Seating depth measurement

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Rifleman87

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I used to just go off overall length (bottom of case head to the tip of the bullet), I gave up on that long ago. Today was a good reminder to myself of why I gave it up. I was reloading some 308 loads for my wife (125 nosler ballistic tips), I was feeling lazy (she shoots irons so I wasn’t going for all our precision) and was just going off OAL (going for 2.735”). Then I thought I’d check base to ogive, it was all over the place. I got base to ogive all within 0.005” of each other then remeasured OAL, the spread was from 2.728-2.764, almost 0.040” spread.

I find get much better accuracy and SD with consistent base to ogive vs OAL.

What works for you?
 
Potashminer said:
So, how is that done when loading - is the seating stem adjusted for each bullet??
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For me, yes. It depends on the projectiles I’m using and how consistent they are. This box of ballistic tips was pretty bad, so after getting each one set to the desired depth I would back the seating stem off about 1/3 of a turn. I seat the next bullet, measure base to ogive, adjust, raise the ram, measure again, until I get to the desired depth. Total pain, but I find I get much more consistent accuracy and SD.
 
Janeau said:
Always CBTO.
Only time I check OAL is for a magazine gun..then I go CBTO when this is established.
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Excellent point on double checking OAL for mag length! If my mag was limited to 2.750” OAL (it’s obviously not), almost half of my rounds would have been too long with my desired base to ogive length. For some of my other loads in other rifles I load to my desired base to ogive then double check that the OAL will still allow it to cycle through the mag.

The fun we have, hahaha
 
I load a dummy round with the bullet seated out long and closed the bolt, allowing the bullet to push back. I then put the dummy round back in the press, run the ram up all the way and wind the seating stem down until it touches the bullet. Once the stem touches the bullet I wind it down another .020". I load and fire single shot so don't have the worry about mag length nor do I care what the COAL is.
Base of the round to the ogive is the only important measurement. Regardless of what the numbers are this must be consistent.
 
maynard said:
I load a dummy round with the bullet seated out long and closed the bolt, allowing the bullet to push back. I then put the dummy round back in the press, run the ram up all the way and wind the seating stem down until it touches the bullet. Once the stem touches the bullet I wind it down another .020". I load and fire single shot so don't have the worry about mag length nor do I care what the COAL is.
Base of the round to the ogive is the only important measurement. Regardless of what the numbers are this must be consistent.
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What seating dies do you use? If I used this method my base to ogive numbers would be all over the place. I use Lee dies for my 308’s, I have Hornady custom dies for my 6.5cm’s. I bought the proper seating stem for the bullets I use with the Hornady dies, I still find base to ogive varies, much less than the Lee dies though. For my Lee dies I just use the stem that cake in them, but I don’t load ELD style bullets for my 308’s, mostly SST’s and NBT’s.
 
I would think the seating stems can (or should) only contact the bullet at one point - at one diameter? If that happens to be the "ogive" diameter (?) than all of the batch would be the same CBTO length. I have 19 different sets of reloading dies here - none do that - they all make contact somewhere along the radius / slope of the bullet. Have had at least one stem that was hitting the very tip of pointy bullets - opened that one up on my lathe so contact was along the slope, but quite certain I am not at the "ogive" diameter. I understand that "ogive" diameter to be the point where the curve of the bullet front meets the straight wall of the bullet side, so essentially the same as the bullet body diameter?? If that is correct, then what keeps the bullet body from slipping through the particular ogive gauge?
 
Rifleman87 said:
What seating dies do you use? If I used this method my base to ogive numbers would be all over the place. I use Lee dies for my 308’s, I have Hornady custom dies for my 6.5cm’s. I bought the proper seating stem for the bullets I use with the Hornady dies, I still find base to ogive varies, much less than the Lee dies though. For my Lee dies I just use the stem that cake in them, but I don’t load ELD style bullets for my 308’s, mostly SST’s and NBT’s.
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Redding Competition seater. Once your seating die is set you are good for about a 1000 rounds or so until you need to start chasing the lands.
 
Potashminer said:
I would think the seating stems can (or should) only contact the bullet at one point - at one diameter? If that happens to be the "ogive" diameter (?) than all of the batch would be the same CBTO length. I have 19 different sets of reloading dies here - none do that - they all make contact somewhere along the radius / slope of the bullet. Have had at least one stem that was hitting the very tip of pointy bullets - opened that one up on my lathe so contact was along the slope, but quite certain I am not at the "ogive" diameter. I understand that "ogive" diameter to be the point where the curve of the bullet front meets the straight wall of the bullet side, so essentially the same as the bullet body diameter?? If that is correct, then what keeps the bullet body from slipping through the particular ogive gauge?
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I completely agree, of all the seating dies that I have, they do the same thing as yours. What I find is inconsistency in bullet profile leads to inconsistent depth of the ogive, even though the COAL might be the same. Seeing as how the ogive is the first part of the bullet to contact the lands, that’s the part that matters. You are correct on what ogive is, where the bullet stops tapering and becomes full diameter.

As for my “gauge”, I’m cheap, I resize a worn out casing, then cut it so that I have the sized neck and enough body to cover the end of the bullet. I square the now open end of the body and measure the length of my tool, I shoot for 1 inch (keeps things simple). I slip it over my assembled round (neck down) and measure from the case head to the end of my tool with calipers. Subtract the tool length, boom, case head to ogive length. No, it’s not as good as a proper ogive measuring tool, but it’s close and the price is right, haha. I’d say the important thing is consistency. I may not be measuring EXACTLY at the ogive, but I’m very close and measure the same spot (diameter) on each bullet. So for my 308’s, my tool is 0.307” ID. I’m not sure what it would be on one made by Redding or something like that? Anyone care to measure theirs?
 
Rifleman87 said:
For me, yes. It depends on the projectiles I’m using and how consistent they are. This box of ballistic tips was pretty bad, so after getting each one set to the desired depth I would back the seating stem off about 1/3 of a turn. I seat the next bullet, measure base to ogive, adjust, raise the ram, measure again, until I get to the desired depth. Total pain, but I find I get much more consistent accuracy and SD.
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I do similar, ( Redding and Forster Mic seating dies ) But I started sorting bullets, then I only back my seater out 3 thou before creeping up to the exact BTOG length. If one gets too short, it turns into a fouler/sighter round. Not too bad at all really.
 
So, really, on a newly cut chamber, the "ogive" could be defined around the angle of the end of the "lands" - so a diameter greater than the "bore" - top of rifling - but less than the bottom of the grooves. As the "lands" erode with firing, do not see any guarantee that the angle at the end of the lands stays the same. So really, this is about picking a diameter on the bullet that is less than groove (less than bullet body size) and greater than top of rifling, and using that as the reference point to establish the "clearance" to the lands on the reloaded cartridge. A true "ogive" (from geometry or architecture) would be a point along the bullet body, whereas the ends of the rifling are not necessarily a point. I have some older, well used barrels that show in the bore scope that the "lands" are not even all the same length to each other! But still, a seating stem nose sized to that diameter- less than top of rifling; greater than bottom of groove - would seat various "shapes" of bullets to similar "depth", I think.
 
I just find my somewhat accurate finished round BTOG, ( Hornady tool ) set to mag length minus a bit of wiggle room for bullet OAL differences. I jump my bullets lots, so If I'm not exactly correct in finding my lands, it does not matter, no danger. Its just a reference number.
 
Rifleman87 said:
Interesting. Does the seating stem seat directly on the ogive with those dies?
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No the seating stem hits farther up on the bullet than at the ogive. What I am doing with the long seated dummy round is allowing the rifling to push the ogive of the bullet back. By putting the dummy round back into the press and moving the ram up and screwing the stem down until it touches the bullet would not leave the bullets touching the lands. This however isn't the greatest idea because a bullet could get stuck in the rifling if there was ever a cease fire during a match (ask me how I know this) That will result in a action and chamber full of powder.
Of all the 155 gr .308 match bullets in several different rifles and barrels that I have tested .020" off the lands just seems to be the magic number.
 
With good consistent bullets I find it's easier to measure base case to tip. Once in a while, if bullet lots change, I'll look at the base case to ogive measurements between the two lots.

Base to tip can vary a few thou on either side of the intended length but it doesn't matter much ime.
 
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