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Posted: 3/6/2026 7:34:51 PM EDT
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First, what is the degree of the stock locking piece? It just has a number on it that matches the bolt and carrier. The conversion was done by a reputable smith. The gun barely cycles 115 grain. Will not run with the AS Designs lower in super mode. 147s run fine and works with the super safety. With either bullet, it seems way to loud, like it's not hearing safe. I think it's the locking piece. Seems like I need a higher number. The recommended lp is 120, but I don't know what I have. |
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Got a response. He said the default locking piece is 120. The issue is that I was trying to run a super safety lower, and it won't work with the 120. He does not recommend running the SS, but if I do, drop down to an 80 degree. I'll do more testing tomorrow when it's not raining. |
Joined:
Jan 2023
Posts:
56
EE: 100% (2)
NV, USA
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Originally Posted By macloud: Got a response. He said the default locking piece is 120. The issue is that I was trying to run a super safety lower, and it won't work with the 120. He does not recommend running the SS, but if I do, drop down to an 80 degree. I'll do more testing tomorrow when it's not raining. How'd it go? Did you ever run it in stock configuration with the standard ap5 lower group it came with? just curious if same issues or only issues with your SS setup. What suppressor are you using? What SD O-ring did you use, genuine HK or RCM (orange one) or HKP "enhanced" one? I have issues dropping in other lowers on mine but I think it's just MKE's shelf spec that varies from gun to gun, as my other AP5 and AP5p have no issues swapping lowers. I will say I purchased an RCM 115 and 120 lp just in case (I think currently I have the 115 in) and haven't even used the MKE one it came with. Mine's been running smoothly though with no port pop, I'm also using an H&K gasket sealing O-ring, little things like that can make a difference. |
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Better, but not where it should be. I went with the Ronin conversion. The sealing ring is black, and there is no indication that it's leaking gas in front of the bolt head. Rounds are subsonic. I am 100% sure the noise is coming from the port. I ordered a 120, 115, and 110 locking piece to try and tune it. When I shot it Saturday, it was stock from Century, with the exception of the new barrel and can. The stock locking piece is not marked, other than the ID number that matches the bolt head and carrier. I'm very hopeful one of the new locking pieces fixes the issue. One strange thing is that it still runs on 147s, and Ronin said it shouldn't. There is really nothing else that it could be. The 115s and 147s produced about the same noise. |
Joined:
Jan 2023
Posts:
57
EE: 100% (2)
NV, USA
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Originally Posted By macloud: Better, but not where it should be. I went with the Ronin conversion. The sealing ring is black, and there is no indication that it's leaking gas in front of the bolt head. Rounds are subsonic. I am 100% sure the noise is coming from the port. I ordered a 120, 115, and 110 locking piece to try and tune it. When I shot it Saturday, it was stock from Century, with the exception of the new barrel and can. The stock locking piece is not marked, other than the ID number that matches the bolt head and carrier. I'm very hopeful one of the new locking pieces fixes the issue. One strange thing is that it still runs on 147s, and Ronin said it shouldn't. There is really nothing else that it could be. The 115s and 147s produced about the same noise. Originally Posted By macloud: Better, but not where it should be. I went with the Ronin conversion. The sealing ring is black, and there is no indication that it's leaking gas in front of the bolt head. Rounds are subsonic. I am 100% sure the noise is coming from the port. I ordered a 120, 115, and 110 locking piece to try and tune it. When I shot it Saturday, it was stock from Century, with the exception of the new barrel and can. The stock locking piece is not marked, other than the ID number that matches the bolt head and carrier. I'm very hopeful one of the new locking pieces fixes the issue. One strange thing is that it still runs on 147s, and Ronin said it shouldn't. There is really nothing else that it could be. The 115s and 147s produced about the same noise. I think the 115 or 120 LP should fix it. They say not to run 147gr in a true SD, I believe because it can bleed off velocity enough to cause tumbling/baffle strikes but don't quote me on that lol. I don't know if this is fact, and some people say they run 147gr no issue, but I'm not willing to chance it and I've been sticking to 115/124 as intended for the SDs. Mine was converted through GreaseGunner (aka John / FB Unlimited) and it's been amazing. I will say the first time I took mine out I also thought the port pop was unreasonable for an SD, the second time I took it out it blew me away how whisper quiet it was. Idk if it was in my head or if things got broken in and/or a little coating on the suppressor helped quiet things down. Regardless, I've only heard good things about Ronin, you should be in good hands. What suppressor are you running? Originally Posted By chargerdude70: Be sure after changing between LP's that you check bolt gap. Bolt gap will affect bolt velocity and in turn functionality. If it's not the same between changes, your testing results could be skewed. This ^ |
| I'll add my experience with the SD that I had Michael's Machine build for me from an HK SP5. I'll start off saying I only shoot 124gr bullets so YMMV. I could not get it to function flawlessly in SS mode. I tried all the different deg LP tricks. Was even going to go as far as changing out rollers to adjust bolt gap for more bolt speed. It would run but only strings of fire, never a full mag. I was going to cut down my recoil spring (take a coil at a time) but then remembered I had my old PTR9 on hand. I took out that spring and measured the amount of resistance it had against the factory HK before starting to collapse. Difference was shocking to say, PTR was pounds lighter. I put that in the SD and it ran flawlessly. So I ordered one up from PTR and it's been in there since. Just some food for thought. |
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Originally Posted By xtremegibs: I think the 115 or 120 LP should fix it. They say not to run 147gr in a true SD, I believe because it can bleed off velocity enough to cause tumbling/baffle strikes but don't quote me on that lol. I don't know if this is fact, and some people say they run 147gr no issue, but I'm not willing to chance it and I've been sticking to 115/124 as intended for the SDs. Mine was converted through GreaseGunner (aka John / FB Unlimited) and it's been amazing. I will say the first time I took mine out I also thought the port pop was unreasonable for an SD, the second time I took it out it blew me away how whisper quiet it was. Idk if it was in my head or if things got broken in and/or a little coating on the suppressor helped quiet things down. Regardless, I've only heard good things about Ronin, you should be in good hands. What suppressor are you running? This ^ The can came from Ronin as well, I think it's called the Katana. The 147s were just for testing and I don't plan on using them. I think the locking piece will fix the issue, they should be here tomorrow. Right now, it's no where whisper quiet. I know about the bolt gap, my fear is it will change and I'll have to order rollers and wait even longer to get this figured out. |
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Originally Posted By chargerdude70: I'll add my experience with the SD that I had Michael's Machine build for me from an HK SP5. I'll start off saying I only shoot 124gr bullets so YMMV. I could not get it to function flawlessly in SS mode. I tried all the different deg LP tricks. Was even going to go as far as changing out rollers to adjust bolt gap for more bolt speed. It would run but only strings of fire, never a full mag. I was going to cut down my recoil spring (take a coil at a time) but then remembered I had my old PTR9 on hand. I took out that spring and measured the amount of resistance it had against the factory HK before starting to collapse. Difference was shocking to say, PTR was pounds lighter. I put that in the SD and it ran flawlessly. So I ordered one up from PTR and it's been in there since. Just some food for thought. I'm done with the SS in the SD. I'll leave it as is. I have an early MKE/Zenith full size. It runs flawless with the AS Designs lower, so it will just stay there. Once AS Designs releases their true HK FRT, I'll try that in the SD. |
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Originally Posted By xtremegibs: I think the 115 or 120 LP should fix it. They say not to run 147gr in a true SD, I believe because it can bleed off velocity enough to cause tumbling/baffle strikes but don't quote me on that lol. I don't know if this is fact, and some people say they run 147gr no issue, but I'm not willing to chance it and I've been sticking to 115/124 as intended for the SDs. Mine was converted through GreaseGunner (aka John / FB Unlimited) and it's been amazing. I will say the first time I took mine out I also thought the port pop was unreasonable for an SD, the second time I took it out it blew me away how whisper quiet it was. Idk if it was in my head or if things got broken in and/or a little coating on the suppressor helped quiet things down. Regardless, I've only heard good things about Ronin, you should be in good hands. What suppressor are you running? This ^ Yup. Mine has port pop with a clean can. A couple hundred rounds in and it sounds much better. |
| The AP5 apparently doesn’t come with a 120* LP. I had grease gunner do my barrel swap. He had some 120* RCM’s on the shelf so I had him include one. These guns aren’t too complicated. For all Turkish guns, replace the mags with HK mags, ejector lever, and extractor spring. If you’re still having issues replace the extractor and recoil spring. Use actual HK parts. My AP5 SD wouldn’t run for shit until I did that. Now I’m 2k+ rnds without a stoppage. |
| HTA did my conversion and they specifically said to use 124 NATO spec. 115 wouldn't always work correctly, and 147 was called out as something to absolutely never use. Even some commercial spec 124 that was loaded to non-NATO spec/pressures wouldn't always be compatible. |
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Originally Posted By vanrichten: HTA did my conversion and they specifically said to use 124 NATO spec. 115 wouldn't always work correctly, and 147 was called out as something to absolutely never use. Even some commercial spec 124 that was loaded to non-NATO spec/pressures wouldn't always be compatible. This is what HK says, and I trust them more than anyone else on the matter. The MP5SD was designed to be used exclusively with supersonic ammunition with a muzzle velocity of at least 1,088 feet/second at sea level. It should not be used with subsonic ammunition with a projectile weight of less than 140 grains! While subsonic ammunition with a projectile weight of less than 140 grains fired in the MP5SD may provide enough recoil energy to cycle the action of the weapon it may not provide sufficient terminal ballistics downrange to incapacitate the target. |
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Originally Posted By Goosemaster: This is what HK says, and I trust them more than anyone else on the matter. The MP5SD was designed to be used exclusively with supersonic ammunition with a muzzle velocity of at least 1,088 feet/second at sea level. It should not be used with subsonic ammunition with a projectile weight of less than 140 grains! While subsonic ammunition with a projectile weight of less than 140 grains fired in the MP5SD may provide enough recoil energy to cycle the action of the weapon it may not provide sufficient terminal ballistics downrange to incapacitate the target. |
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Originally Posted By vanrichten: I agree and why I think the 124 NATO spec is what HTA calls for. 115 out of a 5" barrel might not reliably exceed 1,088 FPS. Why would you think that? It's handgun ammo, so any factory ballistic data will be from it being fired out of a handgun, probably with a 5" barrel. I have never found any factory 115 grain ammo that was subsonic in my MP5s. And what they say about 147 grain ammo is bullshit. Plenty of people fire 147 grain ammo out of their MP5SD with no ill effect. It's just a waste of good subsonic ammo. |
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Originally Posted By Goosemaster: Why would you think that? It's handgun ammo, so any factory ballistic data will be from it being fired out of a handgun, probably with a 5" barrel. I have never found any factory 115 grain ammo that was subsonic in my MP5s. And what they say about 147 grain ammo is bullshit. Plenty of people fire 147 grain ammo out of their MP5SD with no ill effect. It's just a waste of good subsonic ammo. |
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