Too little headspace - Don't shoot?

[Shooter Magavin]

Iv'e read one thread that basically says that if your bolt doesn't close on a GO- gauge it's not a big deal. Just means you have a tight chamber. As long as it will chamber and extracts a factory cartridge.
Then I read a thread about a Bear Creek barrel that won't close on the Go-gauge and the response was " don't shoot it" and " contact the manufacturer" ...?

I understand the issue with the BCA barrel was a short throat or free bore. That's understandable, but I don't know of any headspace gauge that measures past the shoulder. So I'm not sure what that had to do with it.

I'm on my first 6.5 Grendel build and the bolt will not close on either gauge. It Chambers and extracts factory new brass with no issue. However, It is just shy of being permanently attached to a Seekins proprietary upper/handguard with matching Ceracote job. If this barrel's headspace is too tight and must be returned ..then it's a MAJOR loss. So I'm concerned and confused.

[Dead Center Miss]

Iv'e read one thread that basically says that if your bolt doesn't close on a GO- gauge it's not a big deal. Just means you have a tight chamber. As long as it will chamber and extracts a factory cartridge.
Then I read a thread about a Bear Creek barrel that won't close on the Go-gauge and the response was " don't shoot it" and " contact the manufacturer" ...?

I understand the issue with the BCA barrel was a short throat or free bore. That's understandable, but I don't know of any headspace gauge that measures past the shoulder. So I'm not sure what that had to do with it.

I'm on my first 6.5 Grendel build and the bolt will not close on either gauge. It Chambers and extracts factory new brass with no issue. However, It is just shy of being permanently attached to a Seekins proprietary upper/handguard with matching Ceracote job. If this barrel's headspace is too tight and must be returned ..then it's a MAJOR loss. So I'm concerned and confused.

Personally, I like a bit of a tight chamber since it's easier on brass. If you end up needing to take some off, finish reamers are fairly cheap to rent

[Klem]

If you can chamber factory ammunition and the bolt closes properly, and also does not close on a NOGO gauge then as long as there is enough space around the neck to release the bullet your upper will be fine.

In your shoes I would want to confirm there is enough clearance around the neck to release the bullet. Normally we assume this is OK when both GO and NOGO gauges pass. But, as your chamber is shorter than spec I would want to confirm the neck and throat are not also short. For example, when you load factory ammo and it goes into battery does it push the bullet back into the case (i.e. touching lands)? It might also be crimping the mouth of the case as it gets jammed into the leade.

Yes, you can fire it from the hip for the first round (I do that with every new barrel) and it will probably be fine. The fire-formed/ejected case will then tell you a lot about the specs of the chamber, but for that you have to fire it. Or, you can contact the manufacturer with your concerns.

[Shooter Magavin]

Thanks for the replies. I'm planning to shoot it for the first time this weekend. I'll take measurements of fired and un-fired cartridges and even use some Dykem on a dry fit to see if I can reveal any chamber anomalies.

I didn't consider a finish reamer. Good to know. Can you use a reamer with the barrel still attached to the upper?

[Dead Center Miss]

I've done bolt guns while on the action so I don't see why you couldn't do a AR.

Take a loaded round and cover the whole thing with black sharpie, including the bullet. Close the bolt on it and then take it out. You should be able to tell if the shoulder is slamming into the front of the chamber, or the bullet into the rifling before firing it the way.

[JASmith]

I've done bolt guns while on the action so I don't see why you couldn't do a AR.

Take a loaded round and cover the whole thing with black sharpie, including the bullet. Close the bolt on it and then take it out. You should be able to tell if the shoulder is slamming into the front of the chamber, or the bullet into the rifling before firing it the way.

+1!

This is a good way to do the checks Klem suggests.

Adding some detail. BFT created a sticky thread with the SAAMI and CIP Grendel cartridge and chamber drawings so we can easily see them. The SAAMI drawing is here: http://www.65grendel.com/forum/attac...6&d=1392825490

[Shooter Magavin]

Thanks for the link. I read your explanation and followed along in the diagram. Very interesting. The Hornady case comparator (.350) is the same reference on the case shoulder as the diagram for min& max headspace..very useful. I'm sure that's not a coincidence.
I only reload one bottleneck case (until now). The 300blk. But it barely qualifies as a bottleneck case so I've never really paid much attention to the SAAMI specs.

[Klem]

Thanks for the link. I read your explanation and followed along in the diagram. Very interesting. The Hornady case comparator (.350) is the same reference on the case shoulder as the diagram for min& max headspace..very useful. I'm sure that's not a coincidence.
I only reload one bottleneck case (until now). The 300blk. But it barely qualifies as a bottleneck case so I've never really paid much attention to the SAAMI specs.

Shooter,

Correct, the Hornady .350 is no coincidence.

I would be cautious using measurements taken with the Hornady Comparitor and then comparing them against precise standards like SAAMI or your GO/NOGO gauges. The Comparitor is a cheap-and-cheerful gauge which is not machined to the same fine tolerances as your GO NOGO gauges. They are great for comparing lengths and differences when using the SAME gauge but fraught when using its measurements against standards. I say this because they are rarely exactly .350". Mine for example is narrower at .3425" which means it sits higher on the case shoulder and this makes any measurement to the case base longer than from the .350 Datum Line. In other words any measurement using my comparator is going to be longer than it should be. But...using it to compare before and after on a case with the same comparator is perfectly accurate and that's what most buyers use it for.


If you did want to use this gauge against standards then knowing the Grendel shoulder angle is 30degrees and we are talking about a right-angled triangle you can use an online triangle calculator to find the difference between your gauge and .350. For me the difference is having to subtract .0065" from every measurement. This is the case length difference between my gauge's .3425 datum line and SAAMI's .350. Like I said, if all you want to use the gauge for is comparing it against itself then it doesn't matter where the datum line is on the case shoulders.

If you wanted your gauge to be precisely .350 then it wouldn't be hard to spin some stock on a lathe and mimic the shape of the Hornady insert. I use mine as a comparator so have never bothered.

[Shooter Magavin]

Again, I am corrected.
Good point Klem. I didn't even consider that until you pointed it out. And it makes perfect sense.
Guess that's why Hornady calls it a "Comparator" and not a gauge. Liability in marketing.

[Klem]

LOL, Exactly! Got to have an excuse up your sleeve for when the lawyers are circling.

[Sticks]

LOL, Exactly! Got to have an excuse up your sleeve for when the lawyers are circling.

Well...The saying is that there is a Lawyer attached to every bullet...