Am I making an OAL mistake???

[mihkmihk]

I am new to using a comparator and OAL gauge. I was under the impression that a bullet seated closer to the lands could improve accuracy, and this will often result in a longer COL than published. I did make sure the modified case was screwed in tight between measurments. I was looking at my two rifles chambered in .223 (Kimber 84L bolt action and Bushmaster Varminter AR style).

Using a Hornady OAL gauge and comparator, I got the following measurements with Sierra 52 gr Match King HPBT:

Bushmaster Varminter (nine measurement with 3 bullets)
Cartridge Base to Ogive average 1.888"
COL 2.229"

Kimber 84 bolt action (eight measurements with 2 bullets)
Cartridge Base to Ogive average 1.919"
COL 2.260"

Published max COL is 2.260

Sierra 50 gr Blitz King:

Bushmaster Varminter (nine measurement with 3 bullets)
Cartridge Base to Ogive average 1.914"
COL 2.317"

Kimber 84 bolt action (six measurements with 2 bullets)
Cartridge Base to Ogive average 1.913"
COL 2.316"

To sum it up, in both rifles the 50 gr Blitz King will be loaded longer than 2.260 (as I expected), but the 52 gr Match King will be right around 2.260 in the Kimber, and actually shorter in the Varminter.

Does this make sense??? Are some rifles (chambers?) on the short" side?

 

[jonbearman]

Chambers can go either way depending who chambered them and especially on factory guns where they are always long to allow owners to shoot all aftermarket ammo safely and the lawyers have it their way so as not to cause an overpressure situation.

 

[mihkmihk]

Jon: So is the varminter an anomoly since it seems to come in short with the 52 gr? Or is it something about that round?

 

[rocketron]

you may be getting false measurements due to a differance in headspace...modified case may be longer or shorter than the chamber or a fired case.

Ron