full auto problems

docwuwu

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Hello everyone. I am new to this forum. I am from the Philippines. Although we have stricter firearm laws here (all firearms are registered and licensed), time and again, we as civilians enjoy what is called an amnesty period. During this period, unregistered firearms of most any type (we call them loose firearms here in this part of the world) may be registered and hence legally owned, without fear of reprisal from the government. It is how we here as civilians get to enjoy owning select fire weaponry like you do in the US.

I had recently acquired and registered through the government amnesty protocol, an old MAC 10 in 9mm. It is not my first select fire weapon but it is my first sub gun. The markings say it is made by RPB. It's finish is understandably worn however the inner workings look just fine. It had just one mag with it. It is steel with the characteristic "serpent" markings at the bottom.

I tried it at the range a couple of days back and found out it would only occassionally fire in full auto regardless of the selector settings. I gave it a good cleaning but got no change in it's behavior. The inner workings look fine to me with very little evidence of wear and tear (I seriously doubt this weapon has found any hard use in it's past because ammo is really prohibitively priced in this part of the world).

Just a frank question here.....where should I start my trouble shooting? Could it be the mag?

Thanks a lot in advance. I am hoping to hear from some of you soon.
 

AZ Doug

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Welcome to Uzitalk.

What type of stoppage did you have?

If the gun returned to the cocked position then it is most likely a disconnector related issue. Often times the disconnector spring weakens and does not hold it down, as it should, on full auto fire. You can test this by removing your disconnector and firing the gun. Removing the diconnector renders the gun full auto only. Try this and see if it works.
 

docwuwu

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Thanks for the reply Doug. The gun simply fires semi-auto. The bolt is left open after every shot so I guess that leaves me with the disconnector spring problem. I will try your suggestion. There is a scarcity of knowledgable and skilled smiths here when it comes to full auto/open bolt weaponry so I guess would have to do that myself for now. I really don't know how to go about doing that. Will likely have to search around for blueprints and blow-up diagrams of the weapon. Is there an easy way of doing this? I don't even know which among which is the disconnector. Thanks a lot again.
 

docwuwu

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Thanks so much for the indulgence doug. I am quite sure I will find my way from here on.
 

tunnelrat

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Ummm...

AZ Doug said:
Removing the diconnector renders the gun full auto only. Try this and see if it works.

I believe you meant that removing the "trip" renders the gun full auto only...removing the disconnector from the trigger renders the gun "useless" :)
 

AZ Doug

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You are right. I had the right part in mind, wrong nomenclature. Thanks

Sorry for any inconvenience.
 
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tunnelrat

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docwuwu said:
time and again, we as civilians enjoy what is called an amnesty period. During this period, unregistered firearms of most any type (we call them loose firearms here in this part of the world) may be registered and hence legally owned, without fear of reprisal from the government. It is how we here as civilians get to enjoy owning select fire weaponry like you do in the US.
Damn I'm jealous...I like your way much better than ours.


docwuwu said:
I tried it at the range a couple of days back and found out it would only occassionally fire in full auto regardless of the selector settings.
This is unusual in that most of the time the opposite occurs: runaways or burst fire, usually due to the sear notch in the bolt rounding off, or the sear itself rounding off, both due to improper hardening of the steel. As a result the gun will cycle more than once due to the lack of proper bolt/sear interface. Your problem in a nutshell is that the disconnector is not pulling the sear down far enough to disengage completely from the bolt. Check your safety to make sure it is forward in the fire position, and not back slightly. Even on "safe" the factory tolerances will allow for some downward movement of the sear, possibly allowing the gun to discharge. A fully depressed trigger in either semi or smg mode should drop 7/32"-1/4". Make sure there isn't any trash that could be keeping the sear from being fully lowered. Roll the selector switch from semi to smg, and observe the trip to make sure it raises up in semi mode, and lowers in smg mode. This camming action acting against the disconnector is what allows for select fire. If the trip is not fully lowered into the slot in the selector switch it could be riding high enough to pop the disconnector from the sear. It should be a easy fix. The fire control group is pretty basic and easy to troubleshoot. Let us know how you fare.
 

alexl650

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if you need trigger parts there are a number of sellers which will ship to you. ftf industries i'm sure would help you out.
 

docwuwu

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Thanks to all of you. I am pleasantly surprised about the behavior of people in this forum. Quite franky, this is the first forum I had braved to join. You all seem cordial, pleasant and eager to be of help.

Tunnelrat, the firearm laws here are pretty tough. The amnesty period the government grants occurs just once in a blue moon (say once in 10 years). It is granted for one and only one purpose......REGISTRATION! Gun ownership here is a privelage not a right. To purchase say a pistol (not a military weapon or a select fire weapon or a high powered rifle), one would have to get local and federal police clearances, local and federal government clearances then apply for a license from the feds before actual purchase. The firearm gets to be released when the approval comes out. It usually takes anywhere from 6 to 8 weeks to get everything OK'd. Since the piece is licensed, you'd have to renew it every two years. Select fire weapons and high power rifles (anything above a .22) are not available for civilian purchase outside of the said amnesty/grace periods that the government grants. And yes, the government keeps a good record of each and every firearm transaction. We do not have anything in our constitution to protect us from this kind of oppression.

Sorry for straying from the topic. I will attempt disassembly according to the plans AZ Doug has provided me with and I will go through the steps you had shared with me as soon as I get home. I will let you know.

Again, thanks so very much for the indulgence.
 

tunnelrat

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If you don't mind me asking; how are the prices of full auto weapons over there?
 

docwuwu

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Hello Tunnel Rat. Prices here are horrendous and prohibitive. It is usually double the CONUS prices, sometimes a bit higher. I bought my select fire AK (type 56) for $1,000.00 and paid $200.00 in government fees for the amnesty bit. I got my Bushmaster M4 (select fire) for $2,000.00 and paid another 200 for the amnesty bit again. I do believe I got the MAC cheap.....around $1,000.00 (previously owned) but then again, the amnesty provisions got me for another 200 again. A pistol (regularly made available to civilians), say a Glock 19 would cost upwards of $800.00 plus around a $100.00 more on permits, clearances and licensure fees. That's the way it is in the islands. I couldn't really complain because at least we as Filipinos can enjoy firearms more than our Asian peers where, to a large extent, civilian ownership of firearms is absoloute taboo.

I checked the MAC last night against the pics AZ Doug had provided. It looked a bit different. For starters, the FCG retaining pin looks like it is shorter (it's end may have been broken). It stops just right at the top surface of the selector pin instead of continuing forward towards the front of the trip. I wonder if it would affect functioning of the firearm. Secondly, there is only minimal change in the position of the trip when I slide from semi to full (almost unappreciable). Regardless of the switch's position, the disconnector holds down the sear assembly continuously when the trigger is pulled down (there is no reset, the sear remains down for as long as the trigger is pressed; but I don't know if this is normal). If this is the case, shouldn't it be firing full auto only regardless of switch position instead of firing semi auto only or at best, bursts at a time? With regards to the safety switch, etc, it doesn't seem to be getting in the way and I have also made sure nothing is in the way of the sear's downward travel. I have a feeling I'd be better off purchasing a whole FCG assembly. Is there somewhere I could get this from? Thanks a whole lot Tunnelrat. Thank you also AZ Doug and alexl650 for the input. You all have been of great help.

My MAC
MAC10receiver.jpg


Pic of the assembly
MAC10firecontrolgroup.jpg
 
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tunnelrat

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From looking at the pics you have an original semi automatic open bolt that has been converted to select fire, hence the difference in the pics. I can tell this because the FCG is housed in a U shaped carriage. Also the "S" stamping right before the "M10" on the receiver denotes an original semi auto gun. From looking at the FCG it looks like the semi auto provisions are still in place. The bushing that retains the trip in position looks like it's still there, unless I'm looking at it wrong. You do have a full auto retaining spring. The semi auto spring goes under the retaining pin, not on top. There was no slot in the retaining pin for the trip, hence the semi auto only function. The FCG was installed in the carriage, and the whole assembly was spot welded in the lower receiver. Unless the slot was machined after the fact that would explain why the trip doesn't drop out of the way, hence a big part of your problem. The disconnector will always pull the sear down when the trigger is pulled, regardless of selector position. It is when the bolt reaches forward battery where the difference lies. If the selector is in smg, the slot being on top allows the trip to fall out of the way, so that it does not cause the disconnector to disengage from the sear...as long as the trigger is held down the bolt will continue to cycle until you let up. In semi mode the slot will be on the bottom. This raises the head of the trip higher than in smg mode. The front of the bolt now strikes the head of the trip, forcing it down, causing the back end to raise up against the disconnector rod, which in turn pops it loose from the sear shelf. The sear, no longer held down by the disconnector, raises up via the sear spring, and catches the bolt at rearward travel. When the trigger is released the disconnector re-engages the sear for the next shot. This is the heart of semi auto function. Is there any way you can remove the selector switch? I'm curious as to how they did the conversion...
 
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alexl650

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for your specific case with it being a conversion done by an unknown person it is hard to say what parts were used in the conversion. you could order a mac10 smg trigger parts kits and see if the selector included in that would work with your gun. if that didn't work you could try to cut a notch into the selector you have, to allow the trip to not be engaged by the bolt and allow full auto fire. i'm sure you could do it with a dremel or other rotary tool or even a hasksaw and files.
 

docwuwu

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Hello again guys. Thanks so much for these. I think I have discovered the problem. Upon disassembly of the FCG, I took stark notice of a sharp edge on the bottom surface of the trip which may represent a broken off part. It could very well be the problem. Then again, it might not be.....also, I paid so much for the registration of a select fire weapon and waited long for the amnesty bit so even if it were actually just a "converted" piece, I would still want it to be select fire in nature and keep it. The next amnesty might not be till 2017.

Quite frankly, I had my suspicions before I purchased and registered this piece. My father told me stories about how they used to convert semi MACS and TECS into full auto only pieces, in the '80's. I even showed the piece to a few "knowledgables" who said the piece is likely "factory" select fire because the converted ones had no selector switches.

Geez, all said, I am stuck with it. I can't like return it to the owner for a refund because it is already registered under my name. That occurs before actual purchase you see. It's one of the provisions of the amnesty protocol. Do you guys think I can solve this by getting me a FCG assembly? Thanks a whole lot, once again.

The selector pin (it looks like it is cam slotted):
Selectorpin.jpg


The sear assembly and the trip (the trip doesn't look original):
SearAssemblyandTrip.jpg


The trip up close (there is a sharp edge on the bottom surface):
Trip.jpg

Is there something that's supposed to be there, where the sharp edge is?


The trigger assembly in place less the trip and sear assembly:
TriggerGroup.jpg

Any problem there, you think?


Thanks a mil again.
 

tunnelrat

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Yes, you have a definitely modified open bolt semi FCG. The problem is that the conversion was done allowing for the U shaped carriage. Because of this the standard FCG parts won't interchange with yours. In order to use standard FCG parts you would have to remove the carriage. There is nothing wrong with the trip; it is the correct trip utilized in the semi auto open bolt. It looks funky because it is designed to interface with the carriage. I believe that you can do one of three things to remedy your situation:

1. Remove the carriage. If you have access to metal shop equipment the spot weld can be milled out from the inside, and the carriage simply removed. This will allow for replacement with standard FCG parts available at several vendors listed on the "web sites" thread.

2. Like I mentioned earlier, I believe that the trip head is riding a little too high, preventing the disconnector from keeping the sear held down reliably during full auto fire. This can be fixed by simply grinding a little off the trip head or...

3. Grind the cam deeper so that the trip will sit lower in smg mode.

Either way will lower the trip head. Do a little at a time. After each time check proper function by charging the bolt to begin. Start in smg mode. The bolt should remain in the rear position. Pull the trigger, and the bolt should slam forward. Keeping the trigger depressed, simply cycle the bolt by hand back and forth, simulating smg fire. There should be free movement, as the trip should be out of the way, allowing the disconnector to keep the sear down. When you release the trigger, the sear will raise up, catching the bolt. If at any time the disconnector pops off of the sear, the trip head is still too high. Grind a little more off of it, or more off of the cam, and try it again until the bolt will cycle uninterrupted. To check semi function, charge the bolt as before, and pull the trigger. Keeping the trigger depressed, cycle the bolt. The bolt will strike the trip head, raising the tail end, popping the disconnector loose from the sear. The bolt should cycle one time. Release the trigger, and the disconnector will raise up to engage the sear once again. You will have to pull the trigger again to repeat the cycle. Once both objectives are reached you will be done. Don't grind too much off, or you will lose your semi auto function.

As you mess with the gun more you will see how everything works together. It is a rather simple system. The trip is the key to proper function. This is why the semi open bolt FCG was encased in the carriage; to prevent the easy removal/tampering of the trip. Good luck and keep us posted!


Hope this helps, and keep us posted!
 
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docwuwu

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Thanks so much Tunnelrat. With that said, getting me a new retainer pin and a new trip will not solve my problems now, would it?
 

tunnelrat

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I doubt it...however, after looking more closely at the first pics it looks like the disconnector is barely grabbing the sear. It's hard to tell though. It may be slipping off, which in turn would also cause interrupted mag dumps. With the upper removed, check your disconnector/sear shelf interface by operating the trigger. Make sure there is positive interaction in this area...
 

docwuwu

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Hello again Tunnelrat. The disconnector's grab on the sear is very positive. I guess it's the lighting and the angle that gave you that idea. I tried working the bolt's action on semi and smg modes and you are right. The bolt resets (returns to the locked open mode) a lot of times even when on SMG mode. It resets 100% of the time on semi mode but resets around 50-60% of the time on SMG mode. I now believe the trip is sitting way too high. I will try to shave off a little metal from the cam slot with Alexl650's Dremel. It is the easiest thing to do for now and I will work my way around that. All the same, I think I will be ordering me a spare retainer pin and maybe a trip just in case I mess this one up. If the new parts don't fit as a drop-in then I'd just have to work my way around that again. I will let you guys know what happens either way. Thanks again.
 

tunnelrat

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Sounds like you have it under control. Since the smg mode is working halfway normal you shouldn't have to shave much. Should be an easy fix.
 
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