Technical Updates  (Updated 13 Jan 2009)

XCR^TM Upgrades

We have made some changes to the XCR^TM.  Make sure you check this page of our website to see if these changes apply before you shoot your rifle.  Click here.

THIS SECTION CONTAINS SOME VALUABLE KNOWLEDGE WHICH WILL HELP YOU ENJOY YOUR XCR.  HOWEVER, YOU MUST READ UNDERSTAND AND FOLLOW THE WARNINGS AND INSTRUCTIONS CONTAINED IN THE XCR OPERATOR'S MANUAL BEFORE HANDLING OR USING YOUR XCR.

Gas Adjustment

There's some confusion on how the gas adjustment should be used on the XCR.   Here is the definitive word on how to set it.  Different brands of ammunition use different propellants (powders).  These different propellants have different burn rates and create different pressures.   The higher the pressure, the lower the gas setting needed for the XCR.  So which gas setting should you use?

To use the XCR, you don't need to know anything about ammunition.   For any given ammunition, just set the gas dial on a setting which throws the brass consistently 8 to 15 feet.   If the gas setting you're using is only throwing the brass 2 to 5 feet from your rifle, you will have a jam sooner or later with that ammo because the pressure can vary from round to round (especially when using ammo like Wolf).  On the other hand, if your rifle is throwing the brass 18 to 30 feet, you've got your gas set way too high. 

We ship all the XCRs with the gas valve set to "4" which is the highest position.   Typically, the gas setting should only be left there for the first 200 to 300 rounds.   Then typically, you can turn the gas valve down to "2" or even "1".  Again, see how your XCR is throwing the brass and adjust the valve as necessary to throw the brass 8 to 15 feet.   Set this way, the rifle will be almost 100% reliable.

Some shooters leave their gas set on "4" thinking that this will make the rifle more reliable.  It won't.  It will just abuse your shoulder and your rifle.  You are sure to go through recoil buffers if you do this. 

7.62x39mm Conversion Kits

Here are some notes on the new 7.62x39mm conversion kits and rifles.  They seem to work very nicely but there are a few things you should be aware of.

We are now shipping the 7.62x39mm kits with a heavier hammer spring.  The standard hammer spring had trouble setting off some but not all 7.62x39mm ammo.  However, the heavier hammer spring increases the amount of pressure required to pull the trigger.   The Enhanced Trigger Group now offered gives a light consistent trigger pull with either hammer spring.

We also found that when C-Products 30 round magazines are new, the followers stick a bit.  We've found this with some of the AR-15 magazines as well.  The problem seems to be sharp edges on the top edge of the followers.  If you want, you can take sand paper and sand down the sharp edges slightly. 

We hope you'll have lots of fun with the 7.62x39mm kits.  Let us know what you think zdf@robarm.com

NOTE:  C-Products is working on a stiffer spring for the 7.62x39mm magazine.  One of our favorite customers put used an spring from an East Block AK-47 magazine.  It worked perfectly with C-Product's follower.  

Instructional Videos

Here are some video clips which show how to disassemble, assemble, and maintain the XCR.  Click here.

General Maintenance/Common Sense

After the XCR is broken in, it perform s almost flawlessly.  People who have had their XCRs for some time report shooting thousands of rounds without any failures whatsoever.  This is simply not possible with most other rifles.

However, to keep the XCR running at this level, a small amount of maintenance is required.  The rifle needs little cleaning and only a small amount of lubrication after break-in.  However, there are some bolts ( such as the ejector bolts, the selector switch bolts, and the bolt catch bolt) which need to be checked from time to time.   We suggest that you check these bolts periodically to make sure that none have come loose.

Firearm training experts suggest cleaning your rifle after each shooting session.  The reason is simple, it allows you to inspect your rifle carefully.  Though you may not need to clean your XCR often it's not a bad practice.  Common sense would dictate checking the extractor, and other bolts periodically.

On the XCR bolts will usually come loose within the first 1,000 rounds if they do at all.  Check them and you'll enjoy years of fun shooting the XCR.

NOTE:  It is not recommended that the ejector be removed for cleaning.  Just make sure the bolts are tight.  You can use a 1/4 wrench.

Rifle Cycled Fine for 250 Rounds then Quit Cycling

We've had this happen a few times.  The first thing to check is your gas block.  Once in a while the gas block comes loose and moves forward.  If it moves forward, it will not let the gas go where it should and it won't cycle.

1) Just undo the allen head screw.
2) Move the gas block into place.
3) Re-tighten the allen head screw.

There's always a little gas which leaks around the gas block. This gas actually locks up the allen head screw so no Loctite is needed.   This usually happens if that screw was not tight enough to start with.  Once it's tightened up right, it will never come loose on its own.

Bolt Won't Close/Pierced Primers

If your bolt won't close sometimes, check your primers and look for little brass slugs in the barrel extension (sometimes smashed flat).   

WHEN LOOKING AT THE PRIMERS IF THERE IS A HOLE IN THE PRIMER WHERE THE FIRING PIN HIT, STOP SHOOTING YOUR RIFLE IMMEDIATELY.

What is happening is that the firing pin hole has a sharp edge and the pressure of the primer against the bolt face cuts a little slug of primer out and leaves the hole.  The slug from the primer can get caught in the action. 

The fix is very simple.  We very slightly break the edge of the firing pin hole.  Don't do this yourself.  If you break the edge too much you can ruin your bolt.

DO NOT CONTINUE TO SHOOT UNTIL FIXED.

Symptoms are that the bolt closes sometimes but not others.  I'll post some pics as soon as I can.  We can fix the bolt in 20 seconds.

If you have any questions, email or call our service department.  801-355-0401 or terra@robarm.com
 

Old and New Gas Systems

Our customers wanted a new gas system which could be adjusted without tools.   XCR's shipped since July 2007 have this new gas system.   Learn more.  All new XCRs, Barrels, and Caliber Conversion Kits will come with this new gas system.  The only parts affected by the change are the gas block and the piston of the operating rod.   Here's where you can order parts to update your gas block and piston.

IMPORTANT BREAK IN PROCEDURE!!!

The XCR is one of the most reliable rifles money can buy.  However, they must be "broken in" properly before they are reliable.  The break in period is approximately 300 rounds.   During this period parts slightly wear against each other until they glide smoothly. 

If you use weak ammunition such as Wolf during the break in period, you may experience malfunctions which are caused by the bolt not moving back far enough when the rifle is fired.   Here's a list of these malfunction:

1)  The bolt does not go back far enough to pick up the next round and forces the round forward by the middle of the cartridge case.  (We refer to this as a "short feed").  Many think this is a failure to feed; it is not.
2)  An empty case gets caught between bolt and receiver such that the empty case is sticking out of the ejection port.  (This is referred to as a "stove pipe".)
3)  An empty case is not ejected and an empty case is shoved back inside the chamber.  (Note:  sometimes the empty case has swollen and it's hard to pull back on the charging handle.) And
4)  An empty case and an unfired case get stuck in the action.

These malfunctions are all caused by the same thing - The bolt carrier and bolt are not traveling far enough to the rear of the rifle when fired.    All these malfunctions will go away as soon as the rifle is broken in.

Suggestions for Easy Break In

1)  Make sure the rifle is well lubricated during the break in period.  (You should not need much lube after the break in.)
2)  Use hot ammo such as "American Eagle" during the break in period.  (Note: Weak ammo such as "Wolf" and other light ammo will cause you grief during the break in period.)  And
3)  Leave the gas setting to setting 4 (the highest setting).
4)  We love to talk to our customers.  However, it's best to follow these procedures before calling.
 

Reason for the Break In

The more the XCR is shot the smoother it gets.   The XCR's parts are made on modern CNC equipment and have nice surface finishes.  However, some parts simply need to wear together to work their best.  We could have designed the XCR so that it used additional force to cycle the system from the beginning so that no break in would have been necessary.  Had we done so, there would have been little difference between the highest and lowest gas settings and the rifle would always cycle harder that it would need to once it was broken in.

After the Break In

After the break in, the rifle will function reliably with hot ammo such as "American Eagle" on position 2 (this may vary from rifle  to rifle).  Weak ammo such as "Wolf" will function reliably on setting 4 (the highest setting).

If you are still having problems, check the following: (Follow safety precautions in the "Operator's Manual" and make sure the rifle is not loaded.)

1)  After the firearm cools, grab the gas block and make sure it is tight and not moving.  Tighten it if moving.
2)  Remove the upper receiver from the lower receiver.  Check the ejector and make sure it is tight.  Then with the upper receiver upside down,  take a hold of the recoil spring guide and slide the bolt carrier assembly back and forth in the receiver.  Make sure it slides freely and does not bind against the ejector.

The gas valve should be set so that the empty cases are ejected approximately 8' to 15' from the rifle.  If some empty cases are ejecting only a few feet, you're gas setting is not high enough and your sure to experience a malfunction.

We thank you for purchasing our product.  Should you have any problem or question whatsoever, please do not hesitate to contact us.

OPERATOR'S MANUAL CLARIFICATION

In some of the early Operator's Manuals on page 15 it states: 

To ensure the mildest recoil without sacrificing reliability, use the gas setting which throws the spent cartridge cases approximately 5 to 10 feet from the rifle . . .  

That distance should be 8 to 15 feet.   If the gas adjustment is set to throw the spent cases 8 to 15 feet, the rifle will function flawlessly.   If the gas setting throws the spent cases further than 15 feet, you may feel more recoil than is necessary.  If the gas setting throws the spent cases less than 8 feet, you may experience some malfunctions.

SOUND SUPPRESSORS/GAS VALVES

The XCR is designed for use with Sound Suppressors.  For owners wishing to shoot their XCRs with suppressors, a special gas valve with four settings is available.   This gas valve has the same settings as the standard gas valve for settings 2, 3, and 4.  However, setting 1 on the special gas valve for suppressors is different from that of the standard gas valve.  The advantage of this special gas valve is that there is almost no recoil nor movement of the rifle when fired, yet there is excellent reliability

SLINGS

We get asked continually about slings.   We will be making a sling adapter to go through the eyelet on the back of the receiver.   This sling adapter will allow any most slings to be mounted on the eyelet.   We do not recommend using a metal or plastic clip to attach a sling to the eyelet, especially if such hangs down and interferes with the charging handle slide. 

For the front sling attachment point, choose a 1913 rail mounted type.  These can purchased from many sources.