R51 Magazine lips

[David]

Using a set of calipers, I am measuring the space between the lips on the r51 magazine. 

Width, very back of magazine:  .351

Width, middle of magazine, front of lips before they roll away to the sides:  .338

I think this is revealing as to why the bullets have a tendency to nose dive.

Because the rear of the magazine lips is wider than the front, the rear of cartridge will set higher in the lips and flatter, in other words, more parallel to the slide and barrel.

Because the front of the lips pinch the approximate middle the cartridge, it causes a pivot point at the approximate middle of the cartridge.

The slide pushes the cartridge from the top rear of the casing.  The pivot point is roughly the top center of the cartridge.  This causes the front of the cartridge to dip down.

I have modified one of my magazines so that the numbers above are about reversed.  With dummy cartridges, it loads perfectly almost every time.

[FlatEarther]

I found the same on all six of my mags. Adjusted the front to make the lips parallel.
Agree with you 100% and also think the tapered lips increase friction even though everything is smooth and polished.
Instantly improved feed reliability. Also found it stopped the nose dives when unloading a mag too... Joe

[David]

Agreed.

I'm going to take some pic later today to help illustrate what we are talking about.

It is quite possible the measurements I made were reversed somewhere in Remington's process of drawing blueprints and manufacturing - because the way they come from the factory just doesn't make sense.  A really stupid mistake on R's (or their subcontractor's) part.

Opening the front of the lips slightly wider than the back, perhaps a .010 difference, may reduce friction as the cartridge moves forward compared to parallel lips.  It should also angle the front of the cartridge slightly up.

[FlatEarther]

** Edited **

I have two types of IMI factory ammo that constantly nose dive or misfeed only in the R51.
R51 owners manual says to lightly oil everything including the mags.

So for troubleshooting I used an unmodified mag. Disassembled, cleaned, lightly oiled entire inside surface. Follower, lips, ridges... Everything.
Then lightly oiled seven rounds of the IMI ammo.
The oiled ammo loaded and unloaded from the mag by hand much easier than normal. Also fed and cycled flawless by hand though the R51. Everything worked perfect with reduced friction: brass to feed lips, brass to mag ridge, and brass to brass...
I did not live fire this setup. Lube can damage ammo and should not be necessary.

Then looking at the empty mag body I found the feed lips were not parallel. I don't drop or otherwise abuse the mags. The other five mags measured about the same so were made this way.
Next I found ammo did not fit freely between the ridges in the side of the mag. The ridges were slightly clamping the brass. Don't know if this is by design but is a source of friction and seems wrong to me. The outside of the body measured approx 0.585 to 0.590 on all of my mags. It was a struggle but spread the body sides approx 0.010 so the outside measured near 0.600 inch. That was enough to stop the brass interference fit and the mag body still not drag in the mag well. Only test fired once since these mods but all worked good.... This is turning into work    - Joe

[R51Fan2017]

** Edited **

The oiled ammo loaded and unloaded from the mag by hand much easier than normal. Also fed and cycled flawless by hand though the R51. Everything worked perfect with reduced friction: brass to feed lips, brass to mag ridge, and brass to brass...
I did not live fire this setup. Lube can damage ammo and should not be necessary.
- Joe

Joe,

In relation to John Pedersen. This is after all a pistol he designed. It is interesting you mention lubing the ammo. During the late 20s and early 30s there was a push for the Defense Department to adopt a semi auto service rifle for our troops. The two contenders among others were John Pedersen and John Garand. Pedersen had designed a semi auto rifle in .276 which would be named .276 Pedersen in his honor. Garand had designed another rifle in the same caliber. Long story short, Pedersen's rifle required lubed ammo to function correctly, as without it, extractions and feeding problems became manifest. What made Garand's rifle so attractive (and ultimately wound up with him winning the contract to produce what would become the M1 Garand), was that his rifle did not need lubricated ammo to feed and extract correctly. He designed a rotating bolt to accomplish his purpose without any extra lubrication. Also of note is that Pedersen's rifle was also of the retarded blowback design, just like the model 51. I couldn't help drawing the parallel between lubed ammo, and a couple of Pedersen's most famous creations. Wonder if I should try lubing some ammo and see how it does. However, that should not be necessary in today's guns. Just saying. 

[FlatEarther]

Interesting history... I was told an old school way to safely dispose of unwanted ammo was to soak in oil. Kills the primer and probably not good for the powder either. Don't know if this applies to modern ammo... I have some Federal +P and Speer ammo that functions fine in unmodified mags. Some folks here say their R51 eats everything fed. Mine is picky. Seems to like hotter ammo... Joe

[R51Fan2017]

Joe,

The lubed ammo Pedersen originally used wasn't by any means dripping in oil. It was very lightly lubed. In fact, you could hardly tell by looking at it. But it was just enough to do its job.

[FlatEarther]

Range report follow up to my previous post.
350 rds since the above mods and all six mags function perfect with a variety of ammo.
I have settled on these three mods for all six mags: open feed lips until parallel, open body until no drag on brass, and trim follower stop bend... I have not modified the follower or spring. Works fine with full mag, partial mag or 7+1... Yes 7+1 requires extra effort to seat the mag but that is not how I typically load this pistol.
I trimmed the bend about 45 degrees angle. This removes the place where most nose dives grab but leaves just enough bend to act as a follower stop. Can be done with a bench grinder then small files and emery cloth to clean up... I'll add that this mod may not be needed as I think one or both of the other mods are more likely to help with feed issues.
Pictures from before all mags were trimmed... Joe

[David]

Thanks Joe.

I do the same with the front of the magazine, trim and flatten.   Followers do not come out even though I shorten the follower just enough to close the slide on a full magazine (not the ridiculous amount I cut away originally - those do pop out). 

I think the most significant mod I did was open the front of the magazine lips and narrow the back, so the front is slightly wider than the back - which is completely reverse of how the mags were originally configured.  This eliminates the pinch point that the cartridges pivoted on to nose dive.  Its debatable if wider in the front of the lips is adventitious to parallel - I think what matters is eliminating the pinch the front of the lips.

I note you opened the body of the magazine by .010.  What is your technique for doing that (I am envisioning compressing the front and back in a vice).

[FlatEarther]

I note you opened the body of the magazine by .010.  What is your technique for doing that (I am envisioning compressing the front and back in a vice).

Yes! Good guess!... Tried prying and wedges etc inside. Very inconsistent. Careful compressing in a vise did it without any unwanted distortion.
Disassemble and the body fits perfect across a four inch jaw. Goes pretty quick once you figure out the "spring back"... Joe

[crosstrains]

Do you have a picture of how you did it in the vice?  I'm imagining a few different ways but I don't understand how that opens up the front of the feed lips. 

[FlatEarther]

Two different operations...
Vise was used to slightly increase the width of the mag body.
Pliers used to adjust front of feed lips out until they are parallel... Joe

*Edited to add pics*
Bench vice is not a precision tool  so your experience may vary... Protect mag body. I used aluminum in jaws.
Pressure from vice should cause sides to bulge out. Measure several places across body and adjust as required.

Used tooth of pliers to hook lip and leverage out... About .005-.010 per side as required.

[crosstrains]

Thanks - I'll give it a go when I have some time (and patience)...

[funflyer]

Here's what I got on mine. One mag has been problematic, causing the last live round stovepipe issue. The other has never given me any trouble.

[David]

exactly what mine were - pinched in the front of the lips, causes the bullet to pivot and nosedive.  Almost like someone read the specification backwards.

Good work on the pics.