Head Space Gauge Differences

[Old Bob]

After reading on here about different depth bolts & issues some folks have had with head spacing, I ordered a set of 6.5 Grendel head space gauges from Brownells. What I forgot was that I bought a set from PTG two years ago. So now I have two sets of gauges. I removed the ejector plunger from my bolt & first dropped in the PTG no-go gauge. The bolt didn't close. Great! Next I dropped in the PTG go gauge. Not so great! The bolt wouldn't close on it either. I'm scratching my head, a bit puzzled. Do I have a short chamber on this high dollar Wilson Combat barrel? I hope not!

So... I repeated the process with the Brownell (Manson) gauges. The no-go didn't go as I suspected, but to my relief, the bolt did close on the go gauge. Dummy rounds made from new, unfired brass fed & ejected without any problems manually cycling the BCG. Next, I went to the range & shot a few rounds. Checking my fired brass they were only .002" longer than unfired rounds. That told me that my chamber is good.

I repeated all the above with an Odin Grendel barrel & got the same results. The bolt closed on the Manson go gauge but not the PTG.

Here's what's a bit strange: Measuring the gauges with my Hornady comparator (B350 unit) shows the PTG go gauge is a hair shorter than the Manson. At the .35" datum line, the PTG is 1.2145" & The Manson is 1.215". So why don't my bolts close with the PTG go gauge? What's wrong with the PTG gauge?

[A5BLASTER]

It's made by PTG.

[VASCAR2]

There have been numerous threads concerning problems with PTG reamers and gauges when it comes to 6.5 Grendel. Manson is the go to company IMHO when it comes to reamer or gauges for the 6.5 Grendel. Years ago Satern/Liberty group buy debacle with short chambers happened to use PTG reamers. Out of spec according to SAAMI approved design is out of spec regardless if a reamer, cutter or gauge. I’ve never heard of an issue with 6.5 Grendel related product from Manson other than slow delivery and no email update on an order.

[Old Bob]

Thanks A5 & VASCAR2. I haven't been here long enough to read all old posts about PTG issues. Comparing the PTG with the Manson, it kinda looks like the angle of the shoulder might be slightly different. Cartridge & chamber specs say it's supposed to be 30?. I don't have any tools to measure angles & there's no way I can say for sure my eyeball is good enough to confirm differences in the angle. I just may be seeing things...

[Klem]

You'd think the shorter PTG gauge would permit the bolt to close if the longer Manson gauge does. I'm thinking axial headspace. It might be too fat to permit it to go all the way in. The Hornady gauge measures length only, not girth.

[Old Bob]

You'd think the shorter PTG gauge would permit the bolt to close if the longer Manson gauge does. I'm thinking axial headspace. It might be too fat to permit it to go all the way in. The Hornady gauge measures length only, not girth.

I thought of that but both head space gauges have identical dimensions (.432" at the head & .4215" at the shoulder) so being "too fat" isn't the problem. Actually, unfired ammo (Hornady 123gr SSTs) is wider than either gauge & seem to chamber easily. This is still a mystery to me but I don't think it's anything I have to worry about.

[Klem]

Bob,

It is a mystery for sure. Still, if you figure it out let us know because you've got me thinking.