FNC Barrel Replacement Overview

[okpud]

Attached is an overview I worked up on how to rebarrel a FNC using one of Green Mountain Rifle Barrel's new FNC-556 barrels recently made available. After having done multiple FNC barrel replacements, including one with the GMRB prototype barrel, these are the procedures we developed by trial and error. This overview is not intended to be a detailed step-by-step instruction manual, but does list the steps involved in removing an existing barrel and fitting/installing a new barrel. It is written to allow customers and gunsmiths to understand the scope of work involved in replacing a factory FNC barrel with a new one from GMRB.

For those interested, we provide rebarreling services for these barrels at a price of $270 + return shipping. Additional services, such as cutting and rethreading, are available at additional cost. Interested parties can send me a PM or email us at hipesgunsmithing[at]gmail[dot]com.

 

[hoblit]

Thanks for posting!

 

[roarincreek]

what is the shortest barrel possible? and are ther any gas blocks around ? i would like a quick change barrel ,but since that cant happen how about a short barrel new gas block and flash ,without messing with my barrel at all other than removeing it?saw a 16" barrel ,would 14" work.? or 12?

 

[okpud]

Since FNCs use long stroke pistons, the barrel can only be shortened to the length of the gas block w/o significantly redesigning entire gas/piston system. 14" is as short as it can go, and would put the flash hider right up against the gas block. Most times going below 14.5" also requires the gas port to be opened up a bit for reliable operation.

To the best of my knowledge, no one is producing after market gas blocks at this time.

 

[hiropro]

great thanks

 

[Quake Guy]

How are the GM barrels? They seem hit and miss with many of their other products?

 

[okpud]

How are the GM barrels? They seem hit and miss with many of their other products?

The GM FNC barrels I have worked with are all of good quality and I have had no issues with them. Fitting is as expected and accuracy is good. I have not seen any inconsistencies from barrel to barrel.

To your "hit and miss" comment on GM, I have never personally found this to be true. I have used GM barrels, along with others like Douglas and Shilen, for years and never had an issue with their quality. This includes both finished barrels and barrel blanks. I personally believe the Internet rumor mill has improperly lumped GM in as a source of problems with some Century rifle builds. Anytime a company buys a large amount of imported parts kits and mixes/matches pieces from them in an attempt to build rifles at the lowest possible price, there are going to be tolerance issues. I have never talked to another gunsmith who has used a GM barrel and had an issue with its quality. The Web forums I have seen where people have expressed dissatisfaction with them have had vague explanations about them being "out of spec" with out stating specifically why. This leads me be believe that some folks got in over their heads on a parts build and wanted to blame something other than their own abilities for not getting it to work properly. Of course, I could be wrong, but I'm sure anyone who's had an issue will step in and say so.

PS - I have no personal or business relationship w/ Green Mountain other than as a customer.

 

[Quake Guy]

How are people managing a front sling mount on the shortened barrels? Are they reusing the front sling mount or is there another option?

 

[okpud]

How are people managing a front sling mount on the shortened barrels? Are they reusing the front sling mount or is there another option?

There are several groves in the factory profile barrel that allow for the factory front swivel sling to be reattached on barrels as short as 14" w/o interfering with the flash hider.

 

[Dr.Gee]

can these be sent out(i.e. over state lines) for work?
Local gunsmiths look at me like im a three headed alien when I inquire about such a replacement.

edit-sorry,i didn't read the original post through.

 

[Dr.Gee]

BTW-How can you tell when your barrel is toast?

 

[okpud]

You can use a bore scope to check the throat and rifling for wear. Also, you can use a throat erosion gauge, which is typically much less $ than a good bore scope. When it starts to get "really bad", you'll be able to see the throat erosion w/ your naked eye just by looking down the chamber w/ a light at the end of the barrel. Factory FNC barrels are chrome lined, as are the Green Mountain replacement barrels, so they tend to last a long time (10k-20k rounds). Many people choose to re-barrel their FNC just to get a faster twist (1:7 vs factory 1:12) in order to use a wider range of bullet weights. That, or because they want a short barrel and want to keep the original barrel "stock" in case they want to return it to factory specs someday.

While I think you found the answer you were looking for on your earlier question, the answer is yes, your rifle can be sent out-of-state for work to any FFL 01 or 07.

 

[TehVice]

BTW-How can you tell when your barrel is toast?

This is usually a pretty reliable indicator...

 

[Dr.Gee]

This is usually a pretty reliable indicator...

Heh.

 

[Idaho Spudboy]

Are you still in the FNC re-barreling business? If so, how can I contact you by your business phone or e-mail?

 

[AK74U]

I've seen the paratrooper models with 13 inch barrels, are those made different than the 16 and 18 inch barrels?

 

[okpud]

I've seen the paratrooper models with 13 inch barrels, are those made different than the 16 and 18 inch barrels?

I believe you are thinking of the AK5 series. The "short barrel" FNC is 14.3", which is about as short as you can go with its piston system/gas block.

The AK5C has a 13.8" barrel and uses a different gas block from the FNC. It also has different pin location in the gas block to retain its handguards. I just had a barrel and gas block for one in the shop to "covert" a FNC to an AK5 style rifle.

The AK5D has a noticeably shorter barrel than the AK5C, but I'm not sure of the exact length. Their gas block goes in a different location, to go with the shorter piston and handguards. The handguard retention on the gas block is also different to accommodate the short handguards.