Fathom Arms

Mil-Spec Bolt and Carrier Group Review

By Will

Photo Credit: Blacksheepwarrior.com

When building or upgrading an AR-15/M-4 project it is easy to get carried away with the external appearance/components. Usually folks are more concerned with the hand guard, charging handle or choice of optics/back up sights than a quality trigger group or bolt and carrier group (BCG).  Now don’t get me wrong, I am all about quality exterior components, why else would I choose to spend my hard earned cash on Trijicon optics? However, all those quality components are useless if your weapon platform doesn’t cycle properly and lead doesn’t hit its mark!

That is where Fathom Arms comes in!  Fathom Arms is run by Guy Kemp, who lets just say, has made his fair share of trips to the sand box.  Guy’s approach to sourcing quality Mil-Spec components comes from his background overseas and designing weapon platforms for special applications. 

Guy sells more than just Fathom Arms BCGs, in fact you can visit his website and see his line of rock solid complete uppers as well.  How do I know its rock solid? Because Chris Tran and TracerX Photography just put the finishing touches on a full blown review, but that is for later down the road! For now, lets tear this Fathom Arms Full Auto BCG apart and see what it takes for Guy Kemp to put the Fathom Arms stamp of approval on one.

The BCG:

The first thing to note about the Fathom Arms BCG is that it is “Mil-Spec to the letter”, in fact, these are the same exact BCGs that comprise the M-16 contract that FN has. Guy light heartedly refers to them as one of the only true Mil-Spec BCGs due to the lack of laser engraving which compromises the phosphate finish, but thats just Guy being picky.

The phosphate finish is impressive to say the least, so much so that I referred to it while reviewing the North Eastern Arms Compact Carbine Stock.  Guy actually told me on the phone that he can identify out his BCGs based solely on the quality finish that he demanded.

Continuing with our outward inspection, it is easy to see that the gas key hardware has been properly staked (something that Guy personally hand inspects on each and every BCG).

Moving on to the less flashy parts of the Fathom Arms bolt carrier:

The bolt carrier itself is made from 8620 steel and features a hard chrom bore. Additionally, the gas key is machined from tool steel and again features a hard chrome lining.  The hardware wasn’t skimped on either and is Grade 8 and staked to Mil-Spec standards (not sure what grade 8 is but it sounds sexy ;))

The Bolt:

The Fathom Arms bolt is a Carpenter 158 and is shot peened, as is the tool steel extractor.  The extractor is complemented by Mil-Spec, black extractor spring and, more importantly, a Viton O-Ring.

The bolt is Individually High Pressure Tested (HPT) as well as magnetic particle inspected (MPI) which, for a gear guy like me, is just too much information (TMI).  The bolt itselff is marked as such and like all the other components, is finished per MIL-STD 171 for AR-15, M-16 and M-4.

To wrap up the whole package, the hard chrome firing pin, cam pin and retaining pin are all Mil-Spec.

According to Guy Kemp,

What really separates our BCGs vs a lot of other companies? We hand inspect every BCG (paying particular attention to the staking, gas key hardware, extractor and extractor parts, and bolt lugs) then check head spacing on a within spec barrel/barrel extension to ensure the bolt is within spec. After we verify, each carrier is then hand wiped down with oil. We have not had one BCG come back or any problems reported from users using this QC method.

All Fathom Arms BCGs have a lifetime warranty!

Wrap up:

After firing a few hundred rounds through Fathom Arms BCG, I am pleased to say that I did not experience any issues whatsoever! We will continue to use it and if any further commentary is warranted we will add it here.

Until then, I highly recommend it as a valuable upgrade/addition to your current AR-15 platform rifle!

Where To buy it:

You can find the Fathom Arms BCG and other Fathom Arms products at Fathomarms.com.  Don’t forget to follow them on Instagram and Facebook as well!

Keep your eye out for our upcoming Fathom Arms Complete Upper Review (with the all new Enhanced Nitride Full Auto BCG) featuring in depth commentary from Chris Tran as well as photos from none other than TracerX Photography

Special thanks to Down Range Photography for providing supporting imagery for this review