CLE headspace gauge

[PrimoLuvr]

Not sure if this should go hear or the Reloading Depot...
I recently purchased an AR upper and lower from Compass Lake Engineering. I requested their CLE chamber and purchased the headspace gauge for this. What's nice about this gauge is it's cut from a section of barrel blank using the CLE reamer. So I was able to easily determine seating depths for the bullets I stock. The first 20 rounds through the gun were factory Sierra brand ammo using their 69gr MK. Out of curiosity I put the loaded rounds into my headspace guage and they were nearly .015" longer than the gauge-recommended length. The ammo chambered and shot OK but I don't understand how the headspace could be that much longer and still chamber. Does anyone else here use this gauge?

I'm teeing this up for the next part. I started putting together some light to mid range loads to use up a few bullets that I've had for awhile. The brass is new Starline that was purchased 4-5 years ago, it was all sized to meet the CLE headspace gauge recommendation. I shot 30 of these loads yesterday through a chronograph and out of curiosity used the gauge to measure headspace on the fired casings. Brass from most of the lightest loads grew .005" in headspace. Some of the loads that were running quicker grew to .015" greater than headspace. I even a few pieces from a load that grew over .030".

I'm trying to understand how brass could grow that much. Does the headspace gauge recommendation overly size the brass? Does it really need that much room to chamber? When the brass is starting to be extracted, as the bolt unlocks, will it continue to lengthen? The load that grew over .030" was starting to show signs of pressure, it needs to be backed down a little.

 

[Molon]

First of all, your post makes it seem that you’re conflating two different issues; headspace versus COAL/CBTO for jump to the lands. Secondly, what you’re describing is physically impossible for a properly manufactured and assembled AR-15 barrel and bolt, so you either have some majorly fucked-up components (which would be rather unlikely for CLE) or you’re doing something wrong. Get some standard gauges and take new measurements.

...

 

[Evintos]

It sounds like you bought a case/cartridge gauge and not a headspace gauge.

Generally speaking, cartridge gauges checks to see if your cartridge (diameter of case body at various points, base-to-shoulder length) would fit a SAAMI spec chamber. A SAAMI spec cartridge max dimension is usually smaller than a SAAMI spec chamber min dimension (for the same caliber).

When you size using a case gauge as a reference, you nearly guarantee reliable feeding/chambering of that cartridge in all chambers within that chamber spec (assuming the case gauge is made to max cartridge spec). When you size to whatever the actual chamber spec is, you can control the amount of case expansion and growth (to a degree). When the case gauge is sized to the minimum cartridge spec and the chamber is machined to the maximum chamber spec, you will see the most case expansion and growth.

Cartridge overall length and headspace are two different things. The other thing I think (but I could be wrong) is you're confusing headspace and case length (cartridge base to case mouth) and that is what I think you're actually measuring (the 0.005" to 0.030" growth is a part of the case neck lengthening).

 

[PrimoLuvr]

CLE Chamber Gauge

Compass Lake Engineering Chamber Gauge This gauge is used to check the headspace and overall case fit of sized brass to the Compass Lake Engineering Chamber. INSTRUCTIONS FOR USING THE COMPASS LAKE…

compasslake.com

This is the gauge I purchased. In talking with CLE it is a headspace and chamber gauge that works on new or fired brass that has been resized. I shouldn't have tried using it to check headspace on fired brass, sorry for the confusion...