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Posted: 10/14/2003 8:36:41 AM EDT
Okay, I put my new 7.62 upper on my RRA lower and loaded 1 Wolf 7.62 round in the Colt 7.62 AR-15 magazine. It fired fine and ejected the shell. I cleaned the barrel and did it again; fired fine and ejected the shell. I cleaned the barrel again and repeated - same thing - fired and ejected fine. However, now on the fourth time, I loaded one bullet like before and fired... nothing. I removed the mag, and pulled back on the charging handle which ejected the unfired bullet. I looked at it and could see that the firing pin hit perfectly in the middle with what should have been enough force to fire the round, so I chalked it up to a bad round. I loaded one more round - same thing happened. I decided it could be two bad ones in a row, but not three, so I loaded one more up... same thing: nothing. I examined all 3 failures with the three spent cases and all looked fine. So I loaded the next bullet in the box into my Maadi and it fired just fine. I then put the next round into the 7.62 AR again - it didn't fire. Grrrrr...

I am fairly new to AR's in general (built 5 of them and all worked fine). The 7.62 is a DPMS facotry complete upper (DPMS built it) and is headspaced properly.

Does anyone have any ideas on this, or was I just plain unlucky with the rounds I put into the AR?
Link Posted: 10/14/2003 9:06:54 AM EDT
Sounds as if the AR hammer needs to impart a bit more "uumppffh" to the firing pin, in order to set off the hard Wolf primers. (assuming ya checked the end of the firing pin) Try different "brand" of 7.62x39 rounds, ya may have to stick to something w/ softer primers. Mike
Link Posted: 10/14/2003 9:13:31 AM EDT
Thanks. I thought that may have been the problem (harder hammer spring), but it worked fine with the same lower and a DPMS 16" 5.56 upper, but I was using different ammo (Remington and Lake City), so I suppose the Wolf ammo could be the problem. Does anyone know of any other inexpensive 7.62x39 ammo that has "softer"(?) primers?
Link Posted: 10/14/2003 2:47:04 PM EDT
Step one, pull the firing pin and clean the channel out with a q-tip. It may just be packed with bullet sealer and causing the pin to not fully protrude into the channel. Step two, use 600 grit sand paper and clean the burs off the back of the bolt that is keeping the firing pin from fully seating during impact. Use the paper on your thumb and twist the back of the bolt against your thumb a few time to break the burs off. Step three, mic the firing pin protrusion for a depth of no shorter than .032. If needed, spin the firing pin on a drill and spin file the stop collar face on the firing pin to get the correct protrusion. Bottom line is to set up the firing pin for a protrusion of +. 030, but no greater than .040. By doing this, you can run all hardness of primers and have no problems with light strikes, even with a reduced power hammer spring.
Link Posted: 10/19/2003 3:34:33 PM EDT
Originally Posted By Dano523: Step one, pull the firing pin and clean the channel out with a q-tip. It may just be packed with bullet sealer and causing the pin to not fully protrude into the channel. Step two, use 600 grit sand paper and clean the burs off the back of the bolt that is keeping the firing pin from fully seating during impact. Use the paper on your thumb and twist the back of the bolt against your thumb a few time to break the burs off. Step three, mic the firing pin protrusion for a depth of no shorter than .032. If needed, spin the firing pin on a drill and spin file the stop collar face on the firing pin to get the correct protrusion. Bottom line is to set up the firing pin for a protrusion of +. 030, but no greater than .040. By doing this, you can run all hardness of primers and have no problems with light strikes, even with a reduced power hammer spring.
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I did this a long time ago when I first got my 7.62X39 upper. I first checked my Polytech AK firing pin protrusion,, .045". I had to turn both the stop collar and the lengthen last step on the firing pin (where it goes through the bolt face) to get .040". Be sure to mark that pin with red paint so you know it's been modified.
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