The Firing Line Forums

Go Back   The Firing Line Forums > The Hide > The Art of the Rifle: Semi-automatics

Reply
 
Thread Tools
Old May 10, 2013, 03:51 PM   #1
JustinBiscuit
Senior Member
 
Join Date: September 18, 2011
Location: Wisconsin
Posts: 184
New AR15 build - Headspace Check

Finally got all the parts and finished off two AR builds. One is for me One for my Dad (his x-max present)

On my Dad's I took the bolt apart and checked headspace with no-go gauge - Pass

The other rifle is the same; bolt carrier group (PSA), barrel (FN) and upper (AERO). I should check head space on this? Is it worth the time?

thx
JustinBiscuit is offline  
Old May 10, 2013, 03:57 PM   #2
JustinBiscuit
Senior Member
 
Join Date: September 18, 2011
Location: Wisconsin
Posts: 184
Pics

JustinBiscuit is offline  
Old May 10, 2013, 04:16 PM   #3
Striker1
Senior Member
 
Join Date: May 22, 2004
Location: TX
Posts: 635
Yes
Striker1 is offline  
Old May 10, 2013, 04:16 PM   #4
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 4,908
You need to check it with a GO gauge. If that won't chamber and the bolt did not close on the NO GO gauge, then some ammo won't chamber easily as chamber headspace is too short.
__________________
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master
Bart B. is online now  
Old May 10, 2013, 04:28 PM   #5
JustinBiscuit
Senior Member
 
Join Date: September 18, 2011
Location: Wisconsin
Posts: 184
Thanks for the help. What does one look for on the GO gauge?

Also, I have both 5.56 and .223 no-go gauge. Neither allowed the bolt to close. Do I GO gauge on both calibers?

thanks again.
JustinBiscuit is offline  
Old May 11, 2013, 01:03 AM   #6
Palmetto-Pride
Senior Member
 
Join Date: May 31, 2009
Location: Charleston, SC
Posts: 1,903
Headspace on a AR barrel is done when the barrel extension is installed (usually at the factory) and is non adjustable once it is drilled and the pin is installed. The barrel extension and your bolt would both have to be out of spec on the opposite ends of the spectrum in order for the headspace to be of concern. The bottom line is the odds of that are pretty damn slim. Unless you are the one that installed the barrel extension on your barrel I wouldn't worry about it....

__________________
“The problem with socialism is that you eventually run out of other people's money.”

-Margaret Thatcher-

Last edited by Palmetto-Pride; May 11, 2013 at 01:12 AM.
Palmetto-Pride is offline  
Old May 11, 2013, 07:59 AM   #7
Nathan
Senior Member
 
Join Date: July 1, 2001
Posts: 1,962
For AR's, I shoot a round and measure. . .My choice, my eyes, my body

For advice, I would suggest you get a GO and NO GO gage set. If I were going the gage route, I would get a GO gage and then add thin tape to the bottom until it did not chamber. That will give you a bettter idea about where your chamber is at.

I've never tried this, but in a pinch, I think a decent GO gage could be made by taking a 223 case, sizing to minimum headspace on an FL die, filling with steel bed to stabilize and trimming to 1.760". Then add tape shims to the bottom to see where it is at. You may need to spin this case and "cut the base down to min spec". Frankly, I would measure it and determine how close it is to factory ammo you may already own. It is likely good enough. You want it to be same diameter at the case head or slightly bigger like +.001".

Anyways, a GO gage is the right tool. The case taper is guaranteed by the cut , not really by the gage. The gage is to determine shoulder datum position.
Nathan is offline  
Old May 11, 2013, 01:23 PM   #8
Palmetto-Pride
Senior Member
 
Join Date: May 31, 2009
Location: Charleston, SC
Posts: 1,903
Quote:
For AR's, I shoot a round and measure. . .My choice, my eyes, my body
Whatever helps you sleep at night I say go for it!
__________________
“The problem with socialism is that you eventually run out of other people's money.”

-Margaret Thatcher-
Palmetto-Pride is offline  
Old May 12, 2013, 08:48 AM   #9
Bart B.
Senior Member
 
Join Date: February 15, 2009
Posts: 4,908
Nathan, I've bet money with people making rimless bottleneck case GO headspace gauges by full length sizing a fired case with the shell holder stopping against the bottom of the die with the press ram at the top of its stroke. Every one of those resized cases ended up shorter than a proper "GO" gauge. I won each bet.

Also, setting each one of those dies to just barely touch the GO gauge with the shell holder just barely touching the die's bottom does not make sized cases' headspace the same as the gauge. Presses have a few thousandths spring so the sized cases have a greater headspace dimension than the gauge.

Measured all 6 of my .308 Win. full length sizing die's results sizing fire cases the same way. All were shorter in headspace than my GO gauge used as a reference.

Such gauges should be at SAAMI specs else problems will arise. A SAAMI spec'd GO gauge for the .223 Rem's got 1.4636" from its head (squared to its long body and shoulder angles) to the .3300" diameter on its shoulder. Is that what your full length sized .223 Rem cases have? Note SAAMI specs for ammo has the minimum case headspace at 1.4666" -.007", so some factory cases may well be at 1.4596" case headspace; a full .04" shorter than minimum spec chamber headspace.

Is the rifle's bolt face squared up with the chamber axis 'cause if not, fired cases from it will have out of square case heads and that'll cause up to .002" spread in how they fit the chamber.

GO headspace gauges are only used to ensure the rifle's chamber will accept a case with maximum dimensions.

No headspace gauge is used to determine any shoulder data position. Where that .3300" SAAMI spec for shoulder datum is rarely is the point where case or gauge shoulder contacts chamber shoulder. Rarely, if ever, is it the same place in chambers that are exactly at SAAMI chamber headspace specs. The actual chamber and case shoulder angles are at are not always exactly the same. Reamers making chambers in barrels and sizing dies don't all have exactly the same angles. Which is why the best "standard" is a well made chamber headspace gauge.
__________________
US Navy Distinguished Marksman Badge 153
Former US Navy & Palma Rifle Team Member
NRA High Power Master & Long Range High Master
NRA Smallbore Prone Master

Last edited by Bart B.; May 12, 2013 at 10:27 AM.
Bart B. is online now  
Old May 12, 2013, 11:05 AM   #10
tobnpr
Senior Member
 
Join Date: August 1, 2010
Location: Tampa Bay
Posts: 2,987
No real need to headspace an AR barrel where the barrel extension was installed by the factory- any more than you would headspace a brand new, off-the-shelf Remington 700...

As P.P. said, barrel headspace is set at the factory, as are bolt dimensions. Only an egregious factory error would result in a headspace issue.

In bolt guns that might use factory ammo- or fireformed cases from another rifle, I use go gauges.

Usually though, I use an average of fireformed cases to set the shoulder bump on my FL sizing die. This means the rifle might have problems chambering factory ammo ( but I don't use it)- but I'm working the brass less, specifically to the chamber to that rifle and maximizing brass life.
__________________
Custom Bent Bolts and Gunstocks for the Mosin-Nagant
www.biggorillagunworks.com
tobnpr is online now  
Old May 12, 2013, 11:29 AM   #11
James K
Staff
 
Join Date: March 17, 1999
Posts: 19,521
The main reason for headspace concern is that ammunition varies while still being within specs. A NO-GO gauge ensures that the rifle will not have excess headspace even with the shortest cartridge. The GO gauge ensures that the longest cartridge will fit in the chamber.

Headspace can increase in used rifles due to the battering, wear, or abuse of the locking lugs or lug seats. In a new rifle, the headspace will USUALLY be OK, IF the makers kept to specs. In assembling a rifle from diverse source parts, I would never assume that everything will be OK and in spec.

Jim
__________________
Jim K
James K is offline  
Old May 12, 2013, 05:33 PM   #12
Striker1
Senior Member
 
Join Date: May 22, 2004
Location: TX
Posts: 635
Quote:
In assembling a rifle from diverse source parts, I would never assume that everything will be OK and in spec.
Me neither...and it's such a simple check to do.
Striker1 is offline  
Old May 12, 2013, 10:36 PM   #13
JustinBiscuit
Senior Member
 
Join Date: September 18, 2011
Location: Wisconsin
Posts: 184
Thanks for the help.

I checked both rifles with GO, NO-GO, and FIELD and everything checked out. Worth the piece of mind.

My results -

Go - Full Close
NO-GO - Bolt will not close
FIELD - Bolt will not close
JustinBiscuit is offline  
Old May 13, 2013, 08:47 AM   #14
Jim Watson
Senior Member
 
Join Date: October 25, 2001
Location: Alabama
Posts: 11,117
Well, that's good, but my question is, what would you have done, what could you do if it did not pass headspace gauge checks?

If short, not taking the Go, you could ream the chamber, but if long, eating the No Go, you would be stuck, short of swapping bolts around looking for a difference.

There was a guy here who used one of those RCBS gadgets to "measure" his headspace and concluded it was .007" excessive. This greatly troubled him, even though the rifle was brilliantly accurate and commonly used in 3-gun where brass recovery and care is not good. He threw a hissy fit and the vendor replaced the barrel. It is ok for his purpose, but not as accurate as it used to be.
Jim Watson is offline  
Old May 13, 2013, 10:51 AM   #15
Palmetto-Pride
Senior Member
 
Join Date: May 31, 2009
Location: Charleston, SC
Posts: 1,903
Jim, I agree some people want to fix stuff until it breaks. I would rather have a barrel that is more accurate than one slightly out of spec on the headspace, but that's just me and my opinion before I get flammed.
__________________
“The problem with socialism is that you eventually run out of other people's money.”

-Margaret Thatcher-
Palmetto-Pride is offline  
Old May 13, 2013, 07:37 PM   #16
tobnpr
Senior Member
 
Join Date: August 1, 2010
Location: Tampa Bay
Posts: 2,987
Quote:
It is ok for his purpose, but not as accurate as it used to be.
I had to chuckle over that one.

Wonder if he's gone back to the manuf. to get the "defective" barrel back so he can win some matches?
__________________
Custom Bent Bolts and Gunstocks for the Mosin-Nagant
www.biggorillagunworks.com
tobnpr is online now  
Reply

Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -5. The time now is 07:57 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2014, vBulletin Solutions, Inc.
This site and contents, including all posts, Copyright © 1998-2014 S.W.A.T. Magazine
Copyright Complaints: Please direct DMCA Takedown Notices to the registered agent: thefiringline.com
Contact Us
Page generated in 0.09831 seconds with 9 queries