Since the unit is an Oly, the bolt should have been modified already, but we will get into this in a bit.

First step is to confirm that you have the hammer spring installed correctly.  The hammer cross bar spring should be on the backside of the hammer, and the spring legs on top of the trigger pin.


Now that we are sure that the hammer spring is installed correctly, lets move back to the bolt.  With just the bolt and FP in hand, insert and bottom out the FP stop collar against the back of the bolt (the stop collar section of the bolt), and mic the distances that the FP protrudes out the face of the bolt.  On 223/5.56 bolts, the range for in spec is .032 to .037, but on the 7.62 X 39, you need .039 protrusions or there will not be constant joy.

The way that Oly modifies the bolt is to remove metal from the back section of the bolt (at the stop collar section of the bolt).  This allows them to just grab a standard 223 FP and use it for the upper.   So you have this option, but since just lightly chucking the FP tip section in a drill and spin filing (use a small jewelers file) the FP collar back the needed distance works better if you lack the larger tools needed to shorten the bolt, you may want to just correct the problem if needed this way.


Also, before you take any readings, make sure that the back of the bolt had been debur’d.  If needed, use some 400 sand-paper on your thumb, and just spin rub the back of the bolt against it to remove any stop collar ridge burs/high edge ring that may have been left over from production and limiting the true amount that the FP should be protruding when bottomed out.

Quoted: Dano523. I seem to be having the exact  problem with my Model 1 Sales upper.  Got it complete with BCG.  Just won't fire every round,  there are dents in the primers, but "no joy" as you put it.  14 out of 80 did not go bang.  I contacted Model 1 and they told me to try brass cased ammo, blaming steel cased ammo for the problem.  (which I did myself initially).  In any event, do you know where I can get the specs for the 7.62x39 bolt?  Best I can tell, I need about .005 more on the FP to meet the specs described in your post.  I can certainly chuck the FP up and file it a bit, but just wanted to verify my bolt deminsions. Regards, C1

What a minute since I need you to back up a bit,

You bought a 7.62 X 39 upper, and they told you not to shoot steel case ammo????
WTF, in 7.62 X 39, steel case ammo is the standard!!!!!!!!!!

Is the problem coming from the bolt not locking up, or the problem from the FP not protruding to .039?  If the later, just mod the FP stop collar the .005 needed and be done with it.  But if the chamber is too tight and causing problems with lock up with steel case ammo, then the upper needs to go back.

Note: Oly is the only one that mods the bolts to increase the protrusion that I am aware of.

If the FP protrusion is .032 to .037 out of the bolt face, then it really is in spec for American ammo.

The deal as Oly found out is that you need to have .039+ to get reliable ignition on the thicker cup berdan primers that is found in most of imported ammo.  Their solution was to just take .004'ish off the back of the bolt, and when a standard FP was installed, it gave the needed .039'ish protrusion needed to get reliable ignition. Trust me, you mic a couple of AK's/SKS’s, and you will find the FP protrusion in the .042 range.

Since some of the other vendors are new to the 7.62 X 39 game, with enough returned uppers to them to fix, then will start doing the bolt mod in house before sending the parts out the first time around.

As a side note, just went threw a few hundred rounds sighting in the VEPR  (Red Dot on BP-02) last weekend, and didn't have a single problem.
And, the FP protrusion on VEPR is .043, so go figure!!!!!!!!!!!

To sum it up, the barrel chamber has to be the correct head space, and dimensioned reamed/smooth chamber wall conditions to allow the coated steel ammo to feed, bolt lock/unlock, and ammo to eject (the case is tapered so it's really not that hard to pull off).  And then, you need the stronger than .223 standards FP protrusion to ignite the imported ammo (read wolf).   We can all dance around the facts, but until these conditions are meet, the rifles are going to be ”No-Joy City” even at their best.

Now just don’t get me started on trying to find a rust worthy working mags for the AR-7.62 X 39 rifles since more than a few produced types are less than stellar (read the real reason that I am a bigger fan of the AR-47 since it uses AK mags).


Side note: The guy that I helped lube your S&W AR last week at Cherry Creek Shooting Center to get it to cycle correctly (forgot your name).  When I grabbed my tools off the bench, I picked up your needle nose pliers and threw them in my shooting bag by mistake (didn’t notice it until I dumped my bag on at the house).  Log on, and drop me an IM so we can hook up and I can give them back to you.

Wolff springs has the extra power hammer springs.

www.gunsprings.com

The only downfall to installing the extra power hammer spring is that your trigger release break point (lbs) will increase as well.