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got got my stamp back for my suppressor for my mp5, and ive got a 100/ locking piece, and 158 gr 9mm ammo, safe to shoot or should I get another locking piece/ ammo?
 

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That is up to you. HK, the people that came up with the design, says to no higher grain bullet than 147. You have been waiting months for the stamp. Now that you just get it you ask the forum if you can. There have been several threads on this subject. If you have read them you know, some say they shoot 158 in their guns and others follow the HK recommendations. So what are you going to do?

Scott
 

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Generally speaking, the 158 gr. subgun ammo of yesteryear was loaded hotter than the 158s you'll find in today's marketplace. The older legacy ammo is where the recommendations come from. Warranty issues may push you to stay away from this ammo, but in my experience you won't have any undue wear shooting something like Fiocchi 158s.

Personally, I find my handloaded 147s to be just as quiet, and 147 gr bullets are much easier to get a hold of than either 158gr .355 bullets or factory loaded 158s.

YMMV
 

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There was some 158 +P+ type ammo that was made for the Uzi SMG. Often when they talk about 158 not being good, they mean that stuff. the 158 subsonic hasn't harmed any of my guns (doesnt mean that it never will) but just know that 158 is officially no bueno per HK.
 

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There are several threads on the subject here and I post the same thing every time as a PSA. If your mp5 is a K, I had several light baffle strikes in a K gun using 158gr ammo a couple of years ago. Here is what I was using at the time:

HK SP89 converted to K with sear
Factory German K-N barrel (late model with laser engraving)
YHM Wraith XL supressor w/3 lug
Fiocchi 158gr 9mm


The suppressor sounded like a baby rattle after a few semi auto rounds. The strike was so light I didn't even realize I was striking until I lowered the gun because I was confused as to why I wasn't even on paper. Interestingly enough, the same ammo and can performed flawlessly with a full size mp5n, uzi and sterling. I still use the 158gr, but mostly with the uzi.
 

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There are several threads on the subject here and I post the same thing every time as a PSA. If your mp5 is a K, I had several light baffle strikes in a K gun using 158gr ammo a couple of years ago. Here is what I was using at the time:

HK SP89 converted to K with sear
Factory German K-N barrel (late model with laser engraving)
YHM Wraith XL supressor w/3 lug
Fiocchi 158gr 9mm


The suppressor sounded like a baby rattle after a few semi auto rounds. The strike was so light I didn't even realize I was striking until I lowered the gun because I was confused as to why I wasn't even on paper. Interestingly enough, the same ammo and can performed flawlessly with a full size mp5n, uzi and sterling. I still use the 158gr, but mostly with the uzi.
Interesting. I guess the heavier bullet wasn't stabilized through the short barrel and wobbled a bit going through the can. Good to know.
 

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Interesting. I guess the heavier bullet wasn't stabilized through the short barrel and wobbled a bit going through the can. Good to know.
That's the best I could come up with. I guess it could be a fluke with my ammo batch and barrel and suppressor and the alignment of the stars. One would expect there to be a lot more tales of baffle strike woes online if 158gr regularly caused such issues in shorter barrels (particularly in pistols). All the same though, I haven't used it in a short barrel since that happened with the K. I can get my suppression on fine with 147gr.
 

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That's the best I could come up with. I guess it could be a fluke with my ammo batch and barrel and suppressor and the alignment of the stars. One would expect there to be a lot more tales of baffle strike woes online if 158gr regularly caused such issues in shorter barrels (particularly in pistols). All the same though, I haven't used it in a short barrel since that happened with the K. I can get my suppression on fine with 147gr.
My limited understanding is barrel twist is directly related to the range of mass of the projectile that is planned to be used in that barrel and the length of that barrel. The early 5.56X45 HK33 was a 1/12 twist for 55gr. ammo. When a shorter barrel (33K and 53) with heavier bullets (62 gr to 77 gr) were desired the twist rate was moved up to 1/7 twist rate for all 5.56X45 rifles. Could it be, liability wise, that HK was concerned that the twist rate of the MP5 series was not within the operation range that HK felt a 158 gr projectile would be stabilized? Those Germans are pretty fussy. I don't know, just wondering aloud.

Scott
 

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My limited understanding is barrel twist is directly related to the range of mass of the projectile that is planned to be used in that barrel and the length of that barrel. The early 5.56X45 HK33 was a 1/12 twist for 55gr. ammo. When a shorter barrel (33K and 53) with heavier bullets (62 gr to 77 gr) were desired the twist rate was moved up to 1/7 twist rate for all 5.56X45 rifles. Could it be, liability wise, that HK was concerned that the twist rate of the MP5 series was not within the operation range that HK felt a 158 gr projectile would be stabilized? Those Germans are pretty fussy. I don't know, just wondering aloud.

Scott
That makes perfect sense, but with only 4 inches no projectile is going to get a full twist regardless of twist rate. I know there's at least one guy that knows the real answer (paging @G3Kurz)
 

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Good points guys, looks like more research needs to be done. I knew about the twist rate difference on the early vs late HK33/93s, but I don't know what the twist specs are on the mp5 series. Surely it makes some difference, even in that short of a barrel. Now I need to crack the safe open tonight and get them all out to examine ..oh dear! :biggrin:
 

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My limited understanding is barrel twist is directly related to the range of mass of the projectile that is planned to be used in that barrel and the length of that barrel. The early 5.56X45 HK33 was a 1/12 twist for 55gr. ammo. When a shorter barrel (33K and 53) with heavier bullets (62 gr to 77 gr) were desired the twist rate was moved up to 1/7 twist rate for all 5.56X45 rifles. Could it be, liability wise, that HK was concerned that the twist rate of the MP5 series was not within the operation range that HK felt a 158 gr projectile would be stabilized? Those Germans are pretty fussy. I don't know, just wondering aloud.

Scott
77gr 5.56mm ammo came around in 2002, so it was not a driver for the switch to 1/7 twist at least not in the M-16/M-4. Most articles talk about 62gr driving the change to 1/7, but others point to the M856 Tracer as the reason since it is very very long. AND there was discussion that it was in artic conditions where the 1/7 was required to stabilize said tracer.

Most folks on the AR side have realized that 1/8 barrels are great and stabilize everything up to 77gr.

With respect to 158gr 9mm, the calculators all say it should stabilize with 1/10 barrels and guys are running them in pistols with shorter barrels than the MP5K. But I have seen pictures of baffles being hit in the middle of the can and nowhere else, so weird things can and do happen depending on gun, bullet, and suppressor.

I have a G26 with a 3.43" barrel. Maybe I need to shoot some 158gr at 25 yards to prove this.

EDIT: Found a good link discussing the history of 62gr and barrel twist:
:: Ammo Oracle

"The military settled on a twist rate of 1:7, which is a compromise between the 1:9 twist ideal for SS-109 bullets and the 1:6 twist ideal for L-110 tracers." SS-109=M855 and L-110=M856.

EDIT EDIT: :380:Looks like us same folks were talking about this in the past:
http://www.hkpro.com/forum/hk-nfa-talk/208671-158gr-mp5k-2.html
 

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I have been shooting 165's thru my HK-MP5 sear gun with a Gemtech MK-9K. With no issues, and they are quiet.

9MM 165 Grain Round Nose FMJ Encapsulated , New Production Factory Primed CBC Brass Cased. Designed to run all suppressed 9mm firearms and it is a heavy 165 grain projectile traveling at 850 FPS out of a 5" Barrel. It hits hard and thumps and will tick out of your suppressed pistol or subgun. We have tested a lot of subsonic and Fiocchi has always tested the quietest with their rare to find 158 grain projectile. We claim ours is as quiet if not quieter. Extensive testing and R&D went into this round and it is finally here. They are packed loose (1000 Rounds) in Plano Ammo can.
 

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That makes perfect sense, but with only 4 inches no projectile is going to get a full twist regardless of twist rate. I know there's at least one guy that knows the real answer (paging @G3Kurz)
Page rec'd.
Most projectiles do not need a full twist (360 degree rotation) to "receive" the gyroscopic stability req'd and provided by the barrel twist. If that was the case a 4" barrel P7 or 5.5" barrel MP5K-PDW would never shoot accurately and they do. SIG's new .300BO PDW called the Rattler has a 5.5" barrel and shoots extremely well.

To the question of 158 grain ammo in the MP5. I wrote the MP5 Family Operator Manual for HK. At that time HK GmbH recommended anything from 115 - 147 grain ammo.
I do not recall the 158's being mentioned but I see no reason why they would not work well in the MP5. With subsonic the heavier the better IMO. One way to know if to fire some an d look for any impact (witness marks) in the rubber buffer in the retractable stock. That will indicate overfunction caused by the ammo impulse. Try to avoid that.

The issue with TZZ was not its bullet weight but the chamber pressure and more importantly the recoil impulse it generated. Now there are many TZZ loads in 9mm, but some (115 grain) was loaded to blow the nearly 1 pound UZI bolt back reliably. When fired in the MP5 it broke bolt heads prematurely. HK improved the bolt head (and locking roller holder) to address this for the SEAL's who were shooting TZZ in training and breaking MP5 bolt heads and M9 slides on a regular basis. I think we gave tem 1000 improved bolts FOC. It improved the service life but still broke bolts. Later the SEAL's dropped that round. THAT TZZ AMMO is what HK waves people off of. I would not use that is any firearm except what it was designed for (the open bolt UZI).

Hope that helps. Now back to what I was doing.

https://forum.cartridgecollectors.org/t/imi-9mm-carbine-israeli-color-codes/8378

G3Kurz
 

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As usual, thanks for the insight G3Kurz! Just to clarify, I had no issues with the 158 in any MP5 full size, just the MP5K-N (Unfortunately I don't have another K to test it against). Maybe some folks with the SP5Ks and new B&T barrels can give the 158gr a try.

@G3Kurz I got caught up in that IMI ammo discussion you linked. Very interesting! I acquired a few boxes of 80s Isreali 9mm with an UZI part purchase, now I want to run home and see what kind it is!
 

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Page rec'd.
Most projectiles do not need a full twist (360 degree rotation) to "receive" the gyroscopic stability req'd and provided by the barrel twist. If that was the case a 4" barrel P7 or 5.5" barrel MP5K-PDW would never shoot accurately and they do. SIG's new .300BO PDW called the Rattler has a 5.5" barrel and shoots extremely well.

To the question of 158 grain ammo in the MP5. I wrote the MP5 Family Operator Manual for HK. At that time HK GmbH recommended anything from 115 - 147 grain ammo.
I do not recall the 158's being mentioned but I see no reason why they would not work well in the MP5. With subsonic the heavier the better IMO. One way to know if to fire some an d look for any impact (witness marks) in the rubber buffer in the retractable stock. That will indicate overfunction caused by the ammo impulse. Try to avoid that.

The issue with TZZ was not its bullet weight but the chamber pressure and more importantly the recoil impulse it generated. Now there are many TZZ loads in 9mm, but some (115 grain) was loaded to blow the nearly 1 pound UZI bolt back reliably. When fired in the MP5 it broke bolt heads prematurely. HK improved the bolt head (and locking roller holder) to address this for the SEAL's who were shooting TZZ in training and breaking MP5 bolt heads and M9 slides on a regular basis. I think we gave tem 1000 improved bolts FOC. It improved the service life but still broke bolts. Later the SEAL's dropped that round. THAT TZZ AMMO is what HK waves people off of. I would not use that is any firearm except what it was designed for (the open bolt UZI).

Hope that helps. Now back to what I was doing.

https://forum.cartridgecollectors.org/t/imi-9mm-carbine-israeli-color-codes/8378

G3Kurz

I wish we could pin this post. Seems like the hot 158 Israeli ammo gets brought up almost on an annual basis.
 

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As usual, thanks for the insight G3Kurz! Just to clarify, I had no issues with the 158 in any MP5 full size, just the MP5K-N (Unfortunately I don't have another K to test it against). Maybe some folks with the SP5Ks and new B&T barrels can give the 158gr a try.

@G3Kurz I got caught up in that IMI ammo discussion you linked. Very interesting! I acquired a few boxes of 80s Isreali 9mm with an UZI part purchase, now I want to run home and see what kind it is!
Glad I could help.
A lot of otherwise useless HK historical info roaming around in my head.
G3Kurz
 
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