I went round and round with HK in 2013. The only way I could get them (10.4" HK416DSF's) to run semi-reliably suppressed (YHM) was with a 1/2 pound XH buffer and Wolff XP spring. They were still not reliable enough for duty use AND all the benefits that I thought a piston system would offer up on a suppressed SBR weren't. They were still filthy and gaseous. The only 'benefit' was a cold BCG. Ended up trading them in. Email excerpt below.
HK Recommends either B&T or Knights Armament. All others are pot-luck in terms of what will and will not function well.
Regrettably, I am not too familiar with the YHM QD, but I have many bad stories with GemTech.
There are numerous suppressor manufacturers who make a product that "works" well and by that they typically mean a greater decibel reduction.
For many instances, this is vitally important to the operator(s) of course. However, functionally, these suppressors by design, capture/trap significantly higher amounts of the expended gases in order to achieve the increased sound suppression.
In so doing, the rate of 'back-pressure' also increases significantly which translates into significantly higher rate of speed for the rifle's action... full auto or semi.
Capturing the cyclic rate is not simple on a semi-auto of course, but internally there will be indicators of the increased rate as well as functional issues such as you are experiencing. This magazine issue is NOT that the springs are 'worn or weak', but simply that they are not able to feed the ammo at a fast enough rate to flow with the speed of the action. The result is often the feed malfunctions you have pictured.
And, YES, it is also possible for the suppressor to function in such a way as to actually slow down the action specifically if the device has a "bleed-off" of any kind. This will expend the excess gases that would otherwise be used for the rifle function and result in weak or sporadic ejection. Your experience seems to be a weak or poor ejection pattern... Odd. Weak ejection would seem to indicate "under-gassed" function. In either case, the feed malfunction would/could be the same.
It is also very possible, depending on the connection to the barrel, that the suppressor is "leaking" around the flash hider.
Do your suppressors use the factory HK flash hider or a proprietary one included with the device?
My instinct, at this point due to what seems like contradictory facts, is to suggest some study and testing. Assure at the outset that the rifle is properly lubricated. The primary point being to eliminate some of the variables... Does it do the same with both 55gr and 62gr ammo etc.
During firing, have a guy pay close attention to the ejection only. Then;
1. Examine the cases, by specific ammo types (55gr / 62gr), after suppressed and unsuppressed fire to see any peculiar damages specific to the form of fire.
2. Conduct the same test (supp and unsupp) with heavier projectiles, i.e. 69gr and/or 75gr.
3. Document the function and ejection by specific ammo types for later discussion.
4. Document at what round number in the mag, by specific ammo types, the malfunctions occur.
Pardon the excessive verbiage.
Let me know what you think.
V/R, XXX (Mgr/HK USA Repair)
XXX (Mgr/HK USA Repair), I have been doing further research and perhaps it would have assisted your diagnostics to know that these are AI date code rifles with 10.4” bbls. XXX (area LE sales Mgr) sold them to us this past fall (received this spring) and I erroneously assumed that they’d be current production rifles and not 2008 models… I am now assuming that this is why they were sale priced.
I also found (during my research) that many folks had issues (same described malfunctions as we have) when running these older rifles suppressed. HK perhaps did not ‘admit’ to the issues but did ‘update’ the rifles with a vented gas block and then later (currently) an AGR in the gas block. Our ten rifles have neither the vented gas block nor the AGR.
http://www.hkpro DOT com/forum/hk4...ergassing-fixes.html
http://vuurwapenblog DOT com/2010/...r-a5hk416-test-data/
http://vuurwapenblog DOT com/2013/...r-base-malfunctions/
http://www.m4carbine DOT net/showthread.php?t=14820
http://www.hkpro DOT com/forum/hk4...31-free-hk416-s.html
http://www.hkpro DOT com/forum/hk4...-agr-gas-blocks.html
http://www.hkpro DOT com/forum/hk4...g36-hk416-mr223.html
I was going to conduct all the tests you asked for in that last email but then thought about it more… our duty ammunition is Federal 62 gr bonded (LE223T3) of which we have 10’s of thousands of rounds that run fine in all of our other rifles. I need this rifle to run with this round so I went and did some testing (with this particular round only).
*I ran 90 rounds unsuppressed with 0 malfunctions (three Gen3 PMags; brand new) while shooting at a rate of approx 50-60 rpm. Ejection was between 2-4 o’clock and 4’-15’ away
*I then cleaned and lubed the rifle.
*I then attached the Yankee Hill suppressor and proceeded ahead with those same three magazines (90 rds) at the same rate of fire…
Mag 1 (PMag) – malfunctions at round 10, 25, 27, & 29
Mag 2 (I decided to switch out and try a brand new HK steel mag) – malfunction at round 30
Mag 3 (PMag) – malfunctions at round 2 & 4… I stopped, removed the remaining ammo and loaded it in the HK mag
Mag 4 (I reloaded and used the same HK mag) – malfunction at round 24 (stove piped fired round) & 30
Suppressed ejection pattern was from 1230-2 o’clock and 0’ (didn’t leave the table) to 8’ away.
All of the malfunctions were the same/similar bolt over base type except for the one where the empty stove piped but the new round was in the angled bolt over base configuration .
These were purchased with the intent to be duty rifles carried and depended upon by law enforcement SWAT officers… I cannot issue them as such in their current state.