Insane 9mm M16 trigger slap

Deerhurst

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Buddy of mine has a blowback 9mm M16 that i am trying to help him tune. It has a maxim stock and something like a 5" barrel with a can on it. What we want to solve is as follows:

-Want to slow the ROF
-Want to feel our fingers after shooting more than 3 rounds

The trigger slap is insane on this thing. It has already damaged hammer pins. I am assuming the bolt velocity is really high and causing this. He has upped the spring rate a LOT. Said it has helped some but the issue is still bad. Im thinking heavy buffer (he has a 10oz in the mail) and lighter spring but lighter spring may allow a high bolt velocity opening making trigger slap worse.

Suggestions where to start? Close bolt isnt what Im used to.
 

theduke

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They had bolts that were ramped right..and others that weren't iirc.

Could be a starting point or not.....I just recall this same topic.

Or is the hammer an issue..?......Some mention of the notched hammer vs other options...comes to mind as well.
 

Deerhurst

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Ramped? At the back of the carrier for the hammer? Got a photo?

Hammer has been modified at this point. Probably will end up replacing it.
 

chili17

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Check to see if the hammer is hitting the disconnector, I bet it is. Ramped bolt, heavy hammer spring, cut a divot in the disconnector if the hammer is hitting it, heavy ass buffer. The slower the blowback M16/9 shoot, the bouncier they are
 

A&S Conversions

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A&S Conversions

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It is my understanding that the two best ways to slow the cyclic rate of a blowback system is to increase the stroke or increase the mass of the bolt group. Because of the mechanism it would be challenging to increase the stroke of the Colt blowback system. It would be possible with some machine work done to the bolt group, but the amount of slowing of the bolt group would be minimal compared to adding mass. The first link goes into that quite a bit. If you are limited by having the carbine buffer tube staked on, then the second link has information as what you can do with the carbine length receiver extension. The member "amphibian" in the second link has quite a bit of research that has has done on his website which is the second link.

While a stronger spring will ease the the energy of the buffer striking the end of the receiver extension, the addition energy that the stronger spring absorbs will drive to bolt back into battery, speeding up the cyclic rate. The flat wire spring does a much better job at having enough strength to strip the top round out of a full magazine while slowing the cyclic rate.

The "ramped" 9mm bolt has the same profile on the bottom of the bolt as a rifle caliber carrier on the bottom that cocks the hammer. Colt chose to not ramp the bolt to slow cyclic rate. The problem is the mechanical advantage puts extra stress on the hammer pin. The pin can break, but the gun will still run. The pin being broken makes the pin at an angle which will enlarge the hammer pin hole in the expensive registered receiver. Colt did start to use stainless steel pins as they were not as brittle as the standard steel pins. KNS makes fire control that ties the hammer pin to the trigger pin to try and relieve some of the stress. I would highly recommend the KNS pin system for any M16 RR. Even more so with a 9mm blowback system.

There is also a steel weight pinned into the back of the Colt bolt. Several manufacturers, including Colt, offers a replacement tungsten weight for the 9mm Colt blowback bolt. The tungsten weight can reduce the cyclic rate about as much as ramping the 9mm bolt increases cyclic rate. I had a configuration that would not run with a ramped bolt without a tungsten weight.

Good luck with slowing down your friends 9mm M16. I don't know what your friend has in his collection but the Colt 9mm blowback system is harder on the lower than the rifle caliber systems. Some manufacturers converted Colt SP-1 9mm carbines to M16 RRs. Colt did have a run of M16 SMGs just before the NFA registry cut off. Since there are only 100 M16 RRs in the registry and most of those were purchased by Police Departments, the Colt SMG guns are quite a collectors item. If your friend's gun is a SP-1 9mm, I would pull the magwell blocks and use the https://www.meanarms.com/products/detail/endomag-9mm Endomag system. Then the gun could be used for lots of other calibers.

Scott
 

Deerhurst

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It is hitting the disconnector very hard. That has already been clearanced quite a bit. Hammer and disconnector have been clearanced.

It's not an expensive receiver, it's a postie so nothing as fancy as a SP1.

I still think his recoil spring is wayyyy too heavy (it's difficult to charge the gun). I will see if it is ramped or not. I'll see what the weight in the carrier is and see if I can convince him to put a "normal" spring in it when the 10oz buffer arrives.and see what happens.

I'll do some reading from the link.
 

A&S Conversions

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There is an old discussion https://www.uzitalk.com/forums/index.php?threads/henry-tatro-m16.91949/page-2 and on post #31 there are pictures of the modified fire control. A heavier hammer (spring) might help a little, but it is my understanding that the 9mm firing pin is not as tough as the rifle caliber firing pin. I would think adding mass would be the way to go.

Scott

ETA What a great thread. Lots of great information. The Tenko has drawn up most all of my resources.
 
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Deerhurst

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Thanks for FCG photos!

When he gets caught up on stuff we will look at it again but in the meantime I've sent him some more info. Hopefully we can go to a lighter spring and much heavier buffer as well.
 

amphibian

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The slower the blowback M16/9 shoot, the bouncier they are
+1....getting them to run slow is easy. Getting them to be slow and smooth is hard with a straight blowback. I had my old straight blowback running with the old tungsten AAC buffer, their supplied week spring and SAW's tungsten bolt weight. It was under 500RPM. I think 488 or something but not smooth at all.
 

A&S Conversions

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I wonder if instead of solid tungsten if hollowed out tungsten with weak springs inside added to the back of the hydraulic buffer would spread loading of the sharp recoil of the 9mm blowback system. It strikes me that the 9mm blowback feels to me that the recoil pulse seems to be in an instant. The rifle caliber is more energy but is spread over time. I think that the MP5 roller delay system, like the direct impingement rifle caliber speads the recoil over time because the bolt is delayed by mechanical means. Maybe if the loading of the energy of recoil could be spread over time with a delaying action of the additional mass being added over time through the use the the hydraulic buffer and spring weighted tungsten might help with the smoothness. I have some weights and springs from a MGI mechanical buffer. I wonder if combining the two together would work better than the Kynshot and solid weights. Just a thought.

Scott
 

SecondAmend

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I wonder if instead of solid tungsten if hollowed out tungsten with weak springs inside added to the back of the hydraulic buffer would spread loading of the sharp recoil of the 9mm blowback system. It strikes me that the 9mm blowback feels to me that the recoil pulse seems to be in an instant. The rifle caliber is more energy but is spread over time. I think that the MP5 roller delay system, like the direct impingement rifle caliber spreads the recoil over time because the bolt is delayed by mechanical means. Maybe if the loading of the energy of recoil could be spread over time with a delaying action of the additional mass being added over time through the use the the hydraulic buffer and spring weighted tungsten might help with the smoothness. I have some weights and springs from a MGI mechanical buffer. I wonder if combining the two together would work better than the Kynshot and solid weights. Just a thought.

Scott
As well as the up/down ramp off axis lost motion delay, at least part of the legendary MP5 smoothness is due to the anti-bounce weighting of the bolt being implemented as tungsten granules (powder) as opposed to rods or blocks. As is noted in the H&K patent (U.S. Patent No. 3283435), the granules provide inter surface friction damping. The earlier 21 and 28 Thompson implemented a similar up/down ramp, off axis lost motion delay but used oil pads instead of rollers to minimize friction. Auto Ordnance did experiment with an added on hydraulic buffer, but did not go into production with it.
As well as on axis, linear, lost motion delay, typical automotive (and firearm) hydraulic buffers provide friction damping in the form of hydraulic fluid being forced through orifices. Prior to the late 1920's, cars and trucks used friction pad dampers instead of hydraulic shock absorbers ("buffers" as it were). Since the early 1950s's, virtually all auto automotive shock absorbing is via hydraulic buffers. Of course, firearms (and automotive, for that matter) hydraulic buffers are not cheap. For many firearms unlike an automobile, the cost of a hydraulic buffer represents a significant percentage of the potential total cost. Thus, while the firearm hydraulic buffer can generally provide softer, smoother operation (and lower full auto rate of fire), the typical firearm buyer may not feel that the cost to benefit is worth it.

MHO, YMMV, etc. Be well.
 

Haris1

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Deerhurst Posted

-Want to feel our fingers after shooting more than 3 rounds

I shot a MPX Full auto and the trigger slap was so painful, i wore gloves to keep it from hurting. I solved it with a Geiselle Full Auto M16 Trigger group. Code is SSF. Its pricey at $400 but the trigger slap is gone
 

amphibian

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Deerhurst Posted

-Want to feel our fingers after shooting more than 3 rounds

I shot a MPX Full auto and the trigger slap was so painful, i wore gloves to keep it from hurting. I solved it with a Geiselle Full Auto M16 Trigger group. Code is SSF. Its pricey at $400 but the trigger slap is gone
I experienced the same thing and for a short time I put an SSF in mine too and later found that Geissele will not warranty the use of the SSF in an MPX. There is a "bridge" in the factory MPX to absorb the impact and I seem to recall I removed that to install the SSF or other firecontrol can't remember if it actually got in the way. Regardless, pretty sure they won't support you doing that if you care.
 

Deerhurst

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Not an MPX but actually an M16. Postie Glock mag PSA lower.

I'll ask him if he has thought about a SSF.

Hopefully he has gotten caught up on customer work, the heavy buffer should be here by now.
 

amphibian

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I'm pretty sure Geissele won't support using the SSF in a straight blowback 9mm either.
 

Deerhurst

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10oz buffer and a lighter but still quite stiff spring seems to have fixed the trigger slap. Hopefully I'll get to play with it soon and confirm this.
 

nuge

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Best set-up I have found for the standard Colt HT M16, 9mm is modified FCG (don't forget the trigger mod!), the flat spring - Tubbs 300 BLK OUT, the Kynshot 5005 buffer, and a heavier hammer spring. The 3 FCG mods by themselves will eliminate trigger slap, pin breakage, and any wear and tear on the receiver pin holes. The others combine for what I believe is the smoothest, and most controllable FA possible for the standard Colt SMG, but I have no plans to verify this or study it further. I am quite happy with it at this point.
 

nuge

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Link to the expired Derrick Martin patent is here. A drawing from it, and realized FCG parts are shown below. All three FCG mods are essential to remedy trigger slap, and wear & tear on the receiver from 9mm blow back.

FCG Mods.jpg

Trigger Mechanism.jpg
 
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SecondAmend

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Best set-up I have found for the standard Colt HT M16, 9mm is modified FCG (don't forget the trigger mod!), the flat spring - Tubbs 300 BLK OUT, the Kynshot 5005 buffer, and a heavier hammer spring. The 3 FCG mods by themselves will eliminate trigger slap, pin breakage, and any wear and tear on the receiver pin holes. The others combine for what I believe is the smoothest, and most controllable FA possible for the standard Colt SMG, but I have no plans to verify this or study it further. I am quite happy with it at this point.
I find your choice of buffer somewhat surprising. From the KynSHOT website, RB5005 buffer section: "DO NOT USE IN 9mm AR-15s. For 9mm AR15s use KynSHOT P/N RB5007, RB5015HD, or RB5020SS. See Selection Matrix for proper buffer choice:."

MHO, YMMV, etc.
 

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