Receiver cover scope mount mod

[John Galt]

Hey guys,

I was messing around with my mixmaster bubba project and have the urge to mount a scope.  Im not a fan of drill and tap mounts but considered a crazy ivan from feebay.  As I was looking at my receiver cover, I thought about installing dowels (small set screws) into the flats of the top of the receiver where the cover sits.  I would drill an tap for 2 dowels.  These set screw dowels could be turned down or removed for installation of a regular cover and turned up and indexed into matching holes in the bottom of the cover.  Also, I would remove the take down lever and tap for the bolt down mod that I hear works well. 

This next thought is far out there...but on the other forum a guy drilled and tapped the gas block and installed an adjustment screw.  Turn the screw in and gas port is closed down.  He is saying it works well and reduces the action's "slam" a lot. This might help hold zero on a cover mounted scope.  Too bad my mixmaster isn't a yugo, I could just play with the gas valve!  Any way, there are too many unknowns with the gas block idea for me and changing that if I mess it up would suck!

I guess, before I do something dumb, does anyone here have a good review of a scope mount?  I'm not going for a plastic, tacticool  , bubba special.  My goal is clean and classic.  I will post pics when its done.

[1mlt]

Here's what I did. Remove the cover, remove the cover lever, replace the cover, do not drill, just tap the hole with a 1/4-20. Get a 1/4-20 1 3/4" long button head. Screw it in, cut it off flush, cold blue the end. That LOCKS the cover in place. It won't move.

Mount a rail of your choice to the cover and you have a "zero" hold scope (or whatever) mount.

Marcus

[Loose}{Cannon]

I like the setscrews up front on both sides idea. Im my mind, even with the lever/bolt replacement idea, there is still room for movement at the front of the cover.

[John Galt]

L-C, that is what I was trying to get rid of.  My cover moves from side to side a little...maybe 1/32 each way and set screw/dowel pins would solve that...I think

[John Galt]

Marcus, did you just bolt down a rail to your cover and give up the iron sights?  I have been playing with ideas and I don't like when the scope gets too high or just looks dumb.  Did you post pic of your setup?

[1mlt]

I like the setscrews up front on both sides idea. Im my mind, even with the lever/bolt replacement idea, there is still room for movement at the front of the cover.

LC, the cover is absolute zero movement. I've done maybe 10 of these for customers and it won't move in the front. Some years back, Boomer and I did some calcs on how much holding power there was. It was very dry stuff, but the numbers were off the scale. It's posted on the "other' boards along with pics. The cross bolt, because it IS thread to thread and screwed tight, prevents the font from moving. Physics 101. And with the set screws, because there are what they are, you can't be sure you return them to the exact same position from the previous mount. The single screw is the better way, IMHO.

JG, I d/t the top of the cover and screwed the rail down. Dremel off the screws on the inside so they follow the curve of the cover. If you don't do that the bolt won't clear. BUT, you r/r the top for cleaning and it returns to zero.

Marcus

[Loose}{Cannon]

I remember your posts etc.  I simply think that the bolt through alone can act as a pivot point and rotate if the front of said cover isn't 100% tight fited and secure.  The setscrews just add another precaution/prevention to the the equation.

[John Galt]

Marcus, the holes in the cover for the take down lever must not be all the same size.  I tapped with 1/4-20 and the bolt is loose.

I have been thinking a little more and have come up with two more ideas.  It seems like the ramps of the cover slide nicely under the ramps of the receiver up front by the carrier.  As one would push the cover into those ramps, the cover would tighten.  I have 2 ideas:

1:  Remove cover.  Grind down a flat in the takedown pin that would face forward when the t/d lever is in the up (to remove) position.  Drill and tap the inside flat (facing the bolt)of the square lug that the t/d pin goes through.  Install a 8/32 ball end set screw so it just protrudes into the t/d pin hole.  Grinding the flat on the pin would provide relief for the protruding set screw and allow for easy take down.  Replace cover and turn t/d lever down.  Test for tight fit and adjust set screw as needed.  Resulting interference would "jam" the cover into the "ramps" of the receiver and tighten up the whole thing.

2:  Remove cover and pin.  Shape a bit of steel to fit the machined out area forward of the pin area.  Drill and tap for 1/4-20 button head.  Secure threaded bit of steel into machined recess area ahead of t/d pin by mechanical means or weld in place .    Drill through hole in the back of the cover below the serial number, through the square lug.  Install rear cover and tighten the bolt.  This will force the cover forward engaging the ramps and tightening the cover in place.

[John Galt]

Here are some pics of my bubba....It is a mixmaster and had a beautiful 30 round metal magazine, an amazing plastic folding stock with beautiful seams from the injection molding process, and piles of rusty, cruddy, scale stuff on the inside and the bubba before me decided to "jewel" the carrier with a belt sander...a truly unique design that causes jealousy at the range!  I thought about saving it but I decided to focus my restore-mojo on a Navy Arms Sharp Shooter that I'm in desperate need of a scope and mount for.  For the purists out there....I have done a de-bubba job on my 1951 Russian and my 1958 Romanian. 

Here is a pic of my project.

[Brawny]

I like the setscrews up front on both sides idea. Im my mind, even with the lever/bolt replacement idea, there is still room for movement at the front of the cover.

LC, the cover is absolute zero movement. I've done maybe 10 of these for customers and it won't move in the front. Some years back, Boomer and I did some calcs on how much holding power there was. It was very dry stuff, but the numbers were off the scale. It's posted on the "other' boards along with pics. The cross bolt, because it IS thread to thread and screwed tight, prevents the font from moving. Physics 101. And with the set screws, because there are what they are, you can't be sure you return them to the exact same position from the previous mount. The single screw is the better way, IMHO.

JG, I d/t the top of the cover and screwed the rail down. Dremel off the screws on the inside so they follow the curve of the cover. If you don't do that the bolt won't clear. BUT, you r/r the top for cleaning and it returns to zero.

Marcus

Marcus, is my sending a bolt cover to you for this mod doable? I want to put a small 4x scope on mine with an option to see the irons.

[1mlt]

I like the setscrews up front on both sides idea. Im my mind, even with the lever/bolt replacement idea, there is still room for movement at the front of the cover.

LC, the cover is absolute zero movement. I've done maybe 10 of these for customers and it won't move in the front. Some years back, Boomer and I did some calcs on how much holding power there was. It was very dry stuff, but the numbers were off the scale. It's posted on the "other' boards along with pics. The cross bolt, because it IS thread to thread and screwed tight, prevents the font from moving. Physics 101. And with the set screws, because there are what they are, you can't be sure you return them to the exact same position from the previous mount. The single screw is the better way, IMHO.

JG, I d/t the top of the cover and screwed the rail down. Dremel off the screws on the inside so they follow the curve of the cover. If you don't do that the bolt won't clear. BUT, you r/r the top for cleaning and it returns to zero.

Marcus

Marcus, is my sending a bolt cover to you for this mod doable? I want to put a small 4x scope on mine with an option to see the irons.

No, because you need to do this with the cover on the rifle so the threads will line up properly. If you just d/t the cover, then tap the rifle, they won't align. I don't have an FFL so I can't accept your rifle. Take it to any gunsmith and tell him what you want done. It is a simple 10 min mod. You aren't limited to 1/4-20 either. You can go metric if your hole is oversized from use.

Marcus

[Brawny]

Thanks marcus, because of my ignorance I am not following your process but I will figure it out.

[1mlt]

Thanks marcus, because of my ignorance I am not following your process but I will figure it out.

You have a hole that needs threads. In order for the screw to go all they, the threads must be a continuous spiral from start to finish AND match the thread on the bolt. If they don't match, the bolt will "jam" and stop screwing in when it hits the part of the threads that isn't continuous with the rest of the threads or is a different "pitch". Maybe this will help. Have you ever started to screw in a bolt hole and it started to screw in and then suddenly "locked up" and wouldn't go any more? That's because you tried to screw in a bolt that had a different set of threads, say 1/2x20 bolt into a hole that had 1/4x24 threads in the hole. The thread patters (pitch) are different and won't work together.

Marcus

[Brawny]

Oh ok, I understand now.

[echo1]

B man,

You thread it with the spring removed and the cover in place. The "tap" part must be long enough, to go through the receiver on one side while tapping into the cover block at the same time, then through the block while tapping the other side of the receiver. One continuous threading, as if it were a single piece of solid steel. A bottom tap won't get it. PAX

[Brawny]

Please indulge me with pics. I think my problem is nomenclature.

[Justin Hell]

Basically consider it like a sandwich.

Either wall of the receiver is the bread and the cover is the meat. Imagine wanting your sandwich wanting to be cut in half...perfectly. You wouldn't slice each piece of bread individually...and then the meat and expect it to line up perfectly when you reassemble it.

With the RC cover mod, you are trying to match up three holes with one bolt...with a continuous uninterrupted thread lining up as if all three were one solid piece of metal. To accomplish this, all must be together when tapping the holes for the bolt otherwise your threads would start at different locations on each hole and the screw wouldn't be able to pass through all three holes.

[1mlt]

And I promise, once it's done, the cover will NOT move in any direction.

[Brawny]

And I promise, once it's done, the cover will NOT move in any direction.

Oh I think I get it now. The screw replaces the cover lever. So can the cover never (easily) come off again?

[1mlt]

And I promise, once it's done, the cover will NOT move in any direction.

Oh I think I get it now. The screw replaces the cover lever. So can the cover never (easily) come off again?

It will come off easy enough with an Allen wrench. I use 'button head' screws. The 'look' is clean as there is no large bolt head on the side of the cover.