Finally got my new SAR kit build on ATI 13" barreled receiver out to the Range. Several surplus metal and Orlite mags both fit and function. Federal .223? fed and fired fine out of all mags at first, 5 rounds each out of seven Orlites and 10 rounds each out of four metal surplus mags. Ejected at 2o'clock.
Started second round of metal surplus mags when hammer follow started, with barely dented primers that fired on the second try. Pistol turned into a single shot until a case head separated and now its deadlined until I get a shell extractor.(Never needed one, in decades of shooting).
One weird thing I noticed was some kind of goop on the muzzle device, almost like I accidentally got grease on it from the workbench.
Any constructive, helpful, suggestions? ;)

who built if you dont mind me asking.
Im looking to do a SAR as well.
thanks!

Me. That may be one of the problems.

Did you check the headspace?  How was it?  ...I have seen all sorts of issues with the ATI barreled receivers...head space to tight, too loose, one lug tight the other loose, etc.

This. That's something I knew would happen when ATI started selling those already barreled receivers but didn't include a bolt that the barrel was headspaced to.

That’s one of the things I was wondering about. Been researching ways to verify/ alter headspace on a Galil type but results are sparse. Figured I’d have to research milled AK headspace in general.

Before adjusting anything you need to confirm the headspace....I would recommend using  gauges, but if you dont have headspace gauges, you can use a live round and the sticky end of a post it note! (they are about .004 thick) I would either remove your firing pin or your hammer if you use this live round technique  (just for safety, so you do not accidentally detonate the primer)  Without  the bolt carrier, just the bolt, chamber the live round and rotate the bolt into lockup...can you wiggle the tail of the bolt?  Is the tail of the bolt square with the rails?  If it rocks side to side, is it equal on each side?  Add one layer of post it note cut in a circle to fit inside the bolt face or the back end of your live round....will the round chamber?  with the round chambered and the bolt locked up is the tail of the bolt parallel with the rails on the receiver or cocked to one side or the other...add another layer of post it note the the face of the bolt or back of the live round.  How may post it notes stacked do you need to add before the bolt will not completely rotate...  You can now try it with the bolt carrier...if one lug on the receiver is out of spec and your bolt is not square in lockup, you will probably have a different result when using the carrier compared to not using the carrier... (because the carrier will keep your bolt square and your bolt will only engage one lug if you are out of square)


One layer of post note and a live round is about the same as a go gauge (if I remember correct) and 7 layers is about the same as a NOGO

...Assuming your firing pin is not damaged, and not knowing where your headspace is,   I would guess your gun probably originally passed a quick go/no go test at ATI, but you had a small burr or one lug was milled out of spec and only partially engaging AND the check was using a bolt carrier and now your headspace is growing as the pressures cleanup the lugs....growing in a bad way to the point you now have excess headspace.  

It would be nice if IMI had a number system that identified different bolts for different depths so a simple bolt swap could be used to cure excess headspace, but I have measured many bolts, and have not been able to figure the numbering of the bolts. other that the depth of the extractor...but from what I can tell, if the bolt face is deep, the lugs on the bolt are ground to match the bolt face, so swapping bolts doesnt solve the problem..

unless I am wrong about the bolts, the only way I know to tighten the headspace involves tightening the barrel on the receiver and most likely removing some material from the barrel shoulder if your barrel it torqued correctly.  And then you will have to deal with everything that rotates as the barrel rotates...

On the other hand.......If headspace is tight, check for burrs, polish the chamber,,,,check again,,,,then if needed just lap the lugs on the bolt and receiver with some lapping compound until you can close on a go gauge....this is what I will be doing on my next ATI barreled receiver build...It is tight and out of square!

Good LUCK and keep us posted...

Thank you.

As you are using a parts kit - Did you use the SAR trigger components?  Seems like the hammer follow through might be because the lever might be moved to the lowest position - This is because hammer follow through as you don't have a disconnector in that position to hold the hammet temporarily back for FA fire -  it is going to just follow the bolt home.  

Try making sure your safety/selector is in the right position for semi.

Will do.

check that headspace man!


Then check the reciever to make sure everything is lined up.

New FCG didn’t get much of a workout. Second or third? round jammed up under the previous, fired, round. Drop mag, point pistol down range as I clear the jammed round. Let bolt slam closed. BANG! ND down range. Notice the hammer pin has fallen out. Back to the work table to see if I can tell why the retaining plate came loose.

Just use E clips to keep the pins in instead of fighting with a retainer plate.

I've done that with my SAR and my VZ58.

Hammer follow through and single shot sort of make me think you have your selector to FA position with semi parts or in between semi & full positions.

Check your selector!  I did this my first range trip out after I did a build.  In FA position and without an auto sear the hammer will follow through and not hit a primer hard you will have to re-cock it manually.

Sometimes its these simple things.