Fix gap between upper and lower?

[Stefan1235]

My ‘73 M10/45 has a noticeable gap where the rear of the upper meets the lower, allowing the upper to wiggle up and down on the lower. I know some folks use layers of aluminum tape to fix some of this slop but is there a more permanent fix?

 

[StenAtopia]

My ‘73 M10/45 has a noticeable gap where the rear of the upper meets the lower, allowing the upper to wiggle up and down on the lower. I know some folks use layers of aluminum tape to fix some of this slop but is there a more permanent fix?

You left out some variables? Is it all uppers that have the slop? What I would do is epoxy a few aluminum or brass strips to the bottom rear of the said upper. Question is by raising it up will it over run the sear? Another option is to lower the “Hood” of the rear of the lower which will give you a more snug fit. Sound like you might have an out of spec stock block or your hood is to high? Imho. YMMV.

 

[root]

I'd just drill it and tap the upper for a set of grub screws like the Lage uppers have.

 

[Gaujo]

I'd just drill it and tap the upper for a set of grub screws like the Lage uppers have.

Wait the lage uppers have screws?

 

[root]

My 10/15 does and so does my 10/31 never had to adjust the 31 it was nice & snug upon arrival.

 

[LawBob]

Wait the lage uppers have screws?

The 15 does.

 

[Deerhurst]

Nylon tipped set screws to take up play at the back of the receiver on both my Max 10/31 and Max 10/15 uppers.

 

[Stefan1235]

Follow up, on my ‘73 Powder Springs the gap in red is 1.37mm, anyone else willing to measure theirs for me? Just curious if this much of a gap is normal, lots of play between the upper and lower.

 

[MitchWerbellsGhost87]

View attachment 40236
Follow up, on my ‘73 Powder Springs the gap in red is 1.37mm, anyone else willing to measure theirs for me? Just curious if this much of a gap is normal, lots of play between the upper and lower.

It’s normal, all MACs are like this.

 

[Deerhurst]

0.054" sounds pretty big but it's been quite some time since I put a factory upper on.

As said above, they all have some slop.

 

[Stefan1235]

It’s normal, all MACs are like this.

I know these aren’t precision built but a 1.37mm or 0.054” gap seems pretty big, I’m chasing down some FTF issues and was wondering if this slop could be a cause of my issues.

 

[MitchWerbellsGhost87]

I know these aren’t precision built but a 1.37mm or 0.054” gap seems pretty big, I’m chasing down some FTF issues and was wondering if this slop could be a cause of my issues.

Tolerances are pretty loose on these guns, as far as I know, the slop with the upper is not a cause for malfunction. FTF issues with these guns are 99% related to the magazine, or the feedramp.

 

[A&S Conversions]

I am very much in agreement with “Mitch…”. The actual feeding area of the upper is in the center of the upper, so pivoting on the front pin, the feeding area of the upper would have half that movement. There is also the pressure of the rounds in the mag would tend to push the upper to the top of the slop.

So what is the actual FTF problem? Is this a .45 gun or 9mm? Are you shooting .45 or 9mm? What magazines are you using to shoot that caliber? What are you using for a bolt? If using the old style bolt, does the barrel have the clearance for the old style extractor? How old is the recoil spring? The list goes on… This community has an enormously amount of experience and wants to help. Please let us know how we can help.

Scott

 

[Stefan1235]

Appreciate the info and support folks. It’s a .45, when running the factory MAC suppressor it feeds flawlessly with all of my magazines and any round-nose 230gr FMJ I have on hand.

Without the suppressor on it will feed 3-10rds before one is jammed 45 degrees into the chamber with the bullet pushed back into the case, happens with S&B, PMC, and WWB ammo. Standard bolt, barrel has the clearance cut, using factory 10rd, 30rd, and 40rd magazines along with some keep shooting grease gun 30rd magazines and old USGI grease gun magazines. I’ve swapped all the fire control parts with new FTF industries parts, replaced the recoil spring, new buffer, cleaned and lubed everything like I have OCD, but still jams up without the suppressor, a bit less often now but still will happen at least a few times per range trip.

Everything cycles properly with snap caps, so I think the feed ramp is okay, the only thing I can think of now is the upper is bouncing around without that extra weight of the suppressor and the rearward force my left hand applies while holding onto the first stage.

 

[Hey...]

My M11/9 had a lot of mods for reliability and the final issue was like yours. 100% with a silencer and not as good without.

I put in a stronger extractor spring and it became 100% with or without the suppressor.

I have both of these kits which are currently out of stock. I picked one with the same wire thickness as factory and cut a piece with one (or two I forgot) coils longer than the factory one. Since then it’s been perfectly reliable. The suppressor backpressure is helping take up the slack for the weak extractor.

 

[skoda]

Take a big hammer and wail on the top of the lower a bit. That will take up the slack.

 

[A&S Conversions]

So is the extractor spring original or is it the original style and is the original extractor? My understandings is that the original style extractor is hard to find a replacement for. I would think that if the claw was rounded, dressing it up with a small fine file and putting a little more bow in it might clear up the issue. That is the handy thing about the late model bolts, the spring and extractor are easy to replace. Please let us know how you make out with the problem.

Scott

 

[Stefan1235]

Extractor is original to the original bolt, seems to extract snap caps just fine though. Wonder if a new style bolt will eliminate the issue, guess it couldn’t hurt.

 

[MitchWerbellsGhost87]

Take a big hammer and wail on the top of the lower a bit. That will take up the slack.

You can do this with a frame that isn’t welded at the top edges where the center meets the sides, but on the factory MAC and RPB guns they are welded at those seams, and they have that little gap for a reason where the top of the lower tilts upwards slightly to provide a little wiggle room. when the top of the lower is too tight against the top of the upper it makes it so the upper won’t fit properly because of the stock block.

 

[skoda]

I hope that my words are taken as a silly joke because that's all that they were. No one would be expected to wail on their registered lower. Uppers - sure if it fits the situation. Shims - of course, even welded onto the upper. But I wouldn't touch the lower unless it was clearly out of shape from the original construction.