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Getting started on my receiver casting

5732 Views 17 Replies 10 Participants Last post by  tssrshot
Using the DSA FAL receiver as a guide, I'm jumping into the deep end and beginning mill work on this receiver casting. Let's hope I don't hit any show stoppers, but even if I do this can be a fun time waster :D I think this is going to take quite a bit of time to do and I'm going to do this in small bite-sized chunks so as not to get burned out on it. So it will probably be next year before I finish it :)

Here are my observations to start with:

The rear of my casting is warped to the left, and so to true it up I have to cut enough off that it will make the rear of the receiver too thin. Quite a warp! I'm going to compensate by cutting everything at an angle to try to even out the cutting between the front and the back. That should work but the existing starter holes will be useless as-is. Also the magazine will sit slightly crooked in comparison to the barrel. Should not affect function, it doesn't look like it will hurt anything except cosmetics.

I'm using the top "rail" as the starting point for references. There is enough meat all over that a non-warped receiver would require cuts on all surfaces both inside and out. I should therefore have enough meat left to cut all the rails and everything even after truing up the sides. It is also too long and will require cuts from both the front AND the back. Since this makes everything relative, I really don't have a GOOD starting point other than that top rail. That and the magazine well are the only two constants.


Once I true up the sides I'm going to start on the barrel threads. I looked high and low and taps for the FAL barrel threads - 1" x 16 TPI NS (national special) - are not to be found for less than $65 :( So I'm going to see if I can get 16 TPI out of my mini lathe, and if so I am going see if I can clamp the receiver on the bed in order to use a boring tool arrangement to cut the threads. That will save me 1/4 of the price of a new receiver ;) IF it doesn't look like it will work then I guess I'll just have to buy a tap and deal with it. Could probably sell it on the FAL Files once I'm done with it I suppose.

I'm scratching my head over how to get this properly assembled. I think the build order is barrel threads, locking shoulder, rails, lower. The big trick looks like it is to get the barrel threads timed correctly for a used barrel to "time" at 12 o'clock top dead center when torqued to 80-100 foot-lbs. Which from what I've read means hand-tight to about 10 o'clock. Since I doubt seriously that I'm clever enough to figure out how to properly start the barrel threads to make this time up, even if I did know where to begin, I believe the safe bet is to just cut the threads and then use the standard kit-build process of file/shim on the barrel end to get proper timing. That's the safe money for my skills :) One rotation of the barrel is about .055" from my measurements. The available shoulder sized FS from DSArms suggest that there are shoulder sizes for "all" timing needs through one rotation of the barrel. They even have custom ground lengths available, which indicates I should be able to set headspace no matter what.

So assuming I can get the threads cut, I will have a starting point from which to set the headspace.

Then after that, there's the "trivial" matter of getting the locking shoulder hole drilled. Fortunately I have two locking shoulders out of my parts stash, so I am reasoning that cutting on these locking shoulders will be easier than trying to find a really wide replacement shoulder. I'm not sure there is an absolute value for this measurement as the headspace is set based on how close the bolt sits to the barrel, so it stands to reason the different shoulder sizes are for variances in the distance "left over" from the barrel threading installation process. Assuming I will need to over-time the barrel, the locking shoulder will have to be the part that gets ground down to get proper fit. I would rather grind that locking shoulder down than find out I drilled the hole "correctly" only to find it is too far from the barrel.

Among the other areas that will be challenging are the rails. It looks as if I'm going to need to buy several small cutters for the rails. It appears that I will need a carbie woodruff-style cutter to reach into the sides to make these rails. That or make a dedicated tool from a smaller carbide cutter that is ground away leaving only a small cutting section. Either way I broke my last carbide cutter so I need to tool up again :(

For the lower receiver pivot screw, the hole is too small. So I need to cut that hole larger. Seems it would be easy to do with a dremel grinding stone. However I think the best bet would be to use a rotary table on my mill to make it pretty.

Finally, between my two SA FAL kits, I do not have an ejector block. Also the DSA FAL I have uses a less-desireable one-piece ejector. Apparently every other FAL on the planet uses a removeable ejector, which makes replacing a worn ejector a breeze. So I'm going to need to hunt down a correct ejector block and pick up a few spare ejectors. It looks like it is going to be fun trying to locate retaining pin holes correctly!

I can't for the life of me figure out where the semi-only modifications are made. These are apparently on the ejector block itself? I presume that like the VZ-58 there is a sear notch that need to be welded up for semi-only.

My plans are to use a Para "kit" from either DSA or Falcon Arms. I'm aiming for a Congo Para build (pun intended). Prices are steadily climbing and at a minimum, assuming I get my barrel timed correctly (I am assuming I won't) then I will need to buy the lower assembly package deal which includes all the US parts I will need, and a barrel.
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Hello hc,
The few FAL's I have worked on needed barrel shims to get the proper timing.

The bolt when locked should bear against the breach not the cartridge head. The reason for that is to avoid cartridge compression on ammo that extends out the chamber a bit but otherwise seems to headspace. Therefore check your barrel vs the bolt with a guage or round first to see if the round or guage separates the two.

On a 16 TPI threaded barrel one rev of the barrel equals 1/16 inch axial displacement. Therefore a shim of less than 1/16 inch may be needed to get the barrel timed. Sometimes a tiny bit off the shoulder will do the job.

Marshal Tool and Supply Corp has the 1 x 16 TPI tap (p/n 2144-0401) listed @ $49.03 each. Metric FAL barrel sizes HSS taps are a few bux more.

Can you tweek the warp manually (arbor or hydraulic press) from your receiver casting ??? The steel is supposed to be in the soft condition.

The FAL ejector block is the BATFE control item. A semi-auto only E-block will be needed.

I'm looking forward to your build.

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On the FAL the controlled part is the upper receiver, on a full auto the tab that sticks down for the lower to mount/pivot on is thinner to allow the autosear to fit. The FA ejector block simply has a recess in it to allow the autosear to fit in there. Weld a few beads across the recess to prevent the autosear from mounting and you have a semi auto block. The only other mod needed is to prevent the selector from rotating to the FA position or recut the selector to have two semi positions.
I found this at Victor Machinery...

$38.30 TAST-1-16 1"-16 HS Special Tap 1" 16

Is this what you ar looking for?
TK I'll have to look at that - SOUNDS like the correct tap! That's half price of what Brownell's wants for it! Looks like they have the gas tube thread as well:

Special Pitch Taps - High Speed Steel - special threads

Ah that's great - both taps for about $50. I can handle that. Now if I can tap the hole properly is a different story :D

The ejector block weld up seems to be the general FAL BIY process. Doesn't seem to matter at all from what I can glean.
Every ATF tech letter on the subject of FA ejector blocks I have seen posted never did answer the question. "It may be a full auto rifle with it installed, but then again it might not be." A weld is cheap peace of mind.
Have some input as I built my own FAL receivers from 4340 bar stock about twenty years ago. I hobbed my threads on a CNC so barrel timing wasn't an issue. My suggestion is to use a NEW take off barrel from GB in 308 Ruger, Winchester or some other 1-16 threaded barrel (Stainless would be cool) and machine the shoulder back to control headspace with the lugs you already have. Contour your barrel for your componets and drill your gas hole. Using this method timing would not be an issue. As the other poster suggested use a press to straighten your casting before machining. One of the guys I work with finished his "Century" receiver and used an IO kit with a GM (no gas port so timing not an issue) barrel. Turned out pretty good ( I gave him many tips and loaned him my headspace gages). As for taps got my 1-16 Greenfield off of FleaBay for $4.50 if you have patience taps, barrel, anything can be accomplished. Barrel less kits can be had. I would suggest you go Metric. I own one of each Metric, Inch and Israeli. Best of luck. Willie
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Just talked to Mike. He did thread hobb because the extractor slot and wrench flats were cut in the GM barrel. Using the method described above with a take off barrel (Ruger or whatever 1-16") you could avoid the BS of using special locking lug and washer. By pushing the barrel shoulder back or making your own shim. The wrench flats, extractor slot and gashole can be timed and controled by you. The reason suggested going metric is there are more stock/accessories available. HTH

message sent on the taps

again since I did this build with hand tools,( files and dremel, hand drill) please feel free to ask for advice, though you seem to have a grasp

I had to true the 70% first I started with the face then the top of the rails and end measured up from the inside of the bolt track and worked from there
like in my message I have the taps you need, for the barrel timing I used a cut stub you can use this also to help

be real careful with the chamber and the rails

for the new guys see my old post on this build

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Thanks for the offer Sprat, PM inbound!

So long as there is enough on the bent rails to be trued up I should be OK. Won't be a museum-quality looker but it will throw bullets downrange :D

Willie a block of steel is my plan "B" but I do not know a good place to buy that big a chunk at a good price... seems like steel these days keeps going up in price and makes it real pricey.
There is an additional cut in the receiver for the safety sear on select fire receivers. Semi auto receivers normally don't have this cut. Select fire ejector blocks and bolt carriers are allowed. Without the receiver cut, the safety sear won't fit the receiver, even with the military ejector block. The Century castings may be reject castings and this may explain the warped one. Also every one I've seen has the front magazine catch too low in the receiver.
. Select fire ejector blocks and bolt carriers are allowed. Without the receiver cut, the safety sear won't fit the receiver, even with the military ejector block.
I neutered my bolt carriers twenty years ago when I machined my receivers from bar stock. At that time better safe that sorry and info was a heck of a lot harder to come by then.
HC, pretty sure I have a spare ejector block in the parts bin, will look when I get a chance.

I offered to sell or rent or borrow my dies to cut the barrel & gas block threads to HC, he never replied, he probably got caught up with other projects. this has happened to me

Yes, the century castings for sale are warped, I compensated for that and as far as the mag release I installed it where it should be. There is a70% for sale at sturmgewher at the moment

and no I still have not heat treated my build, I am enjoying shooting 32acps with the adapter, even cheaper that I use wheel weight reloads

this is a tough build whether by hand or with a bridgeport, there are several lads over at weapons guild geting ready to to this build via bridgeport

Hey sprat I have been heads-down with real work and haven't done anything else to the blank other than true up the sides. At the rate I'm going this will be a winter project or perhaps next year. So I'm not close to needing the dies but I'll have to ping you when I make more progress :)
Hey sprat I have been heads-down with real work and haven't done anything else to the blank other than true up the sides. At the rate I'm going this will be a winter project or perhaps next year. So I'm not close to needing the dies but I'll have to ping you when I make more progress :)

not a problem, I am stalled myself with work and little time to build right now, I am trying to finish what I start. I have a sig P-228 I build that just does not want to work the way I want. I have built 6 so far but this one is driving me crazy, I have done 3 alum frame and 3 steel frame. worst yet its got a mix of aftermarket and factory sig parts, all my builds are with factory sig parts

for you new guys you can't buy 80% sig frames anymore

on another note I just saw a build concept of using a demilled SKS receiver stub and barrel and mounting on a extra FAL lower using AK mags over on weapons guild

Anyone seen any plans for a FAL on CNC lately?
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