Measuring at the ogive

[Ozzyblu]

How is primer seating taken into consideration? Uniform pockets and seating depth. My calipers are centered on the primer.

 

[Nature Boy]

Any takers on the double blind test?

I’d like to try. Currently I don’t sort bullets but I’ve been thinking about it. Got a memorial weekend and at the moment, no rain in the forecast.

I’d sort into two groups. The highs and lows in group 1 and bullets with the same measurement in group 2. I could get a family member to camouflage the two groups so I don’t know which is which

I’d shoot them at 500 yards.

Any feedback on that test protocol? What should the sample size be?

I have a 6BRA that constantly shoots unsorted Berger 108 VLDs in 5 shot groups at sub 0.3MOA at 500 yards so if sorting makes a difference it should show up.

Thoughts?

 

[Bc'z]

I think the high/ lows will have more vertical dispersion than target with
measured /sorted .

Would cases be sorted by weight or volume?

 

[Nature Boy]

I think un sorted will have more vertical dispersion.

Then a set sorted to the extreme highs and lows would have a lot more vertical dispersion, right?

 

[Bc'z]

Yes I believe it will be noticeable. How much I couldn't say.
I believe case volume would also be a contributing factor.

 

[Nature Boy]

Yes I believe it will be noticeable. How much I couldn't say.
I believe case volume would also be a contributing factor.

Well heck Bc'z, I don't sort cases either.

 

[BoydAllen]

Cartridge base-to-ogive (CBTO) variance of up to a few thousandths is not uncommon. As has been mentioned, bullet length variance is most often the cause. A significant portion of bullet length variance will reside in the nose region, presumably due to the manufacturing process used to produce jacketed bullets. Sorting bullets base-to-ogive (BTO) will not fix this issue because it is caused by length variance in the nose region. More specifically, it is caused by length variance between the caliper insert and seating die stem contact points, which lie outside the base-to-ogive measurement as shown in the cartoon below (critical distance, in green).

A tool such as Bob Green's comparator sorts bullets based on this specific dimension and facilitates more uniform seating depth without having to constantly tweak the seating die micrometer. Alternatively, the seating die micrometer can be set such that the bullets having the longest caliper insert-to-seating die stem contact measurement will be seated at the desired depth; those having a shorter distance between those two critical points will be seated slightly longer (CBTO). In other words, some of the loaded rounds will have the desired CBTO, all others will be slightly longer. Those can be set aside and given another stroke with the seating die after adjusting the micrometer by the appropriate amount. Of course, this approach requires more time/effort and also necessitates that each loaded round be measured.

The reloader will have to decide how much CBTO variance is acceptable and whether it is worth the extra effort. I test seating depth in .003" increments and try to keep the CBTO of all my loaded rounds for matches within .001". For someone that isn't loading for competition or that tests seating depth in .005" (or larger) increments, trying to hold loaded rounds to .001" CBTO variance may be unnecessary.

For loaded rounds where the bullets have length variance in the base-to-ogive dimension (i.e. have not been sorted BTO) that have loaded with very uniform seating depth (CBTO), by definition there will be variance in the length of bullet shank in the neck and the effective case volume. This is solely due to the bullet BTO length variance and can be improved by sorting bullets BTO. However, in my hands, changing the seating depth for jumped (not jammed) bullets during seating depth testing by as much as .010" to .015" in either direction does not cause a statistically significant change in measured average muzzle velocities, even though the effective internal case volume (and therefore pressure) is clearly altered by the different amount of bullet shank in the neck. In other words, my average velocities during seating depth testing over perhaps a .024" total seating depth range do not vary by more than the individual SDs. In contrast, changing seating depth by .025" to .030" (or more) may be enough cause detectable velocity variance. Clearly small differences in seating depth, or by analogy, bullet shank length (i.e. less than .010" to .015") are not usually sufficient to cause significant case volume/pressure/velocity changes. Again, the reloader will have to decide for themselves whether BTO sorting is worth the time and effort. It should be noted that the length of bullet shank in the neck can also affect neck friction and release of the bullet, in addition to the typically minor effects on case volume/pressure/velocity. It may be that the friction and bullet release are a more important reason to sort bullets BTO than the relatively minor changes in case volume/pressure/velocity caused by a few thousandths BTO variance.


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Thank you very much. Your response is extremely well written, and covers the subject very well, one of the best that I have ever read.

 

[Bc'z]

Well heck Bc'z, I don't sort cases either.

Nor do I!!
I've got 22 primed lapua cases ready to fill
I could weight sort them into 3 groups. High medium and low .
Also grab 6 bullets out of a different lot that
Measure .6910 giving a variation of .009.

I by no means am the best shot or reloader.
But if you were to put the longer shanked bullets in the smallest volume cases and the shorter lot into the largest volume cases....
What would the out come be?

 

[Texas10]

I’d like to try. Currently I don’t sort bullets but I’ve been thinking about it. Got a memorial weekend and at the moment, no rain in the forecast.

I’d sort into two groups. The highs and lows in group 1 and bullets with the same measurement in group 2. I could get a family member to camouflage the two groups so I don’t know which is which

I’d shoot them at 500 yards.

Any feedback on that test protocol? What should the sample size be?

I have a 6BRA that constantly shoots unsorted Berger 108 VLDs in 5 shot groups at sub 0.3MOA at 500 yards so if sorting makes a difference it should show up.

Thoughts?

I'm not trying to put you off on your offer, but to make a statistically significant test would probably require shooting hundreds or thousands of rounds in controlled conditions like an indoor range, large single lot of bullets, cases, primers, propellant, climate controlled conditions in loading room, the list goes on including accounting for barrel wear, cleaning rituals, and control rounds and control firearms. It would be quite an undertaking if you're up to it. There's no doubt in my mind that you'd wear out a barrel or two in the process.

It also may have already been accomplished under a gov't study, but I have no idea of how to search for that.

 

[BoydAllen]

How is primer seating taken into consideration? Uniform pockets and seating depth. My calipers are centered on the primer.

I can tell you that every short range group benchrest shooter that I am aware of seats primers by feel, not by depth. Out to 300 yards they produce the highest level of accuracy. I suggest that if you want to learn if there are any differences for longer ranges, that you ask someone who is actually winning benchrest matches at those distances. With high quality brass, such as Lapua, I do not think that primer pockets need cutting, and I am pretty sure that it does nothing for any brass. I have never seen any hard data on this. Personally I think that it is a case of people being sold on something because the rationale provided by the folks selling the tools sounded good, and shooters are always looking for a way to make their ammo better. As far as your calipers' position on the case goes, primers should always be seated well below flush, and for measuring fired cases, they should be removed or reseated below flush.

 

[Nature Boy]

I'm not trying to put you off on your offer, but to make a statistically significant test would probably require shooting hundreds or thousands of rounds in controlled conditions like an indoor range, large single lot of bullets, cases, primers, propellant, climate controlled conditions in loading room, the list goes on including accounting for barrel wear, cleaning rituals, and control rounds and control firearms. It would be quite an undertaking if you're up to it. There's no doubt in my mind that you'd wear out a barrel or two in the process.

Well, none of us shoot in those controlled conditions in real life so if that's what it would take to make the difference show up in the data then shorting BBTO doesn't matter.

Why don't I load 20 each per the protocol I outlined above see what it shows. I'm only out the time and components for trying.

 

[rwj]

Well, none of us shoot in those controlled conditions in real life so...

What were the findings of the Houston warehouse shooters? Sorry, couldn’t stop myself!

 

[Straightshooter1]

Here's an experiment I did in Feb of last year when I had a box of 500 168 SMK's with a bearing surface length difference as much as .033. After sorting with Hornady Comparators, I load 20 each from each end the spectrum into my precision tuned Lapua brass with 41gr of Varget and used a Magnetospeed V3 Chrono that I've attached to my hand guard of my RPR for measuring the MVs. I not only measured the bearing surface length, I also measure the bullet's length and their weights. There was little difference in these latter measurements, which did not directly correspond to what I got in bearing surface length. I made it a point to seat them all at the same COAL (that being around .001 difference).

So . . . Total of 20 shot each at 100 yds and alternating bearing length batch every 10 shots to see if there's some consistency between the groups. A pretty windy day at the range at this morning and my last group I felt I was loosing focus.

A substantial difference in MV and a noticeable difference in POI. Interesting to me that the bullets with the shorter bearing surface were slower than those with the longer bearing surface. Using my Forster seating die that uses the ogive to seat the bullet, I had seated the longer ones first and when I went to seat the shorter ones, they were actually seating with a much shorter COAL and hand to adjust the micrometer on the die by about .010 to get the same COAL.

As a result of this test, I now measure BSL rather than BTO of the bullet, but have not found this much difference in BSL in subsequent batches . . . like about .005. Even if it were twice that, given the number I got when there was a difference of .033, .010 isn't going to make much of a difference. But, I measure and will sort to batches within .005 each other and it seems to be working well for me and I notice I get consistent BTO measurements to +/- .001 after loading.

BTW: since then, I've improved on my powder measuring skills where I tend to get much better ES's and SD's now. But, still a lot of room for improvement.

 

[TJV]

my experience with a-max is that the point where the seating stem contacts is noticeably more soft compared to other bullet options/choices ... case mouths over sized, too square/lack of chamfer can cause small deformations at the stem contact area of the bullet when starting the seating entry ...

might see if slightly deeper chamfer & dry lube help your numbers

I use graphite to lube the inside of the neck prior to bullet seating. Is there another lube that can be more effective?

 

[Mikemontminy]

I use graphite to lube the inside of the neck prior to bullet seating. Is there another lube that can be more effective?

I use a dry moly lube. Applied wet with a Q-tip. When dry the powder doesn’t stick to it when charging cases and the bullet doesn’t push it out of the way when seating. I also believe it leaves a barrier between case and bullet preventing corrosion or bullet weld.

 

[DUSTY NOGGIN]

I use graphite to lube the inside of the neck prior to bullet seating. Is there another lube that can be more effective?

im assuming you've figured out a consistent tension , maybe try lightening up a bushing size

the right tension a good and graphite is the way you will get them to seat the same , if you feel a hard start when seating , then possible you may want to try a longer chamfering point like the lymans , be careful these will turn your cases into gasket cutters quick or possibly an expander

https://www.lymanproducts.com/brand...e-prep-tools/vld-very-low-drag-chamfer-reamer

they sell just the end at brownells for like 8 bucks

if the angle of your chamfer tool is equal to the angle of the boat tail it would basically create a hard stop .. once you get past the start its smooth sailing

 

[T-shooter]

Most bullets usually vary a little and here are a couple of Hornady's from different lots. These are from measured from both ends with a Hornady comparator. With my .308 and .223 inserts, the bore is .010 smaller than the bullet diameter. The 1st are the 168g BTHP Match (.308). This is why seating bullets from the tip is not an accurate way. I seat every round using this tool and to the point near where the ogive and bearing surface meet (as in the bottom picture) and try to keep it to within .001"

These are 75g BTHP Match (5.56mm)