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Discussion Starter · #1 ·
Hey guys, my experience with 5.56X45 subsonic ammo has been with the AR platform. There isn't enough gas to cycle the action and keep a 77 gr bullet subsonic. Since the roller locked guns can be "tuned" with a different angled LP, I was wondering about using the subsonic in a 53 or a 33K clone with a can and a 70 degree locking piece. I'd think that with such a high angled LP, one or the other gun might function with the extra energy a can would add.

Sorry if this has already been covered. I have no idea how to specify this application in a search. I was just wondering if anyone had tried it. Please let me know what you think.

Scott
 

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Hey guys, my experience with 5.56X45 subsonic ammo has been with the AR platform. There isn't enough gas to cycle the action and keep a 77 gr bullet subsonic. Since the roller locked guns can be "tuned" with a different angled LP, I was wondering about using the subsonic in a 53 or a 33K clone with a can and a 70 degree locking piece. I'd think that with such a high angled LP, one or the other gun might function with the extra energy a can would add.

Sorry if this has already been covered. I have no idea how to specify this application in a search. I was just wondering if anyone had tried it. Please let me know what you think.

Scott
I have limited experience with subsonic 5.56mm ammo in the HK53 and HK33K, more so with frangible training ammo - neither was good frankly. We tried various/all available locking pieces with poor results. There simply was insufficient recoil impulse from the cartridges to reliably operate the roller-delayed bolt. The plan was to develope a unique subsonic bolt broup (like the blank "blue" bolts) but that did not meet the user requirements for interchangeable ammo w/o weapon adjustment. The HK53 frangible ammo adapter had a so-called "self-adjusting" valve so that the weapon could be used with combat ammo too. It did not work out. True subsonic function in 5.56mm with most any type operating system has always been less than reliable. The best results I know of were with some special Black Hill's made 100+ grain ammo in the HK416. Folks are still working on it but 55-77 grains at 1000 fps is hardly impressive from a terminal ballistics stand point thus things like the 300 Black Out and Whisper rounds.

G3Kurz
 

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I have been interested in trying subsonic ammo as well .
I have an IGF 53 & a YHM phantom with a #15 lp .
It does well with standard ammo but would be a lot cooler with SS ...
I have had some FTF malfunctions while shooting suppressed in SA
I have been kicking around the idea of experimenting with different LPs ( #3 & #20)
& SS ammo .
 

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Discussion Starter · #4 ·
I have limited experience with subsonic 5.56mm ammo in the HK53 and HK33K, more so with frangible training ammo - neither was good frankly. We tried various/all available locking pieces with poor results. There simply was insufficient recoil impulse from the cartridges to reliably operate the roller-delayed bolt. The plan was to develope a unique subsonic bolt broup (like the blank "blue" bolts) but that did not meet the user requirements for interchangeable ammo w/o weapon adjustment. The HK53 frangible ammo adapter had a so-called "self-adjusting" valve so that the weapon could be used with combat ammo too. It did not work out. True subsonic function in 5.56mm with most any type operating system has always been less than reliable. The best results I know of were with some special Black Hill's made 100+ grain ammo in the HK416. Folks are still working on it but 55-77 grains at 1000 fps is hardly impressive from a terminal ballistics stand point thus things like the 300 Black Out and Whisper rounds.

G3Kurz
Thank you for the insights. To me the use of subsonic would be for the novelty in 5.56. I remember reading somewhere that 77gr subsonic in a 14.5" barreled AR had a muzzle energy of 155 ft/lbs. Standard high velocity .22lr I believe has 140 ft/lbs. I have used EBR 7.62x39 Jackhammer subsonic. The EBR website used to list the 7.62X39 subsonic as having 500 ft/lbs at the muzzle, but I no longer see the energy rating listed. I've shot it through an 11.5" AR upper with a AAC M47-2000 can. It was about as loud as my converted HK94 with my Gemtech Raptor can.

Tonight I was actually looking at the EBR website. There is an article at Engel Ballistic Research entitled "The Use of Subsonic Ammunition in gas operated and other "Tactical" firearms". In the sixth paragraph it states that subsonic ammo should not be used in a fluted chambered firearm. What I got out of the article was that because of the low gas pressures the case won't seal consistently. If the case doesn't seal the chamber, the propellant gas can leak out of the back of the chamber, possibly causing a squib. Because of the inconsistency of chamber seal, function would be erratic. STR Arms is the nearest distributor to me. At there website there is a page with pricing for EBR ammo. Near the top of the page it states "Not for use in H&K firerams (SP) with fluted chambers".

There was a thread about some commercially available 100 gr subsonic that would have enough gas cycle a standard semi auto action. The link the guy gave listed the ammo at over $2.00 a round. That would be a rather expensive novelty. Especially if I have to build a "Subsonic Only" 53 with a non fluted chamber. I believe Jeff (ghilliebear2000) has had some luck with the low power 7.62x39 surplus ammo by reducing the spring pressure in the bolt locking lever in the carrier. That might be helpful if building a non fluted purpose built subsonic only 53. I think that a subsonic only 53 would be a project when I consider myself as an "advanced collector". Again, thanks for the input.

Scott
 

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What about going another direction and building a 53 type firearm to shoot 300 blackout? I am rather new to the HK stuff but it seems to me it might be the same as the AR platform with only a barrel swap needed. The 51 barrel would be .308 but I am not sure if the .308 and .223 platforms are that interchangeable. It should use the same bolt, mags, etc as a 53. I am hand loading the 220 grain subs as well as a range pinker using surplus 147 grain ball pull downs and they are both awesome suppressed in full-auto. The only irritating thing is the subs are so quiet the "boing" of the buffer spring drives me crazy. After shooting 300 blackout for a few months it is by far my favorite M16 caliber. An HK sear host would be awesome in my opinion.
 

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Discussion Starter · #6 ·
While 300 Blackout/Whisper is very cool, who's going to make the barrel? Do you try to have it fluted or use it for subsonic only? What locking piece do you use? After this custom gun is built, will it actually run?

While subsonic ammo in 7.62X39 is not as widely available as 300 Blackout/Whisper, roller locked barrels in 7.62X39 are commercially available. Certainly 300 Blackout/Whisper is a very cool caliber in the AR platform. I'm not aware of anyone building a roller locked gun in 300 Blackout/Whisper. I don't have the kind of money it would take to fund the R&D for a master builder capable of building a roller locked gun in 300 Blackout/Whisper.

Scott
 

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I may be off base but I thought using a 53 type host and looking for a 51 barrel type blank might be possible. The 300 blackout reamers are cheap and easy. Barrel fluteing is another variable Again I have not sourced the parts so it may not be possible. I searched the Internet high and low today for 7.62x39 subsonic reloading data. I found a good bit of conversation about it but only 2 loads. One I trust because it is similar to a 300 blackout load and I know the cases are similar. EBR makes subsonic 7.62x39 ammo but oh boy is it pricey. The goods news is it supposedly cycles in an AR chambered in that runs so it may run in a roller lock platform. If a barrel host for a 300 BO would not workout. I would think going the Ptr-32 route and trying the EBR would be next. If that ran then working up a reload to match would be last. I know a lot of ifs but I agree 100% with what end result you are working towards. I just don't know of anyway to get there with a .223...
 
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