My Machine Rifle Rest

Discussion in 'Rifle Country' started by JDinFbg, Apr 11, 2020.

  1. JDinFbg

    JDinFbg Member

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    Around the first of the year I embarked on a project to construct a machine rifle rest for testing hand loads in the rifles I own. In testing hand loads, when one does not achieve the results one hoped for, there are always the nagging questions of whether the problem is the rifle, a sight or sight mount issue, the inability of the shooter (that would be me) to get a consistent sight picture each shot, and all of the sundry factors that affect the ability to find a load that achieves a small group size. Further, on the rifles I own that only have iron sights, my old eyes would not allow me to get anywhere close to being able to differentiate the viability of one load versus another. Additionally, in developing loads for a rifle, one can burn through hundreds of rounds of ammo to find the optimum load, and not having to endure the wear and tear on my shoulder is certainly a plus for having a machine rifle rest, especially when testing large-caliber rifles.

    So, that is the genesis for my desire to have a machine rifle rest. I discovered that there are some commercially made machine rests out there, but I was not particularly impressed with what I saw. Further, I'm always interested in having a project as much as the end result, so I decided to build my own. For better or worse, I've attached some pictures of what I built. Without question I put way more steel in this thing than was needed (the carrier that holds and moves with the rifle recoil weighs 71 pounds), and in hindsight I probably would build it differently if I were doing it again. Hey, it is said that Thomas Edison did not have any failures in developing the incandescent light bulb, he learned thousands of ways not do build the bulb.

    I did run down a rabbit hole or two in my initial design which became evident when I first tested the machine rifle rest at the range. The main problem with my initial design was with the rifle butt clamping mechanism which was also the facility for making the needed windage adjustments. The first picture is of my initial design for the butt clamping mechanism. This relied on two opposing, 3/8" hand screws to clamp the butt of the rifle and allow me to adjust the windage. The mechanism had enough play so as to allow the rifle to twist slightly in the clamps during recoil. Further, in making windage adjustments, the twisting action of the hand screws transferred to the rifle making the adjustment difficult. Also, I realized that the strapping mechanism I chose to hold down the forearm of the rifle needed to be changed. The second picture shows the binder strap I used for securing the forearm of the rifle. I used a pull-tight type nylon binder strap I already had, but realized that in this application I could not pull the strap tight enough to firmly hold the rifle forearm.

    I quickly realized the deficiency of my initial design, so it was back to the shop to devise an alternative. Luckily, I was able so salvage the majority of what I had built and with a small investment in some additional steel and materials and a lot of cutting and grinding to remove my "mistake", I was able to produce a machine rifle rest that worked to my satisfaction and achieved what I was after.

    The third picture is a view of the revised butt clamping facility I built, and this puppy clamps the rifle butt rock solid. To provide for needed windage adjustment of the rest as shown in the fourth picture, I installed an additional steel plate to the rear of the rest base which rides on a steel plate that gets bolted to the bench and has a bolt for locking the rest in place. This allows the entire rest to swivel but maintained the bolt pattern to match the mounting holes I had drilled in my shooting bench. The fifth picture shows the completed redesigned machine rest in my shop. The last picture is of the rest at the range with my Model 94 Winchester clamped in it during my recent tests.

    This machine rifle rest allowed me to develop a new load for my 94 Winchester using the Hornady 160 gr. FTX bullet and identify the powder level that produced the smallest group (shown in the attached PDF). For this group, 4 of the 5 shots had a 0.722" group size. Given that my 94 only has open sights, it would have been impossible for me to differentiate which load produced the smallest group if I had been shooting from sandbag rests. The machine rifle rest made this possible, and I didn't have to endure the recoil from the 50 rounds I shot during the testing.

    37-Completed Butt Support.JPG 22-Hold-Down Strap Installed.JPG R106-New Butt Clamp Assembly.JPG R105-New Rear Brace on Old Mount.JPG R109-Completed Redesigned Rest.JPG R110-Rest at Range.jpg
     

    Attached Files:

  2. 22BR

    22BR Member

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    Very nice and obviously effective! Great creativity.
     
  3. JDinFbg

    JDinFbg Member

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    Thanks. It was a fun project.
     
  4. NIGHTLORD40K

    NIGHTLORD40K Member

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  5. mshootnit

    mshootnit Member

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    The build is very nice, and beyond my skill level. I have thought critically about strapping down a rifle barrel in a rest. Would that not add significant pressure to the barrel, changing POI as well as harmonics? (adding forearm pressure to the barrel) I see rests for sale which do strap the barrel down.
     
  6. ApacheCoTodd

    ApacheCoTodd Member

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    That's some level of commitment right there.

    Seeing the rifle locked up really makes the earlier pictures pay off.

    Todd.
     
  7. JDinFbg

    JDinFbg Member

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    On lever guns where the barrel is, by design, the mechanical link that connects the forearm, there could be the effects that you noted. However, in my machine rest design the V-rest contacts the rifle forearm just in front of the receiver and the retaining strap contacts the rifle barrel right between the V-rest and the front of the receiver. This hopefully minimizes the torques or stresses applied to the barrel, and any such forces are right in front of the receiver. However, some form of strapping is needed to constrain the front of the rifle during recoil and to prevent it from bouncing around in the front V-rest and not staying in a fixed position. I tried to not overly cinch down the strap on my rifle during the tests, but just hoped I found a reasonable balance between keeping the rifle in a fixed place and not overly affecting barrel harmonics. On a lever gun, some of those effects would likely be present even when shooting the rifle from a sandbag rest. For bolt-action and semi-automatic rifles where the barrel can be free floated, the strap pressure can be applied to the front of the receiver which is already mechanically connected to the stock and not change barrel harmonics.
     
  8. redneck2

    redneck2 Member

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    I’ve used multiple lead sleds in the past. If you use a vise type rest, your point of impact may be different from when you shoot holding the rifle yourself. The bullet is affected by the movement of the firearm before it leaves the barrel

    May affect your accuracy testing also

    I’d pretty much guarantee holding down the barrel will affect accuracy
     
    Last edited: Apr 12, 2020
  9. Alaskan Ironworker

    Alaskan Ironworker Member

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    Heres one I put together a few years ago, solely for developing a load for my .375. Haven’t really used it since, was more just something that sounded fun to build. The front “Y” rest moves horizontally by way of an all-thread inside tube steel trolley. The elevation can be adjusted by large amounts with the front threaded out riggers, and by small amounts by spinning the big red wheel which pushes or pulls the big wedge under the front mount. The rear mount is fully adjustable for stock length or different butt stock angles. Pretty happy with it, but I dont think it would work with an AR. I put a bungee cord over the rifle when I shoot, and yes the point of aim was a few inches off when I took it out of the rest, but it works for load development.
     

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  10. JDinFbg

    JDinFbg Member

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    Yes, I built my machine rest purely for testing handloads to find the powder/bullet combination that produced the smallest group. For something like my '94 Winchester with iron sights, it would be impossible for me to delineate the handload that produced the smallest group, and for any rifle, eliminating as many variables (probably the biggest of which is me) as possible is a good thing.
     
  11. 792mauser

    792mauser Member

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    Very nice
     
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