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Posted: 5/7/2004 1:32:45 PM EST
I just bought an olympic 9mm upper and tried it out for the first time today. I was using it on eagle arms lower with a CAR styple stock. It fuctioned great except it was slamfireing (spelling?). I think the 4th round I fired I had a double-tap. I finished that mag, then had a second mag. Then the first round on my 3rd mag did the same thing. I think out of 5 mags I had 4 slamfires. I used the mag that came with it and different sten mags with socom block. Any ideas? Thanks for the help.
Link Posted: 5/7/2004 1:40:01 PM EST
sounds like your lower not your upper. You may have a weak spring in your trigger.
Link Posted: 5/7/2004 3:15:40 PM EST
Do a function test and verify correct operation of disconnector, especially the timing of it when the disconnector trades hammer off to the primary sear. Should take you NO longer than 15 minutes to repair yourself.
Link Posted: 5/7/2004 3:34:40 PM EST
If there is a problem with my lower, wouldnt I have a problem with my .223 upper also? I shot my .223 upper 2 days ago about 100 rounds without a problem.
Link Posted: 5/7/2004 8:28:21 PM EST
I constantly have problems with my Oly Arms 9mm uppers doing the double and triple tap on semi-auto on my M16 lower. I had four uppers out at the range the other day. One of them belonged to a friend who had just had his built by a gunsmith using a side cocking flat-top upper. His gun wasn't double tapping, so I took out his bolt and carrier, and found that any one of my uppers I put his bolt and carrier into, they worked perfectly. I took my carriers and bolts to the gunsmith and we compared the one he had put in my friend's gun with all of mine, and all that we could see was that he had smoothed out the sharp edges on my friend's bolt carrier when he bead blasted it. He did the same to mine, and I went back out to the range, and I found a little improvement, but the problem was not completely gone. One thing I found while doing this was that some mags seemed to make the problem happen much more frequently. I was using the mags that have the adapter welded to the Sten mag. However, I also had the SOCOM adapter and plain Sten mags, and I did not find that using that setup got rid of the double tap issue. I do not think it is your lower as my friend's upper works perfectly on my lower, and one of my uppers works perfectly on my lower. It's the other two uppers I have that I am having problems with. Try different mags in your gun. I had about 10 mags that were the modified Oly Arms mags to play with. You might also try smoothing out the rough edges on your bolt carrier with a Dremel tool. This is not an easy problem to fix. You might try sending it back to Olympic Arms. It has my gunsmith stumped too, and he does a lot of work on AR15's and M16's.

Charles Tatum
Alamo Professional Arms
Link Posted: 5/8/2004 2:34:22 AM EST
+1 with Oly 9mm upper double/triple tap problem.

I have an Oly 9mm upper - same problem as described above - using mags with attached mag block adapter - no problems with .223 uppers..............
Link Posted: 5/8/2004 7:01:20 AM EST
Is Oly arms still putting firing pin springs in their bolt carriers?
Link Posted: 5/8/2004 8:59:57 AM EST
Not sure of the age of my upper, but it has a firing pin spring.
Link Posted: 5/8/2004 4:47:18 PM EST
Glad to know that I am not the only one with this problem. Yes my firing pin has a spring.
Link Posted: 5/8/2004 5:43:22 PM EST
I have the firing pin spring also. I have had 0 problems with 5 sten mags (with socom block), and no problems with 3 mags (dalphon modified stens), and no probs with 5.56 uppers (3) on the same lower.
Link Posted: 5/8/2004 6:28:19 PM EST
[Last Edit: 5/8/2004 7:00:58 PM EST by Dano523]
The Oly 9mm uses the standard 5.56 hammer and not the shortened Colt 9mm hammer. If you have modified top of the standard hammer firing pin contact pad, then chances are it is not be lowered far enough by the carrier and being retained by the disconnector. This may be only the case on light load, since a full strength load may have enough force on the carrier moving back to sling shot the hammer past the disconnector sear.

Note: if you are running the AR-15 "L" cut hammer, switch over to the modified M-16 A-2 hammer with the auto sear tab removed. The top edge is higher than the AR-15 top edge and will guarantee that the hammer is lowered past the disconnector hook (just remember to shorten the tail of the hammer to prevent it from contacting the disconnector tail and penning the tail/ causing trigger slap).

On the tail section of the standard hammer, make sure that it is not penning off the back of the disconnector tail. If you have a white telltale sign on the disconnector tail just behind the hook from the hammer tail, then chances are the hammer may be bouncing the disconnector open.

Remember to check the timing of the hammer release from the disconnector. It may need to be retarded, and what you think is auto doubling may just be trigger finger bounce.

Another item that comes to mind is the disconnector spring; make sure it is installed with the large coil side down.

Check the bolt firing pin channel and firing pin's surface. If needed, polish both and make sure that there is not a bur on the firing pin bolt face opening that may be binding the tip of the pin forward. If the firing pin is sticking forward in the bolt during charging, then bingo, you have a bolt acting like an open bolt system and causing the problem. On the same token, make sure that the firing pin’s return spring is in working condition. If needed, get/make a stronger retention spring out of spring coil stock. On a strong bolt cycle slamming home, the firing pin maybe be overcoming the spring’s retention and igniting the primer.

Granted that I may have rambled on a bit, without having the rifle in hand to check, I can just point out some of the key points to check.

P.S. I don’t wander over in this forum much, so if you need me, IM or just post in the trouble-shooting forum if you narrow the problem down.
Link Posted: 5/15/2004 2:20:09 AM EST
I had the same problem, and everyone said it was the trigger mechanism. Not so. I finally solved my problem by going with a heavier firing pin spring and a titanium firing pin. Not a single "unplanned full auto event" in the past 3 years, and they used to be every time I shot. Hope this helps.
Link Posted: 5/15/2004 2:42:07 AM EST
Greg where did you get heavier firing pin springs?

Link Posted: 5/15/2004 6:00:27 AM EST
Some good info on what sound to be a not totally uncommon problem....hmm, maybe this deserves a place in the FAQ?

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