Home Forums Hunting & Shooting Gunsmithing What to use to stiffen a fiberglass stock fore-arm

More effective than embedding an arrow might be to open up the barrel channel (only a skin cut) just enough to apply a layer of carbon fiber tow set in epoxy resin, creating a large CF channel.

Also heavier for the same stiffness, which is why the structural forms. But it's a compromise, a tapered foam core carbon fiber box beam would be close to ideal, depending, but overkill. So whichever solution works for you.

Two shafts firmly fastened together, stacked vertically, have significantly more than twice the stiffness of one shaft for up and down deflection. Remember that you're making a lever arm and force multiplies towards the breech so if you can run stacked shafts part way from the breech end and one shaft the rest of the way you're still ahead.

Of course it depends on how stiff you want the forearm, how much additional weight you will tolerate, and how much effort you want to put into it. Engineering is an art of compromise.

Jeff, you can use aluminum with no worries and it will work fine. Get a dremel and remove just enough material to allow for Devcon bedding all around and on top of the shaft. Tape off where you don't want bedding and after cured sand off where you need to.

good luck.

A tube is a good idea in my opinion and lighter than threaded rod, I used a piece of 3/8" steel fuel line to stiffen my Steven's.

Auto parts stores will have short lengths of brake line that will work too.

Pultruded unidirectional carbon fiber rod provides the best stiffness to weight I've found. www.graphitestore.com sells rod, square and tube. The 3/8" rod in 6" length deflects less than 0.055 with 300lbs on it. 3 times the stiffness (Youngs modulus of steel). Been using 3/8" in barrel channel and 3 slots with 1/8" at the front action screw for years. It is just the ticket for the old non reinforced ABS Steyr stocks and any other non-woven or reinforced plastic stocks. Make sure you choose you adhesive wisely for the material you're bonding. BTW had a customers forend bend 3/8 " all thread, but not Solid carbon fiber rod.

Stiff yes, and 37.00 +/- per foot plus shipping.

These guys are excellent:
http://www.goodwinds.com/goodwinds/merch/list.shtml?cat=carbon.pultrudedcarbon

I bookmarked that for future use- thanks!

I went ahead and milled a channel and glued in some arrow shaft and got it back together last night. It's noticeably better. I'm going to shoot the damn thing and see if it even likes being floated-- it shoots great with a pressure point-- and if it does, re-bed it AGAIN to get more barrel clearance, rather than sanding any deeper into the stock.

Thanks mucho for the help and suggestions, guys!

I used a piece of an old fishing rod that I bet was carbon fiber (Ugly Stick) I used Brownells acruglass(not the gel) to cement it in,then I mixed up the acruglass with plastic BB' used in air soft guns to fill the remaining voids in the barrel channel.That kept the weight down vs soild epoxy.

Good idea, and fairly light. To keep it even lighter, use Microbaloons (hollow glass spheres) to minimize weight.



Brownells' has this (or used to, anyway). Easily found at any epoxy-oriented shop.

WARNING: These microballoons (especially the thin-walled white ones as opposed to the more common grayish ones which are slightly heavier) are SO light that just looking at them sideways will cause them to take flight and go into your lungs. Wear a respirator if you EVER work with microballoons of any sort!

John

Microballoons make a very lightweight, easy to sand, but WEAK mixture.

Good point.

I should have mentioned that this is not as strong as pure epoxy -- which is why you would only use a microballoon/epoxy mixture to fill gaps around your super strong carbon fiber arrow shaft -- and even then ONLY if you had a huge channel to fill and the weight of pure epoxy was a problem.

Mostly I use the microballoons to create cheekpieces on stocks which do not come with them, a Wundhammer swell on one side of a pistol grip, to raise a comb a small amount, etc.

John

Weak, yes, you're essentially making an epoxy foam with you choosing the density. Usual advice for a non-structural filler is to add microballoons until you reach the consistency of peanut butter, something like six parts balloons to one part epoxy but the ratio varies. Dust mask is mandatory, the lung disease silicosis - hard rock miner's disease - is very nasty.

I should have added that a strong, gap-filling mixture can be made by adding coloidal silica, as a thickener (like adding cornstarch to make gravy), then adding microfibers until the mixture no longer sags/runs.

This makes an extremely tough, tenacious and long lasting, but resilient, gap-filling glue when W.E.S.T. epoxy is used. Mating surfaces should be roughed up for best adhesion. It can be tinted with various specialized products which slightly reduce its mechanical properties. A very nice black mixture can be made by adding a tiny amount of powdered graphite.

Edit to add: If you have a huge channel to fill, a larger CF tube (or group of bonded CF tubes) should be used.

I can tell you that I have tried several of the 2 part fillers and epoxies. Most didn't work as it was a very expensive to fill a large void, or too heavy, took to long to set up.

So far my best fix has been fiber glas rods with some 2 part epoxie.

I tried steel rods. It would have worked, I think. But, It was polished and I didn't degease it.

Pal, epoxy and cotton floc makes an extremely strong and very abrasive resistant mixture but is heavy. I used it on the end of a paddle mainly used to push off rocky bottoms and no damage after years of abuse. Also on the parts of a small boat that bang into rocks and get dragged across stuff, very resilient. Not much application for stocks though.

A quick report.... I shot the rifle today. The fore-arm is still disturbingly flexy but, it did shoot well. Seemed fine off the bipod as well as a bag.

The B&C Ultralight "mountain rifle" stock is quite flexible... much more than I'd have thought, and much more so than my Kimber MT stock. On the positive side it is light at, if memory serves, 22 oz and it's cheap at $230.

If it continues to function satisfactorily I will probably try to disengage the gears of obsession and roll with it as my mulie backup this year. It's getting late in the year to keep dicking around...... If I just can't help myself I'm gonna mill some more slots and glue in graphite rods or rectangles per the suggestions here.

Best thing I have found is carbon fiber sheet. You hog out the forend a ways, mix in some resin that is heavily thickened with glass beads and overlay one or two layers of carbon fiber sheet cut to fit over it. I then put two layers of 10 mil pipe wrap down the barrel and bed the whole thing. It will be as stiff as a honeymooner's, well you get the picture.

Do the glass balloons have a stiffening function, or are they to lighten the mixture, or what?

The glass baloons make the mixture thicker so it is less runny and thus easier to work with (and much lighter), but the balloons DO weaken the set epoxy.

I only use the balloons when weight is of primary importance and little real strength is required (e.g. an added cheekpiece -- but even then I put a layer of pure epoxy on top to provide a stronger surface).

John