DDM4/SLiM rail anti-rotation problem?

[awdxtc]

The NEW V7 does away with the bbl nut....... look at a pic of one there is a plate that attaches to the bbl/extension, which is held by the rail system , there is no bbl nut.
they adopted this from the 308 M5 which uses the same system as the NEW V7.

from DD's website

Innovative 4-bolt connection system utilizing a unique barrel extension securely attaches free-floating CHF barrel and KeyMod hand guard mounts securely to upper without barrel nut

This is incorrect, the DD5V1 (308) has a flange machined into the barrel where as the MFR XS (new v7 rail) uses a standard barrel nut much like the DDM4 Rail (V9,V5) I have sent a message to Joe Marler on AR15.com asking him how the 2 rails differ in mounting.

[pezboy]

putting blue loctite on the 4 screws won't solve a thing. What is "shifting" is the plate the rail attaches to and it is held in place by the bbl nut. You can only tighten that nut so much. Perhaps they should have rough textured the nut and the plate to keep it from shifting .? The V9 attaches the same way does it not? the new V7 attaches completely differently.

The plate is loose on the Lite Rail/RIS II/DDM4/MFR XS. The way the rail is held in place is the clamping force on the front and rear of the barrel nut at the same time by the screws. If it is shifting, it is because the clamping force isn't enough to keep it from shifting. Texture might help though.

[XM15M4Guy]

This is incorrect, the DD5V1 (308) has a flange machined into the barrel where as the MFR XS (new v7 rail) uses a standard barrel nut much like the DDM4 Rail (V9,V5) I have sent a message to Joe Marler on AR15.com asking him how the 2 rails differ in mounting.

Please let us know if he replies.... and thanks!

[awdxtc]

Will do

[jackblack73]

The plate is loose on the Lite Rail/RIS II/DDM4/MFR XS. The way the rail is held in place is the clamping force on the front and rear of the barrel nut at the same time by the screws. If it is shifting, it is because the clamping force isn't enough to keep it from shifting. Texture might help though.

I've been trying to figure out how that system works. Is the only clamping force on the front and rear of the barrel nut? If so, I could see how it would be less resistant to twisting than a rail that clamps onto the entire surface area of the barrel nut. Is there any other provision made to prevent rotation? From what I've seen most rails that have tabs to prevent rotation usually have a little space between the tabs and the receiver. So while they will prevent extreme rotation they won't prevent small movement. It seems like the DD rails are designed more to prevent a rail from being pulled off than to prevent rotation.

[pezboy]

I've been trying to figure out how that system works. Is the only clamping force on the front and rear of the barrel nut? If so, I could see how it would be less resistant to twisting than a rail that clamps onto the entire surface area of the barrel nut. Is there any other provision made to prevent rotation? From what I've seen most rails that have tabs to prevent rotation usually have a little space between the tabs and the receiver. So while they will prevent extreme rotation they won't prevent small movement. It seems like the DD rails are designed more to prevent a rail from being pulled off than to prevent rotation.

Correct. They have two nubs on each side of the receiver. The type of "anti-rotation" tab that these rails have (including the RIS II) will only prevent the rail from completely unscrewing. It may cant, but the rifle will still function. Now, at least on the first instance, AKOU's most definitely was not the barrel nut turning but the rail moving on the barrel nut since the screws were loose. When the rail is loose, it can not only rotate but can move in all directions a slight amount.

[G.B.]

The v7 uses th same system as the v11 other than the back of the rail is a little shorter and a spacer goes between the rail and the mounting plate. If the bolts are tight its making contact with front and back of the barrel nut. I don't think it would be easy to rotate, and if it did it couldn't rotate very much.

[SmugPePe]

They replaced 6 large screws with 4 small screws. Smaller/lighter on the same exact design means weaker.

The best anti-rotation is the Geissele set screw style IMO.

1+

I had HDSI upper with rare 13" Geissele SMR keymod mk4 handguard I love that handguard, I would align the Handguard to upper using set screw on bottom one on each side and after its tight and aligned I would further tighten them while holding alignment so the set screw bite into bottom of upper preventing rotating for I was planning on treating it just like my other rifles.

kinda hard.

I had to sell it before I could really use it and if I had use it it would quickly accumulate marring, dent, yadada.

Geissele smr is one of few ff handguard i would trust for hard use.

[justin_247]

Not to reopen an old thread, but I felt this was the most appropriate place for it.

I noticed that DD now seems to be shipping a different type of screw for their DDM4 rails and the threads appear slightly more coarse (although this could be some kind of photo or compression distortion):

OLD VERSION https://www.ar15goa.com/product/ddm4...aniel-defense/



NEW VERSION https://danieldefense.com/screw-pack.html



Has anybody had a chance to try these?

[17K]

That new version is like what the RISII has always had.

This is whole bunch of unnecessary drama to have the cosmetic appearance of a continuous top rail.

The old locking collar was a better method than pretty much anything new.

The only new rails I like are the BCMs.