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Old May 24, 2017, 16:12   #1
Mr. Farknocker
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Buy an in-between pin gage to headspace my FAL?

I'm completing my first Imbel Kit on Imbel receiver build and need some advice.

I only have the LS left to do and I've read through the forums on the how-to process to familiarize myself. However, I'm still not sure on how I should proceed.

I headspaced my FAL using a stripped bolt and Forster Go/No-go gauges and have a determined that the bolt will close without any resistance on a .260 Vermont pin gage but will not close with the no-go gage inserted.

The next size up that I have in my tool kit is a .262 pin gage. When inserted, the bolt will not close using the go-gage. My questions is, "should I purchase a .261 gage and continue with the process or am I good to go with the .260 gage?"

My haunch based on what I've read is that a .261 gage is not necessary because I've already found a pin gage that close on the go-gauge but not the no go-gage. I'm just not sure. Am I correct?

Secondly, assuming I don't need a .261 gage, should I order a .260 locking shoulder or .259? I've read various postings where a .001 set-back is used and haven't been able to determine which is correct.

TIA.

~F
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Old May 24, 2017, 18:01   #2
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You have said that you are a first timer setting the Head space. I would advise that you make sure that your rifles Bolt and Chamber are very thoroughly cleaned, then retest.

If you achieve the same results, I would use a .261" LS. I like to set Head space for my rifles on the tight side or 1.630". If you are want to ensure reliability with all 7.62X51 ammo, then a .259" or .260" LS can be used to bring you rifle HS to NATO standards of 1.632".
I haven't had any trouble with setting my FALs to .308 Win. and using milsurp military ammo.

Quote;
"My (haunch ) based on what I've read is that a .261 gage is not necessary because I've already found a pin gage that close on the go-gauge but not the no go-gage. I'm just not sure. Am I correct?"

Yep, you said that the Bolt closes with no resistance on a .260" pin and won't close on a .262". This leads me to believe the Bolt would close with a little resistance on a .261" pin.

Like I said, I like them on the tight side. The safe bet is a .260" or .259" Lock Shoulder, either will do the job. It would be the .260" for me if choosing between the two sizes.
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Old May 24, 2017, 18:15   #3
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Originally Posted by MAINER View Post
You have said that you are a first timer setting the Head space. I would advise that you make sure that your rifles Bolt and Chamber are very thoroughly cleaned, then retest.
^^^this^^^ clean clean and then clean again. Also after you install a LS recheck the headspace with both gauges.

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Old May 24, 2017, 19:05   #4
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Quote:
Originally Posted by MAINER View Post

Quote;
"My (haunch ) based on what I've read is that a .261 gage is not necessary because I've already found a pin gage that close on the go-gauge but not the no go-gage. I'm just not sure. Am I correct?"

Yep, you said that the Bolt closes with no resistance on a .260" pin and won't close on a .262". This leads me to believe the Bolt would close with a little resistance on a .261" pin.

Like I said, I like them on the tight side. The safe bet is a .260" or .259" Lock Shoulder, either will do the job. It would be the .260" for me if choosing between the two sizes.
Yep
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Old May 25, 2017, 19:41   #5
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Quote:
Originally Posted by Mr. Farknocker View Post
I headspaced my FAL using a stripped bolt

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Since you emphasized your noob status, I must ask, are you using the bolt and bolt carrier together to check headspace?
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Old May 26, 2017, 00:50   #6
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Quote:
Originally Posted by Hebrew Battle Rifle View Post
Since you emphasized your noob status, I must ask, are you using the bolt and bolt carrier together to check headspace?
What's a bolt carrier?

Just kidding. I head space using the stripped bolt and carrier together.

I took G3isMe's advice last nite and cleaned the bolt/carrier, the receiver and chamber/chamber face before head spacing my rifle again and there was no change in my initial measurement. I have decided to go with a .260 LS. I have a .259 LS from the kit but prefer the .260 so I've place a WTT/WTS post in the Wanted section to see if someone would be interested in swapping their .260 for my .259.

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Old May 26, 2017, 01:37   #7
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Quote:
Originally Posted by Mr. Farknocker View Post
What's a bolt carrier?

Just kidding. I head space using the stripped bolt and carrier together.

I took G3isMe's advice last nite and cleaned the bolt/carrier, the receiver and chamber/chamber face before head spacing my rifle again and there was no change in my initial measurement. I have decided to go with a .260 LS. I have a .259 LS from the kit but prefer the .260 so I've place a WTT/WTS post in the Wanted section to see if someone would be interested in swapping their .260 for my .259.
If you are not going to use that .259, then use a .261 If it were mine, that .259 would already be installed. You are borrowing trouble by swapping shoulders. Just press it in and press on.
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Old May 26, 2017, 05:54   #8
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^this^. Pound in the 0.259 recheck with gauges and go shooting.
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Old May 26, 2017, 09:07   #9
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Agreed, use the .259 and count yourself lucky you had the right size shoulder.
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Old May 26, 2017, 09:31   #10
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Quote:
Originally Posted by Hebrew Battle Rifle View Post
Since you emphasized your noob status, I must ask, are you using the bolt and bolt carrier together to check headspace?
Does it make a difference ?

I almost always HS with just the bolt, HS gauge and pins.
When I find what I like, I recheck using the carrier also.

Dont have a clue how many I've built like that, but it must be damn near a pick up bed full by now....And I dont think I've ever had one that was different when I added the carrier..
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Old May 26, 2017, 12:54   #11
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I took the advice of installing the .259 LS this morning and rechecked the head space after cleaning the bolt and chamber/chamber face. The bolt now closes with applying firm (but not gorilla strength) pressure using two thumbs. It will not close on a no-go gauge with any amount of finger pressure.

From what I've read, a generally accepted practice is to back the LS down by .001 and go with that (i.e., .258). Some of you have indicated, however, that you prefer "tighter" head space dimensions which would indicate that the .259 LS may be acceptable. Any recommendations on how I should proceed from here?
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Old May 26, 2017, 13:36   #12
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Quote:
Originally Posted by Mr. Farknocker View Post
Any recommendations on how I should proceed from here?
Load, shoot, repeat....

Its easy to get overwhelmed with HS the first few times around and expect the worst, but its really not that critical and it sounds like youve got a handle on it and are good to go...
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Old May 26, 2017, 16:24   #13
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Any recommendations on how I should proceed from here?
Go here http://www.sgammo.com/product/308-wi...lus-ammo-am203
and buy copious amounts of this ammo. When the leaf springs on your pick up collapse then you will have enough.
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Old May 30, 2017, 21:40   #14
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I am pleased to report that I installed the .259 locking shoulder and successfully test fired the rifle at the local range this weekend. I did, however, run into a problem with FTE.

I started my tests by inserting a magazine loaded with 5 rounds into the magwell and then by manually racking the slide to make sure that the extractor was working properly.

I then loaded a single round of Federal American Eagle 150 gr. FMJ through ejection port with a magazine inserted into the magwell and then fired it with the gas regulator wide open. The rifle fired the round but did not cycle the bolt or extract the spent case. This was not unexpected since the regulator was in the wide open position.

I continued to fire single rounds using the method described above while closing the gas regulator one notch at a time. Unfortunately, I was never able to get the rifle to extract a single round even after closing the gas regulator completely.

I examined the bolt and carrier position after firing each round and found that the bolt carrier was opened approximately 3/4" from the closed position with the spent case and bolt still in the battery position (at least from what I could see) as if the carrier was pushed back just a little. I was able to manually rack the slide after each round and was successful at ejecting the spent cases from chamber with no difficulties. In order to verify that the bolt was not moving, I videoed the ejection port while firing a round and confirmed that there was no detectable backward movement of the bolt.

While at the range, I was able to check the gas system by:

1. Making sure the gas plug was in the correct position with the "A" facing upward;
2. Checking the position of the gas tube to make sure that it was aligned properly with one of the two cut-outs on the gas tube where the tube fits in the gas block;
3. Verifying that the piston and spring were correctly installed and freely moving in an out of the gas tube retaining nut without binding;
4. Removing the front sight post, fixing plate and spring and checking the gas port by dropping a long punch down through the gas block and gas port on the barrel.

Everything seemed to be in order from what I could tell. Nonetheless, the problem persisted.

When I got home, I tore down the gas system and checked it again and came to the same conclusion that everything appeared to be in order. I reassembled the gas system using a different piston thinking that the original piston's 4285" to .4305" variation in diameter might be contributing to excessive blow-by.

I will measure the length of the gas plug to make sure I have a metric pattern plug before taking it back to the range once more for further testing. If the problem persists, I am planning to spring for another gas tube just in case my parkerizing affected the I.D. of the gas tube and increased the tolerance between the tube and the piston.

After reading post like http://www.falfiles.com/forums/showthread.php?t=108077 and other similar threads, I’ve come to the conclusion that there is an insufficient amount of gas working against the piston. There is enough gas working on the piston to push the bolt, bolt carrier, and spent case back slightly but not enough to completely cycle the bolt/carrier. The end result is that carrier is pushed back slightly by the piston only to return to the closed position by the recoil spring. The brass case, having expanded after being fired binds against the chamber walls and prevents the bolt from fully closing. This accounts for the 3/4" gap between the carrier and the face of the receiver.

Does anybody have a different opinion of what the problem might be and/or how to fix it?

TIA

~F
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Old May 31, 2017, 08:34   #15
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Yup,,Check that gas plug.
And load from the mag, not by dropping a rd in the ejection port. That way the rim is slipping under the extractor, not jambing in the chamber and forcing the extractor to snap over it.
Thats all I got for now..
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Old May 31, 2017, 10:08   #16
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Yup,,Check that gas plug.
And load from the mag, not by dropping a rd in the ejection port. That way the rim is slipping under the extractor, not jambing in the chamber and forcing the extractor to snap over it.
Thats all I got for now..
True on a 1911, mauser, 03, etc. not a FAL. FAL always snaps over.
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Old May 31, 2017, 11:22   #17
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Your original post indicated that a .260 closed on a GO with no pressure, once you put a .259 LS in, it should still close with no pressure.

If its now two thumbs with .259 installed, you are at the minimum headspace, and your original measurement must have been in error.

Minimize all resistance in the system, lube the rails, close the gas all the way, use your larger diameter gas piston and find some hot surplus like Port or MEN and test again. I don't know what the typical muzzle velocity of American Eagle is.

You want the inside of the gas tube to be smooth. Try one that hasn't been parked.

Also, test it without a mag in place to see if something is hanging up there.

If none of that works, you could loosen up the gun with a .257 LS.
I've had good luck on shorty's with that method in the past.

Last edited by DesertFALrat; May 31, 2017 at 11:24. Reason: additonal info
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Old May 31, 2017, 13:13   #18
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double thumb pressure on a round pin gauge has more leverage/camming than on a sharper-angled locking shoulder. The "cam" is initiated at an earlier point.
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Old May 31, 2017, 15:12   #19
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Gentlemen,

Thank you for your input.

Mark, are you suggesting that it would not surprise you if there was some amount of resistance closing a bolt on a LS whereas there is no resistance using a pin gage of the same diameter?

I didn't think this piece of information was relevant for purposes of this discussion but I'll throw it out for what its worth: When I initially installed the .259 LS and tested it with a go-gage, I applied the two-thumb pressure technique to close the bolt and met slight resistance even though there was none when I HS it with a .260 pin (as discussed in my OP). I then removed the LS to touch up the ends with paint (just the ends) for the final assembly and reinserted the finished LS into the receiver. When I checked the HS again, the bolt offered no resistance. I plan on rechecking the HS later this evening when I'm done with work.
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Old May 31, 2017, 18:45   #20
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Gentlemen,

Thank you for your input.

Mark, are you suggesting that it would not surprise you if there was some amount of resistance closing a bolt on a LS whereas there is no resistance using a pin gage of the same diameter?
Correct


Quote:
I didn't think this piece of information was relevant for purposes of this discussion but I'll throw it out for what its worth: When I initially installed the .259 LS and tested it with a go-gage, I applied the two-thumb pressure technique to close the bolt and met slight resistance even though there was none when I HS it with a .260 pin (as discussed in my OP). I then removed the LS to touch up the ends with paint (just the ends) for the final assembly and reinserted the finished LS into the receiver. When I checked the HS again, the bolt offered no resistance. I plan on rechecking the HS later this evening when I'm done with work.
Don't overthink it. I consider a tight close on a .308 to be too tight. I do a loose close on a .308 (tight + .0015-.0020"). A tight close on a 7.62 GO.

I've also noticed very slight variations in gauges by manufacture.

FN doesn't use a GO/NOGO per se, but "ranges".

Also, rear locking specs are generally looser than rotational front lock - at least they have been in all my Russian/Chinese/German manuals for rear-locking weapon groups. They even use a different gauge for a 7.62 AK (rotational) than a 7.62 SKS (rear) or 7.62 RPD (side)
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Old June 12, 2017, 12:47   #21
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I am pleased to report that the FTE/Cycling problem previously described has been resolved. After triple checking the components and making sure that everything was working the way I thought it should, I sprung for a replacement gas tube from APEX. After taking some measurements of the old and replacement tube, I installed the replacement gas tube and took her out for a spin. She now cycles and locks back with the gas nut set at "3". I've turned it down to a "2" and will be running her through the pace to make sure that she consistently extracts and chambers the next round and locks back after the last shot. My conclusion is that the ID of the old tube was too large, allowing for an excessive amount of gas to blow by the piston. Whether that condition pre-existed the assembly or was the result of an errant parkerizing procedure is unknown.

Here's a comparison of the two gas tubes. Please note that the hand written notations are on the wrong sides of the pic and should be swapped. The old tube is on the right. The Apex tube is on the left. The piston OD measures 0.4295-0.430":


Last edited by Mr. Farknocker; June 12, 2017 at 12:53. Reason: Clarification
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Old June 12, 2017, 14:58   #22
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Nice, good work!

What a difference 5 thousandths makes!
Makes me want to measure all of my rifles for comparison.
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Old June 13, 2017, 14:52   #23
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Had the opposite problem on my CAI Imbel/Aussie. The Gas Piston (Century two-piece 922 part) was .427" and the rifle would only cycle on 1. New DSA Piston of .430" allowed for the Gas Reg to operate at 4.

The FALFile xperts said the old Two-Piece was dangerous anyways and I took their advise.

Congrats on your repairs, now go shooting.
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