Heckler and Koch Hk MR 556 Modifications and Upgrades

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Prices for MR556 Barrel Modifications and Engraving

Full Services for HK's MR556 Rifle

Full Services for HK’s MR556 Rifle

Heckler and Koch’s MR556 is a great rifle right out of the box.  The biggest problem most customers have with it is the extra heavy barrel that comes in it from the factory.

We offer two options to shorten and lighten the barrel.  We can shorten, thread, and modify the barrel to both the 416 factory 14.5 and 10.4 inch lengths.  Typical Turn around time for the work is 3 to 4 weeks.


14.5″ 416/M4 profile

Shorten to 14.5 and Thread 1/2 x 28
Re-Profile to M4/Socom
Permanently Attach Muzzle Device  (for non-SBR)

*Reprofiling the barrel will make refinishing necessary, refinish options are below


10.4″ 416/M4 profile

Shorten to 10.4″ and Thread 1/2 x 28
Standard Gas Block Modification (vented mod available below)
Reduce Barrel Profile to .720


416 Barrel Markings

Somes guys really like to get as close to a 416 as possible, plus the 416 has some pretty artistic looking Caliber Markings.  The photo below doesnt do it justice, they look pretty sweet.  Price engraving the Hk logo, Nitro Proof Stamp, and Caliber is $145

Titanium Barrel Nuts and Gas Pistons

The factory MR barrel nut is made from steel and is pretty basic without much thought of keeping weight down on the firearm.  IGF Titanium Barrel Nuts weigh approx half as much as the factory barrel nut and do not sacrifice any strength of the design of the firearm.  This was achieved by using Titanium and a series of lightening holes around the diameter of the nut.  The nuts are finished with a smoke bronze color titanium anodizing.

The barrel nuts are available in 3 versions:

A standard barrel nut which has the same dimensions such as outer diameter and forearm mounting groove location for those running a 416 and similar style forearms.

Geiselle makes and excellent forearm for the MR556, but some of them can be an extremely tight fit on the factory nut so I made some slightly smaller OD barrel nuts that allow the Geiselle forearm to be installed and removed much easier.

Finally most of the new MRs are coming with Keymod forearms which have a pretty big gap between the forearm and receiver, so I made a third version of the nut with the retaining groove moved back to help elliminate that gap between the forearm and upper receiver.

All 3 versions are $195 each, if you would like to order one email me jayson@investmentgradefirearms.com and I can get you payment instructions.  Unfortunately the shopping cart is down on the website right now and I’ve not had an opportunity to fix it.

Titanium Gas Pistons not only weigh less than the original MR piston, but also reduce the reciprocating weight which helps to reduce muzzle rise between shots.  I also designed the Titanium Gas Pistons to have a tighter fit at the front to help reduce blowback and a tapered design towards the rear to reduce friction.  There is also a double ringed gas piston available for guns that can have trouble cycling the action with certain ammunition such as some factory MR762s, the extra set of rings helps reduce the blowback that the Hk gas system is known for and convert that blowback to force used to cycle the action.   The titanium gas pistons are finished in the same smoke/bronze anodizing used on the barrel nut.  The cost for the standard piston is $95 and the double ring version is $125.   If you would like to order one email me jayson@investmentgradefirearms.com and I can get you payment instructions.


Vented Gas Block Modification

A very small number of 10.4 416s had a vented gas block, with basically a smaller gas port in the block. I can replicate that modification as well, the cost for that mod is $165. With this modification we machine out the original gas port, weld in a new smaller port, and finish it down so it looks similar to the standard vented gas block.  See this page for full details http://www.investmentgradefirearms.com/vented-gas-block-modification-for-the-10-4-inch-hk-mr556/


Refinish Options 

The steel alloy that the MR barrel is made from does not hold parkerizing well.  The steel will parkerize, but it tends to lose the park crystals fairly easily resulting in finish streaks and light spots over time.  The factory MR barrel finish is a brown oxide and it will often show the streaks and light spots as well, especially after moderate use and cleaning.

I have found that bonded resin both looks better than the original finish and holds up much better.  The cost to refinish a barrel assembly in the bonded resin finish is $75.

Another finish option that has been very popular is Nitride Treatment.

Nitride Treatment

Nitride also known as Melonite barrel treatment is available, the cost for that service is $155 for the barrel and $45 for the gas block.  The nitride treatment adds about 6 to 8 weeks to the turn around time.  The nitride finish is a nice jet black finish that hardens and slickens the steel surfaces and also increases corrosion resistance both outside the barrel and inside the bore.  This surface hardening and added corrosion resistance makes the barrel easier to clean and noticeably increases the life of barrels and parts such as the gas block.

Some guys also have their carrier nitrided which makes a noticeably smoother action and imparts less wear to the receiver internals, the cost to nitride the carrier is $30.  I can also have the operating rod steel pieces nitrided for $30 as well.

14.5 bare barrel


Full Auto Bolt Carrier Conversion

If you have a registered receiver lower etc for your MR556 upper we can modify your carrier so that it will trip your sear.  The cost for the conversion is $275


Auto Picto Engraving

Want your lower to look more like the 416?  We can engrave the selector 3rd position 30 bullet picto on your lower.  The cost for the engraving on both sides of the receiver is $345.

We can engrave the 30 bullet picto to the selector 3rd position.

We can engrave the 30 bullet picto to the selector 3rd position.