Custom Carbon Fiber Stock Round 2

[RepeatPete]

Time for round 2. Last year I decided to build my own stock and really enjoyed the process. I’m happy with the outcome for a first build, but wanted to try again to tweak some things and build for a different application. The first stock is documented here:

https://rokslide.com/forums/threads/custom-carbon-fiber-stock.322053/

With a good deal on a Kimber from @kad11 and tons of advice and support on all things carbon fiber/stock making from @Gobber I was ready to go again.

This is the starting point: a Kimber Hunter in 6.5 Creedmoor with an 18” barrel. My goal is the perfect eastern US whitetail rifle. I have three main aspects for the stock build.

1. Shootable design: This means more vertical grip, negatively sloping comb, the top of the recoil pad above the bore line, and a forend that is parallel to the bore. This rifle will rarely, if ever, be shot with a rear bag, so I chose to keep the bottom of the buttstock on a more traditional slope.
2. Lightweight: This will be carried pretty much exclusively in my hand, so a lightweight, great balancing rifle is a high priority. The factory Kimber stock, as I bought it with the gel removed, is just at a pound and a half, which is already very lightweight and will be hard to beat. If I end up at that weight or even lighter I’ll be stoked.
3. Classic appearance: I appreciate the Rokstok for all its functionality, especially using a rear bag for more long range work, but think it’s pretty ugly. I want to make this stock very functional and easy to shoot, but also want it to look a bit more traditional. I’m envisioning something that looks like a Winchester M70 featherweight, but is lighter and has better ergonomics.

This won’t be a quick documentation, as I have only just started the foam mold, but will hopefully be complete to have sufficient trigger time before November 2024.

 

[RepeatPete]

Diving a little more into the design:

I knew I wanted a negatively sloping comb to reduce the perceived recoil. When the comb slopes down towards the action, on recoil, the stock moves away from the shooters face. It’s only a 6.5 Creedmoor, but will hopefully be very lightweight (I’m aiming for scoped with sling and 3 rounds under 6 pounds), so the recoil may be a bit snappy. I settled on the top of the recoil pad about 1/4”-3/8” above the bore axis. This worked out well for placing my cheek where it needs to be for a consistent but light cheek weld. With my crude measuring this works out to about a 7 degree comb slope. For comparison, the Rokstock is 12 degrees and 1/2” above the bore line.



For the grip, I wanted more vertical than a traditional sporter stock. I really like the feel of the wide, tightly curved trigger of the Kimber, but with the sporter stock the trigger feels awkward. The pull angle is too much diagonal up and back, instead of straight back along the axis of the rifle. A more vertical grip will help this feel better, and make the trigger pull more consistent. The grip-to-trigger distance is shorter than most stocks, matching my previous build and the Rokstok at 1.7”.



This rifle will almost exclusively be used on game at 150 yards or less, and on a steel plate for practice out to 400 yards. Because of this, i decided to keep the bottom angle of the butt at a more traditional slope (for aesthetics and weight savings) than a stock designed for longe range use with a flat toe. However, because the forend will be rested on a backpack, branch, or shooting rest often, the bottom of the forend will be parallel to the bore. On recoil, the rifle will move straight back, whereas with the tapering forend of the Kimber stock, the rifle would move back and down on recoil, making spotting shots difficult.

 

[RepeatPete]

Construction:

This will be a foam core with carbon fiber layered over the core, like my previous stock. I’ll be using plain carbon fiber sheet, as the braided sleeve didn’t conform as desired last build.

For the grip, I am planning to shape it thin, skin it with one layer of CF and then use lightweight epoxy dough to build back up a custom fit grip. The epoxy filler has a long working time and is easy to shape/sand so I can add a small palm swell and fine tune the angle and thickness. Then, I’ll probably skin it again over the hardened filler. I shaped a few sample grips out of the foam to see what works and feels best.

Two 1” layers of the green insulation board from Lowe’s were glued together with 3M spray adhesive. Then, the Kimber 84M stock profile was traced on and I played with angles to make the changes I wanted. I shortened the forend by 1 3/4” to save a little weight and correct the proportions with the 18” barrel. As mentioned earlier, the top of the recoil pad is around 1/4” - 3/8” above the bore line, and the comb slopes roughly 7 degrees towards the action.

I left the trigger guard section in the foam to approximate where the trigger lies. Once I’m happy with the shaping and contours, this will just be trimmed off. The top section of the grip is ~ 1 3/4” from the trigger to keep my tigger finger at a 90 degree angle.

Here’s where I’m at currently:

 

[RepeatPete]

Small update for the recoil pad:

I used a Microcell recoil pad on my last stock and had no complaints, so I got the 7/8” thick, extra soft version. And because I’m shooting for classic looks, I chose the “leather effect” in red. It’s listed at 2.5 oz., though I did not weigh it before modification. The website states that there are metal washers at the screw holes, so I used a spade bit to drill out some of the plastic backing pad and remove the washers underneath. I’m planning on gluing this one on anyway. Then, a bit more removal of the backing pad with a Dremel and I ended up at 2.0 oz.

Not bad for a wider and longer than stock full recoil pad at flip-flop pad weight.

 

[Gobber]

Nice looking foam core to apply the carbon fiber fabric. This one should be really cool to watch come together.

As mentioned in other posts, a good vacuum source is a salvaged refrigerator pump. Been using the same one for close to 10 years and it does a really good job for CF bagging. One items that really helps getting the vacuum bag positioned correctly is the use of a Low volume pump. The extra time it takes to begin to pull the Stretchlon tight allows for adjustments of wrinkles & repositioning of layers inside the bag.

Here is my ole faithful rig that runs like the Energizer Bunny. It will easily pull 27-28+ inHg (Full vacuum = 29.92 inHg) which makes for a very tight pull to squeeze out excess resin for a really nice CF to resin ratio. I have imploded a few projects with it which were good lessons learned.





I made the carrier out of extra 3/8 plywood and salvaged the power cord and rubber mounts from the original unit.

The black part between the gauge and pin valve with wires coming out is a variable vacuum shutoff switch. It can be dialed in to a 5 inHg range and will cut the pump on and off to maintain that specific vacuum. Turns out it's not needed with this pump as the unit can easily run 100% of the time for a 24+ hours.

What is needed for the plumbing is the gauge, pin valve, and filter to keep any possible crud or resin droplets from getting into the pump. The brass fittings and tubing are from Home Depot.

The pin valve is what I use to control the vacuum level. Simply use it to introduce a controlled leak in the system and it holds steady for as long as the cure time takes.

Good thing about a vacuum setup is that the pressure is negative, meaning it pulls the fittings and surfaces inward. Much easier to patch and seal than a positive pressure setup.

If you want to set one of these up, I highly recommend finding a pump unit from an older fridge that is as big of a unit as you can find. Smaller fridge pumps will work, but don't have the constant run time capability as the older ones. Smaller units will also shut off after running for a few hours straight due to a thermal shutoff in the small black control box to the side. PRO-TIP: A small shot of canned air held upside down will put liquid propellant on the control switch to get it running again. These vacuum rigs are used extensively in the RC Glider community with excellent results. That is one ingenious and thrifty group!

 

[Stearinlys]

View attachment 702943

Really looking forward to watching this come together. I have a question though about that scallop. Once you fire, will there be a tendency for the stock to deflect to the right since that left side looks like it has more straight line support? Or will it be a non issue with the foam core being wrapped in carbon?

 

[RepeatPete]

Great question - I think deflection will be very minimal due to the final strength of the CF over foam core construction.
However, as I’ve been tweaking the grip shape and the relief behind the grip I found that the shape I like comes right up to the centerline, but doesn’t cross over. So, I’m going to mirror the scallop on the other side so my lefty brother can shoot it occasionally too. If there is any deflection/bending it should be uniform side-to-side.

 

[RepeatPete]

Inletting:
Because the Kimber action has a round bottom, I’m using a carbon fiber tube as the foundation for the inletting section of the stock. The Kimber action is 1.14” in diameter, which is 28.956 mm. 29mm ID/32mm OD carbon fiber tube is readily available, so I ordered some from Amazon.

After cutting to length, cutting in half lengthwise, drilling holes for the action screws, and filing slots for the recoil slot and trigger:






Next, I ordered a blind magazine box, spring, and follower from Kimber. Easy transaction, no Montana or Mountain Ascent serial number needed. I extended the magazine with a piece of foam and wrapped with three layers of thick, rubberized tape to create clearance, then wrapped with carbon fiber. After curing, I sanded a radius in the top and mated it to the CF tube.



Then a final CF iteration to make a floor for the magazine well.




The CF tube fit on the action is perfect. I left it big to accommodate for final sanding, currently at a little over half of the tube diameter, so it snaps into place beautifully on the receiver. The magwell has enough room for the magazine to float a little and, while the CF layup isn’t pretty, it is plenty rigid while remaining lightweight. Pretty happy with it at this point, and creating the exact dimensions and mating surfaces needed was way easier than I expected. I got a decent set of needle files to slowly and precisely take away material, and just broke it down in simple steps.