Relentless Knives M4 Viper Knife Test  
Relentless Knives USA
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Capt Ian Humphrey on the range


   Knife Test or Evaluation
by: Capt Ian Humphrey

M4 Viper

As Sharp As It's Namesake!

by: Capt Ian Humphrey

M4 Viper: As Sharp As It’s Namesake!

I received an early Christmas gift this year with the arrival of a M4 Viper for testing and evaluation.  This knife is special because it features the highly acclaimed s30v steel that is the current “hot steel” for custom and high end production knives.  The M4 Viper is the perfect size knife for everyday use with a balance between blade size and overall comfort.

First Impressions

     The Viper came with the usual custom touches that I have come to expect from Relentless Knives.  The knife has clean lines and rounded edges for easy handling.  This model of the Viper came with sharp looking Rosewood handles that really added a touch of class to the knife.  The Viper has a nice blade shape that allows the knife to be used for a variety of different cutting chores.  The Viper came with a wicked edge and a nice looking set of serrations along the spine.  I was immediately impressed with how comfortable the knife was to hold.  I feel this is due to the good balance and thin handle which allowed for a secure grip.  The thin handle also allows for a slim profile when carried.  The Viper also includes double lanyard holes in the handle, which allows for comfortable use of the included wrist cord.  The double holes also allow the user to easily secure the knife to a branch for a makeshift spear, secure to gear, etc.


     This is the first knife I have used with the new s30v steel.  I can say without a doubt that I was impressed!  The Viper was the sharpest knife I have tested and sliced through sheets of paper like a razor.  The “handle heavy” design of the knife allowed for easy cutting.  The tip of the knife also cut extremely well with the paper.  Heavy cardboard was also no match for the M4 Viper.  The blade design allowed for good hand placement that allowed me to effectively grip the knife and sail through the heavy material.  The serrations also cut very well through the cardboard.  The Viper also cut 550 cord very effectively.  The knife could consistently cut through two strands of 550 cord at once, while individual serrations could slice through a single cord.  The overall blade size was the only limitation to cutting more 550 cord at the same time. 
     The s30v steel continued to impress me with the ease it could cut branches and sticks.  Fresh and dry wood were no match for the Viper and I soon had a small pile of sharpened sticks, fuzz sticks, and stripped branches for making a spear.  The serrations on the knife also worked well and were extremely handy in making notches in the pole to aid in spear building.  The serrations also tore through the branches and made good fuzz sticks with little effort.  In terms of throwing, while not practical in normal use, it is a good test to check on blade hardness and point retention.  The Viper was thrown at several targets and suffered no damage to the blade.  Proof that the Viper is not designed for such use resulted in scratched wood handles, which would be minimized with micarta handles.  The Viper did make an acceptable spear and was easily attached to the branch with the included cord from the handle and sheath.  The end result was a makeshift spear that would be effective in a survival situation. 
     Since this was the first time I have used s30v steel, I wanted to see how long it would take to dull the knife and how easily it could be re-sharpened.  After several days of testing that included throwing the knife and cutting objects, the blade still cut well through a sheet of paper (although not as well as before).  In order to dull the edge, I continued to cut long strips of heavy cardboard.  After 14 strips the blade began to noticeably dull.  I tried the paper test again, and while the knife still cut the paper, there were some distinct rough spots along the edge.  I used a standard kitchen steel to touch up the edge, and after only 10 passes on each side, the knife was once again able to cleanly cut through paper.


    The M4 Viper came with a rugged, overbuilt kydex sheath that will stand up to any punishment you may face.  The sheath comes with a large TekLok fastener which allows for easy removal and attachment to web gear, belts, packs, etc.  A nice feature to the sheath is the ability to rotate the TekLok fastener and lock the swivel in different positions.  This allows the user to create custom carry angles to meet their needs.  There are also numerous grommet holes on the sheath that allow you to secure the knife to different locations when the TekLok will not work (MOLLE gear, etc.).


     While the sheath is well made, I would prefer a slimmer design (less wide).  The width may be due to the large TekLok, but if possible a slimmer profile would be better.  I would also like more holes in the swivel plate on the sheath.  This would allow more angles to secure the knife (this can be easily done yourself by drilling more holes in the plate that holds the TekLok).  One drawback to the TekLok is that you can not attach the clip to MOLLE vests, etc.  This can be offset by using the numerous attachment points on the sheath and the included cord or zip ties.  When I first received the knife, there was a lot of play between the knife and sheath.  This was easily fixed by heating the lip of the sheath with a lighter and bending the kydex around the blade.  In terms of the knife, the cutout for the thumb rest seems a little too far back for extended comfort (based on my hand size).  And as I have already mentioned, the Rosewood handles look great, but for serious use I would recommend the standard rough finish micarta handles. 

Last Impressions

     I was really impressed with Dan Certo’s M4 Viper.  I had asked Dan which knife he felt would be best for everyday use, and he recommended the Viper.  The blade size is big enough for almost any task, yet the knife still carries unobtrusively.  I carried the Viper on numerous hikes, trips to the range, around the house, etc. and never minded the weight or bulk of the knife.  The Viper also fit well on my LBE and performed well during some recent military exercises.  The s30v steel performed every test with great success, and the best part was the lack of maintenance needed to keep the steel looking like new.  If you are looking for a great all around knife to take on your next adventure, the Viper is your knife!


Take it with you on your next adventure. It's built to withstand extreme conditions, and waiting to become your faithful companion.

Also remember to send photos of your adventures for our "ABOUTYOU" webpages.

I'm sure you'll be pleased. . Thanks for your interest, Dan Certo.

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