M10/45 troubleshooting

[Beowulf]

Well, rather than continue to beat my head against the wall, I'll ask here and risk looking really stupid (or more stupid than I already appear).

So, I got the FTF Industries bolt assembly for my transferable PS M10/45. I also got a basic top cocking upper from US Machinegun.

When I put those together on on my lower, I get two issues:

1. The bolt is really tight at the rear of the upper, which tells me at least one of them is probably out of spec. I'm seeing a little bit of wear on the top and right side of the bolt finish as I try to work it, so maybe its something that will work itself out. However that brings me to the greater problem.

2. The bolt will not lock back. I will get far enough back that the ejector rod is exposed, but either it's not going back far enough to lock or the upper is holding it too high to lock. I did notice that when I pull the bolt out of the upper and just lay it on the lower with no upper at all, I can actually get it to lock back, so I'm thinking it's something about how it sits in the upper.

I'm really hoping it's really obvious that I've forgotten about in the 10 or so years I've been MACless, but I'm a bit stumped at the moment and I don't have a stock of spare parts or alternate uppers to test with. It isn't the safety (I'm fairly sure). It's in the fire position and I can confirm that it does seem to function without the upper on it.

Anyone have any ideas?

 

[GK8041]

On the new bolt assembly, does a small bit of excess rod protrude out from behind the buffer plate(maybe a couple mm)-where is was cut?

 

[StenAtopia]

Well, rather than continue to beat my head against the wall, I'll ask here and risk looking really stupid (or more stupid than I already appear).

So, I got the FTF Industries bolt assembly for my transferable PS M10/45. I also got a basic top cocking upper from US Machinegun.

When I put those together on on my lower, I get two issues:

1. The bolt is really tight at the rear of the upper, which tells me at least one of them is probably out of spec. I'm seeing a little bit of wear on the top and right side of the bolt finish as I try to work it, so maybe its something that will work itself out. However that brings me to the greater problem.

2. The bolt will not lock back. I will get far enough back that the ejector rod is exposed, but either it's not going back far enough to lock or the upper is holding it too high to lock. I did notice that when I pull the bolt out of the upper and just lay it on the lower with no upper at all, I can actually get it to lock back, so I'm thinking it's something about how it sits in the upper.

I'm really hoping it's really obvious that I've forgotten about in the 10 or so years I've been MACless, but I'm a bit stumped at the moment and I don't have a stock of spare parts or alternate uppers to test with. It isn't the safety (I'm fairly sure). It's in the fire position and I can confirm that it does seem to function without the upper on it.

Anyone have any ideas?

FTF products are notorious for being out of spec. The back portion of the upper, lower front(circled red) with a pair of small pliers bend it down. Sounds like the back of the bolt is getting hung up there. Borrowed photo

 

[BlackBelt]

I have had that issue a couple or three times.
Each time the problem was the upper was too tight at the back end and needed a little relief cut.
If you look at StenAtopia's pic above..where the red circle is...thats where I took a dremel cutting wheel and cut that slot a lot back further. I made the slot cut a little wider than a pencil, and at the last half inch of the receiver I stopped the slot and cut just along the center seam only, which opened up the rear of the receiver and the bolt no longer got stuck.
If you decide to try it, go slow and check it as you go.
Conversly, since you got the upper from USMachinegun you can call them and they are usually pretty good about customer service.

 

[Climrox]

Well, rather than continue to beat my head against the wall, I'll ask here and risk looking really stupid (or more stupid than I already appear).

So, I got the FTF Industries bolt assembly for my transferable PS M10/45. I also got a basic top cocking upper from US Machinegun.

When I put those together on on my lower, I get two issues:

1. The bolt is really tight at the rear of the upper, which tells me at least one of them is probably out of spec. I'm seeing a little bit of wear on the top and right side of the bolt finish as I try to work it, so maybe its something that will work itself out. However that brings me to the greater problem.

2. The bolt will not lock back. I will get far enough back that the ejector rod is exposed, but either it's not going back far enough to lock or the upper is holding it too high to lock. I did notice that when I pull the bolt out of the upper and just lay it on the lower with no upper at all, I can actually get it to lock back, so I'm thinking it's something about how it sits in the upper.

I'm really hoping it's really obvious that I've forgotten about in the 10 or so years I've been MACless, but I'm a bit stumped at the moment and I don't have a stock of spare parts or alternate uppers to test with. It isn't the safety (I'm fairly sure). It's in the fire position and I can confirm that it does seem to function without the upper on it.

Anyone have any ideas?

I’m curious if your bolt cocking handle fits and moves with the bolt back to front/ front to back in the channel of your upper.

I recently bought what I assume is the same bolt and handle from FTF, and the cocking handle will install in the bolt while in the upper install position, but will not slide to the forward position in either of my two OEM uppers. I think that the “flats” on the handle are too wide.

The bolt without the handle, however, seems to fit in both uppers (but I have not tried in conjunction with the lower).

I have reached out to FTF via email and phone (starting last week) but I have not heard back.

 

[StenAtopia]

I’m curious if your bolt cocking handle fits and moves with the bolt back to front/ front to back in the channel of your upper.

I recently bought what I assume is the same bolt and handle from FTF, and the cocking handle will install in the bolt while in the upper install position, but will not slide to the forward position in either of my two OEM uppers. I think that the “flats” on the handle are too wide.

The bolt without the handle, however, seems to fit in both uppers (but I have not tried in conjunction with the lower).

I have reached out to FTF via email and phone (starting last week) but I have not heard back.

You do realize on most cocking handles with the detents if you turn them they will lock the bolts from traveling right?

 

[Climrox]

You do realize on most cocking handles with the detents if you turn them they will lock the bolts from traveling right?

Yes. However it never hurts to verify something like that which may get overlooked (especially with a newer Mac owner like me).

I just tried with the handle only, and it is indeed is too wide to travel down the channel in proper orientation (sight cutouts in line with sights). In contrast, my PS original handle has generous clearance side to side.

Hopefully OP and myself get our respective issues sorted out.

 

[timkel]

Was the safety on? You can't retract the bolt all the way back with the safety on.
I edited this to be more clear.

 

[Beowulf]

Was the safety on? You can't retract the bolt all the way back with the safety on.
I edited this to be more clear.

Nope, it was definitely off and the charging handle was in the unlocked position, unless it can be put in wrong, so when it is oriented with the notch not blocking the sights (firing position) is really locking the bolt.

But the bolt opens until the cocking handle is just in front of the handle removal cut out, so it’s pretty far back. I would think it should be back enough to let it lock open.

 

[Beowulf]

FTF products are notorious for being out of spec. The back portion of the upper, lower front(circled red) with a pair of small pliers bend it down. Sounds like the back of the bolt is getting hung up there. Borrowed photo View attachment 41529

I tried that, though it’s not a solid plate there, rather two bars with a gap in the middle (I assume this provides clearance for semi auto components maybe?). I did put a very slight bend on both sides, but it didn’t seem to have any effect on either bolt tightness or ability to lock open.

 

[StenAtopia]

I tried that, though it’s not a solid plate there, rather two bars with a gap in the middle (I assume this provides clearance for semi auto components maybe?). I did put a very slight bend on both sides, but it didn’t seem to have any effect on either bolt tightness or ability to lock open.

Pm sent

 

[Beowulf]

On the new bolt assembly, does a small bit of excess rod protrude out from behind the buffer plate(maybe a couple mm)-where is was cut?

Here is what it looks like

 

[Beowulf]

On the new bolt assembly, does a small bit of excess rod protrude out from behind the buffer plate(maybe a couple mm)-where is was cut?

Here is what it looks like

Here is what it looks like

 

[Beowulf]

This is as far back as it goes (which does appear to clear the ejection port)

 

[JwestAK]

I don't have mine in front of me right at the moment. However here are a couple things to check.

A - The sear relief cut in the upper is adequate for the sear to engage the bolt.

B - The feed lug on the bottom of the bolt is not contacting the back part of the receiver.

C - The feed lug on the bolt is not hitting the stock block in the back of the receiver

It looks as if your upper is cut for a semi auto setup, which is why it's open on the bottom. I've tried numerous uppers on my gun, however never a semi cut one. One of them had the doubler plate welded on the bottom, which was a bit thicker than usual. It fit really tight into my receiver, which squeezed the feed lug when cycled causing binding.

Just figured I'd mention the first things that popped to mind.

 

[Beowulf]

Well, first a huge thank you to StenAtopia for spending his valuable time on a couple of calls with me to go over this and troubleshoot it from multiple ends (bolt, upper, and lower).

As JwestAK speculated above, I'm pretty sure I was sent a semi-auto upper that has no relief cuts for proper sear and sear trip engagement. So nothing to even let the bolt lock back. 🤦‍♂️

I called USMachinegun and left a message, so hopefully he gets back to me and I can get this settled.

Unfortunately, looks like I am SOL on the shoot this weekend though.

 

[JwestAK]

Glad you got it figured out. Ultimately if you have some air tools, or even a Dremel. You should be able to clearance the upper yourself to function with your gun if you really wanted. I could provide measurements tonight after work on the cutout locations if that's a route you wanted to go.

 

[Beowulf]

Glad you got it figured out. Ultimately if you have some air tools, or even a Dremel. You should be able to clearance the upper yourself to function with your gun if you really wanted. I could provide measurements tonight after work on the cutout locations if that's a route you wanted to go.

Thanks. I might go that route if US Machinegun isn’t responsive.

 

[USMG]

he bought it specifically from our MPA semi auto section, part number and item listing is not for an SMG.

MPA45R-BU45
> Product Name: * .45 Barreled Upper receiver for Master Piece Arms/Vulcan/Velocity .45 ACP

 

[Beowulf]

That does appear to be correct.

I apparently bought this one:




Instead of this one: