Seating by ogive or COAL?

[Tesoro]

I now go the lazy route and get excellent results for my purpose ( <moa at 1000). I shoot closed tipped 6mm DTAC bullets and just sort by bto to cull out the occasional wild one. No cbto measurement, I just seat so the bottom of bearing surface just above the neck shoulder junction. Use a powder load that is in top 1/3 of the increasing velocity curve before it levels off, and then finish polish with a tuner. As throat erodes I tweak the tuner to make up for it. Been working well so far at 1000 yds on my hillbilly targets! I pay more attention to uniform neck tension than I do a few tho diff in ogive to lands.

 

[Straightshooter1]

Nice to see you're using my pictures again without referencing the person that took the time to make that image...me.

When one puts the pointer over the picture is shows you as the source. Not good enough?

 

[Eagle Six]

When one puts the pointer over the picture is shows you as the source. Not good enough?

I realize you are asking a question to Ned, however as a member and following this thread I would have no need to place a pointer over the image and would have assumed you were the creator without you providing a credit line or quoted the original post. I offer this as food for thought.

 

[Straightshooter1]

I realize you are asking a question to Ned, however as a member and following this thread I would have no need to place a pointer over the image and would have assumed you were the creator without you providing a credit line or quoted the original post. I offer this as food for thought.

Hmmm??? All kinds of pictures from all kinds of sources are posted without people assuming the poster was the creator. As I understand it, it's plagiarism if the poster was in some way passing them off as their own and/or profiting from it. In this case, I'm in no way profiting from it nor is it on a website different from where it came. I would think that if Ned cared so much about credit for his illustration, he would have put his name right on it, which I will do on my copy for any future use by me, since the file name doing so is apparently not enough.

 

[wkdickinson]

Let me throw you another curve ball. I have been having more success getting smaller rounder groups with lower SD and ES by seating to a seating depth inside the case. I see more consistency on paper by controlling the internal ballistics of the case. With a seater die that is made for the profile of the bullet I am using, I try to control the seating depth and not worry about jump to lands/ CBTO or the COAL. I check the bullet base to ogive and keep that under 0.002" variation. There is a risk that the bullet profile may vary between individual bullets such that the distance between the comparator contact point and the seater contact may vary more than 0.002" but I have not seen that as a huge problem with the .224 and .243 Berger's I am shooting. More variation in length on the bullets seems to occur from the seater stem contact point to the tip.

Ned has posted images of what I am talking about recently.

I have long wondered about this exact concept! In reality, is it really bullet jump that makes the difference, or are we actually varying the case volume, by how deep we seat the bullet in the neck. If that is not what is happening, how then do we explain how the same CBTO continues to work even as the lands move?

 

[Ned Ludd]

When one puts the pointer over the picture is shows you as the source. Not good enough?

Make your own images, please do not use mine. I can't be any plainer than that.

 

[RCE1]

I would say, in terms of accuracy, the ogive would be important. However, if you're dealing with a magazine there will be some OAL limitations.

 

[wkdickinson]

Several years ago I was having a problem with inconsistent CBTO with my 6 Dasher. I was using a Whidden "Micrometer" seating die, with the correct seating stem for Berger 105 Hybrid bullets. No mater what I did I could not get consistent CBTO (0.005 - 0.040"+). Logic told me this was impossible, because the seating stem didn't move. So I made a new compartor insert as close to the diameter of the mouth of the seating stem as I could. When I measured my loaded rounds - they were within 0.001" of each other.

I then I randomly selected 30 bullets from the remaining lot (400/500) and first measured the BTSS. Then measured the BTO and subtracted it from BTSS. The results mirrored the problem I'd been having with CBTO inconsistency.

I don't shoot Berger 105 Hybrids anymore - just my experience.

 

[jelenko]

What is 'btss'?
Thanks

 

[ISS]

Easy near universal answer: .020" off the rifling origin. Probably answered here.

ISS

 

[gunsandgunsmithing]

@Dave M.

 

[wkdickinson]

What is 'btss'?
Thanks

"Base To Seating Stem"

 

[DiffEQ]

For plinkers (i.e. 223, 6.8, 6.5G, etc on my Dillon 650), COAL, only QC checking a random selection along the way.
For accuracy, B2O, and the neck tension better be the same, or you will experience "spring back". When that happens, the B2O measurement can vary 0.002" - 0.005", driving you nutz in the process. If it's annealed and I experience a significant increase in force needed to seat the bullet (feel, no gauges), I'll pull it, dump the powder, salvage the primer and scrap the case.

 

[Tesoro]

"Base To Seating Stem"

ooh a new one for the list of 'B' acronyms. !!! How come noone is talking about jamming which negates all the above?

 

[Wild Bill IV]

if you think about the firing pin pushing the case into the chamber, up against the shoulder before finally igniting the primer, you might conclude the best way to maintain the exact same bullet to barrel lands configuration would be to measure and control the distance from bullet ogive to shoulder datum, rather than OAL or BTO.

That is a good point!!
However, if you keep the sizing die set at one constant point, and watch press loading, the base to datum will stay consistent and CBTO will be easier to measure!! I set my FL die for 1/2 thou shoulder setback!! Done it for 48 years and haven't had any problems!!! I still use a dummy case/bullet with makers to locate the lands!!! This distance is called RIFLE SEATING DEPTH!!! And yes, it changes with throat erosion from plasma ejection!!! I KNOW, FORM-FIT-FUNCTION as an ENGINEER!!! CONSISTENCY IS THE KEY TO PRECISION!!! ACCURACY IS IN THE SKILL OF THE SHOOTER!!! I never use COAL as a gauge!!!

 

[Wild Bill IV]

What I was trying to explain was how I or anyone else, on the other side of this computer screen, can load up a cartridge with the same 1.94" CBTO with my comparator that's most likely very different that your comparator. My comparator could easily give me a .060" difference than yours (like the difference between a Sinclair comparator and the Hornady comparator).

Apparently, I misunderstood what you were trying to understand . . . ¯\_(ツ)_/¯



When we're talking about "seating depth" (that is, how far the base of the bullet goes into to case as measured from the base of the case), is best measured from where the seating stem contacts the ogive rather than where the typical comparator makes contact with the ogive. The difference between these two points of contact can be substantial (several thousandths), especially from one lot to another.

The typical comparator is good for finding the touch point on the lands where you can decide on a starting point for loading the cartridge (like .010 off the lands). To maintain whatever seating depth that .010 off the lands represents and do it consistently, you'll need a comparator that touches the same spot as your seating stem. Doing so, you can have variations is the CBTO (which doesn't really matter much) as the difference between those two contact points will vary. Note that using the seating stem contact point for seating depth isn't effected by variations a bullet's OAL's (base to meplat measurement).

Great presentation!!!
There is a couple of BUTs in there!!!
Looking at this from a process engineer, the bearing surface can vary slightly due to hardness variations from the lead core in the manufacturing process!!
Plus, most variations in bullet OAL occur at the meplat!! The glidden copper jacket at this point has lots of irregularity!!! This causes COAL to very!! I batch sort bullet by weight and BTO lengths with the OLD Sinclair comparators!! Been doing this for 48 years for both target and hunting!! Set micrometer seating stem up 0.005, seat a bullet, measure CBTO, adjust mic, and reseat!! Good enough for < 0.3 C to C MOA 5 shot groups!!!

 

[Straightshooter1]

Great presentation!!!
There is a couple of BUTs in there!!!
Looking at this from a process engineer, the bearing surface can vary slightly due to hardness variations from the lead core in the manufacturing process!!
Plus, most variations in bullet OAL occur at the meplat!! The glidden copper jacket at this point has lots of irregularity!!! This causes COAL to very!! I batch sort bullet by weight and BTO lengths with the OLD Sinclair comparators!! Been doing this for 48 years for both target and hunting!! Set micrometer seating stem up 0.005, seat a bullet, measure CBTO, adjust mic, and reseat!! Good enough for < 0.3 C to C MOA 5 shot groups!!!

. . . always some BUTTs. . . . . I mean, BUTs.

I agree, the bearing surface can vary as you say, and . . . it can vary a great deal from lot to lot. When I found a difference of .033 in bearing surface on some 168 SMK's, it led me to do an experiment to see how that would effect MV and POI. The result was a significant difference in both from 20 shots of both the short set and the long set.

These days, I sort by bullet base to seating stem contact point. I did wonder how much differences in bearing surface affected bullets sorted this way due to those variations causing variation in the timing of the blowby. Since variations in seating depth apparently does effect this timing, I'd think bearing surface variation does the same to some extent. How much? I have no idea at this point. Sorting as I do seems to work well for me.

 

[Ned Ludd]

Hmmm??? All kinds of pictures from all kinds of sources are posted without people assuming the poster was the creator. As I understand it, it's plagiarism if the poster was in some way passing them off as their own and/or profiting from it. In this case, I'm in no way profiting from it nor is it on a website different from where it came. I would think that if Ned cared so much about credit for his illustration, he would have put his name right on it, which I will do on my copy for any future use by me, since the file name doing so is apparently not enough.

Don't use my images at all. Make your own. No one thinks that is OK...no one. It is pure laziness and theft of intellectual property by intent, even if it may not meet any legal definition of such. In fact, you are trying to profit from its use by presenting yourself as a knowleageable member of this forum using work created by someone else. The fact is, except for individuals such as yourself, I would have no need to put my name on an image, because no else would ever try to steal it. I was giving the members of this forum the benefit of doubt as I never even considered someone would actually take one of my images and try to use it as their own. After our first interaction on this subject, I did in fact add my name to all the images I have made and commonly use. Except for you and those like you, I shouldn't have had to do that.

 

[Straightshooter1]

Don't use my images at all. Make your own. No one thinks that is OK...no one. It is pure laziness and theft of intellectual property by intent, even if it may not meet any legal definition of such. In fact, you are trying to profit from its use by presenting yourself as a knowleageable member of this forum using work created by someone else. The fact is, except for individuals such as yourself, I would have no need to put my name on an image, because no else would ever try to steal it. I was giving the members of this forum the benefit of doubt as I never even considered someone would actually take one of my images and try to use it as their own. After our first interaction on this subject, I did in fact add my name to all the images I have made and commonly use. Except for you and those like you, I shouldn't have had to do that.

Ned,

Like you suggested, I made my own for any future use and will NOT used ANY of your images or any part of them, given your sensitivity. Using Microsoft Publisher, it didn't take me much time to do it. I've also deleted that image from all my computer files that it will not ever be used again.

 

[searcher]

Hmmm??? All kinds of pictures from all kinds of sources are posted without people assuming the poster was the creator. As I understand it, it's plagiarism if the poster was in some way passing them off as their own and/or profiting from it. In this case, I'm in no way profiting from it nor is it on a website different from where it came. I would think that if Ned cared so much about credit for his illustration, he would have put his name right on it, which I will do on my copy for any future use by me, since the file name doing so is apparently not enough.

My thinking is that if guys don't want their pictures resurfacing when folks forward for others to view (including on this forum), they probably shouldn't post them. Most of us who share photos and information don't consider it intellectual property when posted on a site intended for the sharing of thoughts and information.