I was able to visit my Griffin M4SDII the other day and put a few rounds through it but I had a double feed (2 live rounds with the bolt hitting the shoulder of the 2nd round).  I only have about 125rds through this upper using the same load, magazine, etc. but never had an issue yet.  It was ejecting at about 1:30-2:00 so I am sure it is over-gassed but I have an H2 buffer in it right now.  I was using an original straight 20rd PMAG.

Would the first logical step be to try an H3?  After that would I then try an extra power recoil spring?  I have read that a true double feed is 99% of the time the magazine but I haven't ever had issues with this combo before so I wasn't sure if that could still be the case simply because I put the suppressor on it.

Top Rifle:
BCM upper receiver
Daniel Defense 12.5" CHF 5.56mm barrel w/ factory pinned low-pro gas block
Griffin Armament Tactical Compensator w/ tabbed washer
Spikes melonited carbine length gas tube.
BCM KMR 10" handguard w/ KAC Panel Kit
BCM Keymod Sling Mount
Spikes Tactical BCG
BCM Mod4 Charging Handle
Daniel Defense front BUIS
Troy rear BUIS
Surefire X300U-A (will be adding a Unity Tactical EXO)
Vltor EMOD Stock
Trijicon TA33G-H ACOG w/ Larue mount *or* Aimpoint CompM4 w/ Bobro mount (ACOG on it for now as it is lighter than the Aimpoint)
Blue Force Gear VCAS sling w/ aluminum adjuster

I have the same barrel and an older SF can. I have been using a spikes buffer and it's been working great.

Which buffer?  I have a St-T2 but the H2 is in it right now.

If the gun is severely over gassed like that, you're only fixing the symptom with a heavy buffer and not the problem. You need to get a gas block.

Thanks but I will probably just wind up trying to send it to DD to diagnose before I put an adjustable gas block on it as I spent a large chunk of money on the barrel to get a factory pinned gas block so over gassed shouldn't be a problem with the light loads I was using I wouldn't think.

There's likely not much they will be able to do for you.  I believe DD has publicly stated that they intentionally overgas commercial guns to ensure that they will function with all available ammo.  I have a DD 11.5" barrel that ejected at approximately 1:30 to 2:00 with a Sprinco Green spring and an VLTOR A5 H4 buffer (i.e. 7 oz).  Anything less and the spent brass was kicked out nearly parallel to the barrel.  I installed and tuned an SLR Sentry gas block on that barrel and the ejection is a perfect 4 -4:30 and the felt recoil has been reduced substantially.  

Just my $0.02....

I did speak with someone at DD yesterday and was told they use a .073" gas port in the 12.5" barrel.  They also said to swap magazines but if I still have issues to let them know as an H2 buffer should be fine suppressed.  They said they would look at it if I still have problems.

Most likely a magazine issue.





The bcg should only be able to contact one new round at a time, the presence of a second fresh round is almost always due to the magazine not retaining control of the rounds.



ETA:  Second round is due to the first round coming out of the magazine before being properly stripped, then the second round jumps up to the feeding position after the bolt has passed but before the carrier has passed.  The carrier drives the second round forward and it gets caught by the bolt on the shoulder.


       

 

I am inclined to agree that it is magazine related but it just seems odd that every round fired from this rifle (granted only 125rds) has been from the same straight 20rd PMAG and I never had an issue before I put the suppressor on it and the magazine was new.

I ordered a 20rd Lancer mag to try out and will see what happens but appreciate the explanation of what actually is happening to cause a double feed.

Hopefully it was just a fluke otherwise I will just sell all of my straight 20rd PMAGs and go USGI or Lancer's(if it works).

From what I've read, a double feed with one fired round followed by another live round is probably a weak extractor spring.

Two live rounds means they both have to come out of the magazine at the same time, so check your magazine for cracks or problems with the feed lips, check yourself to make sure you aren't using the magazine as a rest or pulling it back when you fire, and check your mag release.  Then go and get a new PMAG and throw out the bad one.  

Basically the mag has to be sitting too high in the magwell due to being tilted, worn, or some problem with the mag catch, or there is an issue with the magazine lips.

I've had more issues with older worn mags than fresh new gen 3 pmags, and especially the old 20 round mags.  One I converted to a single feed bobsled cause that was all it was good for.  Even pmags don't last forever.

Interesting.  My Centurion 12.5" was around .065" when I first got it.  I THINK my 11.5" was 0.076" when I measured it.

The rep said that there isn't really a standard for the 12.5" so they kind of go in the middle of the common range.

As a slight update I got the H3 buffer and unsuppressed it now ejects at 4:30 or so but will have to wait to try it suppressed for awhile :(

The Lancer mag worked fine as well.

USGI mags are the solution.

All I have are D&H mags with Magpul followers, and have never had a failure of any kind suppressed or not while using them.