Measuring CBTO With Hornady OAL Gauge Problem

[Ibelieve1776]

I have a 300 wm and changed from FC to WW brass. I had Hornady make a piece of brass from the FC brass when I first started using it which would give me a CBTO measurement of 2.996. Now after firing my WW I sent brass off to Hornady to make another piece for the OAL tool which is giving me a measurement of 2.891. I was about to sit down tonight and load some of my Berger 230's but I thougth Id double check my measurements with the new WW brass threaded for the OAL tool. Im glad I checked it because going off of my old numbers if I wanted to be .015 off the lands Id be jamming .090 thou. Please help me understand how the same chamber & different brass can yield two different measurements.

 

[Mendy300wm]

Cbto?

 

[Ibelieve1776]

Cartridge base to ogive.

Sent from my SPH-L900 using Tapatalk

 

[Rattler56]

Center Base To Ogive, I believe and yes different brass can yield different results.
I once fire the brass that I use say a Win and Rem then FL size them, I drill and tap them, over expand the necks to a
snug fit and use them.
I get a small variance, however not as much as you are experiencing.

 

[Mendy300wm]

Different lot on the bullets maybe, anytime I make a brass switch Ill remeasure using that hornady tool, the only reason I use that tool is to find out how far it is to the lands of the rifling, all rifles overtime will "burn" that rifling back so after 1000 rounds or so I remeasure just to see and document it.

 

[Ibelieve1776]

Different lot on the bullets maybe, anytime I make a brass switch Ill remeasure using that hornady tool, the only reason I use that tool is to find out how far it is to the lands of the rifling, all rifles overtime will "burn" that rifling back so after 1000 rounds or so I remeasure just to see and document it.

I've got 50 rounds in this barrel and I used
the same bullet to get these numbers. I'm baffled



Sent from my SPH-L900 using Tapatalk

 

[Rattler56]

Measure your two pieces of brass and start measuring your Horandy bullets, I got a box of 22 cal V Max that were all over the place.

 

[Ibelieve1776]

Measure your two pieces of brass and start measuring your Horandy bullets, I got a box of 22 cal V Max that were all over the place.

I would do that but my fc has been trimmed for brownells chamber length tool.

Sent from my SPH-L900 using Tapatalk

 

[Ibelieve1776]

Any other ideas?

 

[Rattler56]

Take one bullet and try one case 10 times then with the same bullet try the other case 10 times, add them all up and divide by 10 for your average to see if the case's are different.

 

[Rattler56]

My bad, each 10 on the different case's, take those and divide by 10, not all 20.

 

[near_miss]

I had a similar problem with my 7mm Mag. Case was stopping on the neck instead of the band because it was not sized properly. I decided to try to close a bolt on it and it would not close. Will the bolt close on both pieces of your brass?

 

[Ibelieve1776]

I had a similar problem with my 7mm Mag. Case was stopping on the neck instead of the band because it was not sized properly. I decided to try to close a bolt on it and it would not close. Will the bolt close on both pieces of your brass?

Yes I made sure it would close before I sent them to Hornady.

Sent from my SPH-L900 using Tapatalk

 

[near_miss]

What about after they returned? I can't think of what could change, but worth a shot. Mine was changed and it was head spacing off the neck. Maybe they swapped brass on ya?

 

[Ibelieve1776]

I wish it was that easy. I checked the head spacing and they match my other once fired.

Sent from my SPH-L900 using Tapatalk

 

[near_miss]

300Winny

Any luck yet? I am very interested in the outcome.

 

[Ibelieve1776]

300Winny

Any luck yet? I am very interested in the outcome.

Not yet

Sent from my SPH-L900 using Tapatalk

 

[gstaylorg]

This seems pretty baffling to me. Unless your ogive is actually buried inside the neck on one of the cases, you wouldn't think it was possible to get measurements that different.

How does the overall case length (base to neck mouth) compare between the two? If the case OAL was significantly longer on one, in theory it could make the CBTO seem larger with the Hornady tool, although I wouldn't think you'd be able to close the bolt on a case that long.

Also, How do you have the jaws of the caliper set with relation to the OAL tool? In one direction, the caliper will actually be forced into a slight angle, changing the measurement. Reversing the jaws will fix that issue. Let us know when you figure it out, I'd be interested in knowing the answer myself.

 

[Ibelieve1776]

This seems pretty baffling to me. Unless your ogive is actually buried inside the neck on one of the cases, you wouldn't think it was possible to get measurements that different.

How does the overall case length (base to neck mouth) compare between the two? If the case OAL was significantly longer on one, in theory it could make the CBTO seem larger with the Hornady tool, although I wouldn't think you'd be able to close the bolt on a case that long.

Also, How do you have the jaws of the caliper set with relation to the OAL tool? In one direction, the caliper will actually be forced into a slight angle, changing the measurement. Reversing the jaws will fix that issue. Let us know when you figure it out, I'd be interested in knowing the answer myself.

Im starting to think Im crazy.

 

[near_miss]

In this situation the case should be head spaced against the belt of the case correct? Do the two cases measure the same OD just above the belt? I would think the Federal case is slightly larger and it is not seating all the way.

Sorry for all the questions.... This is the technical stuff I love about reloading....