Base to ogive measurements, anomaly?

[kelbro]

Just sorted through a bulk box of 500 175gr 308 SMKs. Base to ogive variation for 480 of the 500 was +/- .001 which I am guessing is normal. What was surprising was that I pulled two boxes of 100 off my shelf and they were .025 different from the bulk box. Comparator measurement was .646 on the bulk box and .671 on two of the 100 pack boxes.

Those of you that perform base to ogive measurements, is that unusual?

I'm sure that it would show up on target. Before I started measuring, I would have never assumed that there was that much of a delta between boxes of 'match' bullets.

 

[tenring]

When bullet makers change tooling, there are often differences in that measurement. Most competition shooters order several thousands of the same lot number to keep them consistent.

 

[ShootDots]

Lately I have had as much as 4K differences in any one box of Bergers (no matter the caliber). They used to be + / - 1K >> mostly right on the money. Lately though, it has not been like that. I have had one lot of Berger 140gr B/T's that were 30K different from the previous lot. That was a few years ago... Although they were 30K different, the bullets inside the box were all within + /- 1k of each other... Personally, I think all this back-log and making a valiant effort to catch up and keep up has cost us some quality control... Once I run dry, I am SERIOUSLY considering going to JLK's...

 

[stool]

the dies wear and are replaced.
die wear changes the physical size of the finished product.

sierras current policy is only one lot/run in a box, it was not always so.

 

[savagedasher]

We seat our bullets off of ogive. Any changes from the base is just like changing the capacity in a case. I cant say for all but I do case capacity along with ogive to base. Can I see any difference in how they shoot. No. But doing it my sd is always 3' or less. Larry

 

[jlow]

What you are seeing is exactly what I have found with this bullet. This photo I took of a 500 lot of 175gr SMK that was binned based on bearing surface length tells all. You can see that there are basically two lots. One with ~500-501 and the other at 507. I always sort them before I use them for this reason. FWIW, this was done on 5/15/2012 well before any shortage problem. My precision rifle instructor tells me that this is norm and this evidence absolutely proofs it.

 

[LC Tikka]

Another interesting subject, thanks to all writers. Savagedasher is spot on, with large variations in bullet length and seating with only the ogive as a reference shows just how it will affect pressure and performance. I posted "trimming the bottom of bullets" on 22/12 to high light slight differences in bullet shape and possible performance losses for target shooters.
Combing both of these topics confirms what happens in the engine-room of the case is overlooked more often than not.
LC

 

[kelbro]

Exactly. Never realized the importance of this measurement before. I just expected that Sierra took care of that .

 

[Robbieg19]

All the Berger bullets I've checked have been very consistent in the same lot but I've seen the difference between lots be as much as .015.

 

[Bart B.]

I've measured a batch of .308 and .30-.338 rounds with bullets seated to a .001" spread across their .3000" ogive diameter back to the case head. Reasonably good consistancy, in my opinion.

Then a friend suggested I measure the case headspace (head to shoulder datum) across those 50 rounds. That spread was .004"+. Not all that good, in my opinion. Then I tried again being careful to lube each case on the pad the same way every time. That reduced the spread on the next 50 to .003". I asked him about that then he explained why bottleneck cases headspacing on ther shoulders are hard into the chamber shoulder when fired. That was a surprise to me; I'd thought that the case layed in the bottom of the chamber and totally ignored the force of the firing pin driving the case forward into the shoulder (often setting the case shoulder back a thousandth or more) as well as in-line ejectors pushing the case forward into the chamber shoulder when the round was loaded. No wonder full length sized ammo was preferred by all the high power match rifle shooters winning matches and setting records.

He suggested I change the way I lube my cases when full length sizing them by two ways. Whatever spread there was in case headspace would be added to the head to ogive dimension then transferred to bullet jump distance to the lands. Such is life with all bottleneck cases headspacing on their shoulders. Whatever the case headspace spread is, head clearance (space between bolt face and case head) will vary the same.

One was to tumble the decapped and cleaned cases in a foam-lined tumbler with a 60-40 mix of STP (engine oil treatment) and Hoppe's No. 9 bore cleaner. 5 ot 6 drops on the foam in a coffee can turned by my Thumbler's Tumbler worked good as it held 50 cases.

The other was to keep the press ram at the top of its stroke the same amount of time so the press would spring back the same couple thousandths amount after full length sizing each round a tiny bit more. Or use a shell holder with the correct height to stop against the die's bottom to give sized case headspace .001" shorter than fired case headspace. Redding's Competition Shell Holders (.002" steps up from .125" in five increments) weren't made back then so I chose a foam lined tumbler and consistant time at the top of the ram's stroke.

Sized case headspace spread dropped to .001"+

I've always loaded my single loaded rounds' bullets out far enough to set back about .008" when soft seated in case necks. Magazine fed rounds OAL for the .308 would be at magazine length minus 1/16th inch, but tighter grip on the bullets; these needed reasonably consistant jump to the rifling for any decent accuracy. They did just fine after I changed the way I lubed and sized fired cases.

 

[XTR]

All the Berger bullets I've checked have been very consistent in the same lot but I've seen the difference between lots be as much as .015.

I have noticed some variations like that in my Bergers lot to lot; however, my Forster die seats both to the same base to ogive on the loaded bullets so I don't worry about it and just make sure I load from one lot at a time.

I have heard over the yrs that Sierras can pretty obviously come from two different machines and end up in the same box, particularly when you buy the bulk lots of 500 or 1000.

 

[savagedasher]

Here is some Quick Load numbers and my gun is with in 3 fps of what it said
6mm dasher with H4350 42g water capacity case. 36.6 g -4350 108.9 %fill at 2.400 oal 3077 fps 61835 psi. Changing just the oal from2.400 to 2.390 the fill went from 108.9 to 109.3 3077 fps to 3081 pressures went 61835 to 62285 . To me anybody that doesn't trim cases to exact length and then check water capacity is missing the boat. same with ogive to base. Larry

 

[stool]

that is not suppose to be true...anymore.
they received enough complaints about it after they moved from california, that policy was to not mix bullets in a lot.

did they lie to me , i doubt it...they sell lots of seconds out of their store, no need to contaminate the quality for a couple of bullets.

All the Berger bullets I've checked have been very consistent in the same lot but I've seen the difference between lots be as much as .015.

I have noticed some variations like that in my Bergers lot to lot; however, my Forster die seats both to the same base to ogive on the loaded bullets so I don't worry about it and just make sure I load from one lot at a time.

I have heard over the yrs that Sierras can pretty obviously come from two different machines and end up in the same box, particularly when you buy the bulk lots of 500 or 1000.

 

[Killshot]

To me anybody that doesn't trim cases to exact length and then check water capacity is missing the boat. same with ogive to base

Trimming only changes the neck's length, and has little to do with the internal case volume after the bullet is seated - which is where the pressure is created.

 

[savagedasher]

None after your are correct but everything to do with before. Trim then to length then check the capacity is what I said. Larry

 

[Erik Cortina]

Here is some Quick Load numbers and my gun is with in 3 fps of what it said
6mm dasher with H4350 42g water capacity case. 36.6 g -4350 108.9 %fill at 2.400 oal 3077 fps 61835 psi. Changing just the oal from2.400 to 2.390 the fill went from 108.9 to 109.3 3077 fps to 3081 pressures went 61835 to 62285 . To me anybody that doesn't trim cases to exact length and then check water capacity is missing the boat. same with ogive to base. Larry

Actually, OAL does not matter, what matters is where the base of the bullet is.

 

[savagedasher]

First I would read the whole article before I made a comment. Next read what I wrote. I said the water capacity should be checked after trimming. Larry