Seating by ogive or COAL?

[Wild Bill IV]

. . . 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 ! 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.

Very well stated!!!! You are a scientist as you have displayed the use of the SCIENTIFIC METHOD!!

I too have been shooting the Sierra bullets for over 45 years!!! Their record breaking bullets are outstanding!! Bearing surface length variations do cause changes in Velocity and Pressure!! And, some of their bullets increase in BC as the velocity drops!! That means the change of drag is decreasing!!
One of these days, I going to sit down and find the mathematical correlation between BC and DC using Calculus and Related Rates!!

I have no faith in manufacturers that advertise LOW DRAG without publishing their DC!! BIG SALES GIMMICK!!! I'm not buying their bullets until they can prove it!! I have always had problems with long nosed bullets!!! My hypothesis is these bullets have the center of mass closer to the base, which upsets the time of flight for stability!! This causes a serious drop in velocity due to the higher drag during instability!! I am a shooter who believes in super stability over BC!! My dad taught me how to solve the firing solution for 155mm artillery using a series of slide rules!!! There was NO BC ruler!! But, CD (coefficient of drag) was used in the formula for the projectile being fired!!!

I truly understand the physical properties of internal ballistics having studied PHYSICAL CHEMISTRY and THERMODYNAMICS (the study of heat energy)!! I always wanted to be a ballistics engineer!!! But, this field was being saturated with military testing grounds being shut down and consolidated into 2 major faculties!!! So, I chose the field of Industrial Physics which is the applied (not theoretical) physics!!!

 

[ELR LVR]

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

Late to this party but ummmm
.......this means something.

 

[Tesoro]

Late to this party but ummmm
.......this means something.

what? lol

 

[lawebb21]

the lands do not care where the meplat or tip is. It only matters for sorting bullets (which if shooting 1000 yards and not pointing, matters) and mag length. The rifle does however care (at least for a lot of bullets in my experience) where the ogive of the bullet or how far that contact point is to the lands or how far in the lands so when sorting, I sort base to tip. When seating, i care about ogive. This is for long range benchrest shooting and may not matter for all applications

 

[Tesoro]

the lands do not care where the meplat or tip is. It only matters for sorting bullets (which if shooting 1000 yards and not pointing, matters) and mag length. The rifle does however care (at least for a lot of bullets in my experience) where the ogive of the bullet or how far that contact point is to the lands or how far in the lands so when sorting, I sort base to tip. When seating, i care about ogive. This is for long range benchrest shooting and may not matter for all applications

It is pre-6am early here and the coffee has not yet fully neutralized last night's whisky intake, so I don't get what you are saying. Is it for LR I sort length first and cull any odd ones ( if not tipped) and then re-sort them for base to ogive consistency?

 

[MikeRu]

I have a couple questions here. So to start, I've been shooting long range, mainly 1K for the past 25 years, mainly hunting rifles and just 3 shot groups. In the beginning I seated to same COAL. As time progressed I started seating to the ogive. These days I can pretty much hold 4-6" 3 shot group at 1K laying prone/rear bag with my rifles. Which is good enough for me and what I'm doing anyway. I make sure all my rounds are identical to the ogive seating depth, after sorting bullets from longest to shortest, then starting out with the shorter ones I seat to the ogive I need, and turn the seater die down for the longer ones until they all match up ogive wise. It is a pretty lengthy and tedious process.

But, now a days I am almost more confused as when I started. I see people seating to COAL, versus the ogive and saying it's more accurate at long range. How can that be? I understand the BC part of it, but at the same time don't you want them all the same ogive/correlation to the lands also? You can't have both can you?

Its kinda hard for me to put this in words but if a guy seated all bullets to the same COAL, wouldn't there be a .001"-.010" difference in the ogive, or whatever variance is in the box of bullets at that point? Or vice versa by seating all to the same ogive, there'd be whatever difference in COAL due to the difference in overall bullet lengths?

Seems to me your always going to have up to say maybe a .010" variance in either ogive or COAL at that point, so which is typically more accurate at 1K+? Would love to hear from some of you better more experienced long range shooters on this and get some clarification, or at least how you do thing anyway.

Hoping I somewhat made sense rambling on here. Or maybe I'm just over thinking it all and just need to continue doing it the way I have been since I am still getting 1/2 MOA at 1K pretty routinely.

Thanks!

Here is what i do FWIW:
Option 1: No sorting at all and just seat to same CBTO using the Hornady ogive adaptor and a good (mitutoyo) caliper set.This will shoot very small groups at 1k (2.8" on a very good day for 5 shots, Benchrest). So you are living with slight (very slight) differences in bullet length of ~10-20 thou that doesn't seem to matter much. When my groups are big it's not usually one flier, they all are fliers!

Another easy step to add: sort your bullets before seating based on 1) bullet BTO then 2) bullet OAL. There's some good tools on here for sorting bullets by OAL. A good lot of Bergers will have all the same BTO (within 1/2 thou or so as estimated on calipers). Other lots will generate a couple groups by BTO and then additional groups for length. Limit the total # of groups to a handful, sanity is the goal, not perfection.

Third step optional: I think tipping is icing on the cake and sometimes more work for less gain, but i do it now and then and get good results ("do no harm", don't crush your bullet BTO). Someone named Keith G. said in a youtube video they got 8% higher BC from tipping (Berger 180 hybrids), which seems worth it IMO.

I wouldn't recommend seating to the COAL, your changing the bearing surface by 10-20 thou which is getting up there assuming your bearing surface is on the order of 0.500", seems like this could affect MV.

 

[Webster]

The problem with referencing to other people's CBTO is the differences in the caliper insert as there's often a significant difference in the measurement, just as there is with a cartridge's COAL. However, I think one can compensate for COAL by finding a corresponding bullet of the came OAL and using you're own caliper insert to determine the corresponding CBTO.

Unless you're seating to touch or jam, you really don't want to "chase the lands" as the correlation of the CBTO to the lands really isn't very important as seating depth is. This is why as they throat erodes, one can go for a very long throat erosion distance before ever having to make any adjustments to seating depth.

If you really want to get uniform seating depths, consider where you're seating stem contacts the ogive verses where you're caliper insert contacts the ogive. Seating depth is determined by where you're seating stem contacts the ogive, not where the typical CBTO is measured.

A lot here for me to folllow. I’m thinking it’s when the ogive touches the rifling that is part of the pressure time curve. If your trying different seating depths measuring from the tip it’s also charging the ogive to touch distance in an arbitrary way. Either way you try different lengths and see what works the best. There is variation in base to ogive as well as tip to ogive. Seating to ogive would seem to be the most constant since it doesn't reference to the tip. Your seater stem will determine what part of the ogive is pushed against to seat the bullet.

I think setting OAL cartridge total length was started because it’s simple and doesn’t require a gauge, just a caliper. OAL was important to fit in a magazine and feed properly. For many years it was good enough for most shooters. Whatever works! The target is all that matters.

 

[BoydAllen]

Makes a little sense, kinda. So by that you're saying to go by the COAL at that point and not the ogive, correct?

I do not believe that is what he meant. I think that he is saying that you cannot use another shooters numbers. You have to come up with your own. Regardless of what I am loading for, I like to have touch (using the method popularized by Alex Wheeler) , and jam measurements taken from ogive to head. I was around when the tools to measure off of the ogive first came out. If you are trying to have the same distance into or from the rifling of seated bullets, you need consistent bump, so that the case shoulder to head dimension is as close to the same as you can manage, and if you have that, measuring loaded rounds close to where the rifling will first touch the bullet should give the most consistent result. This reall mostly comes into play when a die needs to be reset. If you happen to pick up a bullet that is different from ogive to bullet tip your die will be se to a slightly different relation to the rifling. Do you shoot your brass in strict rotation so that all cases within a set maintain the same number of firings and sizings? That is important because degree of work hardening determines how much bump you get from a given die setting.

 

[Straightshooter1]

A lot here for me to folllow. I’m thinking it’s when the ogive touches the rifling that is part of the pressure time curve. If your trying different seating depths measuring from the tip it’s also charging the ogive to touch distance in an arbitrary way. Either way you try different lengths and see what works the best. There is variation in base to ogive as well as tip to ogive. Seating to ogive would seem to be the most constant since it doesn't reference to the tip. Your seater stem will determine what part of the ogive is pushed against to seat the bullet.

When measuring seating depths, I'm always measuring CBTO. Though when I sort bullets, the CBTO I used is based where my seating stem makes contact on the ogive. I've found this gives me the most consistent seating depth . . even when I measure the CBTO with a standard comparator insert, though there can be a small difference in that distance between the two contact points on the ogive. My objective is to have the seating depth (base of the bullet) the same inside the case. Variance in jump is not a consideration of mine given small variances in jump has little to no effect on the performance.

I think setting OAL cartridge total length was started because it’s simple and doesn’t require a gauge, just a caliper. OAL was important to fit in a magazine and feed properly. For many years it was good enough for most shooters. Whatever works! The target is all that matters.

The only two times I'm interested in COAL is: when trying to figure out just how someone's cartridge is actually configured like, since knowing their CBTO or amount of jump is simply of no help given the huge variations involved; And the other time is when loading to fit into my mags.

When someone give me their COAL, I can then load a dummy round to that length, use my own comparator, which is very likely very different some someone else's , to find what the CBTO measures and how that cartridge configuration might fit into my chamber . . . or not.

Then, if the cartridge does fit into my chamber, I can shoot it and see what I get on target. As you say, "the target is all that matters".