F-Class Bipod Build

’ve I been using a basic, run of the mill, bipod for many years. It has spring loaded legs that are adjustable for height along with rubber feet. It works okay on the bench or prone if the ground is level but it does not have an adjustment for cant and the legs aren’t the most stable design. I wanted something that was more solid with greater height adjustment capability to use for long range shooting. I started researching bipods and found there are several types that vary in design and price.

Some are very pricey. Many raised the height of the bipod by moving the legs inward, narrowing the stance of the legs. These did not appeal to me; I liked the designs where the width of the legs stayed constant and the height was adjusted by extending the legs vertically. The more complex designs were intended for F- Class competition. I shot in F-Class a few times many years ago but did not have the rifle or experience to do so seriously.

After reviewing 75" aluminum plate used for the center sections of the bipod. the various models, I decided to design and build my own bipod based on the features in some of the bipods that are available commercially. The design allows the rifle to be adjusted for cant and has a fine adjustment for elevation.

F-Class, sometimes referred to as "belly benchrest", originated in the 1990s and is named after Canadian shooter George Farquharson (the "F" in F-Class) who promoted a prone shooting match that almost everyone could handle regardless of physical capability. Using a front and rear rest to support the rifle instead of a tight sling made it less demanding physically as well. F-Class also allows magnifying optics to help aging eyes.

The NRA defines F-Class as "a modification of High Power prone shooting, not as a form of bench rest and should not be construed as such". So maybe don’t refer to it as "belly benchrest" at a match. F-Class has two divisions, F- Open and F-TR (Target Rifle). F- Open is the most popular mainly because of the latitude in cartridges permissible, only limited to a maximum caliber of .35. The max weight of the rifle including scope and bipod is 10 kilograms/22 pounds.

An adjustable front rest (like that used in Benchrest competition) is permitted along with a rear bag. "Rail guns" and similar mechanical means to return to the precise point of aim are not permitted. The F-TR division is limited to just two cartridges, being unmodified 223 Remington and unmodified 308 Winchester much like Palma competition. The maximum rifle weight for F-TR is 8.25 kg/18 lbs. including the weight of the scope and bipod.

In F-TR only a bipod is allowed on the front and it must be attached to the rifle. A rear bag is permitted. NRA F-Class rules are included in the High Power Rule Book (Section 22) available for free download at Rulebooks.NRA.org. F-Class competition distances can range from 300 to 1000 yards but are most typically 800 to 1000 yards. The actual diameter of the target rings vary with distance as follows. The X-ring is 0.5 MOA diameter, the 10 ring is 1.0 MOA, the 9 ring is 2 MOA, etc.

At 1000 yards the Xring is only 5" in diameter,

the 10 ring is 10", the 9 ring is 20", etc. The ring diameters are spelled out in the NRA rules. The F-Class competition initially started with the standard mid-range (MR) and long range (LR) targets with 1 MOA X-rings, 2 MOA 10-rings, however, these proved to be too easy for skilled marksmen and the ring diameters were reduced by half. These targets are referred to as MR- FC and LR-FC. Courses of fire are typically 10 to 20 rounds at each of three distances.

Bolt guns are used almost entirely but a few shooters use semi-autos. Bipod Build I decided that I wanted my bipod to attach to a section of Picatinny rail on the forend of the rifle as opposed to a sling swivel stud. I had a spare set of 1" diameter scope rings with quick release levers and thought that one would provide a simple means of installing the bipod on the rifle. The scope ring would provide a pivot point for the bipod to allow the rifle to be canted to level it on uneven ground.

The quick attach lever solidly attaches the bipod to the bottom rail and allows it to be installed and removed easily. A short tube with a 1" outside diameter and 0.75" inside diameter is clamped in the scope ring and a 0.745" diameter rod fits snugly inside the tube. The rod is attached to the upper section of the bipod with a bolt that extends through it. A threaded knob and washer were installed at the rear of the rod and when tightened it prevents the tube from turning on the rod.

The rifle cant is adjusted with this feature. The aluminum rod had a nominal OD of 0.75" and a slight amount of material was removed to get it to fit inside the tube. It was tapped for the bolt that goes through it and was tightened against the upper section. During final assembly, a small amount of Lubriplate grease was added to prevent galling. The upper section of the bipod has two steel rods that slide vertically in the lower section that’s attached to the legs.

The steel rods maintain alignment of the two sections. The rods were made from 5/16" diameter shoulder bolts; the shank of each bolt is 2" long and has a ground surface. The actual diameter of the ground surface is 0.308". I cut the socket head off and cut a slot for a screwdriver blade. The bolts have a 1/4-20 thread on the other end and I tapped the holes in the bottom of the upper section for these threads. The upper and lower sections started as a 0.75" thick aluminum plate that was 6" wide and 4" tall.

The plate was cut across the width to give two sections that were each 2" Far Lower section with the elevation screw, sleeve, washer, and retaining screw installed.

The 0.125" thick front section is not installed. The hole in the right end for the stud that retains the vertical leg was drilled and tapped in the part before it was bonded in place. tall. Before I cut the plate in half, I marked the locations for the guide rods and used a number 7 bit to drill the holes through the bottom section into the upper section so that the holes in the upper section could be tapped for the modified shoulder bolts. This ensured that the holes in both sections would be aligned.

After cutting the sections apart, I enlarged the holes in the lower section with a 19/64" drill and then honed them with a dowel and sandpaper until the guide rods would just slip into the holes. The alignment and hole diameters worked out well and provided a close tolerance fit so that the upper section did not wobble when elevated. The lower section contains a 5/16-18 thread bolt located on the vertical center line that is used to raise the upper section and gives a 1" range of elevation adjustment.

I was concerned that threads tapped in the aluminum might wear with time, so I installed an internally threaded steel coupling with epoxy to prevent that problem. I cut a groove near the end of the bolt for a retaining ring that was captured by a steel sleeve that I installed in the upper section. For assembly, the bolt was installed into the lower section and through the upper section sleeve and the retaining ring installed on the bolt.

The end of the bolt, sleeve, and the retaining ring were slid into the upper section and the sleeve was retained by two small screws. All of this was needed to keep the upper and lower sections together, otherwise the top section would pull away from the lower section and leave the bottom section with the legs on the ground when the rifle was picked up. Unfortunately, I could not cut the groove to the precise width needed for the retaining ring because of the bolt threads.

During a function check, the retaining ring deformed and pulled off the bolt. I got another bolt and drilled and tapped the end for a 6-32 screw and used it to retain a small washer that was slightly smaller than the OD of the sleeve. This proved to be a more robust design. A plastic knob was installed on the head of the bolt.

I decided to use 0.125x2x12" aluminum plate for the front and back of the horizontal leg and sandwich 0.5" thick rectangular bar stock between those plates to give a total thickness of 0.75" as opposed to hogging out a solid piece of 0.75" plate to reduce the cost and time in making the parts. I milled out most of the center of the 0.125"

The new assembly weighs 0.80 pounds, while the initial design weighs 1.29. thick pieces and then cut out the remaining section with a hacksaw; otherwise, the part would have deformed due to the clamping force of the vise. Having a separate piece on the end of the horizontal leg made it easy to drill and tap the hole for the stud that retained the vertical leg. I bonded the pieces together with epoxy. The vertical leg is 1" channel, 6.5" long, with 0.125" wall thickness which gives an internal width of 0.75".

The rectangular bar stock had a nominal thickness of 0.50" and was 0.500" thick. The 0.125" plate actual thickness was 0.132". I milled the bar stock to 0.460" thickness so the total assembled width was 0.724" so it would fit inside the vertical leg with enough clearance to slide freely. The vertical leg is slotted on the outside and has an adjustment range of 4".

The horizontal leg has a 1/4"-20 threaded stud that extends through the slot of the vertical leg and a threaded knob is tightened on the stud to lock the vertical leg into position. I made the foot on the vertical leg from 0.5×1.0" bar stock and attached it to the vertical leg with a 1/4-20 socket head bolt. After completing one leg assembly, I weighed it and found it was 1.29 lbs. Two leg assemblies would total too heavy. Back to the drawing board.

I made anew leg assembly using 0.375x2x12" plate for the horizontal leg and 0.625" square channel with 0.125" wall thickness for the vertical leg. I milled out two sections in the horizontal leg but left a rib in the middle for support so the piece wouldn’t deflect during machining while clamped in the vise. I milled a Legs are attached to the lower section with three 1/4-20 bolts on each leg. The vertical legs may appear to be tilted slightly due to distortion in the photo.

The vertical legs may appear to be tilted slightly.

few thousandths off the thickness of the horizontal leg so the vertical leg could slide smoothly. The vertical leg is slotted on the rear as the retaining stud is threaded into the rear face of the horizontal leg. Using the same foot design, the new overall assembly weighed 0.80 lb., which was much better and it looked more appropriately sized. The vertical legs are 7.5" long and have 5" of height adjustment compare to 4" on the initial design.

The horizontal legs are bolted to the lower center section and are tilted downward 100. This required machining the end of the legs and the center rib at 100 as well to be vertical. The overall width of the bipod is 23.5". The fully assembled bipod weighs 3.30 lbs. The target was 3.0 lbs. so I got close. The total cost The plate is from SWAG Offroad (SWAGoffroad.com) and accommodates several brands of band saws.

This saw uses 0.5" wide blades that are 0.025" thick. of material was $100, including the aluminum pieces, bolts, knobs and other hardware. It does not include the cost of the aluminum for the initial leg design. To reduce the time and effort in cutting the various pieces, I purchased a portable band saw and a mounting plate that holds the band saw in a vertical position. The plate, from SWAG Offroad (SWAGoffroad.com), was clamped in my bench vise and has a foot switch to operate the saw.

The saw uses 0.5" wide, 0.025" thick blades and makes straight, smooth cuts. This setup is very solid and works well. The plate accommodates several makes and models of saws. Total cost for both was $250 and was well worth it. At the Range I installed the bipod on my .308 rifle and set up prone on the 300 yard range. The vertical legs were adjusted to get the scope on the target and the cant and fine elevation were adjusted to get the rifle level and the reticle centered on the bullseye.

The bipod was very stable and the feet made it easy to get horizontally aligned with the target. The scope ring kept the bipod securely attached to the rifle. This was an interesting project that provided hours of fun using the various tools required to do the work. AG