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MPA Mac-10 - Jamming, shell burning question
5/26/2009 12:40:14 PM
I'm posting this for my brother, who doesn't have an account here. It's a copy/paste from his post on UziTalk. Any help would be very much appreciated:
"Hello!
First post, so go easy!
I bought a masterpiece arms mac-10 .45. So, I take it out and shoot it a few times, and it's alright, some infrequent jamming at first.
The last time I shot it, it jammed about every two rounds, and it has always done this odd thing where it burns up the side of the shell, leaves a scorched mark. This is not just soot, or carbon... I cannot wipe it off. The brass is actually burnt. =) Also, the ejector likes to crush shells.
My working theory after the last miserable failure to shoot even 3 consecutive rounds was that something was very wrong with the barrel or chamber. It may be a smaller problem than I can see, but the barrel seems and feels perfect, no chips or cracks, the chamber (excuse terminology if wrong) where the end of the shell sits against the firing pin looks fine as well. But when I assemble it, and pull back the cocking handle, it looks as if they do not align exactly, like a gap perhaps. I can probably provide a picture later, but that could just be the way they look, I do not know.
Is this a problem anyone has seen before? I'm sure the jamming is, but the shell burning speaks to gas escaping when it shouldn't right? And that would be in the connection between chamber and barrel? Any suggestions?
I know the most valid thing would be take it to a gunsmith, I do get the sneaking suspicion I have just done something stupid to it that prevents it from firing correctly. (I have disassembled and reassembled several times to clean and such, it only seems to fit together one way, but who knows... hence asking the experts.)
Thank you very much,
Ben"
"Hello!
First post, so go easy!
I bought a masterpiece arms mac-10 .45. So, I take it out and shoot it a few times, and it's alright, some infrequent jamming at first.
The last time I shot it, it jammed about every two rounds, and it has always done this odd thing where it burns up the side of the shell, leaves a scorched mark. This is not just soot, or carbon... I cannot wipe it off. The brass is actually burnt. =) Also, the ejector likes to crush shells.
My working theory after the last miserable failure to shoot even 3 consecutive rounds was that something was very wrong with the barrel or chamber. It may be a smaller problem than I can see, but the barrel seems and feels perfect, no chips or cracks, the chamber (excuse terminology if wrong) where the end of the shell sits against the firing pin looks fine as well. But when I assemble it, and pull back the cocking handle, it looks as if they do not align exactly, like a gap perhaps. I can probably provide a picture later, but that could just be the way they look, I do not know.
Is this a problem anyone has seen before? I'm sure the jamming is, but the shell burning speaks to gas escaping when it shouldn't right? And that would be in the connection between chamber and barrel? Any suggestions?
I know the most valid thing would be take it to a gunsmith, I do get the sneaking suspicion I have just done something stupid to it that prevents it from firing correctly. (I have disassembled and reassembled several times to clean and such, it only seems to fit together one way, but who knows... hence asking the experts.)
Thank you very much,
Ben"
6/9/2009 8:13:41 PM
The jamming can be any of about ten different causes. I'd call Masterpiece about that, they're pretty prompt with customer issues/questions and have a lifetime warranty on the gun.
As for the burn marks on the cases, that's par for the course when dealing with low tolerance blowback operated SMG designs. Dimpled primers is another common issue. Gas/heat is leaking into the chamber. The guns were originally intended to run anywhere from 1200-1800 rounds/min, so if they were as tight at a 1911, they would not function reliably.
Are you reloading the rounds?
As for the burn marks on the cases, that's par for the course when dealing with low tolerance blowback operated SMG designs. Dimpled primers is another common issue. Gas/heat is leaking into the chamber. The guns were originally intended to run anywhere from 1200-1800 rounds/min, so if they were as tight at a 1911, they would not function reliably.
Are you reloading the rounds?
10/31/2009 10:50:47 PM
I too seem to be having this jamming problem. If fact the cases are jammed against the recevier so hard that it actually bent the ejection port out a little. It shot very well in the beginning, but after running a suppressor the problem seemed to start. Now it does it with or without the suppressor. Actually I think it runs better suppressed then not. Any Ideas on getting it running right? I really enjoy this toy, but the problem is becoming a pain in the @$$. 
Ammo is a mix of personal reloads and White Box trash. I figure why burn up the good stuff in a plinker.
Ammo is a mix of personal reloads and White Box trash. I figure why burn up the good stuff in a plinker.12/14/2009 9:20:35 PM
I removed the bolt for inspection and could not find anything that appeard bad or wrong. So I called MPA and told them about the problem. It looks like there was a known ejection problem with earlier MPA .45cal pistols. Because once I told the lady what is was doing she told me to pack up the upper with complete bolt and send to her for a repaired one. I would have to say for the less then five minutes on the phone there customer service seems top notch. Will report one the returned product once it has been ranged tested.
12/17/2009 6:59:24 PM
There was an extractor change sometime ago. They'll probably replace the extractor, inspect the bolt and replace the upper. Good luck, I hope it works out.
1/16/2010 1:19:37 AM
I had a Cobray that would not feed any type of Remington ammunition. I would run Winchester just fine though. Try switching around ammo types.
1/16/2010 12:14:26 PM
Well I got my reciever back from MPA with a brand new bolt in it. Now I have the perfect reason to go shoot some more. Will up date on how the new bolt acts with and without the can on it.
1/17/2010 9:56:33 PM
Finally got some time to fire off some rounds in my MPA .45 with the new bolt and Bowers Suppressor. It ejected every round just like new and feed both FMJ store bought and HP hand loads.
6/20/2010 10:15:44 AM
Originally Posted By FlowSleeve:
Well I got my reciever back from MPA with a brand new bolt in it. Now I have the perfect reason to go shoot some more. Will up date on how the new bolt acts with and without the can on it.
Well I got my reciever back from MPA with a brand new bolt in it. Now I have the perfect reason to go shoot some more. Will up date on how the new bolt acts with and without the can on it.
Hate to resurrect a dead thread, but my brother in the OP has basically the same update. He sent it in to MPA, and got it back with a brand new bolt - runs like a champ now.
