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Headspace, Torque values, and Barrel Break-in
DoubleFeed  [Team Member]
Headspace:
There is some dispute over the need to check the headspace on AR15/M16 rifles on these forums. Some say you must. Some say you should. Some say you don't have to.

Whether you check the headspace on your rifle is up to you. The following is provided for your information…

First, try this URL for an explanation of Headspacing: www.hybrid.ualr.edu/satu/headspace.html

The Forster/SAAMI gauges available from Brownells are primarily intended for use with .223 Remington civilian rifles, but can be used with your AR15. The M16/AR15 series use their own peculiar specs for headspace, making it necessary to ignore the "Go' and "No-Go" markings, and look instead at the measurement marked on the gauge.

The current military specifications for the M16 series call for headspace of not less than 1.4646” and not more than 1.4706” on a new rifle. The commercial Forster/SAAMI gauges are marked in 1,000ths of an inch instead the 10,000ths of an inch that the dedicated M16 gauges are. When installing a new barrel, the commercial gauge measuring 1.465" can be used in place of the M16 "Go" gauge. Consider the 4/10,000ths of an inch difference an extra margin of safety. The commercial 1.470" gauge (the commercial "Field" gauge) can be used to confirm that the headspace is within spec for a new rifle. Unfortunately, there are no gauges available to measure between 1.470" and 1.4730", the latter being the measurement on the M16 "Field" gauge.

The M16 Field Service gauge measures a dimension of greater than 1.4730”. A rifle with a bolt that does not close on a Field Service gauge is considered safe to fire by the army, but not the Marines who use the military "No-Go" gauge for that measurement. Without using military Go or No-Go gauges, or commercial gauges marked with their measurements, you cannot know whether or not it is truly in spec. An interesting tidbit of information is that the Colt M16/AR15 Field gauge measures a dimension in excess of 1.4736”. It seems that the military has built in a bit more of a safety factor with their gauge.

You should remove the extractor parts and the ejector, which normally requires four hands. Removing the ejector is a two-handed job if you have the proper tools, specifically a Sinclair Bolt Vice for the AR15.

You can’t really reset the headspace on an AR15 with a chrome-lined chamber. That is set when the barrel extension is installed on the barrel. If you have an unlined barrel, with short headspace, a gunsmith can adjust it by cutting the chamber deeper with the appropriate chambering reamers. If the headspace is long, or the chamber chrome-lined, the only option is to try a different bolt until headspace checks good, or you run out of bolts. Then it is time for a new barrel.

To recap, the specs are as follows:

New Rifle Headspace: 1.4646" to 1.4706"
SAMMI headspace gauges to use: 1.465" and 1.470"

Unsafe Rifle Headspace: 1.4736"
Use the Colt M16/AR15 Field Gauge: 1.4736" or,
The US military gauge: 1.4730”

Note: The Forster/SAAMI "No-Go" gauge measures 1.467"

Sources for Gauges -
Brownells: www.Brownells.com SAAMI gauges and a whole lot of new AR15 parts and accessories.
Sarco: www.sarcoinc.com Military “Field” gauge as well as other maintenance items and M16/AR15 parts and accessories.

Originally posted by Tate: Using the 1.4730 GI Field gauge, the carrier stops WAY short of the normal, in battery position - about 1/8" short. When I was checking HS on my ARs, I was REALLY perplexed by the tail end of the carrier sticking out WAY past the end of the upper. I'm thinking "wtf? how could this gauge have any meaning whatsoever if it's 1/8" (.125!) over what's "in battery" for this rifle??? I was initially stumped!

After digging through old posts from the AR15-list, I found that this is due to the last part of the carrier travel being dedicated to bolt rotation, thus the bolt will not move much further back into the carrier (bad way to word that - we know it's the carrier moving over the bolt, not the bolt moving into the carrier). In those old posts I also found that I wasn't the only person confused by this issue.

Torque Values:
Compensator (Flash Suppressor) - 15 to 20 Ft. Lbs.

Barrel Nut - 30 Ft. lbs. Minimum, not to exceed 80 Ft. Lbs. to align the next slot in the barrel nut.

Carrier Key Screws - 35 INCH pounds to 40 INCH pounds.

Lower Receiver Extension (Buffer Tube)
Rifle - 35 to 39 Ft. Lbs.
Carbine - Tighten the locking nut to 40 INCH pounds plus or minus 2 INCH pounds.

[div class='quoteStyle']The following link is a view of barrel break-in and cleaning from Krieger Barrels and Gale McMillan on a discussion forum:

From the Krieger Barrels web site:
www.kriegerbarrels.com/RapidCat/catalog/pagetemplate.cfm?template=/RapidCat/common/viewPage.cfm&PageId=2558&CompanyId=1246


From Gale McMillan, courtesy AR15Fan:
yarchive.net/gun/barrel/break_in.html

From Fulton:
http://www.fulton-armory.com/%5Cfaqs%5CAR-FAQs%5Cheadspace.htm

All information in this thread was originally posted by Dave G, unless otherwise stated.
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jham  [Member]
Okay, let's say that you have an upper that's already barreled. You've fired MAYBE a hundred rounds down the pipe. Now you want to change out the entire bolt carrier assembly put in something better/stronger/lighter (pick one) and leave the rest of the upper alone. What do you say about checking for headspacing in this scenario? Better to be safe than sorry?
AR15Texan  [Member]
Nevermind
Backwoods_556  [Member]

Originally Posted By jham:
Okay, let's say that you have an upper that's already barreled. You've fired MAYBE a hundred rounds down the pipe. Now you want to change out the entire bolt carrier assembly put in something better/stronger/lighter (pick one) and leave the rest of the upper alone. What do you say about checking for headspacing in this scenario? Better to be safe than sorry?


I'd like to know about this too.
lavid2002  [Member]

Originally Posted By jham:
Okay, let's say that you have an upper that's already barreled. You've fired MAYBE a hundred rounds down the pipe. Now you want to change out the entire bolt carrier assembly put in something better/stronger/lighter (pick one) and leave the rest of the upper alone. What do you say about checking for headspacing in this scenario? Better to be safe than sorry?




I'd like to know about this too.

+1
DosZap  [Member]
I would do it/have done it, in a nano sec, and not look back.

I had a Dealer that was a Smith, and he also had the Colt contract for warranty work.
He said in 30 years of business, and working on AR's, he never checked HS on new, nearly new sticks.

Waste of time.



CAVEAT to this, an OLD barreled upper, and a new bolt, or a new Upper, and an OLD bolt.

Check.
AR15Texan  [Member]
Need some help with headspace. I finished building a 24" Varmint AR15. I bought the Forster .223REM GO and NOGO headspace gauges and checked the chamber tonight. The GO Gauge has 1.4636 and the NOGO has 1.4666. I could not close the bolt on either the GO or the NOGO gauge. Below are the rifle's details:

DPMS lower with Rock River Arms LPK and two-stage trigger kit.
RRA A4 Stripped Upper with charging handle and foward assist
DPMS 24" Bull Barrel with Extension installed.
JP Enterprise free-float handguard
DPMS flat top gas block and gas tube
Mil-spec BCG
Magpul PRS stock with Rifle buffer tube, spring, and buffer

I separated the upper and lower receivers. I then removed the extractor and ejector. I placed the bolt back into the bolt carrier. Installed the key, firing pin, and retaining clip into the bolt carrier. I inserted the GO gauge and then slide the BCG into the upper. I pushed the BCG forward and saw that the bolt started to rotate about 10 degrees and stop. The NOGO gauge was about the same.

I then grabbed another BCG that has seen about 350-400 rounds. I only removed the extractor as I was having trouble getting the ejector roll pin out. I then installed this BCG assembly into the upper. I applied more pressure than before as I could feel the ejector spring compress. The bolt then snapped into battery. I then tried the NOGO and it too snap into battery with about the same pressure. I figured I was pushing too hard in order to overcome the ejector spring and concluded that this test was no good.

I then spent some more time on the used BCG and finally got the ejector roll pin out. I then tried it back in the DPMS 24" upper. This time the bolt closed on the GO gauge but it still took more pressure than I thought should be used. Shouldn't I see the bolt rotate easily on the GO gauge? Next I tried the NOGO gauge on the used BCG. The bolt started to rotate a few degrees but then stopped.

I then tried the brand new BCG on the older upper. This is a J&T kit upper with a 16" barrel. The new BCG would not close on the GO or NOGO gauge. So it looks like my chamber and bolt are too tight. Doesn't the GO gauge measure maximum SAMMI length. Should I not run any ammunition through the new AR? Should I try some other bolts?

FALARAK  [Team Member]

Originally Posted By jham:
Okay, let's say that you have an upper that's already barreled. You've fired MAYBE a hundred rounds down the pipe. Now you want to change out the entire bolt carrier assembly put in something better/stronger/lighter (pick one) and leave the rest of the upper alone. What do you say about checking for headspacing in this scenario? Better to be safe than sorry?




I'd like to know about this too.


No need. Bolts are NOT fitted to a barrel. There are in spec barrels, and in spec bolts. As long as the new bolt is in spec, then there is no issue with headspacing. Replace away.

However, you have two choices:

1) trust the bolt is in spec
2) check the headspace with a COLT II FIELD GAUGE to ensure the headspace at least meets minimum safety specifications.

My advice - is simply to shoot it. Headspace issues are extremely rare.
FALARAK  [Team Member]
Originally Posted By AR15Texan:
Need some help with headspace. I finished building a 24" Varmint AR15. I bought the Forster .223REM GO and NOGO headspace gauges and checked the chamber tonight. The GO Gauge has 1.4636 and the NOGO has 1.4666. I could not close the bolt on either the GO or the NOGO gauge.

Below are the rifle's details:

DPMS lower with Rock River Arms LPK and two-stage trigger kit.
RRA A4 Stripped Upper with charging handle and foward assist
DPMS 24" Bull Barrel with Extension installed.
JP Enterprise free-float handguard
DPMS flat top gas block and gas tube
Mil-spec BCG
Magpul PRS stock with Rifle buffer tube, spring, and buffer

I separated the upper and lower receivers. I then removed the extractor and ejector. I placed the bolt back into the bolt carrier. Installed the key, firing pin, and retaining clip into the bolt carrier. I inserted the GO gauge and then slide the BCG into the upper. I pushed the BCG forward and saw that the bolt started to rotate about 10 degrees and stop. The NOGO gauge was about the same.

I then grabbed another BCG that has seen about 350-400 rounds. I only removed the extractor as I was having trouble getting the ejector roll pin out. I then installed this BCG assembly into the upper. I applied more pressure than before as I could feel the ejector spring compress. The bolt then snapped into battery. I then tried the NOGO and it too snap into battery with about the same pressure. I figured I was pushing too hard in order to overcome the ejector spring and concluded that this test was no good.

I then spent some more time on the used BCG and finally got the ejector roll pin out. I then tried it back in the DPMS 24" upper. This time the bolt closed on the GO gauge but it still took more pressure than I thought should be used. Shouldn't I see the bolt rotate easily on the GO gauge? Next I tried the NOGO gauge on the used BCG. The bolt started to rotate a few degrees but then stopped.

I then tried the brand new BCG on the older upper. This is a J&T kit upper with a 16" barrel. The new BCG would not close on the GO or NOGO gauge. So it looks like my chamber and bolt are too tight. Doesn't the GO gauge measure maximum SAMMI length. Should I not run any ammunition through the new AR? Should I try some other bolts?





Most NATO chambered AR's will close on a civilian NOGO. It does sounds like you are checking them correctly... but the fact you are tight on a civvy GO gauge in both weapons is highly suspect. Are you sure both chambers and bolts, and barrel extension are impeccably clean? What you are describing is extremely rare, and likely something else is happening. Have you tested using a live round? How much force is required to chamber that?
AR15Texan  [Member]

Originally Posted By FALARAK:
Most NATO chambered AR's will close on a civilian NOGO. It does sounds like you are checking them correctly... but the fact you are tight on a civvy GO gauge in both weapons is highly suspect. Are you sure both chambers and bolts, and barrel extension are impeccably clean? What you are describing is extremely rare, and likely something else is happening. Have you tested using a live round? How much force is required to chamber that?


Sure did make sure they were clean. There was only one small spec of dirt or grease in the DPMS barrel extension that I could see. I scraped any traces of carbon off the bolt face of the J&T bolt assembly. The DPMS bolt face was brade new. The barrel of 24" DPMS barrel has 223 stamped in it so I don't believe it to be NATO spec'ed.

ETA, I had to use the forward assist in order to chamber a live round.
cybrscream  [Member]
I hate to change subjects, but...

What actually causes a change in headspace value as rifles are used? Is the bolt face wearing down, or does the barrel chamber or extension go through changes over time? And how many rounds can go through an assembled upper before the problem part needs to be replaced?
Keith_J  [Team Member]

Originally Posted By cybrscream:
I hate to change subjects, but...

What actually causes a change in headspace value as rifles are used? Is the bolt face wearing down, or does the barrel chamber or extension go through changes over time? And how many rounds can go through an assembled upper before the problem part needs to be replaced?


Wear. The bolt's lugs wear on the backside and the extension lugs wear on the front. The bolt face doesn't wear much at all unless primer leakage and that is limited to the primer area. That is HIGHLY apparant.

Wear rate depends on a myriad of influences like port pressure/timing, abrasives/lubricant and overall fit of the parts. The majority of wear happens in the first few hundred rounds until all lugs are lapped in and bearing uniformly. Swapping bolts is a sure way to increase wear as the lugs are now bearing with varying loads until lapped in again.
BBsteel  [Member]

Lower Receiver Extension (Buffer Tube)
Rifle - 35 to 39 Ft. Lbs.


I'm wondering where I can buy a 5/8" wrench with a square 1/2" hole in it to attach my torque wrench to for achieving proper buffer tube torque.

I found an armor's wrench on CDNN for $20 but not sure if it will work. I would rather just check out the hardware store but I'm not sure if this is a specialty tool.
556Cliff  [Member]

Originally Posted By BBsteel:

Lower Receiver Extension (Buffer Tube)
Rifle - 35 to 39 Ft. Lbs.


I'm wondering where I can buy a 5/8" wrench with a square 1/2" hole in it to attach my torque wrench to for achieving proper buffer tube torque.

I found an armor's wrench on CDNN for $20 but not sure if it will work. I would rather just check out the hardware store but I'm not sure if this is a specialty tool.


Brownells AR Buttstock Tool.

It's the best one I can find.
cardude  [Member]
About the 5/8' wrench for the buttstock and torque spec. I use a GI M16 tool. meets all my needs. Another tool that will work for you is a 'crow foot wrench' get a 5/8" with a 1/2" drive hole. That will work great

On a different note.

is it necessary to break in a chrome lined barrel. such as a bushmaster? chrome lined was not mentioned in the procedure listed about.

DHoback  [Member]
There really is no "break in" for chrome lined barrels. Just shoot it. The process of breaking in a new barrel is to polish the surface. Chromium is already a smooth polished surface.

When a Chrome lined barrel finally "breaks in", IT'S BROKEN!!
LoadedDrum  [Team Member]
Does any one have a source for the 1.465" gauge? I could not find one labeled that way. The closest was a 1.464"
samurairabbi  [Member]
-------- added June 4 -------------
I found the answers to my original questions at the Indy gun show this last weekend. The 3-thou range of these Forster guages is intended for checking headspace on BOLT-ACTION .223 rifles.
------------------------------------

I offer a question on the .223 Forster go/nogo guages. I have a set of these go/nogo guages marked the same as in AR15Texan's earlier post: 1.4636 Go and 1.4666 Nogo. Clearly these are different guages than the "3-decimal" Forster ones compared in the lead post of this thread.

The "military" headspace range for a "New" rifle is given in this thread as 1.4646" to 1.4706". This is a 6-thousandth range. The "4-decimal" Forster guages give a 3-thousandth range between the Go and Nogo range, which is HALF the allowable military new range. Does that difference indicate that the "civilian" .223 headspace range has become far tighter than the 5.56 military headspace range?

An earlier post by Falarak in this thread indicated that some new in-spec military chambers could still close on a Forster (civilian) Nogo guage. Is this another aspect of the tighter 3-thou range of the newer Forster guages?
AR15Texan  [Member]

Originally Posted By samurairabbi:
Does that difference indicate that the "civilian" .223 headspace range has become far tighter than the 5.56 military headspace range?


From my research and talking with others the 5.56 x 45 NATO chamber has a longer leade than the .223 REM chamber. Therefore the .223 REM should be "tighter" than the 5.56. Correct me if I'm wrong but this is why one can get away with shooting .223 REM in a 5.56 NATO barrel but not vice versa.
Patriot32  [Member]
I am bulding a complete rifle from scratch. I have a stripped colt upper, Rock river barrel, Dpms Lower, the bolt was a brand new bolt I don't know what kind it was given to me. This rifle will be put together with many other various parts. When I am done should I have the headspace checked? I will have about $400.00 in this rifle when I am done.
Magurgle  [Team Member]

Originally Posted By Patriot32:
I am bulding a complete rifle from scratch. I have a stripped colt upper, Rock river barrel, Dpms Lower, the bolt was a brand new bolt I don't know what kind it was given to me. This rifle will be put together with many other various parts. When I am done should I have the headspace checked? I will have about $400.00 in this rifle when I am done.


Yes, if you get the barrel and bolt together no need to check, anytime the bolt did not come with the barrel it should be checked.
Beyond_Visual_Range  [Member]
What if you change out a barrel on an existing AR upper? Use the same BCG, but with the new barrel. As long as the barrel is in spec, would headspace change?
FALARAK  [Team Member]
Originally Posted By Beyond_Visual_Range:
What if you change out a barrel on an existing AR upper? Use the same BCG, but with the new barrel. As long as the barrel is in spec, would headspace change?


This was answered above.... change a bolt, change a barrel - same thing.

Bolts are NOT (generally in production) fitted to a barrel. There are in spec barrels, and in spec bolts. As long as the new bolt barrel is in spec, then there is no issue with headspacing. Replace away.

However, you have two choices:

1) trust the bolt barrel is in spec
2) check the headspace with a COLT II FIELD GAUGE to ensure the headspace at least meets minimum safety specifications.

My advice - is simply to shoot it. Headspace issues are extremely rare.
friendlysniper  [Member]
Is there a way to reliably install a barrel without a torque wrench (or for that matter, anything else) but still get in the specified range of torque? I'm installing a YHM free float and don't have an armorers tool or even the upper yet. Was more concerned about getting enough magazines first.

Ok, I've changed my mind. Is there any way to reliably install a barrel in an upper WITH an armorers tool and no torque wrench?
rick458  [Member]
Where are some good vendors to get 1/7" Barrels ?
RRA has some good looking 1/8"
FALARAK  [Team Member]
Originally Posted By friendlysniper:
Is there a way to reliably install a barrel without a torque wrench (or for that matter, anything else) but still get in the specified range of torque? I'm installing a YHM free float and don't have an armorers tool or even the upper yet. Was more concerned about getting enough magazines first.

Ok, I've changed my mind. Is there any way to reliably install a barrel in an upper WITH an armorers tool and no torque wrench?


You do not need a torque wrench to install a barrel. It helps for people who have no experience with torque values, and cannot tell the difference between 30ft-lbs and 80ft-lbs with their arm. A torque wrench is simply nice, to set the nut initially to the MINIMUM spec. Then you simply turn more until the next gas tube hole lines up. You don't have to use a torque wrench for this. The risk would be... if you just snugged it up WAY too loose, and then aligned the next gas tube hole - the final torque setting may be under spec (not likely and not a safety issue). The other risk would be - if you set the initial torque too tight... you could not get it to the next gas tube hole - because the nut got too tight and started to gall/malform the upper receiver. Of course with the latter, you would figure that out pretty quick... and just back off, and tighten to the gas tube hole that does line up without breaking your arm.

I do like to snug the nut 3 times... then back it off, then get out the torque wrench, set it to 30 lbs.... click.... then I simply check the gas tube alingment, and tighten until the next hole lines up. However, if I didnt have a torque wrench handy - I wouldn't sweat it a bit. If you are a total newbie... it is better to have one handy.
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