One of my co-workers from Georgia uses the term "so good you slap your grandma"...I never understood that, but yesterday's shooting session made me think of that.   Perhaps my Hungarian AK kit is so happy to be alive again it slaps me.

I recently partially built an AK, I removed the barrel and removed  the old rivets and had a new GS 1.6 receiver mounted on the trunnions and the trigger guard/mag release put on by Global in Houston TX.  I then put the barrel back on (heated the receiver in the oven and anti-seize on barrel and tapped on the trunnion with a block VERY carefully).  The barrel pin hole aligned beautifully and I was able to put the barrel pin back in fairly easily with a punch ( again heated the receiver in the kitchen oven and put the pin in the freezer ).   The ejector had to be carefully ground to allow the bolt to move as it was too wide, I heard this is normal.  When I test fired the bolt carrier would not freely move back and forth and needed help to cycle.  I then smoothed out burrs  ( on the rails the carrier rides on ) until I could slide the bolt carrier freely back and forth.  

When I fired 40 rounds through it, it shot pretty accurately and had no failures, but gave me a red mark and bump on the cheek (no, the face you smart #$@).  It feels like a very sharp pain on your cheek, almost as if someone very quickly pulled your wiskers.  Upon examination on the brass, the cases are a bit dented but otherwise no bulging etc.  The rear trunnion, that was refinished, already shows that the bolt/carrier slams quite hard vs it.  Overall it seems it just cycles very violently.  The bolt seems to close and lock OK, and 3 layers of masking tape on a case head prevent it from closing the first time, but will close if you slam the bolt back on it a secont time.

Is this normal or really bad?  I now put a new spring in it and a recoil buffer, but I am still a bit worried about shooting it any more...

A $25.00 cheeck pad should solve the problem.  Not sure if there is a mechanical problem or not

Your bolt carrier shouldn't be slamming into the rear tang.  It sounds like you don't have enough spring pressure, and maybe this is a case for a Blackjack recoil buffer.  Get the buffer and try that.  They are cheap and it may be all you need to solve your problem.

I put in a buffer and put another spring in (part of a bulgarian spring kit I had) and went to shoot it.  Seems better - no pain!  I also saw that Wolf makes a stronger spring for the AK, should I try it?  Anyone else ran into cycling that seemed a tad too violent?  Eventually I will check the headspace properly, but this seems an unlikely issue with matching barrel and trunnion and original pin, right?
In any case, no failures of any kind so far and it shoots straight; at least one "minute-of-pepsi-can".  Thanks for your suggestions so far, this is my first post and a good experience.

I would try the new spring if any of my AKs were exibiting the same behavior as yours.

It sounds like a weak recoil spring.  It also sounds like replacing that and putting in the buffer has made the problem go away, no?

I think you're done.

At the range, after being slapped a few times, I tried the spring from a friends' AK 74 without improvement, but I don't know if that was a fair test.  The next day, with my cheek still sore,  I did put a recoil buffer from another AK and a bulgarian spring from a replacement spring kit, and now it shoots more pleasantly.  It was hard to tell because my cheek still hurt.  The problem is, the springs out there are mostly old, and the AK action is quite violent so I have no objective way to tell if a spring is weak.  I ordered a 15% stronger spring from Wolff and I'll try it when it arrives.  It's a very weird experience I never had even firing much more powerful rifles, so I was stumped.  It seems to be the speed of recoil rather than the force of recoil.  We were worried about headspace too, and at some point I will have it checked or borrow some gauges.  It does shoot straight and is reliable, so I want to keep it and enjoy shooting it.  What I like about it is that I once went to Hungary before the fall of the Soviet block and "interacted" with the guards who once used those very rifles - those people had no sense of humor....he he he...
Question:  I filed the receiver rails until the carrier slid back and forth without binding, was I wrong?  the reason I did this is that the new receiver was so tight that the rifle was single shot only at first...

So slap it back!

Quoted: So slap it back!

Thanks for the welcome.  I have received and installed the new Wolff spring.  I will test it with it and the buffer next time I go to the range...

BTW, the receiver is not "GS" as I wrote, it's Global Trades' 1.6 mm receiver.

If you cant get it taken care of...

Put the weak spring back on, take it to a gun show, and sell it for some crazy price to a gangbanger.

Welcome to the site ,

Filing the rails was the right thing to do. I don't think you removed too much. Sounds like a weak recoil spring.

Key to understanding above problem is Hungarian kit. Which one?

If AMD65, muzzle brake they use is a gas booster, to make it legal you add extension to the booster making it even more potent. Too much gas.
I do not think there is much options. Start adding gas bleed holes to the gas tube. Fire and tune.

No, no, I'm not selling my first gun I sorta put together ... at least until I build a better one !  Taking the barrel pin and barrel out and then back in again using only a vice, junk metal pieces, a freezer and an oven (thanks to whoever said a true gunsmith uses a BIG hammer) and the help of my wife was a memorable experience.  At some point I may need advice on matching the finish (parkerized receiver with painted kit), but first it must work flawlessly.

It is an SA-85 kit, not an AMD, sorry, I should have been more clear.  There are gas bleed holes on the gas block (4) and tube (8).

Thanks again for the feedback, it's very helpful and reassuring to hear from people with experience in these things...

Are you runing a muzzle nut or a slant brake on your SA-85?  I have noticed that slant brakes on semi auto AKMs tend to make them cheek slappers. Try it without the slant brake and install a Blackjack buffer, should make a big improvement.  I bet the recoil spring in a SA-85 is not worn out yet.  Later.

Possibly related....

Certain combinations of stock design / personal characteristics can cause even mild recoil seem harsh and 'slap' you.

I'm a decent shot, but I couldn't hit a moving target with a shotgun, until someone let me try their over/under. I nailed almost every clay with it. It was a 20 gauge so it had little recoil but it bruised my face pretty good - slapped me every shot, right under the cheekbone. I was so happy to hit with it I kept shooting until I could barely talk. This has not happened with any other rifle or shotgun.

My guess is that you are a little different stock fitment-wise like me - try a different stock?

Extremely interesting points.  I have not had the chance to shoot it since the new spring was installed.  I will bring the old spring and will try removing the slant brake and see if I can fiddle with the stock...this again proves you can't take enough crap with you to the range or do enough experiments...that's what makes all this more fun...

thanks again

OK I have fired it with a stronger spring and a blackjack buffer.  Shoots fine and did not hurt my cheek at all.  I did try without the slant brake and it made no difference.  Now all that remains is to try with the original spring and no brake and see if there is any difference.  No jams at all still even with these changes...in any case I won't argue with success.  Now I want to try to replace the gas piston with a US made one so I can use the original pistol grip...

thank you all for your input!

Shot it again today, now it's slapping again!  Same place but not as hard.  I will try the stock change option.  A rag wrapped around the stock fixes the problem.  I think maybe I'm experiencing what the gent with the shotgun experienced...my face just fits it a certain way.