Berger 155.5 warning on another forum

[Aubrey]

Copied from another forum: "Say, if you are using the Berger 155.5 Fullbore Target Bullet, p/n 30416, Measure your bullets when you change lot numbers. I just started a new box of 500 and for self preservation started to measure any differences between lots. Same p/n. The different length was .040 from base to Orgive and a bit more from base to tip. Weight was still 155.5. That's a huge profile difference. enough that I'll consider it a different load, not just a different batch of ammo. Could ruin your whole day at a Long Range match."

[williada]

Truly a Magnus Moment.

[6.5x55ai]

Have always checked any brand of projectile when changing lot#. Will also do a random check within lots. Anal approach brought on by bad experiences with Sierra 6mm MKs several years ago when there were even substantial measurement differences within the same lots let alone between lots!

[jasmay]

I think you will find berger state this amongst info on their website.

Have done this myself when switching batches.

[shooter mcreid]

I have had 2 batches of the 155 hybrids that showed a similar variation from one to the other. I lined a few up in a row and you could see the difference by eye. Both shot really well though and the transition was made at a 300m club shoot.

[DenisA]

I've seen this with Berger 105VLD's many times in the last few years. I check every batch and have found that with batch changes, the difference has been significant enough that I've had to tweak the load slightly.

[aaronraad]

The different length was .040 from base to Orgive and a bit more from base to tip. Weight was still 155.5. That's a huge profile difference. enough that I'll consider it a different load, not just a different batch of ammo. Could ruin your whole day at a Long Range match."

Yes and no.

For my mind, any batch variation in length I'm prepared to sustain in the shank length only. The boat-tail and ogive length should be relatively fixed and no more than approximately 0.002".

Limiting any length variation to the shank from batch-to-batch results in minimal batch-to-batch BC variations. Changing the lengths of the boat-tail and the ogive will affect the drag more significantly. Changing the ogive length will also result in a change in the meplat diameter, without some extra operations as now practised by relaoders in more recent years.

A change in shank length will give different pressure/muzzle velocity results. Something in the vicinity of 0.009" change in shank length will show up as vertical at 1000y from what I've read.

It would be worth taking some comparison diameter measurements also, as changes in shank diameter can give rise to much larger changes in length. Some recent results for diameter measurements for Berger projectiles (published on ozfclass.com) has shown them to vary from under and over the nominal 0.284 calibre for different weights. ICFRA TR rule T2.19.1. limit 0.308 bullet diameter from 0.3075" to 0.3085". There is no mention of an allowance for the 'pressure ring' inside the +/-0.005" tolerance. This would mean for Berger to stay within limits dies would have to be replaced within these limits. Potentially this would result in 0.0010" diameter change, but realistically Berger would have their own internal quality control trigger points. If you've ever tried EDMing, lapping & polishing carbide down to 0.00003" and then tried measuring that to produce exactly the same die set you can understand swaging lead and copper to 100,000psi shows up any errors regardless.

[AlanF]

I think most F-Open shooters wouldn't consider mixing batches in an important shoot. I normally buy a minimum of 500 and request all from the same batch. At the start of each new batch I normally sort on base to ogive, and check seating depth against the lands. Different batches often have different ogive shapes.

[Aubrey]

What's the best measurement to use? Is measuring base to ogive irrelevant?

[williada]

Aubrey, ballistically speaking the overall length affects the BC for wind bucking and the Magnus moment for bullet stability. The bearing surface length also affects drag but more commonly effects bore time and tune. The contact overall length affects pressures through free flight. This can affect bore time and exit timing on top of the node for compensation or nodal tune. Of course the ogive shape affects drag. You won't notice much at the shorts. Of course I would run the projectiles through a die to sort diameter/pressure ring discrepancies. This is a lot of work ahead of people who want to really get into the mud. If you were concerned with parasitic drag you would measure the angle and length of the boattail. If you were concerned with the core and jacket you would use a Juenke gauge and finally if you were concerned about gas seal and engraving forces you would consider sampling jacket hardness. How easy would it be for a shadow measurements to be taken by digital camera and compared by a computer measurements in a split second on a conveyor system for quality control? Just thoughts. David.

[johnk]

.... or trim the mothers with a Whidden meplatter & sort 'em by eye according to how big the pointy end finishes.

[aaronraad]

What's the best measurement to use? Is measuring base to ogive irrelevant?

I can't confirm it's the best, but it's a relatively simple measurement to perform. It's one way to look for consistency across the batch and pick out any outliers. Everyone has their own tolerances for measuring everything from charge weight to velocity extreme spread.

Questioning a measurement's relevance is prudent and can sometimes only be answered through personal experience. We pay top dollar for quality components and these might only require a small sample from the batch to confirm consistency. Shooters will wisely spend the time they save on inspecting every component from the batch, on other elements/skills of their sport or accruing shooting credits.

How long since anyone here on the forum weighed each of their primers

[AlanF]

What's the best measurement to use? Is measuring base to ogive irrelevant?

I can't confirm it's the best, but it's a relatively simple measurement to perform. It's one way to look for consistency across the batch and pick out any outliers.

Agreed. With some batches I'll measure about 50 and find no outliers, so won't bother with the rest, but usually, even with the best brands, variations will be found. The worst I've seen within a batch has been about 0.020" variation, from Sierra. I believe this is because they mix the output from multiple machines - not sure why.

[williada]

I agree with Aaron and Alan and sample sort for efficiency. Some shooters I know, do plan 6 months out or more for a major campaign and are testing. You only see them at the big shoots which they seem to win. I know a couple who sort every nuance, particularly for 1000 yards. It is certainly something I would not do for club or district shooting.

Yes, Sierra used to supply Winchester Australia with projectiles which I think from memory came off 4 machines. That's why our volunteers sorted thousands of rounds for our Palma Team back then for weight, ogive and concentricity before the rules changed.

JohnK, I just love your humour

[johnk]

JohnK, I just love your humour

It's more or less true, but I'm talking about a huge run of SMKs that Aussie MR shooters sourced some time back. I batched 1500 by bearing surface length while watching a test match only to find fewer than a couple of handfuls of rogues outside an .002" spread. However, when I meplatted them with Whidden's trimmer, which indexes off the base & not the ogive like most, I found they fell into two readily identifiable groups according to meplatted tip diameter & threw a few more rogues.

As I saw it, the location of the tip trim was indicating boat tail form/dimension & it seems from the results that, keeping the two batches separate, I have reduced my second & third SDs on paper.

To the contrary, the Bergers VLDs I'm playing with now (the ones that the SMK was cloned off) have far more uniform meplat diameters when similarly trimmed, so it looks like I might have to run confirming measurements for reassurance.