The AirGun Guild

General Category => Long Range Shooting with Airguns => Topic started by: rcpro88 on April 03, 2018, 02:12:38 PM

Title: .308 Texan Exoskeleton Stock
Post by: rcpro88 on April 03, 2018, 02:12:38 PM
Hey Guys,

A month or so ago I made a titanium barrel tensioning system for my .308 Texan. When in my friends benchrest style gun rest, the Texan with the new tensioner shot a 10 shot group at 130 yards with 8 shots grouping 3/4" CTC and 2 fliers (which if included with the 8 shot group, it would have made it a 1.2" group). Then when I went to a range another day shooting off a bipod, I was getting significantly larger groups/grouped like stock. Since I never shot the stock Texan from my friends gun rest I have no data to compare my barrel tensioner too. So for now the results are inconclusive.

Digging around a little more I found that there have been a significant amount of comments/reviews that criticize Airforce guns for having hold sensitivity. This comes from the apparent flex in the aluminum receiver by the spot where the bottle meets the receiver. Then when the air rifle is shouldered, the torque put on the end of the bottle from your shoulder changes the direction the barrel points (slightly) relative to the scope. Originally I didn't really believe it, but combined with reviews made by reputable sources, modifications like wokgaurd and more famously mad dog stocks have actually given proven results. On top of reviews I find it suspicious that my Texan grouped poorly on a bipod but very well in a heavy benchrest gun rest (lined the Texan up, loaded it, pulled the trigger while standing to the side of the Texan) which virtually eliminated shooter error/held the gun the same every time.

So from here I decided to build a stock for my Texan.
Title: Re: .308 Texan Exoskeleton Stock
Post by: rcpro88 on April 03, 2018, 02:52:28 PM
The stock is not yet done! I will explain my design.
Once complete, I will test for improvements, then I plan on "jeweling" her up. I will also mill out a lot of aluminum to save weight but maintain rigidity - hence the "exoskeleton" part.
My design is solely for long range shooting. I want a rifle to be as steady as it would be in a benchrest gun rest but be a hell of a lot more portable as well as built into the Texan so I wouldn't have tons of shit to deal with.
The stock in the pictures is 2 pieces. They screw together and clamp against the lower 11mm dovetail that runs the whole length of the receiver. Getting this fit perfect was my first big task as I wanted the two halves to clamp tightly against the dovetail but not leave a gap between the two halves. I'm designing the stock to fit on any Texan without modification required to the Texan - figured it might have a market if it turns out as expected.   

I have a custom bi-pod I am building for it. The front of the stock has this block towards the end. There is a 3/4" hole drilled through it which allows a titanium tube to slide in and out of the stock/rotate. This will allow me to move the bipod past the end of the receiver as well as allows the Texan to "roll" left and right when the tube is unlocked. Moving the bipod past the end of the receiver moves the pivot point out which means more input in the rear of the Texan is required to move the muzzle of the barrel - making a more stable platform for long range shooting. Each feet will both have fine and coarse length adjustments.

I also plan on making a monopod. The monopod will be able to slide on 2 tubes (when unlocked) to move closer/further from the shoulder rest. These are the same titanium tubes that are used to connect the shoulder rest to the Texan receiver. The foot will be fine threaded but will also have a coarse high adjustment as well.

The shoulder rest will be adjustable (in and out relative to the trigger). That is what the titanium tubes are for ( I was holding it in place in the picture). The shoulder rest will be mounted to the end of the tubes and the tubes will slide into their respective holes in the receiver. This will take all torque off the bottle and hopefully fix hold sensitivity issue.

Title: Re: .308 Texan Exoskeleton Stock
Post by: adijorio on April 07, 2018, 08:20:34 AM
I was really hoping someone would attempt creating a stock like this, as the Maddog just don’t do it for me.  Please keep us updated.
Title: Re: .308 Texan Exoskeleton Stock
Post by: rcpro88 on April 07, 2018, 04:19:12 PM
Making this stock is a slow process. I keep changing the design slightly and progress has been slow since I don't want to ruin the work I've already done.
I haven't ever seen a mad dog stock in person. I've heard good things about them but for their price tag I think I'd rather make my own. Honestly, the mad dog stock I've seen for the Texans kinda makes the overall gun look like 2 guns smashed together and doesn't have a natural/fluid connection/transition between the two which would make the Texan appear it came with the stock off the shelf... That's just my personal opinion!

I made these changes:
The bi-pod system I designed will not be part of the stock. I still plan on making the design but making a whole bi-pod system on top of the rest of the new stock components would take up more time than I have right now. Also making the bi-pod system separate from the new stock will remove a significant amount of weight, so when hunting it can be removed etc.

Instead of going from 2 titanium tubes to hold the shoulder rest/mono-pod, I am going with a single titanium rod that will be mounted to the opposite side of the Texan the charging handle is on. This is partially due to simplifying a significantly more difficult to produce design to something easier as well as better ergonomics. Of course if you are a left handed shooter the assembly would be mounted to the side the charging handle is on.

The trigger guard/mount for ar-15 grip will be milled out of a single piece of aluminum and bolted to the bottom of the new stock.
Title: Re: .308 Texan Exoskeleton Stock
Post by: rcpro88 on May 01, 2018, 11:24:29 PM
Have been busy with some other stuff, however, I have made a final decision on the design and here is my progress so far.

After test fitting all the possible ways to add a collapsible stock via titanium rod or tubes I found that the design would be useless as I don't plan on taking the tank off the Texan often as I store the Texan in a hard case in one piece, as well it would make the overall width of the Texan wider than the bottle (too wide for my case).

I decided the best way would be to use a single piece of titanium. It would have been much easier to make this out of aluminum but I'm not too confident the aluminium wouldn't flex as it would have to very little aluminum to make the design work.
The new design will lower the AR-15 grip 1.75 mm.
There will be an aluminum block that comprises the adjustable shoulder rest and mono pod.
The AR-15 grip mount/trigger guard will be milled from a piece of aluminum that will be bolted to the titanium part of the stock.
I still plan on cleaning up the stock, removing weight etc.
Title: Re: .308 Texan Exoskeleton Stock
Post by: adijorio on May 02, 2018, 07:49:43 AM
Nice. That's really coming along.
Title: Re: .308 Texan Exoskeleton Stock
Post by: Briar Patch on May 02, 2018, 08:37:15 PM
  I enjoy seeing you guys coming up with ideas on ways to improve your guns, and then creating components, refiguring them and then refining them. Just a fun process to watch.
Title: Re: .308 Texan Exoskeleton Stock
Post by: yemx on June 21, 2018, 02:55:35 PM
Very nice!!!
Title: Re: .308 Texan Exoskeleton Stock
Post by: Alan on June 21, 2018, 03:02:14 PM
I'm too old to start, but instead of taking 3 years of woodworking in high school, maybe I should have taken shop! I am jealous!
Title: Re: .308 Texan Exoskeleton Stock
Post by: rcpro88 on September 05, 2018, 04:41:51 PM
I am still working on the Texan. I have made no more progress as I have moved to a new house and not been able to setup my mini machine shop in the garage to extent i'd need.
Title: Re: .308 Texan Exoskeleton Stock
Post by: steveoh on June 17, 2019, 08:23:24 AM
I am still working on the Texan. I have made no more progress as I have moved to a new house and not been able to setup my mini machine shop in the garage to extent i'd need.

Any update on your Texan? I am curious.
Title: Re: .308 Texan Exoskeleton Stock
Post by: rcpro88 on March 03, 2020, 05:21:53 PM
Yes, I have made some progress on this. The piece of titanium once milled out to contour the tank, developed a bow due to internal stresses after machining. I tried to prevent this by machining material off both sides but still didn't workout. I designed the part to sit 0.05 mm under the tank so there was very little tolerance from the start. The part would not fit because of the bow and the design got scrapped. I have started from scratch. This design isn't going to clamp onto the Texans frame/dovetail like the original design did. Frankly, it might be ideal but I don't think the Texan needs that much reinforcement. The stock merely needs to take the load off the air tank and add some more rigidity where the tank meets the frame.
The new stock will screw to the Texans frame via threaded holes that are already there and will be made from a solid piece of 7075 aluminium - 1" thick, 5" wide and 24" long. I have the aluminium stock, I just need to change my CAD drawings as I have some areas which would be impossible to machine. The stock will have the profile of the Maddog RJ-9A Ranger stock - as in the shoulder rest will come off the bottom of the grip. Unfortunately, I won't be able to use the AR-15 grip I have but the nice part about CNC is that I can mill a similar grip in aluminium as part of the stock.
I would have just gone with the maddog RJ-9A Ranger stock, but they want around $450 for a piece of molded plastic. Frankly, the maddog stocks look too beefy and don't blend in with the Texan. Which I get, the stock has to be beefy because plastic is only so strong and they need the material there for rigidity.
Title: Re: .308 Texan Exoskeleton Stock
Post by: steveoh on March 03, 2020, 05:27:36 PM
My Maddog stock is made of wood that is coated in Bed Liner. I think the wood is poplar.
Title: Re: .308 Texan Exoskeleton Stock
Post by: rcpro88 on March 03, 2020, 05:53:47 PM
Oh god, I wonder why they went with poplar. I was contemplating making a stock from oak as it would be pretty easy to make a rough stock and shape with hand tools. I did find a post of someone making their own stock for the Texan out of wood which ended up cracking and took several iterations before a usable one was actually made. I'd probably go the layered laminated route as I love the way those stocks look but they are heavy and I don't have much experience with making them.
I'm really surprised they are made from wood, I guess they have a CNC router to form the general shape, then hand finish. Probably covered with the truck bed liner for ease of production to hide any cosmetic flaws made during manufacturing. Maybe they inlay some metal to increase strength? Who knows. I guess the company is pretty small so making it out of injection molded plastic might not be in the realm of possibility for that small of a scale.
Title: Re: .308 Texan Exoskeleton Stock
Post by: Loren on March 04, 2020, 04:31:28 AM
Probably popular because it is easy to work, not really expensive, and makes for decent material as far as weight and strength.  Last I seen, Mad Dog, uses a duplicator, and no CNC  equipment and yes small, as in home based shop.  A cool gig for them!!

Here is my DIY stock made from birch. 


I do have the itch to make another one out of walnut and lighten it up some. 
Title: Re: .308 Texan Exoskeleton Stock
Post by: steveoh on March 04, 2020, 07:07:37 AM
I greatly admire the aesthetics of your homemade stock and the leather sleeve over your bottle. Makes your Texan very personal and way more functional to boot.

Then there are your SCBA bags! Amazing quality and utility and once again the esthetics blow me away. Oh the camo!
Title: Re: .308 Texan Exoskeleton Stock
Post by: Loren on March 04, 2020, 01:42:14 PM
Thanks Steve!  I have been blessed with "The Knack"
Title: Re: .308 Texan Exoskeleton Stock
Post by: T3PRanchAGS on April 10, 2020, 04:23:10 PM
The Mad Dog Texan Stock is poplar because of light weight but it has a hard maple area in the center section to "toughen" it up.
Title: Re: .308 Texan Exoskeleton Stock
Post by: d_boom on April 19, 2020, 07:16:08 AM
I have been privileged to visit Mad Dog Stocks, as we both live in Wichita, Ks.  I am impressed with his operation.
The stocks are glued together for strength and light weight.  My condor has a Mad Dog benchrest stock which helps
stiffen the frame.  When I place my cheek on the air bottle, if I am not careful, I spring the frame and my shots go
wide.  Mad Dog stocks have an addition to help.  A "C" shaped aluminum cover attaching to the stock covering the
air tank, then your cheek rests on the cover not the tank.  I need to get one!