FAL headspace

[bollero]

Anyone know how to check head space on a FAL?

[Hateca]

It's done just like any other rifle.

You need a go and on go gauge. If you want to know what locking shoulder you need for a new build you will need a locking shoulder gauge.

[bollero]

finally bought the go no go gauges? anyone wana show me when they come in?

[sarge1572]

try this

http://www.surplusrifle.com/shooting/headspace/index.asp

Jeff

[Creepy]

I forget where I got this from, but I had been surfing the net for a few of the finer points on headspacing in regards to barreling and placing the locking shoulder. Not sure if this is what you were looking for:

This weapon is very forgiving.

It is probably better to go wtih the .264 to be assured of years of safe service.

FN Factory Headspace Dimensions Minimum 1.6315"
Maximum 1.640

Unfortunately, it gets a little more complex. In addition to the absolute maximum, FN also specified a maximum for a new or overhauled rifle of 1.638". That is to say, there are two maximum headspace dimensions, one for a factory new or overhauled rifle and one for a rifle that has been in service. This is shown more clearly below:


FN Factory Headspace Dimensions, New and In-Service Rifles Minimum 1.6315"
Maximum, New Rifle 1.638"
Maximum, In-Service Rifle 1.640"

The equation becomes more difficult when one takes the SAAMI headspace specifications for the .308 Winchester into account. While the 7.62mm NATO and the .308 Winchester are not the same cartridges, and should by no means be considered interchangeable, they are often used synonymously in the United States, and because of their dimensional similarities, only gauges and reamers for the .308 Winchester exist. The SAAMI specification for .308 Winchester headspace dimensions are noted below:


SAAMI Headspace Dimensions, .308 Winchester Minimum (GO) 1.630"
Maximum (FIELD) 1.640

You'll note that there is no "NO-GO" specification. SAAMI doesn't specify one. The NO-GO specifcation, measurement, and gauge are products of the gauge makers, and can be whatever the manufacturer decides it should be (within the bounds of the minimum and maximum dimensions). This is why the Forster .308 Winchester No-Go Gauge measures out at 1.634", while the Clymer .308 Winchester No-Go Gauge measures out at 1.636". However Forster's Field gauge measures out at 1.638", inidicating that Forster builds a .002" margin into its gauges that is not the same as the SAAMI specified .308 Winchester maximum headspace dimension. For this reason, we opted to go with the Clymer gauges. Taking all this into account, the consolidated headspace dimensions look like this:
Optimal assembled FAL headspace range then, is: 1.6315" < Rifle Headspace < 1.638".

As you can see, it is possible to build a rifle with a chamber within SAAMI specification for .308 Winchester, but undersized for the FAL. Since we weren't building a match rifle, but rather a military style self-loader, we opted for fairly generous headspace dimensions so as to ensure compatibility with as wide a range of surplus 7.62mm NATO ammunition as practicable. Consequently, we decided to use the Clymer 1.636" NO-GO gauge as our headspace benchmark.

[Creepy]

I do remember seeing this one on the FAL Files many moons ago:

The following is mostly quotes from posts on falfiles, by the various board members, most notably Radio.

Headspacing is a fun and challenging procedure on the FAL; and unlike many other rifle designs, easily within the grasp of the average shooter. That said, you do want to be cautious; setting headspace is perhaps the most critical step in assembling your FAL... if it's off, either your boomstick is just a stick (too tight, won't chamber) or is a major danger to you and nearby spectators when it explodes (waaay too loose, case rupture or catastrophic failure).

The cost of the proper tools for this job is INSIGNIFICANT compared to the price you might have to pay if something bad happens. These tools will allow you to measure EXACTLY what headspace THAT PARTICULAR rifle demands. You will also have the means to insure that rifle REMAINS safe over time as the headspace opens up due to parts wear. Here's what you will need:

* ZZ pin gages (from MSC Industrial Supply, for example). Sizes .254" to .265" will cost $25 at $2.25 each, even less if you skip every other size (even or odd). A more expensive way to go, but faster, is to buy sizing rods. Board member Casey Elliot, the man who brings you that fabulous receiver wrench, also features those.
* Some method of stripping the extractor from the bolt. I built my own tool; dedicated tools are available from DSA, for example (about $20). You will need this tool anyway for standard maintenance of your rifle. While it's possible to simply use a vise and a nail, the tool makes the job MUCH easier.
* Calipers to measure the existing locking shoulder you got with your kit. (Keep in mind that chances are very great you will need a different size regardless.) You might already have this in your toolbox.
* A set of GO and NO-GO gauges. Will set you back roughly $35 or cheaper for Forster, more expensive using Clymer.

Go/No-go sizes and specifications:

* 1.630" Forster GO
* 1.630" Winchester .308 minimum
* 1.6315" NATO 7.62 minimum
* 1.632" Clymer GO
* 1.634" Forster NO-GO
* 1.636" Clymer NO-GO
* 1.638" Forster FIELD
* 1.638" Winchester .308 maximum
* 1.640" Clymer FIELD
* 1.640" NATO 7.62 maximum

Things to pay attention to when headspacing:

* Barrel is properly indexed (gas block straight up) in the receiver. (You've already gotten this far in your build if you're now ready to headspace.)
* Extractor is removed from the bolt.
* Bolt and carrier are together, NEVER just the bolt alone.
* Be clean: CLEAN chamber, CLEAN headspace gauge, CLEAN boltface, CLEAN gage pin or sizing rod, CLEAN locking shoulder hole in the receiver. Dirt will affect your readings.
* Repeatability, your readings should be about the same on different measuring attempts and even different days. If not, something is wrong with your mechanicals and/or your technique.

With the above ready, select a gage pin or sizing rod (I like to start with .260") and try to close the bolt. If it closes easily, you need a larger pin/rod; not at all, smaller. What you are trying to do is to seat the bolt/carrier using "two-thumbs pressure", or a good firm push with a little resistance. Not too easy, not too hard; it's sort of subjective, I admit, but you'll probably know it when you feel it. (Don't be worried about the pin/rod being smaller than the locking shoulder hole in the receiver; the act of seating the bolt will move the pin/rod rearwards in the hole and give you a true reading.)

Let's assume you've closed your bolt on a .262" pin/rod. That's your starting point for figuring the correct locking shoulder. Next, you need to compensate for something called "setback." Factoring in SETBACK will make your initial pin gage/sizing rod thickness GROW by .001" because the locking shoulder will move AWAY from the chamber, "set back," and thus require a THICKER gage/rod (or locking shoulder) to return to the same headspace dimension you started with.

(People who are smarter than me seem to think that introducing firing pressure into a just-assembled rifle, in addition to affecting the locking shoulder, also seats the threaded barrel into the receiver. It usually all adds up to about .001" anyway. Also, to be fair, some people don't believe "setback" occurs. I always plan for it myself.)

* Your bolt closes with two-thumbs pressure on a .262" pin/rod
* To account for "setback" ADD .001"
* Correct pin/rod will now be .263"
* This is true regardless of which brand of headspace gauges you are using.

Many knowledgeable gunsmiths such as Board member gunplumber of ARS, also the fine folks at Fulton Armory, recommend setting headspace on these rifles at 1.632". This allows for reliability using any 7.62 NATO milsurp ammo, plus the ability to safely fire commercial .308 with its generally thinner brass.
FORSTER GAUGES EXAMPLE

* Your bolt closes with two-thumbs pressure on a .262" pin/rod
* ADD .001" for setback, equals .263"
* You are using a Forster GO gauge, 1.630"
* SUBTRACT .002" from .263", equals .261" locking shoulder.

CLYMER GAUGES EXAMPLE

* Your bolt closes with two-thumbs pressure on a .262" pin/rod
* ADD .001" for setback, equals .263"
* You are using a Clymer GO gauge, 1.632"
* You're done, you need a .263" locking shoulder.

If for some reason you want to resist conventional wisdom and set your rifle's headspace larger than 1.632", take the difference between your target figure and whatever gauge you're using and SUBTRACT from your nominal pin gage/sizing rod/locking shoulder reading, again after first ADDING .001" for setback. EXAMPLE:

* Your bolt closes on two-thumbs pressure on a .262" pin/rod
* ADD .001" for setback, equals .263"
* You are using a Forster GO gauge, 1.630"
* You'd like a 1.634" headspace
* SUBTRACT .004" from .263", equals .259" locking shoulder.

Probably more people use the Forster set than the Clymer. What perhaps contributes to confusion is that +.001 -.002 = -.001, so builders are constantly trying to remember if that's PLUS .001 or MINUS .001 to get where they're trying to go. If you do it the long way, you'll always get it right. SETBACK GROWS THE LOCKING SHOULDER READING BY .001".

Now that you know the exact size of locking shoulder your rifle needs, there's one last question to solve. "To file or not to file" on a larger locking shoulder you might already have, down to the size you need. Very true, indeed, some guys hack away with a file or stone to thin out one that's too thick, but I think such a practice is taking the "backyard" aspect a little too far. Tell me how confident you are to be able to maintain the 11-degree surface against which the bolt seats. Tell me how even the new thickness will be (not .261" on the right side, .259" on the left). Tell me how pounding the locking shoulder in and out as you trial-fit again and again won't open up the hole in the receiver. All this on a critical part that has to hold against circa 50,000 psi, to save $20?? My personal opinion: BUY the correct-size locking shoulder or at least swap out your old one for the proper one at vendors who allow that.

You can do this. You will feel great pride and accomplishment. Be safe and have fun.
How to Order Pin Gauges

For Vermont (US made) ZZ: the ordering number is determined as follows: Class ZZ, Minus Tolerance, 890; next four digits are Decimal Diameter Of Pin. Be sure to use four digits even if ordering full thousandths: .260" would be 2600 for example. Give this seven-digit number to sales; they will tell you the eighth digit." Price $2.78 Each (2007 price)
MSC Big Book, Page 1352 (2007 Edition) (These are for MINUS. Use 889 prefix for PLUS.)
size MSC part #
.252 8902520
.253 8902530
.254 8902540
.255 8902550
.256 8902560
.257 8902570
.258 8902580
.259 8902590
.260 8902600
.261 8902610
.262 8902620
.263 8902630
.264 8902640
.265 8902650
.266 8902660
.267 8902670
.268 8902680
.269 8902690
.270 8902700
.271 8902710
.272 8902720
.273 8902730
.274 8902740
For (Import) SPI ZZ: "Call Nationwide Sales with exact size and ordering number range. 78382462 - 78386851 [Size Range .061" to .500"] National Sales will locate the order number." Price $1.72 Each (2007 price) MSC Big Book, Page 1351 (2007 Edition)
size mfgr. part # MSC part #
.253 CMI11098-243 78384385
.254 CMI11098-244 78384393
.255 CMI11098-245 78384401
.256 CMI11098-246 78384419
.257 CMI11098-247 78384427
.258 CMI11098-248 78384435
.259 CMI11098-249 78384443
.260 CMI11098-250 78384450
.261 CMI11098-251 78384468
.262 CMI11098-252 78384476
.263 CMI11098-253 78384484
.264 CMI11098-254 78384492
.265 CMI11098-255 78384500
.266 CMI11098-256 78384518
.267 CMI11098-257 78384526
.268 CMI11098-258 78384534
.269 CMI11098-259 78384542
.270 CMI11098-260 78384559
.271 CMI11098-261 78384567
.272 CMI11098-262 78384575
.273 CMI11102-23 78384583
.274 CMI11102-24 78384591
Call 1-800-645-7270 To Order. Feed Your Addiction.

[Creepy]

Pardon the multiple/lengthy posts -hope someone finds them useful.

You will need Go/No-Go headspace gauges, pin gauges to determine which thickness locking shoulder to use, calipers to measure the locking shoulders you already have, and an extractor tool.

You may find them for less, but I got the headspace gauges from Bushmaster, $16.95 each, 1-800-998-SWAT. Go is 1.630 inches, your minimum headspace, No-Go is 1.634 inches, your normal maximum. Since the FAL is a mass-produced military rifle for use with NATO-spec ammo, it's possible to have headspace as large as Field 1.638 inches. I've never felt the need to get a Field gauge since if any of my rifles headspace beyond No-Go I'm taking remedial action; after all, despite opinions by certain liberals to the contrary, I'm not an armory. Your Mileage May Vary.

I decided to go with "cheap" and picked up a set of pin gauges from MSC, 1-800-645-7270; the most common sizes needed run from about .254 to .265, $2 each. You could instead go with "fast" and get gauge rods from Casey Elliot, the guy who also makes the best receiver wrench out there, 972-790-2636.

Buy a dedicated extractor tool from DSA, TAPCO, etc, use a cotter pin puller or even a nail, or build your own like my “$2.58 Extractor Tool” as posted earlier this month. If you use a nail etc you’ll a) need good health insurance, b) lots of bandages after you gouge yourself, c) someplace clean and well-lighted to aim your extractor spring at so you can find it later “if” (make that “when”) it gets away from you and launches itself across the room/garage/shop. Part of the charms of building a FAL, that's why I made my own so I can CONTROL the spring.

With extractor removed from the bolt, place the bolt in the carrier and slide into your receiver. Chamber the Go gauge, then select a pin (try starting with .260), insert the pin where the locking shoulder goes, and attempt to close the bolt/carrier. Keep going up/down in size until you find one that allows the bolt to fully close. You should be able to seat the bolt with minor pressure. Double-check, one size down should close easily, one size up should close hard or not at all. That’s your nominal locking shoulder thickness; smithing expert GunPlumber recommends shooting for halfway between Go 1.630” and No-Go 1.634” by subtracting one size from your nominal reading, plus allowing for “setback” of about .001 after the first few times the rifle is shot. Example: your bolt closes “just right” on a .258 gauge pin, with setback would be equivalent to a .259 pin, so use a .257 locking shoulder to obtain 1.632” median headspace. Double check again, replace the Go gauge with the No-Go. You should not be able to close the bolt at all.

Measure your existing locking shoulder(s) with a set of calipers or micrometers. Remember that the locking shoulder tab points to the rear, and you are trying to measure the front/rear dimension (the round part where the tab is, and the flat part on the side away from the tab). Hopefully you’ve got several locking shoulders to choose from and can select the correct size from stock; otherwise buy one from Entreprise or Larry/FN, 913-592-2168. In my opinion grabbing a file and hacking on an oversize locking shoulder down to fit is not the way to go, but again, YMMV and some guys do this, and the world hasn’t ended yet.

[Delta 5]

A little confused.

I see you guys bouncing two sets of numbers around. You start by saying a number like 1.6xx is the min or max, but when buying pins, you at .26x.

I called MSC and got the prices for the diameters listed, but when I asked what the length of the pins were, they were all 2 inches exactly. Are you sticking the gage pin in where the bullet would chamber? If so, how can you get a 1.6xx number from a 2 inch pin?

[bollero]

i finally ordered my gauge pins.. from gunthings.. so soon it will be done...

[tophatjones]

The pin gages go where the locking shoulder goes. Use them along with headspace gages and your bolt/ bolt carrier assembly to find the size of locking shoulder required to close on "Go" but not on "No Go". The extra confusion comes from the fact that commercial 308 headspace gages are different than the original 7.62 specs. (In 308, Go is 1.630" and No go is 1.634" for Forster). Basically, the 7.62 gages are longer by a few thousandths of an inch. It's really up to you what headspace you want to attain, but read the previous posts to get a good idea of what is safe.