The XCR is offered in so many different configurations that it can be hard to choose your first XCR.  (Once you’ve had one, you’ll want more.)  There are two basic models – The XCR-L and XCR-M.   The XCR-L is designed to shoot 5.56, 7.62×39, 6.8 SPC, .300 BLK, 6.5 Grendel, .224 Valkyrie, 5.45×39, 6mm ARC, and other cartridges roughly the same length as a 5.56 cartridge.   The XCR-M is designed to shoot .308, 6.5 Creedmoor, .243 WIN, .260 REM, and other cartridges roughly the same length as a .308 cartridge. 

In deciding which XCR to get, the first thing to figure out is the caliber and barrel length.  You should consider your intended use and consult ballistic charts to see what caliber and barrel lengths are right.  After that, you can use what follows to help you build the XCR to your specification.  Because the XCR is modular and multi-caliber, you should also consider which other calibers and barrel lengths you may to use with your first XCR.

The XCR is a gas piston driven, semi-automatic firearm.  It operates by venting some of the gas from a fired cartridge through a hole (Gas Port) in the barrel into a Gas Block.  The Gas Block directs the gas through a valve which regulates the amount of gas that is used to push on the gas piston and cycle the firearm.   Generally, it is best to locate the Gas Port (overs which sits the Gas Glock) as far away from the chamber as possible, but not too close to the end of the barrel.   If the Gas Port is too close to the Chamber, it can start cycling the action while there is lots of pressure in the chamber making it difficult to extract the empty cartridge case.  On the other hand, if the gas port is too close to the end of the barrel the gas pressure may drop before the action can cycle properly.  In this post, we refer to the distance between the Chamber and the Gas Block as the length of the Gas System.  

To accommodate different barrel lengths and calibers, we offer different length Upper Receivers (Uppers).   The length of the Uppers from shortest to longest are Micro, Mini, Standard, and Competition.   To cycle different calibers properly there are also different Gas System lengths.  With some caliber, barrel length, and upper receiver combinations, the Gas Block, because of the length of the Gas System, may either end up inside the Upper (Buried); or outside the Upper (Exposed).   Whether Exposed or Buried, they can still be adjusted easily with the tip of a bullet.  Next, we discuss the advantages and disadvantages each XCR configuration based on the length of the Upper Receiver.

XCR-L Micro and Mini

The XCR-L Micro and Mini are really the same firearm with different length Uppers.   They were designed to be as short as possible using 7.5 inch barrels.  Other barrel lengths are offered but not suggested.  They both use the Micro length Gas System.  This results in the Gas Block being outside of the Upper (Exposed) on the Micro, but inside the Upper (Buried) on the Mini.  Compactness is the advantage of the Micro and Mini.  They can fit into an 18” briefcase or small backpack.  The Mini has longer handguard area and longer rails to attach accessories.   The disadvantage of both is they are not designed for longer barrels.   Calibers that work well with these two configurations are 5.56, .300 BLK, and 7.62×39. 

XCR-L Micro with 7.5″ Barrel
XCR-L Mini with 7.5″ Barrel


XCR-L Standard

The XCR-L Standard is our most flexible configuration.   It works with all the calibers we offer.  It can accept barrels as short as 9.5 inches and as long as 18.6 inches.  For 9.5 inch barrels or to shoot subsonic .300 BLK ammo, a shorter Gas System must be used that puts the Gas Block inside the Upper (Buried).  For barrels longer than 9.5 inch, it is best to use a longer Gas System which puts the Gas Block outside the Upper (Exposed).    If you buy the XCR-L with a 9.5 inch or in .300 BLK, you will need a longer, Standard Length gas system which includes a longer Oprod and Gas Tube to shoot the longer barrels.  On the other hand, if you buy the XCR-L with an 11 or 12 inch barrel, you don’t need anything else to shoot longer barrels. 

XCR-L Standard with 9.5″ Barrel
XCR-L Standard with 11″ Barrel
XCR-L Standard with 16″ Barrel


XCR-L Competition

The XCR-L Competition has the longest upper receiver we offer and it works with all the calibers we offer.   It can be used with our 14.7, 15.3, 16 and 18.6 inch barrels.  With the 14.7 inch barrel the muzzle threads will be inside the Upper Receiver but the ports of our 2 Slot Muzzle Brake will be outside it.  With the 15.3 inch barrel only the muzzle threads will be outside the Upper.  The Competition model is great for 3 Gun Matches or for those that like hold the rifle in and extended Arm “C” Grip.

XCR-L Competition with 16″ Barrel


XCR-M Micro and Mini

The XCR-M Micro and Mini are almost identical.  The only difference is the length of the Upper Receiver.  The shortest barrel they can accept is 9.5 inch long with a Micro length Gas system.  With the Micro, the Gas Block is outside the Upper (Exposed).  With Mini, the Gas Block is inside the Upper Receiver (Buried).    The Mini has the advantage of being able to accept barrels longer than 9.5 inch.  The Mini can use 12, 13, 14.7, 16, and 18.6” with barrels with a Mini length gas system with the Gas Block outside the Upper (Exposed).  

XCR-M Micro with 9.5″ Barrel
XCR-M Mini with 9.5″ Barrel
XCR-M with 12″ Barrel
XCR-M Mini with 16″ Barrel


 XCR-M Standard

The XCR-M Standard Length upper can accept 14.7, 16, 18.6, and 20 inch barrels.   The Gas Blocks for all these barrel lengths are outside the upper receiver (Exposed).  The Gas Systems are all Standard length.

XCR-M Standard with 16″ Barrel


XCR-M Competition

XCR-M Competition is identical to the XCR-M Standard except the Upper is longer.   It an accept 14.7, 16, 18.6, and 20 inch barrels with the Standard length Gas System.

XCR-M Competition with 16″ Barrel



All National Firearms Act (NFA) Rules Apply

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