Building bipod spikes and black oxide finishing

You're building a what now?

Most bipods come standard with plain rubber feet. This is pretty practical in soft soil, but when shooting from a bench or some kind of wooden decking it's difficult to get a solid purchase on the ground. The rifle kinda slides around and often jumps when firing a lighter rifle, causing everything to slide off target. The solution, is a bipod-foot in the form of a spike. It may not seem like it could 'dig in' to something like a concrete surface, but it does pretty well, allowing the shooter to load the bipod (that is, put pressure against the front) for more stable shots, and faster follow-ups.

Now there aren't many aftermarket feet available for the Harris series, so I'll have to design my own. Keep reading to find out my discovery of the likely reason why there are so few of them. After the machining, I'm going to play chemist for a bit and try my new Caswell Inc. cold black-oxide kit. Black oxide is a non-dimensional finish for plain steel that makes a good looking black color, and changes the surface just enough to accept a penetrating oil and provide some corrosion protection.

Until Caswell came along black oxide solutions were usually much more caustic and had to be applied at elevated (sometimes boiling) temperatures. This new solution doesn't need to be warmed, and is very mild compared to earlier solutions. If this works out all my steel tooling bits and parts are likely to get this treatment.


Designing

First, it starts with the design in FreeCAD.
bipod spike cad drawing
Years ago I saw a design similar to this, but can't find any info or pictures of it now. It was a great idea, the only one I've seen of it's kind- don't make such a deep, narrow point on the spikes. Rather leave a straight portion the original rubber feet can slip onto. Best of both worlds! Spikes on the bench, rubber pads in the sand, and some protection to keep the spikes from poking holes in your soft case.

Lathe work

I'm feeling good about this design. I'm going to go ahead and make sets for all 3 of my bipods. So first some 1" bar gets bandsawed and faced to length.
stock prepped

Next in the lathe the top end is turned, drilled, and sent to the mill to drill the cross-hole.
drilling in lathe
ready for 5c block
Then we adjust the work-stop and change to a smaller 5C collet, and flip them around. Then it's just a matter of turning to a tight fit on the rubber pads, make a pointy bit and clean up the edges.
turned to diameter
cutting the point
Alright, here's the finished machining.
machining complete
But does the rubber pad fit on tight?
fit testing
Success! Easy enough to remove by hand, but it's not coming off by accident.

On to the finish work

I've been bead-blasting a number of round parts recently. Here are a couple small racks I threw together to support round parts in the blast cabinet. Just some dowels glued into some scrap boards.
making blast racks
View into the blast cabinet. This is being done with the milder glass-beads.
view into blast cabinet
So here are the results of that. A bit more even finish and a great surface for applying all kinds of coatings on parts, be it paint, primer, anodizing, alodining, etc.
parts bead blasted


The black oxide begins

Now for the part I've been most excited about. Putting the final finish on these parts. This is a quart of black-oxide solution, which gets mixed in a 1:9 ratio with distilled water; and the penetrating oil the parts get soaked in after.
black oxide jars
Setting up on the weld bench. While the solution doesn't need heating, from what I read online warming up the parts themselves help the solution a lot. So I'm going to use the hotplate on the left to keep the rinse water warm, that should keep the parts warm enough. In the center is a magnetic stirrer to keep the solution moving for me. It sits under a stainless (non-magnetic) riser to keep the gallon bucket that goes on top more stable.
collecting parts

The most important rule of immersion finishes

clean clean clean clean clean. You just can't get the parts clean enough. Caswell has some great powdered cleaners that, when used in boiling solutions could probably strip the flesh off bones. Thankfully I don't need anything that large or dirty cleaned up, so the spikes are getting a Simple Green and ultrasonic treatment for 20 minutes, followed by thorough rinsing.
ultrasonic bath for parts
While that runs I made some wire hangers for the parts. For this first try I'll just do two at a time. The hangers are made from aluminum, which shouldn't be reactive with the solution.
making parts hangers

Ok, here we go

After the clean and rinse, into the solution they go. The magnetic stirrer keeps the solution moving so I don't have to. Between that and warm parts, wow. Fresh solution made the spikes look like this in under a minute! As per some online reccomendations, I let it soak for a minute or two, rinse in warm water, and soak again for another minute. parts in the solution
After another rinse, here is what they look like.
fresh from the tank
Looks pretty even, and it should darken up a bit more with the oil soak. Directions say to soak or brush on the penetrating oil for 5 minutes. So I used a shorter hanger and left them to hang in the oil can. This is it! This is everything I was hoping for:
finished spike
So now all 6 are finished and sitting on the rack for the oil to drip off.
all the spikes oiled

This is great! The parts fit up great and the finish is what I wanted. No black rubs off and it doesn't scratch with a fingernail. Not sure ultimately how durable the finish will be until it get some real world testing but I'm hopeful. All that remains is to assemble these onto the bipods. Assembly, also known as:

The most likely reason Harris bipod feet are hard to find.

What follows here was the result of determination and pinched fingers. One thing led to another and by the time I was done I had pretty much dissassembled the entire bipod in an attempt to get it back together again. Ultimately it can be done but I'm still trying to come up with a clever way of making a tool to help take these apart since it's pretty tricky without one. Lets break this down a bit...

Two types of Harris

Harris bipods come in two leg designs. The first is with notches every 1/2" down the leg, so the extension is adjustable for height or uneven terrain. These pads are easy to replace as it is just the roll pin holding it together. Notched leg Harris bipods- easy swap, highly reccomend putting aftermarket spikes on the legs.

The second style is what I have, and that's with a fully adjustable leg, held in place by a thumb screw, and retractable by an internal spring that pull the legs back together when the screw is released. In practical use I'd say it's just a matter of preference. In changing bipod feet it adds some difficulty. Pulling the spring back down from above is impossible to hold in place while replacing a roll pin, so I'll have to remove each leg, install the new spike with the roll-pin holding the bottom of that spring, and then find a way to hook it up back on the other end.

First, removal of the rubber pad and its roll pin

I held the leg in a small drill press vise and an aluminum scrap helps support the pad. Some wood scraps cut to shape would work great too. removing roll pin
I actually did this part earlier just to test fit the counterbore in the first spike, to make sure the pin hole lined up. test fitting a spike
So first it's a matter of using a pin punch to remove the roll pin holding the foot on. When you pull the pin punch back out again, you'll hear a slight clunk. That's the internal spring snapping back up into the leg.
Next, I put the bipod in a vise and used vise grips to pull the main springs down and off their clips. I didn't get a picture of that, as it was quite a chore of grunting and swearing to get them off. Those springs are under a lot of tension. I have some ideas for a tool to help get it apart if I do more of these, but suffice to say clamp it good and take it slow; you don't want parts flying out of the vise or getting your fingers pinched in this spring. After that, just unbolt the legs, remove the sleeve in the leg the bolt goes through, and pull the spring out.
I removed the split ring that goes on the top of the spring, bent a hook from some 0.032" wire, and pull the spring up from the bottom through the leg.
inserting spring
This lets me put the spike on, line up the holl with the hole in the end of the leg, and then shine a light through it and turn the spring until its bottom loop lines up with the hole.
leg finally removed
Then it's a matter of putting it back together in reverse. As I said the notched-leg version of the Harris bipod is trivial- nothing need be dissassembled except removing the rubber pad and putting the spikes on. It's the ones with the spring in the leg that are difficult to take apart.

Installation complete

Another successful project. The spikes look good, work good, and the rubber pads can be used if desired in the field or just kept on to protect soft cases and rifle scabbards from getting poked by the spikes.
bipod assembled
rubber pads fit
This is my swiveling model bipod, sporting a grass/sage camo paint experiment I tried years ago.
swiveling bipod

Here we are mounted up to the rifle. mounted to rifle forend
unfolded

Well, another completed project ready for field testing. That means, like a freshly washed car or a large scheduled barbeque, it's pouring down rain for days. Updated pictures from field testing to follow when the range is less a mud pit.

So, was this project worth all the effort? Positively yes! On any hard surface, even concrete, these points let you put more forward pressure on the bipod (usually called 'loading' the bipod), providing for a more stable shot as well as preventing the rifle from jumping off target