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Discussion Starter #1
So where do I start. Hmmm...OK the long version.

Here's what my gun has a long history of doing. A picture is a thousand words.

https://picasaweb.google.com/rhouston8/Mp5Problems?authuser=0&authkey=Gv1sRgCJDm65_D3NSJjwE&feat=directlink

FuGLY. Looks like some sort of deranged Menage a Trois, huh? Not uncommon occurrence either.

HK SP89 MP5k PDW conversion with Fleming sear. SEF pack. Owned since '99 or so purchased from the recently deceased Steave Wayman in Dallas, God bless his soul.
The gun has had a long history of intermittent Failure to Eject (FTEj from now on...as opposed to FTExtract).
All the original German parts in the gun were replaced with a new all German complete BCG/assembly a few yrs ago at great expense.
Bolt Gap was fine thru-out this period. Also replaced the FA pack and threw in a retimed hammer to boot. Replaced grip frame as a 'smith told me it might have been riding funny on its shelf.
Swapping out the Locking Piece did greatly improve guns reliability for a while it seems. I honestly can't remember which LP it originally had ( either #16/110 degree, #28/80 degree, or 100 degree one) and what all swaps I've tried) but currently it has a RCM LP with "K" only (...no "-PDW") stamped on it which I believe to be the 110 degree piece.
The original SP89 barrel was in the gun up to this point but fairly worn. Bolt gap was in spec through out these years.

I ended up replacing the barrel with an RCM Navy barrel b/c I wanted to shoot with my can, etc. This did not affect the guns function or maybe it made it shoot slightly better subjectively.
Bolt gap with new barrel was high at .75mm so I put -4 rollers in it. Lately the gap has been running slightly higher than normal at .026" / .660mm and holding steady.

OK..ammo doesnt make a significant difference in function/reliability. I've tried every ammo known to man, brass, steel, NATO spec, +P, etc. The +P does kick out the casings further and drain the wallet much much faster however. Also I can't tell a difference in reliability shooting with or without my Bowers CAC45 can.

I did determine that it doesnt like some Korean 30 and 40 rnd mags, others are fine. Beta is hit and miss. I mainly shoot factory curved 30 rnd and straight stick factory SD 30 rnders. Still FTEs.

Most casings eject about 2 o'clock position, perhaps 6'. They aren't dribbling out but neither are they kicking out 15'. The gun will "jam" on semi as well as FA. I clean the gun thoroughly after each shoot (including flutes, etc). It's clean...always. I believe I now have the rifle caliber hammer spring in it. Hell, I can't remember...b/c I've done so much troubleshooting over the years. The gun has visited at least 3 different 'smiths over the years to varying degrees of success. Overall the gun is shooting better than it was a few yrs ago. BUT it's never shot as well as my MAC 10/45, my ghillie build MP5 (LSC flat and all german parts kit), my HK91, HK33, MM53, or MM51. My PTR 32 shoots more reliably.

The difficulty lies in the fact that sometimes the gun runs fine...and other times like crap meaning 1-2 failures per mag. It's frustrating.

The next time I take it out I will bring uniform ammo type, only factory curved mags, and 3 different LPs in addition to an entirely different reg sear SEF pack.

Something interesting I noticed this past weekend. The gun shot noticeably better (prob just temp. like all the other fleeting "fixes" I've experienced) with the A2 stock + Fleming adapter as opposed to it's original Choate folder. The Choate folder's rubber H buffer is kinda gnarly as this attached pic shows.

https://picasaweb.google.com/lh/photo/2A7dfPbWOTI0a15M91dbw6NhblgclxutgHV0l_2iAmU?feat=directlink

I was wondering if this was my Eureka moment and if a gnarly buffer could be causing all my ills. Thoughts?

Yall chew on that and someone smart lead me in the right direction so I can get a 100% reliable MP5k like it should be.

-HH
 

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Discussion Starter #3
and while I was rummaging thru files looking for pertinent vids I found these gems instead and felt I'd share them for kicks. This is my dad on fathers day. First time shooting a MG since Vietnam. By his corncob up the butt stance you'd think he'd never handled a gun!

https://picasaweb.google.com/lh/photo/uujSrwr1d9vzy4G0TraidKuWqrboCOK4L4Z1CVh02sk?feat=directlink

https://picasaweb.google.com/lh/photo/P8cDGDvn532jVT7GOiNbPauWqrboCOK4L4Z1CVh02sk?feat=directlink

I was just happy he didnt shoot his dang finger off!

-HH
 

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Ones goal should for a 99.995% reliable K gun, the high rate of fire K guns never appear to be the total equal of the full size MP5.

With this much shooting, have you changed your recoil spring yet? Some place standard listed change was every 10K or 30K rounds for the recoil spring and firing pin spring. Friends have had issues with a HK91/G3 recoil spring (we swapped it in a motel room at KCR years ago the night before the Bumb's Rush).

Locking Pieces: The SP89 came with the #16 and much later the unmarked MP5 locking piece (100 degree) is standard, so the store goes. I would sort out all locking pieces and put them in bags with a label of type and s/n, has have seen some locking piece / bolt / carrier combinations not work in three different SP89s and mixing an matching ended up with combinations that work. All parts were German. Thus you need to track "100 degree" unmarked locking piece sn A from an "identical" locking piece sn B.

Well have to water the garden and see if the samples are in for analysis, good luck.
 

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You're not going to make this easy on us, are you? Sheesh...I was going to say "German Bolt Head!" but you spoiled that. LOL.

From the pics, it appears the BH is grabbing the spent case, and the BH is traveling reward with the empty case to the point that either:

A. The ejector lever is contacting the rim of the case with insufficient force to 'tip' the case outwards to the ejection port and puch it outward, and thus is dropping it inside the receiver. This could happen if the BH has lost nearly all of its rearward velocity, leading me to think about recoil spring issues.
B. The case is dropped from the BH prior to contacting the ejector lever like you see frequently with out of spec bolt heads or those with weak extractor springs. Changing entire bolt groups should have fixed this issue, but maybe think about putting a silver rifle caliber extractor spring in the BH.

With my clones I get ejection patterns about 15 feet out - much farther than the 6 feet or so you are seeing.

Talk a bit about the current BH, including extractor, extractor spring, and then about your ejector lever(s).
 

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My Coharie clone is tuned perfectly (by me not TB) and it has a absolutely consistent ejection pattern to the 2 o'clock position about 8 feet away

When I first bought it it was doing what yours is. I found my problem to be the ejector lever.

At the creek shoot I fixed one of their MP5's that was the FA rental gun. It has the same issue you have but that is because they were using a 40 cal extractor. I don't think thats your problem though. The other thing that pops into my mind is a loose extractor or combination of loose/worn extractor and ejector issues.

Just something I have learned- if you are holding the trigger pack by itself the ejector lever should have VERY little side to side movement, it should only operate aft to forward


Anyway I hope that all makes sense...
 

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- Trigger Housing: how many different ones, assume one metal SF that came with the SP89 and one plastic SEF
- Trigger Pack: how many different trigger packs, semi auto and full auto, have you tried? Any difference between them in nominal operation?
- Bolt Head: do you have any Action 3 or F type bolt heads to try (needing the -4 roller does make it harder to swap)
- Ejector: how many different ejectors have you tried and should check where the ejector is hitting the case (i.e. make sure it is making a good sold hit).

The various shelf heights plus any differences in trigger pack and housing could effect the vertical location of the trigger pack with respect to the bolt/receiver and thus change the location of the ejector and timing of the trip lever in the full auto packs. Have been known to coat the bottom of the bolt and ejector etc. with layout dye to see where everything is making contact.

The layout fluid is available at most machine tool supply houses or on line.
 

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Houston, sent you a PM. Your issues with the gun seem to fit perfectly with the way it is setup...

1) Bolt-gap WAAAAAAY to big. Too much energy being transfered to the carrier.

2) You should run a 100-degree LP in PDW config with a pack. 110-degree with a .026" gap, that gun is running waaaaay too fast.

3) Once you experience a malfunction like that, check the extractor spring. Many times the spring gets bent resulting in even more manfunctions.
 

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What was the bolt gap with the RCM barrel before using it? Also how many rounds have you shot to get to 0.66mm?

chuck
 

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Discussion Starter #11
PMs answered.
First..a big thanks to yall. Thats what makes this board great. I only hope one day to reciprocate knowledge to someone else in the future.

Bolt gap is big. I know. I just didnt know how much it'd affect function ...with large gaps. I know small gaps result in basically semi fire only more or less.

Need to check recoil spring...but I think i replaced that with the BCG/assembly a few years ago. Since then no way I've 10,000 rnds on it.
Ejector lever. I did ntice that it sometimes binds just a tad...friction moving in the pack frame. Will address more closely. This was only slightly and not terribly bad IMO.

I do have 2 plastic SEF grip frames to swap out.

I shoot it in PDW config...sometimes with can, sometimes not. I also have the metal buttplate to try out as opposed to the Choate folder.

Bottom line is that I've had issues for years...not crippling and I dont expect 100% reliability out of the Kgun but I would like to get it down to maybe 1-2 jams per ten 25 rounds worth of shooting. That'd be acceptable. 1 jam per 25 rnds doesnt cut it.


Thanks again. I will do a more thorough testings soon , hopefully this wkend, and post the results...and some better pics/vids.

-hh
 

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Discussion Starter #12
OK...some follow up....I got just a tad of range time today with the k gun mentioned in this post. I didn't have enough time (due to rain as you will see in the vid) to completely troubleshoot the gun as thoroughly as I'd like. The RCM LP in the gun has "k" stamped on it and is pictured here.

https://picasaweb.google.com/lh/photo/seqBEhGAnfmoo-Lzm7OLXoAJTDxsFB9bA4RRxF0luh8?feat=directlink

Today ran bulk brass 115gr "something", used factory curved and straight 30 rnd mags only. Seemed the gun had problems with one of the packs (w/ a ground down trip hammer as discussed in another post) and ran great with and without the suppressor. Had new tight extractor spring and I put a new extractor in it which held the round much tighter than previously.

see this:
https://picasaweb.google.com/lh/photo/hdKWD4tABHTt0zxaj1yylYAJTDxsFB9bA4RRxF0luh8?feat=directlink

and here is one run of the gun which I video'd . The others I didnt video. So the gun seems to run fine now and it appears that either the extractor itself or/and the trip lever was causing issues. I plan to take it out for a more thorough running soon to verify.

https://picasaweb.google.com/lh/photo/-APNdcbNatKt_HQXee21N4AJTDxsFB9bA4RRxF0luh8?feat=directlink

-HH
 

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Discussion Starter #14
Just to bring closure to this thread in case some poor soul in the future is searching threads looking for solutions for their poor running mp5k.

The problem ended up being a VERY tiny stress fracture hidden in the curvature of the extractor. It allowed it to flex ever so much thus causing variable FTextract/eject issues it seems. While cleaning the gun I happened to see the crack. I mean tiny. You need a freaking magnifying lens to see it but its def. 100% real. I posted close up pics on this extractor crack on some other thread. The crack would freq. be obscured by a tiny amount of grit/oil making it even harder to see. Amazing. And BTW. Once this extractor was replaced the gun now runs 100%, all ammo, most any mag, etc.
 

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Thanks for the follow-up Houston. A problem like that could drive a guy nuts!!!
 
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