QL Guru - ? about 'short' batch of bullets

[spclark]

Lot of 155's I've been using work great with 45.0 grains IMR 8208XBR. I seat 'em 0.020" off the lands.

I'm just running out of that lot.

The NEW lot I bought of the exact, same bullet measures ~ 0.030" shorter overall (base to tip) while the base-to-ogive dimension is 0.020" shorter than those in the lot I've used up.

Bullets from both batches weigh identically @ 155.0 +/- .05 grains.

Manufacturer's tech support suggests the 'short' bullets ought to shoot just as good as the batch I've used up as long as the 'jump' to lands is the same for both.

Sized, primed but empty case water volume (308) is 55.1 grains.

Question: should I load a week's worth of match ammo with the 'short' bullets exactly the same as their 'longer' siblings?

No time to test, at least not in any meaningful way.

I'd rather not try to keep loaded case volume the same by seating the new lot 0.020" deeper. Nor do I want to risk meaningful velocity loss from seating them the same as their longer brethren.

Would a modest bump in charge weight - maybe 0.2 grains - work to level the difference if the new batch is seated the same?

Hope somebody with QuickLoad and a few minutes to kill can enlighten me.

 

[Nomad47]

I can run some QL numbers for you, Stephen. But more info is needed to give you any accurate info.
Fired case capacity (with a primer in place) is more accurate. Brand of bullet would be nice, but better still is bullet OAL and loaded case/bullet OAL so I can determine useable case capacity.
If you can give me MV and barrel length, I can come up with an adjusted charge to keep the same barrel time.

 

[spclark]

The two lots of bullet OAL are 1.280" for the batch I've used up, 1.250" for the new batch I need to load.

The rest is in a PM I just sent....

 

[Nomad47]

Stephen, when I used generic info in QL, I came up with exactly .2 more grains to maintain barrel time (I used a 30" barrel). But when I used your case capacity of 55.1 grains, I came up with a needed charge increase of .22 grains.

Just saw your post and will check my PMs.

 

[Steve Blair]

As a data point, I run 45.4 behind 155.5 Fullbores in standard Lapua brass. Safe in my rifle.

 

[spclark]

As a data point, I run 45.4 behind 155.5 Fullbores in standard Lapua brass. Safe in my rifle.

That's useful info, thanks! Over across the pond I know a shooter uses 46 grains with the Fullbore 155.5. In my rifle both the 155 Hybrid and 155.5 Fullbore seated off 0.020" shoot great with the same 45.0 grain load.

The Fullbore, with it's shorter bearing surface, can probably take a wee bit more.

Bill, that 0.2 grains is exactly what I was SWAG-ing for lack of further input.

 

[Nomad47]

OK. I plugged in your average cartridge OAL, and when I used the generic case capacity of 56.0 and the default QL Powder Ba for 8208, QL came up with exactly your MV. I then increased cartridge OAL by .020" and I had to add exactly .2 grains charge to come up with the same barrel time. Of interest, MV increaased by 3 fps.
I guess your OAL average will increase by .010", and your boattail/bearing surface junction will be .020" further out in the case. And that in turn will increase useable case capacity.

 

[spclark]

Great! Thanks Bill!

We both know 8208XBR won't really lend itself to 100% load density, at least not in the cartridges we mess with. I truly appreciate your taking time to run the numbers & verify what I was extrapolating based upon my former experiences.