Charlie's has worked hard to bring you a historically correct and functional gas block for the Mk11 sniper rifle system. For many years, military clone rifle enthusiasts have made due with an M110 gas block, because that was the only part available, unless you were lucky enough to get an original Mk11 surplus sniper rifle. There are some Mk11s sold to civilians and many sold to law enforcement agencies up until around 2012, so they do exist, and you can imagine that an original Mk11 is a highly sought after rifle.
The Mk11 saw duty from the late 1990s until the mid 2000's when the M110 took over. The Mk11 was originally a US Navy SEAL sniper rifle, and then the US Marine scout snipers received the rifle in Afghanistan. The Mk11 was the first dedicated semi-automatic sniper rifle, and was appropriate for missions where getting that second or third shot was important.
Potomac Armory has spent over a year researching the original Mk11 and M110 rifle systems, and has created a gas block that is both functionally correct to work with the Mk11 barrels from Potomac Armory or Knights Armament, or a barrel make by specialty gunsmiths who understand the unique design of the SR25 barrel system, which is not just another AR10 barrel. Pretty much everything about a Mk11 barrel is unique, so if you are a building, or having built a Mk11 clone rifle, take care to make sure you are getting the authentic design. Even the gas port is in a different spot! The barrel length needs to be exact, within thousandths of an inch, if you plan on getting a Mk11 suppressor. This is one reason that Potomac Armory spent a year getting the gas block correct, both true to its historical design, but also true to specific tolerance for suppressor to fit, as the suppressor must align to the gas block and use the gate latch and then the muzzle of the barrel must fit precisely into the middle of the suppressor.
As you look at Mk11 and M110 rifles, you will see a lot of similarities. Do not be fooled. the barrels and the gas blocks are different. This gas block will only work on a Mk11 barrel and fit a Mk11 suppressor. The M110 gas blocks, however, are backward compatible, and will work on either barrel. This is why you see two holes in the top and two holes in the bottom of the M110 gas block: to accept index pins for either barrel and either suppressor. Not this guy.
This gas block has been engineered and tested to accept only the Mk11 suppressor. The gas block ships without an alignment pin. The alignment pin, or a small slotted pin is needed for use with a suppressor. The suppressor alignment pin should be installed at 6:00 for the Mk11.
This gas block is perfectly timed for a KAC barrel. Note: KAC SR25 barrels have the gas port in a unique location, so most gas blocks will not work. This gas block will work with a KAC barrel, a Potomac barrel, or one designed to match KAC specs for SR25 systems made from 2000 to 2012. Maybe later, not sure. At some point, KAC moved to the screw-on barrel nut for the gas block. This will not fit on those barrels. This is quite important. Charlie's knows that there are barrel makers who claim to make M110 barrels, but the process requires very tight tolerances, and very few do it right. The barrel itself is unique and the profile very specific, and when manufactured to correct tolerances, some barrels are tossed aside as not meeting spec by the best barrel makers.
Note: This gas block, should be installed only by a qualified gunsmith. The interior diameter of the gas block is machined to fit very snug against a 0.75" gas journal. In most cases, this will require the cooling of the barrel and the heating of the gas block and a strong mallet to push the gas block into place. The three pinholes that need to be drilled through the gas block and barrel to properly attach the gas block are milled out, but not started. A gas block and a barrel should become one unit. Once drilled and mounted, the gas block and barrel become a system, and should not be removed, and gas blocks with three pinholes drilled should not be mounted to a new barrel. The gas block requires (not included) two taper pins and one roll pin.
Note: This gas block is designed to fit a Knights Armament or Potomac Mk11 contoured barrel, and should not be used on another brand of barrel, as it might not align with the gas port. This is super important.
The Mk11 and M110 barrel use alignment pins at the bottom of this gas block for the suppressor. This was done so that one would not mistakenly install the wrong suppressor, while as similar as the Mk11 and M110 suppressor are, they are not interchangeable, largely because the M110 has a flash hider and the Mk11 does not. In the early days of the Mk11 program, roll pins were used as index pins for the Mk11 suppressor. Later, the M110 came with dedicated steel pins. If you intend to use a suppressor, you should obtain indexing pins, or use a roll pin, and install at that time of mounting of this gas block.
This is historically correct for the Mk11 rifle, as the original gas block for the Mk11 did not have the two holes at the top that the later M110 gas blocks had. the holes were created so that the machining equipment could make its way to the bottom to drill to pin holes at the bottom to accept the suppressor index pins for the Mk11 and the M110 pins. The original Mk11 pins were simply roll pins that were hammered into place from the bottom, when the gas block was installed on the barrel. Potomac Armory has designed these gas blocks to accept the M110 pin or a roll pin. Getting the special pins in place in this gas block is a little tricky, but some pressure, and it will seat. Potomac Armory has milled a larger opening for the top of the pin, which has a head, and some pressure to secure the pin is required.
This is not the Knights Armament gas block, but similar in design and all the same in fit and functionality.
Product Note: The walls of the barrel tube are super thin at the point at which the suppressor gate engages. It is not uncommon for there to be small wear points when new from the phosphating process, or as used with the gates eroding every so thin of a layer of steel, probably measure at 1/1000th of an inch. Once you start using the rifle and/or the suppressor, this will be less of an issue.
Product Note: You will need four pins for this project, none are included. Charlie's Custom Clones does sell the taper pins and the roll pin, but the suppressor index pin is currently not available from us. If you need one, contact our sales team, and we can put you in touch with couple of Knights parts dealers who may have them. Or, use a roll pin, as was done in the early days.
Installation Note: This is a tough DIY project, and not encouraged. The tolerance of the internal diameter of the gas block and the outer diameter of a Knights or Potomac barrel are the same. This means that thermofitting is required. This is also the case with many aspects of a true to form SR25 or Mk11 barrel. The gas block will need to be heated, and the barrel will need to be frozen. We encourage the barrel makers to NOT use any coating of the barrel on the gas journal, as that will add several 0.0001" to the O.D. Once installed, care needs to be taken to align the gas port, which is in a different position on true Mk11 barrels, compared to AR10 and .308 AR barrels available commercially. One in place, the top front is drilled and a stainless roll pin inserted. The lower holes are drilled and reamed to accept KAC spec taper pins.
Purchasing Note: We may screen the purchase, as we will sell to qualified armorers or customers using an armorer well schooled in the Mk11 barrel system. We have had bad experiences where gunsmiths have told customers that our gas block was out of tolerance, when it was the gunsmith that did not understand just how exact the installation alignment and tolerances are. This is not a typical gas block installation, and not a DIY project unless you are a machinist and have the correct barrel. Most commercially available barrels are out of spec.
Note: "Knights Armament" is a federally registered trademark and is of many trademarks owned by Knights Armament Co. Potomac Armory and Charlies Custom Clones are an independent manufactuers and dealers, respectively, which are not affiliated with or endorsed by Knights Armament. Reference to Knights Armament and KAC are for explanation and compatibility for the end customer.
Knights Armament (KAC)