometimes choose to insert rounds one at a time into our AR's using a rigid follower in the magazine. I have one magazine that always has that follower in place. We do that in pursuit of accuracy and test for the effect of bullet jump. Please do not assume all readers of this forum are plinkers. A discussion on how much bullet jump affects accuracy and grouping for a given rifle is one for a bench rest forum. "When loading to magazine length ..."; did you miss that part of my comment? 
Don't assume I don't have a magazine with a single round follower. Or 80 grain bullets seated out for single loading. There's no need to assume someone is a plinker, they're easy to pick out of the crowd. Heck, I don't think plinking is a bad thing, except when it's used as an excuse for sloppy shooting and half-ass reloading.
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