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Discussion Starter · #1 ·
Is a #28 locking piece needed when you suppress your mp5? What happens if you don't use the #28? Where is the best place to find a #28 and what is a normal price?
 

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Is a #28 locking piece needed when you suppress your mp5? What happens if you don't use the #28? Where is the best place to find a #28 and what is a normal price?
Do you have an MP5K? The #28 piece is for a suppressed MP5K, not a full size MP5. While I've never shot my MP5 with a suppressor, I've been around people that have, and they did not change out the locking piece when they put the suppressor on.
 

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Is a #28 locking piece needed when you suppress your mp5? What happens if you don't use the #28? Where is the best place to find a #28 and what is a normal price?
Read this thread: http://www.hkpro.com/lockingpc.htm. The #28(80o) is recommended by HK for use in the MP5K PDW when using subsonic 140gr or heavier ammo with a detachable sound suppressor. It's purpose is to slow down the rate of cycle.

I have the MP5K PDW but I'm not aware of it's use on the the MP5.

You can get them from:

http://www.hkparts.net or

http://www.hkspecialist.net
 

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Discussion Starter · #4 ·
I have both mp5 and the mp5k. So if I understand you correctly, one would only need to install the #28 if you use 147 gr in the mp5k suppressed. So if I load 115 or 124 under 1000fps I can use my unmarked locking piece with my AAC evo and no changes needed for any weight on my mp5. Thanks Mel
 

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I have both mp5 and the mp5k. So if I understand you correctly, one would only need to install the #28 if you use 147 gr in the mp5k suppressed. So if I load 115 or 124 under 1000fps I can use my unmarked locking piece with my AAC evo and no changes needed for any weight on my mp5. Thanks Mel
I run 115gr FMJ with or without my SWR can with the 100o LP with no issues but again that is in the "K".
 

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The #28 Locking Piece

Like Mel, I have both the MP5 & the K and I use suppressors with both mostly shooting 147gr and sometimes 124gr. The MP5 uses the same locking piece in both configurations so nothing additional is needed. The use of the #28 in the K is recommended, as I understand, not only to reduce the cycling speed but also to reduce the wear and tear on the action because of the increased blowback. Now I don't know if it's only for a certain ammo weight etc. but I felt this $100+ piece was a good investment for my $4500+ SP89 to MP5K-N conversion.
Now that I have the #28 in place, I found that my K is not reliable when the suppressor is not attached but perfect when it is (using 147gr ammo). This is fine by me because my MK-9K will "live" on the gun. I was more concerned about the "wear and tear" issue.
GM had the best price on this item and shipped it immediately. http://www.hkspecialist.net/
 

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I have "played" with a #28 locking piece in both the MP5K and MP5. For some combination of both head and carrier the #28 locking piece worked great in the MP5K with out a suppressor for several cases of ammo. However, with a different carrier and bolt head had a few percent reliability issue (typically shoot 124 NATO but also tried 115gr S&B plus WW, bolt gap was with in spec, guns were clean and well lubed). In the end I leave the #28 locking piece in one set of bolt, carrier, recoil spring and the SP89 locking piece in the the new bolt, carrier, recoil spring assembly (this tends to stay in a bag and live in the range tool box).

Experimenting started when trouble shooting a couple other guys MP5K's which had issues (one ended up being an out of spec. bolt carrier and the second was adjustment of the trigger pack plus cleaning ;-), plus had a Vector that had to be "adjusted" .... all work now, and was an interesting time that I learn a lot from.

At the same time, a few summers ago, also tried the #28 locking piece in the MP5 (everything was apart, so was a good time to experiment ;-), worked find and ran a little bit slower (using NATO 124gr with a clean, lubed MP5), however, the MP5 at the slower rate of fire was a little bit choppy (slightly like an Uzi), not bad but I did not like the effect as well as with the standards locking piece. So after that summer I went back full time to the 100 degree standard issue (plus got a MP41 to shoot at a slower rate of fire when that was the preference ;-).
 
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