Hk MR556 Conversion to .300 AAC Blackout Now Available.

May 05, 2016

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IGF is now offering modifications to convert the Heckler and Koch MR556 upper to .300 AAC Blackout.  .300 AAC allows for an AR style rifle to achieve ballistics similar to 7.62 x 39 while still using AR magazines at their full capacity.

Currently the conversion is available in 14.5 and 16.25 inch barrel length.  Longer barrel lengths could be available as an option.

Right now .300 AAC will not be available in 10.4″ the gas pressure of the .300 AAC is considerably less than .223 unfortunately the shorter 10.4 barrel length does not allow for enough dwell time to cycle the gas piston action as the gas port is too close to the end of the barrel.  I am working on a shortened gas system for the MR556 that might allow for a 10.4 option later this year, the shortened gas system will move the gas port closer to the chamber and extend the length between the gas port and the end of the barrel.

The standard .300 conversion on an MR includes:

.300 AAC Blackout Barrel Machined from a Quality US Made 1 in 8 Twist Chromoly Barrel Blank (different barrel twist rates or premium barrel blanks are available as an option, email for details).  Barrels will have profiles similar to factory 416 14.5 M4, and 16″ barrels.  The standard muzzle threads are 15×1, the same as most Hk roller firearms and the MR762, that way the upper could be used with the most common Hk muzzle accessories.  5/8-24 muzzle threads are also available as an option.

Replacement of Factory .223 Barrel with the .300 AAC Blackout Barrel into Existing Barrel Extension (right now Hk MR/416 barrel extensions are not available as stand alone parts).  Barrel will be indexed and Headspaced to the upper’s existing extension.  Original barrel will be returned and could be reinstalled into the factory extension if a customer wanted to convert back to .223 later.

Modification of Gas System to cycle the .300 AAC round.

Refinish of Barrel and Gas Block in Bonded Resin Black finish, shown in photos above.  Nitriding the barrel and gas block are available as options for an additional $125

The cost for the standard .300 AAC Blackout conversion is $845 plus return shipping.

For more information send me an email