New reloader - question about bullet comparator

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Hey, I'm a brand new reloader, just built my first bench last weekend. I've only loaded some 9mm so far. I'm planning on loading some 308 rounds, and I'm curious about how a bullet comparator works. I've read that measuring to the bullet tip can be inaccurate because of manufacturing variables and that you can get a much more accurate reading from measuring to the ogive. But I'm wondering, if I have a COL of 2.800, but I'm measuring to the ogive, obviously the measurement that the comparator gives me is going to be much shorter than that. Since different brands of bullets are different shapes, lengths, tc. there can't just be a lookup table.. so I'm confused on how exactly you would set your COL to 2.800 when measuring to the ogive. Is it just about consistency, not nailing that exact COL? For example, seat one to a bullet tip COL and then check the subsequent ones at the ogive to make sure everything is consistent? I realize where the comparator really shines is using the case length guage to check where exactly your rifling starts in your gun. I'm not looking for crazy accuracy as these are being loaded for a Tavor 7, not a bolt action gun that I'm looking to get crazy accuracy with. I would also like this ammo to run in more than just the Tavor.

Thanks guys
 
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I'll be watching. No experiance with that tool but did see a video the other day discussing using the right seating die insert also for each type of bullet. Some of my die sets seat off the bullet tops and some off the angle (likely more accurate) due to inconsistencies and such..
I may need to expand my seater die insert collection some..
It's slways something with this hobby..
 

RVTECH

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If I am reading this correctly I assume you are referencing the possibility some bullets may still be seated not deep enough even though the OAL is within specs and the bullet ogive makes contact with the rifling and may not allow the round to chamber?

If this is the case there is a simple way to deal with this.

Take a fired case and place a bullet you plan to load with into the case. You'll want it snug so give the case neck a 'squeeze' to hold the bullet tighter if necessary.

Gently place the 'round' in the chamber and close the action to lockup. Open the action and carefully remove the 'round' and measure the OAL. Record this measurement and when ready to seat the bullets in prepped brass seat the bullet .003 deeper and check the first round for proper chambering.

I have been doing this all my reloading 'life' with bullets that have no cannelures to establish seating depth and have never had a problem.

I have sometimes done this with bullets that DO have cannelures to establish a longer OAL as well.
 
OP
T
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If I am reading this correctly I assume you are referencing the possibility some bullets may still be seated not deep enough even though the OAL is within specs and the bullet ogive makes contact with the rifling and may not allow the round to chamber?

If this is the case there is a simple way to deal with this.

Take a fired case and place a bullet you plan to load with into the case. You'll want it snug so give the case neck a 'squeeze' to hold the bullet tighter if necessary.

Gently place the 'round' in the chamber and close the action to lockup. Open the action and carefully remove the 'round' and measure the OAL. Record this measurement and when ready to seat the bullets in prepped brass seat the bullet .003 deeper and check the first round for proper chambering.

I have been doing this all my reloading 'life' with bullets that have no cannelures to establish seating depth and have never had a problem.

I have sometimes done this with bullets that DO have cannelures to establish a longer OAL as well.
Thanks for the response, man. I have heard of this method before, but am hesitant to use it because I want this ammo to run in multiple different guns. Not looking to have rifle-specific ammo. I also want these to run in a semi auto, gas operated, magazine fed Tavor 7. I'll try to explain a little better. So, if my load data says 2.800 COL, how would I use a bullet comparator to get as close as possible to that COL? Because the COL is from case head to bullet tip, and the comparator is measuring from case head to ogive, obviously there is going to be a discrepancy. Is there a formula to figure out what to add to the comparator measurement to calculate the actual COL, or a lookup table? Some sort of method to figure that out? Or should I just set one as close as I can from case head to bullet tip, measure that with comparator and then use the comparator from there out?
OR if I were to use your method, how much farther than .003 would I have to seat the bullet to ensure that this round would work in another gun, for example an AR10, and also load into both guns' magazines.

Thanks again,
-Nick
 

RVTECH

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OR if I were to use your method, how much farther than .003 would I have to seat the bullet to ensure that this round would work in another gun, for example an AR10, and also load into both guns' magazines.
Perform this test with all guns you are going to run the ammo in and go with the 'shortest' OAL one gun sets the bullet back.

I have done this for three .30-30 Winchesters I have to run the same ammo in.
 
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If you seat to the coal listed by the BULLET manufacturer, then you'll be fine. I understand you're wanting to load for several guns of the same caliber. That makes sense then.

Where the gauge comes in handy is when you're playing with seating depth in regards to the lands of the rifling. You don't want to unintentionally "jam" the bullet into the rifling.

Once you get to the point of tailoring your ammo to a specific gun, then I'd recommend getting the gauge so you know where you're at and where you're going. Otherwise you won't know how to "get there".
 

awshoot

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If you are loading for a Semiauto and several other rifles, as mentioned above, make the round fit the published COAL (Case OverAll Length) and it should work in everything. Use a full length resizing die rather the type that just bumps the shoulder so the ammo chambers in everything.

Now for the comparator, I presume you have calipers. Grab a handful of bullets and just measure them with the calipers to get a feel for how much variation there is. This isn't a necessary step (though it can be useful for high precision loads) -- it's just to get familiar with the components and I think you'll find that some bullets are longer and some are shorter.

Your bullet seating die is not going to press on the tip of the bullets -- it'll contact on the ogive. The ogive will be more consistent than the tip (although there will also be variation) but to simplify things and skip the caveats, what this means is that the bullets will get seated to the same depth, and the longer bullets will stick out more. As a result you'll see some variation in the COAL readings. Make cartridges (I often use unprimed no powder cases for this and then make plinker rounds out of the bullets when I pull them later) until you get one that is exactly what the book published.

Now that you have a representative cartridge, grab your comparator and make a measurement off the ogive. Bonus if you do more than one and take an average. This is your BTOL (Base to Ogive Length) for that specific bullet brand/type/weight (and no other). Record that somewhere -- in your book next to the specific bullet with an arrow drawn to it is a good place -- and use that measured BTOL to set up your dies in the future for that particular bullet. I'm belaboring this, but BTOL is only for that bullet -- you must go through this process for every other different bullet.

You can also use the comparator as noted above, to mess around with seating depth but personally, I only do that in bolt action rifles and if you want cross platform compatibility, you don't want to be doing that. You want the book value. Seating depth can have a large impact on accuracy but by the time you are doing this step, the ammo is for one specific rifle and no other. The method @RVTECH described above works and there are inexpensive tools you can buy to achieve something similar -- but this isn't what you are looking to do as it will defeat cross platform compatibility.
 

ron

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Some bullets very in length do to differences in the tip. Like the Sierra Hollow point Match Kings. Measure a half dozen
loaded cartridges and seat them under the "over all length" for that specific caliber. They will vary a little. The OAL is important
for the round can fit and feed from the magazine. ;) A bullet comparator measures off the ogive for seating bullets
out further usually a few thousands off the lands. But these bullets will not fit the magazine. These longer bullets have
to be single loaded. Too long to fit the mag. This is an advanced specialized loading technique for long range accuracy.
Also it is important to properly size the brass by bumping back the shoulder of the case to spec to fit your chamber. Chambers
very from rifle to rifle. To fit different rifles in the same caliber or an auto loading rifle you want to bump the shoulder back to
SAMMI spec. This can be checked by chambering a sized piece of brass in your rifle. You should be able to close the bolt and
remove the sized brass easily.
 

Dyjital

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Way more consistent when making a max COAL-.025” from lands.
Don’t have the time to explain it but they are useful when you are chasing accuracy.
I rarely measure that way anymore, my dies are set and they don’t move.
 

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