R51 with DangerCo barrel.  Griffin Armament tri-lug adapter (same kind as on the MP5).  Makes for easy on and off of suppressor. 

I think it looks better than the thread protector, even if its a little longer. 

swaits -  Great report on the new mags - perfectly parallel!

I seriously thing that between REM and their contractor, the specifications on the magazine lips got reversed.  Big Green has a history of screwing things like this up, they totally dorked up the chamber of the 6.8SPC too. 

The good news is easy fix!.  I'm going to try some of those glock springs.  If they reduce the friction in the magazine while still having enough energy to force the last round into up into place, so much the better.  We may have this thing solved.

Sorry about resurrecting a dead thread.  Catching back up after some time away.  Good work guys!

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.

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).

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.

Rog

I haven't noted any difference.  Just drop it in and squeeze the trigger.  It was as easy as a R51 allows.

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.

A  little more looking shows thread protectors are common, low profile, and inexpensive.  I would suggest no need to modify your design.

https://www.midwayusa.com/barrel-thread-protectors/br?cid=21321

Range Report

Back from a short trip to the desert to shoot up an old agave stump (among other things)

147gr HS.  3.5 gr N320.   This load is subsonic, but right on the edge because I can hear the supersonic crack in my MP5K with the same suppressor (5.5 inches).  Its subsonic in the r51.   

Suppressor is a Griffin Armament Revolution 9 (Mod3)

Ridiculously cool.  Noise level is about like clapping hands together, or an air rifle.  Almost Hollywood quiet.  Most of the noise is the bullets ricochet off stuff down range.

I also shot some 115gr Tula.  That stuff is super sonic, and sounds like a really loud air-nailer.  Its loud enough that you don't really hear the ricochets.  It would be cool if I just wasn't shooting the 147 subs.

Sights:  The diameter of the Revo9 is 1.375" (a common diameter), which optically puts the top radius of the suppressor at the same level as the top of the sights.  That means, while the suppressor is in front of the sights, it does not extend above the sights.  So it is  good to go.   

Next I'm going to get a tri-lug adapter and set it up on the barrel.  This is a really cool toy!

(thank you DangerCo)

Got mine today too.

If the ribs on the thread protector were perpendicular to the barrel instead of barrel to the barrel, it would make a great grip for disassembly.

My guess is that thread protector is a stock part and comes the way it does.

Thanks DangerCo!

I'm heading to the range tomorrow!

Ordered One!

What is the coupon code?

I just bought 2 magazines from Buds, under $18 each.

They look just like the ones that came with my pistol, same lip bent inwards to catch the front of the follower - except, the slide will close on 7 rounds which my originals did not without trimming the follower. 

Consider me in for ONE.   How do you want to arrange payment?

David