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Building an L1A1, a couple questions from a newbie

5K views 29 replies 12 participants last post by  RetVet 
#1 ·
I just ordered one of the Australian L1A1 kits from I.O. Inc, and I was wondering if it would be possible to modify a South African barrel to fit the Century Inch Receiver I plan to use.

Would this be a good idea or are there cheaper alternatives?

By the way, how much are the Century 100% kits anyway? I've heard around $200 but I can't be sure because they have the idiotic policy of not making their prices public, and I'm not driving out to my local dealer just to check.
 
#2 ·
First mistake was ordering anything from IO, but that being said the SA barrel is metric, there would have to be some mods made I would think. Find a different barrel. Check falefiles, DSA. etc... And if you can get a different Rec you would be better off IMO.
 
#6 ·
Hello and Welcome!~

1. The threads are "almost" compatible. You should be able to chase them if you can find the right die that matches your upper.

2. Most of the Century Uppers are not Inch pattern, but "expanded" Metric. That is not an accepted term and only means that they can finish tap or thread to suit the parts kit that got pulled off of the top of the pile.

3. You may need to use indexing washers in order to get the timing right. I own two Century FALs, one is South African and the other is L1A1. I have interchanged the barrels by using the washers. They just make it possible to time the barrel correctly.

4. I might suggest that you consider an Entreprise Arms upper instead. Similar price, better quality in my opinion. There are some who don't like them.

Good Luck
 
#8 ·
Metric (except Israeli and very early belgian made) and Inch breach threads on the barrel are both 1-16 threads. You should only have to clean up the threads on the barrel or receiver if they are rough and tight. I believe the barrel you are showing a link to is a green mountain barrel which will have LH threads on the muzzle versus the RH threads of a true Inch pattern barrel. If you use a Inch barrel you will need a breaching washer. If you are using a metric barrel you may need to shave the barrel shoulder for it to time properly, but no indexing washer is usually needed unless it has already had too much material removed from it.
 
#10 ·
The barrel from that website looks like a Green Mountain barrel. Last summer I got an L1A1 kit from IO Inc and it included a Green Mountain barrel.

I have 2 of the Century receivers. Both were extremely tight in the barrel threads. I considered buying a tap, but read on FAL Files to use some lapping compound on the threads. It worked great, and was much cheaper than a tap. The L1A1 bolt hold open is bigger diameter and fit into the Century metric receiver.

At first the kit didn't have the barrel shipped with it. Then a week later I got a package from IO with a nice RPK barrel, called and they shipped me the right barrel and a shipping label. Not bad to work with, they fixed their screw-ups.

According to research, either gas block will work. Just remove the pin and tap off.

The rear sights have differant heights (I think the Inch is taller). So if you install a metric gas block you'll have to find a metric rear sight.
 
#11 ·
Thanks, the reason I ask is because Apex has SA barrels without the gas blocks for $60 as opposed to with the gas block for $120, so I plan to use the L1A1 gasblock on it, but I wanted to be sure it would fit first.

I also plan to go with an Entreprise receiver now if they aren't too much more expensive.
 
#13 ·
Besides the gas port I think the barrel diameter might be an issue to using the Inch gas block on a metric barrel.

The inch and metric barrels have the same threads to the receiver. Only the Israeli is different. You need to make sure the barrel tightens against it's shoulder in the front of the receiver and not having the rear of the barrel butting up against the feed ramp although the feed ramp should be close.

All inch flash hiders are right hand threads. Most metric flash hiders are left hand threads.
 
#16 ·
The inch and metric barrels have the same threads to the receiver. Only the Israeli is different.
The Israeli is the one you can chase the threads and it'll work, so they aren't that different.

Also, a big difference is that one style [metric, I think] uses breeching washers [shim stock washers] and the other [inch, I think] you have to turn the barrel's shoulder on a lathe to get the barrel correctly in there so it'll have the gas block straight up...
 
#14 ·
start all over.
sell the inch kit.
buy a metric kit with barrel, find a metric receiver, buy some 922r parts and build it.

or just save some money and buy one already built. you may have to hunt a little, but i still see them for under $1000.

it will save time and effort.

good luck
ron
 
#15 ·
Hello I like the DSA receivers for the quailty and fit, but I think they are so far backordered. I talked to the man representing DSA about the due dates, he laughed at me and said it was over 5 months waiting to get one of the DSA rifles and still laughing. That rep thought that was so funny. I didn't think so. You may find on Gunbroker or Gunsamerica a DSA item for sale. IRONMULE
 
#17 ·
The Inch uses breeching washers, the Metric indexes on the bbl shoulder. Depending on how it times out with a used bbl, sometimes the Metric also need a thin shim washer to get them to time properly. Other times they need some shaved off the bbl shoulder. Gunsmiths use a lathe, WECSOG folks stick it through the center hole of a sanding disk and twist until it fits.
 
#19 ·
Thanks for all the help guys, hopefully I can get the barrel to work. Just got the kit yesterday, all seems well, it's in good condition besides one of the sight guards being bent a little, I can fix that though. I'm probably going to stick with the Century receiver after all, after seeing the price and all.

I have a few questions about headspace though.

I keep hearing "select the correct locking shoulder" wherever I read about building these things. I never understood this, am I supposed to get a set of locking shoulders or something?

What does the locking shoulder have to do with headspace?

Finally, when installing the barrel, I don't have to worry about headspace like I would a CETME? I take it all there is to worry about is getting the gastube lined up vertically?
 
#20 ·
On the CETME and HK design there is no headspace adjustment, the boltface sits flat aginst the rear of the bbl. Bolt gap is often called a headspace measurement but it is actually measuring the wear in the roller mechanism.

On the FAL design headspace is set by the locking shoulder. The bolt tips down at the rear against the locking shoulder, depending on the thickness of this shoulder the boltface is closer or farther away from the breech when locked. This affects headspace. One should have come with your kit, if you're lucky it is the correct size you need. If not, several places sell them in the various sizes, other places have a sort of "trade in" program that lets you trade in your wrong one for someone else's right one for a small fee.

After the bbl is installed you insert a GO guage along with a stripped bolt and lock it into place without a locking shoulder in place. You then insert a series of guage rods (or a stepped one) into the locking shoulder hole until you get one that is large enough to not allow any movement of the bolt. This measurement is used to select a locking shoulder size. After instaling the shoulder it should take the finger pressure of two thumbs to snap down into the locked position on a GO guage. Once several shots are fired it seats a bit further rearward and now the bolt locks easily on a GO but not at all on a NO-GO.
 
#21 ·
Before I got the gauge rod set,I used a starett small hole gauge to measure.
I recommend a headspace go guage for accuracy. If you don't have either the small hole gauge or rod set, you could use nice drill rear shanks to get one tight and then use a micrometer to measure. Start with a loose one and wiggle front and back to tighten up the fit, then pick a snug fitting bit. Hopefully you have a full set of drills, letter, number, decimal, and maybe metric to work from. A small hole gauge works pretty good, but the guage rod set is tighter and much faster.
 
#23 ·
I got the rifle together today, I decided to shove the locking shoulder in without bothering to measure anything, probably a bad idea, but I didn't care. Well it worked, fired, ejected the first time. Second shot it locked up, taking considerable force to unlock the bolt and eject the spent cartridge, it continued to do this for the ten or so rounds we fired through it.

I think it's pretty obvious the problem is the locking shoulder, I just want to be sure that this is a symptom of the locking shoulder being too big or too small, and which one.

I'll measure it tomorrow and do it properly, I'd just like a little feedback beforehand, incase I overlooked something.

Also, anyone know where I can get all the gastube/gasblock parts for a South African gasblock? I couldn't get the original L1A1 gasblock to work (nothing lined up right) so I just put the South African one on there and haphazardly shoved some of the original parts on, the gas selector thing isn't held on by anything but the spring, so it comes loose regularly, and isn't very reliable, so I need the original parts.

Other than all those problems, the thing is coming together nicely. I got the Century receiver and the fit and finish was overall wonderful, all the parts fit in well, the barrel went in and fit perfectly, I managed to tighten it up with a wrench and used the original barrel shim to get it lined up vertically and tightened up nicely. There was one stupid problem I had though, they left a chunk of metal unmilled, which stopped the bolt from going all the way forward. My palm went straight to my face when I saw that, idiotic mistake. But otherwise it's a great receiver, feeds well, might need to polish the feed ramps slightly, but I really haven't had any problems with it.
 
#24 ·
I got the rifle together today, I decided to shove the locking shoulder in without bothering to measure anything, probably a bad idea, but I didn't care. Well it worked, fired, ejected the first time. Second shot it locked up, taking considerable force to unlock the bolt and eject the spent cartridge, it continued to do this for the ten or so rounds we fired through it.

I think it's pretty obvious the problem is the locking shoulder, I just want to be sure that this is a symptom of the locking shoulder being too big or too small, and which one.
The problem might be that it isn't getting enough gas to eject the spent case, causing it to push it back into the chamber, for some reason it sticks, I've had this problem, just turn the gas regulator closed another notch...
 
#27 ·
I remote fire mine as well, even after checking headspace numerous times and inspecting every part. A bit anal maybe, but I can't afford to lose any more body parts.

The tape idea wont work. It's been tried before. The first round down the pipe will blow it out. If your gas tube screws into the front sight/gas block easily or loosely, you can try flaring the end of the tube out a little bit by putting marble or ball bearing on the end of the tube and tapping it with a hammer. A proper flaring tools works better of course.

Century receivers aren't known for being the most "in spec" receivers around as you've likely found out, but they do work as long as you don't mind fixing the minor flaws. On both of the ones I bought, and ended up using for the two pistol caliber builds below, I found the following problems that needing correcting:

1. Poor or no extractor cut (as you already noted)
2. Tight mag well that required opening up a bit (one wall was slightly bowed inward)
3. Gas piston hole not exactly centered (fixed by opening the hole up a small bit)
4. Barrel threading not fully cut (had to cut it deeper by about a turn)
5. Bolt catch hole too tight (polished to fit)
6. Upper to lower latch hook too thick (filed to fit lower)



What gas block parts are you needing? I might have spares.
 
#28 ·
Basically all the South African gasblock parts minus the nut that screws into the receiver. I think I need a front sight too but the L1A1 sight seems to work fine. I think I'm fine with all the pins and whatnot though, but I can always use some extras if you have any. The gastube screws in fine to the gasblock, it's nice and tight (don't know how the hell I'm supposed to put the pin in though), but that's not the problem, I'm using the L1A1 gasblock that's just barely held on by a spring that just barely fits, I think all the gas is just blowing out regardless of what setting I put it on.

Also, the only problem I had was just that one chunk of unmilled steel that I had to fix, everything else was fine.
 
#29 · (Edited)
Hah, I figured out what the problem was!

I had the gasnut thing (the part that locks into the front of the gasblock to keep the gaspiston and all that shite in. I'm terrible with terminology, I know) was on upside down, preventing the action from cycling.

I fired three rounds flawlessly until the gas selector came loose and too much gas was being released and it locked up again. I'm still going to get some go and no go gauges though just to be sure it's not one more shot from blowing up in my face, but I assume that after 17 or so rounds through the thing with no signs of trouble, that it's atleast somewhat safe.

Also, my flash hider flew off when I fired it and got lost in the brush.

Yeah...
 
#30 ·
The gas plug set to the grenade launching position catches a lot of people, me included. I'll see what other gas block parts I have, inch type as you say it's an L1A1. I know I have some spare gas regulators which is the part held on by just the clip.
 
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