Berger Hybrid bullets - BTO variance == Seating Depth Variance == Pressure Variance

[pat fulghum]

A lesson learned that I need to share.... (or maybe I'm just a newbie and everyone already knows this)...

I'm running Berger 105gr Hybrid bullets.
I'm loading Varget 30.0 with CCI 450 in Lapua 6BR brass.

Lot #9267 measured Base of Bullet to Ogive of 1.650 Overall Length 1.265
Lot #8815 measured Base of Bullet to Ogive of 1.670 Overall Length 1.275

I seat my bullets to Ogive to maintain a slight jump, I don't touch my Bullet Seater.

But I didn't realize that the bullets where .020 deeper in the case, and I was seeing slight pressure signs (slight ejector mark)... and I couldn't figure out why until I started measuring everything.

That is when I found the .020 difference in BTO for bullet batches.


Quickload shows that by pushing the bullet deeper in the case by .020, I increased pressure about 1000 psi...

Just goes to show you that you really need to measure everything.

I sure wish that bullets/primers/powder all came with the right quantities, but I know that isn't realistic. It feels like hot dogs sold in 10 packs, with buns sold 8 to the pack.

Just wanting to share...

 

[spclark]

It's recommended practice to rework loads anytime you change to a new batch of anything. Your post illustrates why this is a good idea.

A couple years ago I noticed quite the same thing with Berger's 155 Hybrid 308 but in my case (pun unintentional but apt) the 0.020" difference between old and new BtO dimension had little to no noticeable difference in the accuracy of the loads I was using for Palma events.

Like with so many aspects of this pursuit, sometimes you get lucky.

 

[CJ6]

That's why I try to buy larger boxes 500-1000 . I've noticed (with Berger anyway) that the lot to lot variations can be larger than I'd like, BUT the variations within the the single lots can be quite good. 3 lots of 155.5 fullbores vary .072 in BTO from short to longest,but vary only .003 in each individual lot (from those I've actually measured..about 40 from each lot).

 

[Gina1]

Ditto .... 500 or more at one time... All the same lot number. when working up a load for an up coming match.

 

[Jet]

Pat

Buying large quantities of the same lot will save you work in the future. I recently went to a new lot of the 105 Hybrids and there is an average .013 difference in bearing surface between the two.

Good Shooting

Rich

 

[Liven The Dream]

I must be lucky never with the Berger's I have.
Sierra a different story 500 box of 155 Palma Bullets two different lots mixed .014 difference.

The story is different press they came out of ?

 

[Ned Ludd]

In general, changing the seating depth of jumped bullets by up to .010" in either direction (i.e. from ~.005 off to .025" off, with the charge weight testing having been done in the approximately the center at .015") does not result in a sufficient change in velocity that most chronographs can reliably record a significant difference. However, I have experienced loads that were running just under MAX pressure that were OK, but became too hot when a new lot of bullets were used that were about .025" longer, just as you reported. The good news is that meticulous recording of velocity during load development will almost always reveal this effect more reliably than pressure signs on the brass, which can be a pretty finicky indicator of excessive pressure.

 

[pat fulghum]

YEs... I was able to measure a statistical difference of 30fps... I load in batches of 50... and With Varget, I get ES usually < 20, and single digit SD.

So seeing my average move by 30fps, and then slight ejector marks (with same brass as before) does show that there is pressure diff.

 

[dcali]

I just opened a new box of 500 Jugs and base to ogive changed by 0.020" - the new lot was shorter. (Bullets within the same lot of each box were within a couple thous of each other). The new lot also seated out about 0.007" longer than the old lot with the same setting on the seating die. So yeah, any time you switch bullet lots, you need to double check - in this case, my optimal seating depth moved by about 0.005" - shorter (as tested at the range).