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Posted: 2/21/2003 8:55:21 AM EDT
| I just finished or thought I had finished my 1st AR15 build. I used a casting that was 80% complete.(really about 40% complete) and done all the work myself.But I have a problem with the firing. If you pull the trigger it will shoot two times. I'm talking about pow pow so quick like it is fully auto.If you pull the trigger and hold it the gun will fire once but when you release the trigger it will fire again.Both of these misfires are a serious problem and need to be corrected. I don't know what to do to stop this. It is not in the bolt carrier because I also have a .22 cal conversion kit and it shoots the same way with .22 or .223. Someone give me a point in the right direction. |
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It is called doubling. The primary sear system isn't getting far enough(or maybe none) engagement before the secondary sear lets go. I don't know how to fix it. I *think* it involves filing on the bottom rear of the secondary sear. You should be able to recreate the condition with the upper off the gun. Use your hand or something else to cushion the hammer otherwise it will run into the bolt hold open or the receiver wall. Get your hand in front of the hammer, pull the trigger and hold it. Push the hammer back through its travel and release. Trigger should still be held. Now remember to cushion the hammer. Release the trigger. Hammer should during proper operation, rotate slightly forward with a loud snap. Pulling the trigger now will drop the hammer. In your case, given the doubling problem, it wil probably go forward after you release the trigger. I don't know how to fix it. It is probably due to the hole relationships on your casting. It could be due to bad parts but I doubt it. Hopefully someone will come on and tell you how to fix it. It makes it a machinegun by legal definition so you really need to keep it in pieces if you can't get it fixed right away. |
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Re-time your disconnector. File the surface that sets on trigger to allow more (deeper) engagement to lug on hammer. Slowly retract the hammer, watch the hook as it pass the shelf on the hammer, should pass so close it may look like it will hit but does not (this is done with out holding trigger to rear). Adjust disconnector to reduce this cleariance, then "function test". Should not take more than 5 minutes to repair. You gun is not mis-firing, it is doubling with each trigger cycle. |
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How did you locate your hammer and trigger pins, transfer punches or did you use a mill? If filing on the disconnector doesnt work, your holes are probably too far apart. I've found the best way to correct this is to over-drill the holes to .250" and fill with JBweld or Devcon (or you could TIG weld the originial holes up, dont overdrill) and then redrill at the correct locations. I strongly suggest starting the holes with a center drill, drill through both sides of the casting using a longer bit and then ream to 0.156". Kharn |
| I did use a mill but it has a lot of slack in it. I did drill all the way on one pass but did not have a reamer of the correct size. I used print measurments and am pretty close on those. Am going to check out the above instructions in a few min. and assess if filing is the answer. |
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You have to be within about 0.002" for both X and Y for both pins, or the disconnector wont hold the hammer correctly. I've even screwed up a 0% forging on my mill due to a drill bit drifting slightly, you really have to be careful and use a new (or recently resharpened) drill bit while going slow to insure it doesnt drift. Kharn |
| If you are correct in this, then I most likely am to blame. I doubt very seriously if I am within .002. My measuring would have been more accurate than the mill because of the slack is has. The next time I build a lower I will make sure the mill is a tight one. ANother thing is I had to teach my self to run it. As I had never run one before. My friend just showed me the basics and turned me loose. Didn't break no bits though I was real careful.The lower was fairly inexpensive and the learning experience was worth the cost even if I have to scrap it. Will see if I can repair, if not I'll start on a new one. Just glad I found this site with all you helpful people to chip in with advice. |
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By "slack" in the mill, you mean backlash? If that's the case, start with the front pivot pin, start above and to the left of it, move down and right only to center the spindle over the hole(if you overshoot, reverse and start over). Once you have that, move carefully to the hammer pin (again, moving only down and right), lock the table, drill, unlock table and move down and right to the trigger pin. Doing this will prevent backlash from getting involved. If your mill has a different form of slack, I'm not sure how to overcome it, but its probably do-able. Kharn |
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Mouseomatic: There is a small range of misplacement in the holes that allows the disconnector to slightly hold the hammer, but it doesnt hold it enough. This lack of retention lets the hammer fall before the trigger surface can reengage. Farther apart, and it wont cock at all, closer together and it works as designed. Kharn |
| The slack I was talking about is side feed in and out and left and right. If you turn the handles the degrees of so many thousands don't correspond to the actual movement of the table. There fore I had to measure the hole centers with a 1/64 rule and get centers as best I could. I could not move mill table so many thousands and arrive at correct hole centers. I just took my lower appart and preformed the filing and ckecking technique. It seems to be catching the sear allright now. I am going to test fire for results. I am going to use .22 cal. conversion for a while to make sure everything is working properly. A lot less explosion if something ain't right. |
| This afternoon I test fired my AR with a .22 cal. conversion kit. It shot every time with no two round bursts. I am very thankful to all who helped me get this problem solved.SBR7-11 a special tanks to you and Mike-L for your info. A little filing goes a long way. I am going to try .223 tomorrow. I don't see a problem. We fired 70 or 80 rounds and it was flawless. Now i can do some sighting in. So far It is as it came out of the box. I will set up a targe tomorrow and zero it in. |
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In case you ever need to repair a aluminum receiver there is a product called Alumaloy on the internet that is supposed to be very good. WWW.Alumaloy.net is their web address. I have no stake in their business. I am by no means a expert but the case hardening on your trigger parts is only a few thousandts thick. A little polishing is one thing but filing is going to take you right past the hardening and you will be needing a new trigger before long.It might start doubeling again. |
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