Charlie's has worked hard to bring you a historically correct gas block for the Mk11. The early Mk11 with the Obermeyer barrel had a a more full gas block than the current M110, which is also technically compatible with the Mk11 sniper system.
Potomac Armory has spent over a year researching the original Mk11 Mod 0 back from 1999 and into 2003, and has created a gas block that is both historically correct, but after testing, failed final QA, so factory seconds. 100% fully funcitonal as a gas block, but will not support the Mk11 or M110 Knights suppressor. The QA failure is in the suppressor alignment pin hole location. The location is off by a couple 100's of an inch, and will not securely hold the suppressor alignment pin hole, which is at 6:00. Otherwise, the gas block is historically correct and for those who will never use, or cannot use a suppressor, like in California, this gas block will work just fine and look the part.
The early Mk11 rifles featured the full double Picatinny rails like this block. Once the M110 program started up in earnest, the gas blocks were changed to save weight, and a second index pin hole was added, as the M110 and the Mk11 suppressors had different indexing, which was done to prevent a user placing the wrong suppressor on the barrel. The Mk11 barrel had flash hider, and the M110 did, so a separate suppressor was made for the M110.
Note: This gas block, should be installed only by a qualified gunsmith. This gas port is perfectly timed for a KAC barrel, but the inside of this gas block is made more narrow than the exterior journal of the barrel. Your gunsmith will need to bore out the last few 1000's of an inch for this gas block to fit. This was done purposely, as some barrels have a journal just slightly less than 0.750", to allow a gas block to fit. Properly designed Mk11 barrels are exactly 0.750", so a correctly bored gas block, would, in most cases, require the cooling of the barrel and the heating of the gas block and a strong mallet to push the gas block into place. Potomac decided to allow the gunsmith to make the adjustments, as not all barrels that are called Mk11 barrels have the correct profiling. Knights and Potomac barrels do, many others are not as snug, maybe like 0.749" or even 0.748", so having your gunsmith fit to your barrel is actually a good thing.
The three pin holes 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 pin holes drilled should not be mounted to a new 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 Mk11 barrels, but the process requires very tight tolllerances, and very few do it right. The barrel itself is very uniquie and the profile very specific, and when manufacturered to correct tollerances, some barrels are tossed aside as not meeting spec.
Note: This gas block is designed to fit a Knights Armament or Potomac Mk11 countoured barrel, and should not be used on another brand of barrel, as it might not align with the gas port.
This is not the Knights Armament gas block, but similar in design and all the same in fit and functionality.
The gas block is sold with a black oxide finish. Some pictures show the prototype with a gray dry lube. This gas block will not have that.