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+--- Thread: Head space (/showthread.php?tid=21869)
Head space - NightStalker - 08-20-2020
First I have to say I'm not new to the AR15 platform, but I am new to the Grendel. With that said I bought a set of go no go gauges and to my surprise the bolt closed on the no go. This is a new tool craft bcg and Balistic Advantage barrel I'm working with, Ive never seen this on brand new parts so I'm confused.
I have a theory i put to much strength on it but didnt seem like it.
With all this said what happens if i fire it and check the casing. Ive never seen one shot with excessive HS so whats the risk?
I should state the gauges were made by Pacific tool.
Head space - NugginFutz - 08-20-2020
We need to have sure that you have the correct bolt with this particular extension. There are two different types, One which is set with the depths of .125 inches at another at a depth of .135 inches.
if your chamber was headspace for the .125 , and you have a .135 bolt, youre going to have an additional .010 head space.
this is something you need to determine before you start working up numbers.
Head space - montana - 08-20-2020
There are normally three types of gauges made; GO, NO-GO and FIELD. The GO gauge corresponds to the SAAMI (Sporting Arms & Ammunition Manufacturers Institute) minimum chamber length, while the FIELD gauge usually matches the maximum chamber depth, or slightly less. NO-GO gauges are an intermediate length between minimum and maximum, that, technically, is a voluntary dimension. A firearm that closes on a NO-GO gauge and does not close on a FIELD gauge may not give good accuracy and may have very short cartridge case life from the ammunition re-loaders standpoint.
Head space - Klem - 08-20-2020
NS,
As long as you can close the bolt on a safe load, or factory ammunition it's almost certain to be safe. It is more dangerous firing hot loads in a normal chamber than firing a normal loads in a too-long chamber.
The worse thing that can happen is the case splits around the middle. This has happened twice to me and apart from a slightly louder noise the bullet exists the barrel and the blast is contained in the chamber which is in battery. Maybe a bit more smoke leaks out of the receiver from the split and there will be a permanent circular mark on the inside wall of the chamber where the case split and the heat was concentrated. Apart from that it doesn't affect accuracy or barrel life.
That said, I recommend firing the first round out of any new barrel from the hip and look away.
SAAMI permits the reaming of Grendel chambers to be within a .01" range - min to max. Add to that the range permitted for ammunition headspace and theoretically with the longest permitted chamber, firing the shortest permitted ammunition you have 0.017" of difference or in other words, case stretch. Any more than that and there is a risk cases will rupture on the first firing. If your first firing was .017" or less, but from then on you bumped that case only .003" it will last the normal life for that brand of case.
If you wanted to be really certain you can cut a disk of sticky tape and attach it to the base of that NO GO gauge to mimic a FIELD gauge. The difference between a NO GO and FIELD is about .004" - .005" or the thickness of sticky tape. In your shoes I would take to the range and fire the first round from the hip.
As Montana said, NO GO is only an arbitrary line in the sand between Min and Max to let people know their chamber its getting towards being too long, but is still within spec and OK to shoot. It is only when a FIELD gauge closes that you start to worry and send it back.
As for putting too much leverage on the bolt handle and it incorrectly closed; the solid metal of a headspace gauge makes that impossible. It's not like a hollow cartridge with a soft brass shell that you can squash into a chamber by leaning on the bolt handle. If you had to put a bit of pressure on the handle to close then it's telling you it is right on the NO GO chamber length, which is less than FIELD so it is a longish chamber but still fine.
Head space - PVBoom - 08-20-2020
Klem Wrote:NS,
If you wanted to be really certain you can cut a disk of sticky tape and attach it to the base of that NO GO gauge to mimic a FIELD gauge. The difference between a NO GO and FIELD is about .004" - .005" or the thickness of sticky tape. In your shoes I would take to the range and fire the first round from the hip.
Is sticky tape the name Aussies/Kiwis use for Duct tape?
[ATTACH=CONFIG]16651[/ATTACH]
Head space - NightStalker - 08-20-2020
So if theres an issue, I would think it would be every round would show some sign, is this right?
My two thoughts on this, I shouldv used a Ballistic Advantage bolt to match the barrel, and this is why I waited to build an upper other than 556.
Head space - NightStalker - 08-20-2020
On a hunch i googled this problem and found a guy on another forum describing the exact same issue, same gauges and maker of the gauges even the same place of purchase, this is what he found bad gauges.
Gauges were checked with calipers and found to be .0005 out of specs
Gauges were PTG purchased at Midway
Head space - Klem - 08-20-2020
NightStalker Wrote:On a hunch i googled this problem and found a guy on another forum describing the exact same issue, same gauges and maker of the gauges even the same place of purchase, this is what he found bad gauges.
Gauges were checked with calipers and found to be .0005 out of specs
Gauges were PTG purchased at Midway
I wonder how he checked his PTG gauges? I ask because if he used the Hornady headspace gauge they are never exactly .350". This will give a false length readings.
Yes, if there's an issue it will affect each round equally. I still reckon you should fire a round and measure the length, then you will know for sure.
Head space - Klem - 08-20-2020
PVBoom Wrote:Is sticky tape the name Aussies/Kiwis use for Duct tape?
We call Duct tape, 'Duct tape'.
Sticky tape is the everyday stuff you find on office desks.
Head space - NightStalker - 08-20-2020
Im going to shoot it a few time and check
Head space - 82HALO - 08-28-2020
Also known as Scotch tape
Head space - Mad Charlie - 08-28-2020
A highly enlightening thread.
Head space - SuperGrendel - 09-01-2020
Mad Charlie Wrote:A highly enlightening thread.
Especially the sticky/scotch tape conversation
Head space - NightStalker - 09-01-2020
SuperGrendel Wrote:Especially the sticky/scotch tape conversation
Yes I got a kick out of that
Head space - mtnlvr - 09-01-2020
NightStalker Wrote:On a hunch i googled this problem and found a guy on another forum describing the exact same issue, same gauges and maker of the gauges even the same place of purchase, this is what he found bad gauges.Calipers are not considered accurate to 0.0005" even though they may display 0.0005" resolution.
Gauges were checked with calipers and found to be .0005 out of specs
Gauges were PTG purchased at Midway
Head space - Mad Charlie - 09-01-2020
mtnlvr Wrote:Calipers are not considered accurate to 0.0005" even though they may display 0.0005" resolution.
What he said.
Head space - Klem - 09-01-2020
NightStalker Wrote:Yes I got a kick out of that
Well, here's one for you. We call 100 mile-an-hour tape, '100 mile-an-hour tape', even though we're metric...go figure.
(the fabric type stuff)
Head space - Mad Charlie - 09-02-2020
100 mile-an-hour tape seems to be easier to say than 160.9344 kph tape. Doesn't matter much what you call it, as long as the other guy knows what you mean.