HK MR556A1 SBR barrel length opinions

[WarriorPoet19]

Hey everyone. I recently ordered an HK MR556A1 with initial intention to SBR to 10.5 inch barrel and use with my Dead Air Sandman. I however made the mistake of not researching far enough into all the Form 1 requirements and laws past a tax stamp and and a few other things. I have no issue with the engraving trust info onto receiver but was unaware of the Form 20 to travel with an SBR for training or in general use aside from my home state.

My questions then are as follows.

1. Would you suggest for shorter option to just cut barrel down to 14.5 and pin flash hider adaptor for dead air to keep rifle at legal length for ease of travel?
2. If you would say go ahead and go for a Form 1, I have heard running a 10.5 inch barrel with a muzzle brake adaptor over a flash hider adaptor is better for use with can to take pressure off of the first couple internal baffles of can for longer life span of devices and system(not sure if true)?
3. SBR and cut to 14.5 so i can still change out muzzle devices as I want for maintenance or repairs ?

Additional info is that I am not familiar with using systems any shorter than 18 inches as I mainly work with longer range systems. Same applies to suppressor use, which has always been on long guns with barrels usually 20 inches or longer.

Thank you for your patience and opinions and advice with this matter. I am really not sure what to do now since I don't know as much about this area.

 

[EXTREMEPREJUDICE]

I have a MR556 so I'll give you my thoughts. As far as I know, there is no adjustable gas block for the HK MR series, so regulating back pressure is dependent upon the "so called' self regulating gas block and the piston system which is not sufficient in reducing pressure to prevent over-gassing, I've tried it with the Surefire Socom .........no go. HK teamed up with OSS to produce a system for the MR series with includes a "back pressure regulator" that is installed between the muzzle and the suppressor to reduce excessive back pressure. If you could obtain that system then I would say go for it. Now, if you cut the barrel down to 10.5 in. (SBR) you'll be reducing pressure overall and it might run fine suppressed (might) ...............but may not have enough pressure to run the system without the can......once again a crap shoot. I've decided to run my MR as the only un-suppressed AR I have until (probably never) HK decides to make an AGB for it. Incidentally, do not purchase the HK416 GB that fits the MR, it only has a bayonet lug...........no adjust-ability. Just one opinion..........there are others I'm sure.

 

[Centuriator]

It's pretty simple actually:

If you want to be able to travel without "getting permission" to cross state lines, do not SBR it.
If you don't want to fill out the forms and pay for the tax stamp, don't SBR it.
If you want to suppress it and don't want to pay both for the SBR and the suppressor, don't SBR it.

 

[WarriorPoet19]

I have a MR556 so I'll give you my thoughts. As far as I know, there is no adjustable gas block for the HK MR series, so regulating back pressure is dependent upon the "so called' self regulating gas block and the piston system which is not sufficient in reducing pressure to prevent over-gassing, I've tried it with the Surefire Socom .........no go. HK teamed up with OSS to produce a system for the MR series with includes a "back pressure regulator" that is installed between the muzzle and the suppressor to reduce excessive back pressure. If you could obtain that system then I would say go for it. Now, if you cut the barrel down to 10.5 in. (SBR) you'll be reducing pressure overall and it might run fine suppressed (might) ...............but may not have enough pressure to run the system without the can......once again a crap shoot. I've decided to run my MR as the only un-suppressed AR I have until (probably never) HK decides to make an AGB for it. Incidentally, do not purchase the HK416 GB that fits the MR, it only has a bayonet lug...........no adjust-ability. Just one opinion..........there are others I'm sure.

Thank you so much for the information. I may for now when it comes leave it as standard add my brake and geissele rail and be done while I continue to research.

 

[Wyfox]

Take a look at IGF (Investment Grade Firearms) he specializes in HK mods and does the MR556 sbr conversion, i'd call and pick his brain. I'm seriously thinking about doing the same thing as you, looking at the 10.4" myself and run it with a Surefire socom556.