Should you always use bullet comparator when measuring COAL?

Manwithoutastar

Manwithoutastar

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Hello, new reloader and finally have my station set up and got a chance to start last night. But when I got to the step of adjusting my die seating depth I read that it’s best to measure from the ogive to get length, not end to end with the bullet and case in the micrometer. I ordered a set but it’s not gonna be here now for a couple weeks. Wondering if there are any tips out there from some of the CGN gurus on this? or should I just wait til I get the comparator set. Thanks!
 
Your best gauge for setting up your dies is your rifle. No one else has one exactly like it, especially whomever made your dies. Establish for magazine length first. Then find where the bullet touches your lands - most reloading manuals show you how to do that. If the magazine length allows it, start with .020" or so off the lands. Vary that distance as your shooting results tell you.
 
There are several ways to find a starting COL for any given bullet that do not involve a comparator. In fact, until you have a COL from which to start, a comparator is not necessarily the best tool. It is great for establishing the same gap from the lands as another successful load with a new bullet, but it is not good for deciding COL from scratch for your chamber and an untried bullet. Google methods of establishing a reasonable COL for a new bullet and give one of the methods a try. I have used cleaning rod measurements with the bullet jammed against the lands and then no bullet and measure to the bolt face. The difference is the COL with the bullet jammed, and then shorten it the amount of jump you want to use as a start. I have also used the old "squeeze the case mouth a bit, insert a bullet a bit, and let the rifling push the bullet into the case as you chamber it" approach. Both worked more or less well. Do one several times and use an "average" to get close. But a comparator is not absolutely essential at all. Useful, but not essential.
 
You want to determine what your overall length should be first. Determine the length to your lands then typically you will want to start around 20 thou back from there. Different rifles and bullets like different jump
The comparator is good to measure your base to ogive to ensure consistent seating depths as bullet tips maybe slightly different bullet to bullet.
Here is a good video on determining you lands
https://youtu.be/TWmIwPwLyyg
 
You can estimate the jump to the lands without a comparator I don't use a comparator, and it does not effect my ability to load accurate ammunition. I put a dent in the case neck of a fired case, so a bullet will slide in the neck with some resistance, barely start the bullet in the neck, then chamber the dummy round and measure the COL to the tip. I repeat a few times to back up the measurement, then I use that particular dummy round to set up my seating die. All of my seating dies are micrometer type dies, so from then on, I use the micrometer to vary the jump, and never bother measuring the COL again with that bullet model and weight. Doing things this way, eliminated the variance in bullet tips.
 
rral22 said:
There are several ways to find a starting COL for any given bullet that do not involve a comparator. In fact, until you have a COL from which to start, a comparator is not necessarily the best tool. It is great for establishing the same gap from the lands as another successful load with a new bullet, but it is not good for deciding COL from scratch for your chamber and an untried bullet. Google methods of establishing a reasonable COL for a new bullet and give one of the methods a try. I have used cleaning rod measurements with the bullet jammed against the lands and then no bullet and measure to the bolt face. The difference is the COL with the bullet jammed, and then shorten it the amount of jump you want to use as a start. I have also used the old "squeeze the case mouth a bit, insert a bullet a bit, and let the rifling push the bullet into the case as you chamber it" approach. Both worked more or less well. Do one several times and use an "average" to get close. But a comparator is not absolutely essential at all. Useful, but not essential.
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Very helpful, there is a tool from Frankfort Arsenal, a cartridge over all length gauge, which I think uses the method you’re describing. I’m going to order it. So finding the coal, reducing it roughy 20 thousandths(to start) and adjust die to seat that length is the best method to start with?
 
stubblejumper said:
You can estimate the jump to the lands without a comparator I don't use a comparator, and it does not effect my ability to load accurate ammunition. I put a dent in the case neck of a fired case, so a bullet will slide in the neck with some resistance, barely start the bullet in the neck, then chamber the dummy round and measure the COL to the tip. I repeat a few times to back up the measurement, then I use that particular dummy round to set up my seating die. All of my seating dies are micrometer type dies, so from then on, I use the micrometer to vary the jump, and never bother measuring the COL again with that bullet model and weight. Doing things this way, eliminated the variance in bullet tips.
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Helpful thank you. So do you measure your loads after at all? Or rely on the die to keep the correct depth. I’m using rcbs die set, I don’t think they have a way to use a micrometer on them
 
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Using a gauge measurement to find the COAL and adjusting the die stem accordingly (.020” back). Can I use the micrometer and measure the case head to bullet tip to find if I’m getting this measurement right? Once I pull it out of the press
 
Well - As a rookie, you should be a bit cautious about playing close to the lands. If the bullet has a cannelure, use that. If not, use published COL from the manufacturer. Save the finesse work until you get a handle on things.
Comparators are a recent invention, and deemed by many of us older reloaders to be a gimmick. To answer your question, once you have established an appropriate COL for a given bullet, then that COL need not be verified from round to round. If you want to check, you can use a caliper and measure to the bullet tip. Yes, there may be some slight variation for soft point bullets, but not to be concerned. If you are setting your dies for a new batch, measure the bullet itself and ensure it compares to your first batch. Then you can use your caliper to set COL...
Playing close to the lands (eg 20 thou or less) means you really have to pay attention to your metrology and record keeping. Case in point, you establish COL for one box of bullets, then buy another box of the same bullet. The ogive profiles are different between the two lots from the same manufacturer, and you end up jamming the bullet - bad news...
 
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cosmic said:
Well - As a rookie, you should be a bit cautious about playing close to the lands. If the bullet has a cannelure, use that. If not, use published COL from the manufacturer. Save the finesse work until you get a handle on things.
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Sound advice, I’m really just making sure I have everything. So using the published COL and using the micrometer to measure end to end is good enough to start with? basically what I’m trying to figure out. I’m using rem brass and nosler 308 165 accubond.
 
Yes - You can get the COL info from Nosler, and it is based upon measurement to the bullet tip, so you can use your calipers. Bear in mind you have a fair mount of bullet jump, so precision is a personal initiative. Also, bear in mind that you can use that COL in any of your 308's - when you start loading close to the lands the ammo becomes dedicated to a specific rifle.
Don't be too concerned about accuracy wrt COL, and going close to the lands. For a hunting rifle, it is a minor variable compared to bullet weight and powder selection.
 
cosmic said:
Yes - You can get the COL info from Nosler, and it is based upon measurement to the bullet tip, so you can use your calipers. Bear in mind you have a fair mount of bullet jump, so precision is a personal initiative. Also, bear in mind that you can use that COL in any of your 308's - when you start loading close to the lands the ammo becomes dedicated to a specific rifle.
Don't be too concerned about accuracy wrt COL, and going close to the lands. For a hunting rifle, it is a minor variable compared to bullet weight and powder selection.
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Thanks again, also I had a question in regards to new brass. Are you required to FL size brass that comes new unfited right out of the bag? I didn’t do that before priming some and am now wondering if I should have sized it first
 
While this isn't true for every .308 ever made, 165gr anything in a .308 is likely a LONG way from the lands. You will be limited to magazine length for reloading anyway unless your rifle is a single shot of some sort. Most .308 rifles tend to be set up so that one can reload long bullets which are in the 200+ gr region. For example, on my Remington 700 5r .308, with a 155gr bullet, I can't seat it at all in the empty case so that it will reach the lands. The bullet is almost completely out of the case mouth with only the boattail inside the neck of the brass with 20thou of jump remaining. With 168gr BTHP such as SMK or Hornady there is only about 1/16" of the actual bearing surface of the .308 bullet that will be held in the case neck with 20thou jump to the lands. Still not nearly enough. With 175gr Juggernaut there is almost 3/32" inside the neck. With a 20thou jump, by the time I am well into the 210-220gr .308 bullets, I am at around 3/16" to 1/4" inside the neck with 3/16" of the bearing surface being the absolute minimum in my opinion to getting a good neck tension with any bullet. So, you will end up reloading those lighter bullets to fit the mag, and you will seat them about 3/16 to 1/4" into the case neck, and this will mean they end up with a BIG jump to the lands. Lots of people above gave good advice for trying to figure out where your lands actually are, but on a lot of the commercial mass produced .308 rifles, they are so far away, that your bullets will end up just about needing binoculars to see them.
 
Especially if struggling with the length, there are sort of three "Golden Rules" - has to fit in and feed from the magazine, you really want to have about a caliber worth of neck holding the bullet (boat tail length does not count), and you want your loaded rounds to be straight - that is concentric, with minimal bullet tip wobble if you roll them over a mirror, or minimal runout (.003" or less) if you use a concentricity gauge.
 
rick357 said:
While this isn't true for every .308 ever made, 165gr anything in a .308 is likely a LONG way from the lands. You will be limited to magazine length for reloading anyway unless your rifle is a single shot of some sort. Most .308 rifles tend to be set up so that one can reload long bullets which are in the 200+ gr region. For example, on my Remington 700 5r .308, with a 155gr bullet, I can't seat it at all in the empty case so that it will reach the lands. The bullet is almost completely out of the case mouth with only the boattail inside the neck of the brass with 20thou of jump remaining. With 168gr BTHP such as SMK or Hornady there is only about 1/16" of the actual bearing surface of the .308 bullet that will be held in the case neck with 20thou jump to the lands. Still not nearly enough. With 175gr Juggernaut there is almost 3/32" inside the neck. With a 20thou jump, by the time I am well into the 210-220gr .308 bullets, I am at around 3/16" to 1/4" inside the neck with 3/16" of the bearing surface being the absolute minimum in my opinion to getting a good neck tension with any bullet. So, you will end up reloading those lighter bullets to fit the mag, and you will seat them about 3/16 to 1/4" into the case neck, and this will mean they end up with a BIG jump to the lands. Lots of people above gave good advice for trying to figure out where your lands actually are, but on a lot of the commercial mass produced .308 rifles, they are so far away, that your bullets will end up just about needing binoculars to see them.
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Well good to know! I will stop worrying about seating it near the lands for now and just start with the recommended OAL. Thank u
 
I use a comparator for measuring. I find the lands using a specific method, then measure and record the length for my records. My measurements are only good for me and the measuring tools I use/used. For some diameters I have 2 comparators (I use both for measuring bearing surface). I have them clearly marked and record which one was used for taking measurements as I'd get different readings depending on the comparator used due to their tolerances.
 
Manwithoutastar said:
Well good to know! I will stop worrying about seating it near the lands for now and just start with the recommended OAL. Thank u
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Make those measurements of where the lands are on on your rifle if at all possible sooner rather than later. Then you will know for certain. Yes, always recommended to load to CBTO (Cartridge Base To Ogive) if at all possible as well.

For now, buy a box of factory rounds close to the grain that you will be reloading that you know will work in your rifle and use the COAL on them as a template for COAL seating of your reloads.
 
What I like about using the comparator is, it gives a bit more accurate way to get consistency on bullet seating. Establish a rough COAL to the lands, back it off, play with it a bit, and come up with what will work for you by shooting it. There is no law that says .050 or .010 off or in the lands will work better or worse for you, your targets will show you what works. Nose profiles on bullets are all over the place, and if you use a few different calibres with a few different styles and brands of bullets, in a few different guns, you'll learn to appreciate the investment in a comparator set. It's a one time investment, and they are not expensive, and it will teach you some stuff about bullets and throats and etc. Learning is one of the fun parts of reloading, and things change all the time, even the one bullet that has been around for 50 yrs has changed a bit here and there.
 
Measuring to the bullet tip can be every bit as precise; if you use the same individual bullet to do the measuring as to set the seating die. A comparator isn't going to tell you that the round wont fit in the mag either. The comparators are more useful for trying to apply a measurement taken with one bullet to one of a different design. I find it easier to just measure again; lands are a moving target around here. If you really want to split hairs, the comparator measures to an arbitrary diameter and angle; one that probably isn't shared by your rifle throat.

Ive had my comparators for 20 years and seldom use them anymore.
 
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