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General Category => Long Range Shooting with Airguns => Topic started by: rcpro88 on March 07, 2018, 08:48:33 PM

Title: .308 Texan titanium barrel tension
Post by: rcpro88 on March 07, 2018, 08:48:33 PM
Hey guys,

I've been working on a barrel tensioning system for my .308 texan. I already have the muzzle brake/tensioning nut made as well as the retaining cup and all I have to do is cut the titanium tube to length and mount it in the Texan. I hope to have it finished by Friday.
I have an autocad drawing of what it kind of looks like. I tried attaching actual pictures of what I have done but the file size was too large and I was unable to post them.
The end of the barrel is threaded with 5/8-24 threads and the retaining cup that will hold the high pressure/thrust from the titanium tube is a stainless steel 316 split ring that gets held together when the retaining cup is press fitted over.
I hope this project will improve my Texans accuracy and maybe others can learn from my accomplishment/failure if anything.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 12:20:42 AM
Well I actually finished it sooner. I still need to finish up a few more small things but I shot the texan 3 times and none hit the muzzle brake exit, so I think all will be good to test soon.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 12:41:06 AM
Starting from top to bottom, these are picture descriptions.

1. Split retaining ring - I made a ring made out of 316 stainless steel on my lathe with an OD of 0.8" and an ID of 0.60 and a thickness of .170". I cut a groove to match in the barrel. After I turned the ring on the lathe, I used a dremel to cut it in half, didn't really cut straight but it'll get her done.

2. This is the retaining cup. It has an OD of 1.03" with a through hole of .671" and a .170" deep recess with a ID of .795" and a shoulder on the other of the retaining cup that has an OD of .895" that the titanium tube sits snugly on. It is crucial that when the split ring is on the barrel, the fit between the retaining cup and the split ring is press fit, this ensures no separation of the split ring halve when I go to torque this puppy down.

3. Threaded the last 1.5" or so of barrel with a 5/8-24 thread

4. This is the barrel assembly without the titanium tube. The retaining cup is pressed onto the split ring halves and the muzzle brake/tension nut is screwed on 7/10ths of the way.

5. This is the complete barrel assembly with the titanium tube in place.

6. This is the retaining cup when the titanium tube is in place. I had to sand the barrel down a tad. There were slight burs left from machining as well as those left from the set screws prevented my .671" ID retaining cup to slide on. I smoothed it out with some 320 grit on the lathe.

7. This is the muzzle brake/tension nut. I put a long hex key through the holes in the muzzle brake and crank it tight.

8. Another picture of the muzzle brake and barrel assembly.

9. The whole thing. Yes the .308 Texan fits in my hard case with tank and new barrel on with an inch or two to spare.   
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 01:12:57 AM
A few things I need to do are:
1. The retaining cup needs holes drilled to allow the set screws to prevent lateral impact movement. Simply pressing up against the titanium tube/aluminum retaining cup will not be sufficient.
2. Make the barrel tension nut separate from the muzzle brake or silencer. This way if switching between an airstripper/silencer/muzzle brake you don't put more wear on the barrel threads.

A few things I've noticed:
1. The new barrel assembly has some weight. Not much, but its noticeable. I will say it seemed to have actually helped steadying when aiming the rifle off hand. The weight is added towards to center and front of the Texan. It could just be me as well.
2. The muzzle brake I made actually worked. When dryfiring a 3000psi fill, the felt recoil with and without the muzzle brake is what you'd expect from any other brake/shroud. The noise is reduced slightly but no where near the dB level of the Texan with an R&L shroud.

Why did i pick a titanium tube?
My local metal supply (Shapiro) stocks some titanium. When looking at buying options of carbon fiber online, I wasn't really sure if I would be getting the quality I'm expecting. Honestly, titanium was just the easier route as I also already knew how I could/can't machine it. 

Tension vs sleeves
When I see carbon fiber barrels, they are generally a carbon fiber tube, pressed and epoxied on and might be repeated a few times to layer up. In this application, you increasing the stiffness/rigidity of the barrel as you are adding more material to the outside as well as using a material that is much more stiff/rigid than the barrel, enhancing overall stiffness/rigidity of the barrel. The reason carbon fiber is often used here over titanium is because of its more stiff/rigid than titanium. However I do not mean to say that you cannot/will never see a carbon fiber tube used in a barrel tension setup.

When a barrel is placed under tension, it not only aids stiffness/rigidity to the barrel but reduces the amplitude of harmonic vibrations/increases their frequency. This is true for whenever you add/remove material/weight to and from your barrel. However this effect is amplified significantly when compared additional weight when internal forces are acting on the barrel/when it is under tension.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 01:23:10 AM
Why I think the Texan has a few hiccups:
When you can't free float a barrel you use a heavy one. The .308 Texan barrel is supported in the center of the rifle with 2 bushings which allow the barrel to vibrate like a tuning fork when shot.

The R&L shroud provides support to the end of the barrel from the body of the Texan. as you screw on the shroud you apply pressure to the end of the barrel which explains why it might be helping the .308 Texans accuracy issue.
Just one last thing, Matt @ R&L is the man to go to for all Airforce questions/ammo/advice. Matt has been a great help and source of GOOD information and advice.
Title: Re: .308 Texan titanium barrel tension
Post by: Christopher on March 08, 2018, 02:45:42 AM
That looks great on your Texan..... looking forward to the accuracy results. How was your Texan shooting before the tensioning system?

Thanks,
Chris
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 08, 2018, 08:34:42 AM
Very nice work.... If I understand your tensioner correctly, it tensions only the part of the barrel forward of the frame of the Texan?.... Is there any additional support for the assembly to reduce flex at that point?.... I would assume that the Texan barrel is either steel or CrMoly?.... Titanium has a thermal coefficient about 70% that of steel, so as you increase the temperature you will have less tension on the barrel.... This can have a large effect on the axial load (tension) on the barrel.... Are you torqueing the "nut" to provide a consistent tension, and if so, what is the approximate tension/torque you are using?....

Bob
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 02:17:46 PM
The way the Texans are designed makes it very tricky to tension the whole barrel. I don't think having the whole barrel under tension would make much more difference as you mainly want to support/control the muzzle end of the barrel.
This barrel tension system tensions the barrel from where the original rear barrel bushing was to the muzzle of the barrel (about 21 inches).

As of right now the nut/muzzle brake that provide tension on the barrel when tightened is just one piece with no counter nut or beveled washers, it will be replaced soon.
As for the thermal properties of the titanium vs steel, this would matter significantly more if this was a firearm in which the barrel heats up after a few shots, from what I've experienced, I can shoot 50 shots through the Texan, grab the barrel and it won't feel any warmer than it did before the shots.

As far as barrel tension changing in various external temperature, such as tightening the tension nut inside then going outside in the cold to shoot - there might be a significant change in barrel tension, I haven't tested it out yet.

My plan is to use beveled washers to provide constant tension on the barrel regardless of temperature.

Last night I tightened the muzzle brake to around 90 ft-lbs which should put around 1200-1500 lbs of tension on the barrel.
 
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 02:40:05 PM
Airforce claims the .308 Texan will shoot a 1" group at 100 yards out of the box. I would normally shoot 200 yards with the Texan, I would get anywhere from 4 inch - 6 inch groups at 200 yards with various types of pellets. I never really spent a lot of time shooting 100 yards with the Texan before so I can't really compare my results today with past results.

Today I took the Texan to a 100 yard range and it shot consistent 1.2" 10 shot groups BUT if you were to remove the 1-2 fliers the 8-9 other shots were all touching/overlapping with a group size right around 0.75". I believe the groups can get better and well I'm also not a perfect shot either, I would try to put the cross hairs on the bulls eye every time but there was a guy shooting next to me with a loud gun and honestly I would jump sometimes when he shot which would effect my shot of course.
This is gear I was using: 
.308 Texan
Primary Arms 4-16 zoom scope (should probably be upgraded)
$30 scope rings (no i did not lap them either, shame on me)
115 grain High Arc pellets

I used a scuba tank to refill the Texan. I don't have a regulator yet so I would fill to 3000psi, take two shots, refill to 3000 psi and so on.
I have the Texan power wheel all the way turned up. Matt at R&L told me the High Arc pellets like to be shot around 930-950 fps. I didn't chrono the gun yet with the High Arcs yet but I'm pretty sure a few of them cracked, so chances are they are moving around 1000-1100 fps.
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 08, 2018, 03:35:33 PM
PCP barrels actually get colder when you shoot from the expanding air, but the effect is rather minor compared to the swings in external temperature between freezing conditions and desert heat.... The Belleville (cup/spring) washers will provide a huge reduction in the percent change in tension when the external temperature changes.... I use them in my tensioned barrels for that reason.... Your tensioning setup will greatly increase the stiffness of the barrel itself, reducing the harmonics.... However, the rather thin, weak area where the assembly meets the receiver will still allow the primary frequency a lot of freedom of movement.... by that I mean the end of the barrel moving relative to the receiver.... The only way around that is to take the loads from the shroud into the receiver somehow, like by sliding it over a turned stub on the receiver, and using the receiver as part of the tensioning system.... not an easy thing to retrofit....

Bob
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 08, 2018, 04:58:11 PM
Bob,

The barrel assembly slides 8 or so inches into the receiver and 8 set screws hold it in place. The rear set of 4 set screws seat against the aluminum retaining cup and the other 4 seat against the titanium tube, there is actually a 9th screw which is on the bottom at the very end of the receiver. I plan on drilling a few holes in the retaining cup so the screws are actually seated in a 1/4" into the aluminum to prevent any impact type movement/shock.

I plan on swapping out the stock hammer with a brass one (I haven't settled on a weight for it but it will be heavier than stock)
I also plan on filling the gun to 3500 psi, if the heavy hammer has issues, I'll see about a slightly heavier spring.
Goal with the power increase is to shoot longer ranges/have a flatter trajectory as well as the ability to use spitzer rounds once pellets are flying mach.

I just ordered these pellets:
Hunters Supply - 154 grain SP
High Arc - TAWA 115 grain HP
Aeromagnum - Stinger 109 grain HP (these were $25 for 50! but reviews for the .357 version makes me optimistic)

I will also go ahead and order some belleville washers and machine a new tension nut and locking nut as well. I might even have time to make an airstripper attachment as well. I also want to build a titanium bipod (I have a good bit of titanium in my basement) as the one I currently have is a $45 POS.

Also I will probably get a new scope, this one seems like it will fit the bill without breaking the bank.
Mueller 8-32x44
https://www.amazon.com/Mueller-Tactical-8-32x44-Focus-Reticle/dp/B00MQUCBFE/ref=pd_sbs_200_1?_encoding=UTF8&pd_rd_i=B00MQUCBFE&pd_rd_r=BZMPX21JY3RQG0EK656N&pd_rd_w=fibXg&pd_rd_wg=j7ws1&psc=1&refRID=BZMPX21JY3RQG0EK656N
Title: Re: .308 Texan titanium barrel tension
Post by: Steelhead on March 09, 2018, 07:11:35 AM
As a .308 Texan owner I'm watching this thread very closely. While I am a Neanderthal among geniuses on this topic, I'm just glad that another person out there is working on the .308. Most info, mods,  and tuning is centered on the .45 so this is very cool. I'm learning a lot so thank you.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 09, 2018, 10:49:32 AM
No problem! A big thing I've learned from reading things on forums is to take it with a grain of salt. I try to post accurate information but not everyone is like me.
Also if you need help with .308 Texan problems, give Matt at R&L a call, he personally owns a .308 Texan and has shot many, so if you have a problem, contact him as he has shot many .308 Texans so he knows what they should and shouldn't be doing.
Also keep in mind that a poor scope can leave you chasing your tail trying to find out what's wrong with your .308 Texan - either try a friends good scope or buy a good one, if the gun shoots the same then return the scope if you don't need it.
Title: Re: .308 Texan titanium barrel tension
Post by: Steelhead on March 09, 2018, 02:02:12 PM
I've gotten mine to what I consider satisfactory. I've got 1"/touching groups at 100 and 2.5" to 3" groups at 200. But that took a lot of work and trial and error. Out of the box it sucks...it needs to be played with and IMO a Mad Dog stock to stiffen it up.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 09, 2018, 03:59:50 PM
Did you get 1" groups at 100 yards before or after the mad dog stock? I don't see how it would tighten groups unless it aided in ergonomics which then would be dependent on the shooter.
Since people are viewing this page to checkout mods/tips with the .308 Texan, care to share what "tinkering" you did with yours to tighten group up?
Title: Re: .308 Texan titanium barrel tension
Post by: Steelhead on March 09, 2018, 05:50:25 PM
The stock helped a lot...whether it be ergo or mechanical. Right now I'm running full power on the wheel. There's a thread in Big Bore I think about what my shot string was with a medium tune. I spent money on the AAO upgrade springs and they are still sitting in hobby room. Airforce told me to turn the tune all of the way up and then I started getting results. At one point I also had severe lead fouling.

So to get back to your original point of whether the stock helped or not, it was hard to tell what was helping what because I was solving multiple issues at the same time. But now if ain't broke, don't fix it.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 10, 2018, 01:30:54 AM
I polished up the titanium tube and muzzle brake...
I also drilled holes for the set screws to seat into.
I went ahead an made a new hammer out of brass, around 20 grams heavier than stock. After one shot with the tank filled to 2900 psi, the tank read 2400 psi...thats about 1/3 of a larger drop then I'd get with the stock hammer.
I plan on running the Texan at 3500 psi but i'll mess with pressure, ammo weight and see what speeds I can get out of it.
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 10, 2018, 08:15:55 AM
A 500 psi drop in pressure in one shot indicates that most of the air is going out the muzzle long after the bullet has departed.... Just because it's loud, doesn't mean it has any more velocity.... I would strongly suggest that you try all possible power settings and do a simple graph of velocity vs. setting, like this....

(http://i378.photobucket.com/albums/oo221/rsterne/Hayabusa%20PCP/Hayabusa%20457%20Maximums_zpslzyinfjj.jpg) (http://s378.photobucket.com/user/rsterne/media/Hayabusa%20PCP/Hayabusa%20457%20Maximums_zpslzyinfjj.jpg.html)

You will note that once you reach a certain hammer spring preload (power setting) you don't get any more velocity, all you do is waste air.... You only need to shoot a shot or two at each power setting to find where the plateau starts.... There is no point in using even that power setting, as dropping the velocity back about 3% from there will use half the air....

Bob
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 11, 2018, 10:17:48 AM
Bob,

The new hammer actually weighs 24.63 grams more than the stock hammer. It is also significantly longer which I believe is actually tad too long and I plan on trimming the new hammer to size once I get my scuba tank refilled/ammo comes in. I'm buying a chronograph today from cabelas and I understand the point of diminishing returns when it comes to how much air consumed per shot, I will test/tune accordingly. Keep in mind I plan on filling the Texan to 3500 psi, so it might not drop as much at higher psi.
I will of course take my chrono to the range when I test accuracy again with different ammo/modifications to barrel assembly and will post my findings on here.

Admittedly, I did make a mistake on my previous post. When I went to the range the first time with the new tension setup, the tension nut/muzzle brake was only torqued to 30 ft-lbs and not 90 ft-lbs. I now have it torqued to 90 ft-lbs, I'll double check it at the range before I start shooting.   
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 11, 2018, 12:10:47 PM
You might be interested in how much tension you are applying to the barrel at 90 ft.lb. (1080 in.lb.)... 8640 lbs....  :o

https://www.engineersedge.com/calculators/torque_calc.htm

Tom at American Air Arms uses a tensioned barrel, and finds that the group size shrinks dramatically at about 800 lbs. of tension (80 in.lb. of torque), and after that changes little.... It will be interesting to see what you find.... You will not be able to find Belleville washers that don't compress completely flat at much over 1500 lbs. of force, unless you stack about 6 of them in parallel (nested).... My tensioned barrels use Bellevilles that go completely flat at 1300 lbs. of force, I use five in series to allow a larger temperature range without affecting the tension so much.... Did you do a buckling calculation on the Titanium tube to see what happens at that huge compression load?.... Mind you, I guess it didn't collapse or you would have noticed it....   should not be an issue....  ;)

Bob

Title: Re: .308 Texan titanium barrel tension
Post by: Monkeydad1969 on March 11, 2018, 09:32:27 PM
Wow rcpro88, all I can say is wow.  Looks good.

Joe
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 12, 2018, 04:08:21 PM
Monkeydad,

Thanks very much for the compliment!

An update on the chrono tests:
I got my order of 250 pellets from Hunters Supply yesterday (154 grain SP)  but my scuba tank will be refilled by tomorrow. I'm getting more pellets in the mail tomorrow and Wednesday. 
Mean while I've been using my "boosted" hand pump to top off the Texan, shoot 1-2 shots then repump for chrono testing only.
I bought a Caldwell "Ballistic Precision Chronograph" and I'm not sure if it was a defective unit but I either got and error or the shot just didn't register when I would use it. I tried 10 shots with the chronograph under direct florescent, then tried under direct LED and wasn't any better...So I took it back to the store for a refund.

Good News!: I bought a Magnetospeed Sporter, it has 3 sensitivity settings, with the sensitivity set to HI 2 (the highest) I was able to get the Megnetospeed to register the pellet/velocity. I plan on messing around with it a little to make sure the velocity readings are accurate and not all too low or too high.

I have many projects/ideas and always needed a chronograph to test velocity but never bought one. It is kind of a bummer than the Caldwell Chronograph didn't work out as it should typically register any projectile that travels between the gates regardless of the material the projectile is made of. The Magnetospeed chronograph only works on metal projectiles and they have to be large enough for the magnetic sensors to pick them up.
Title: Re: .308 Texan titanium barrel tension
Post by: Monkeydad1969 on March 12, 2018, 04:51:47 PM
On the Caldwell, don't use florescent lights.  LED or IR lights.  But still looking forward to your results.

Joe
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 12, 2018, 06:05:45 PM
I tried using my LED work lights and got nothing, half the time it would register the other half I'd get errors, tho I only gave it about 20 shots in total before boxing it back up.
I just got done with the first round with the chrono.

.308 Texan settings:
Stock hammer and 1 hammer weight, total 109 grams. (Matt at R&L told me his Texan and another .308 Texan in the shop had 2 hammer weights but I've sent my Texan into Airforce and it came back with 1 hammer weight just like it went in with.)
Ammo: Hunters Supply 154 grain SP, ACTUALLY 10.15 grams/156.68 grain - I weighed out about 50 rounds and used 20 that weighed in from 10.14 grams to 10.16 grams range.
Power setting: 100% max/can't turn up anymore.

Results:
3400 psi - 927
3300 psi - 926(clean barrel)
3250 psi - 895
3150 psi - 892, 895, 909(clean barrel)
3100 psi - 889, 891(clean barrel)
3000 psi - 881, 881, 876, 882(clean barrel)
2950 psi - 873
2850 psi - 868, 864, 860, 862(clean barrel)
2800 psi - 858
2750 psi - 849
2700 psi - 847, 845, 852(clean barrel)
2625 psi - 832
2600 psi - 828
2500 psi - 800




Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 12, 2018, 06:18:53 PM
Note that the above shot string was not all on one fill, there were 5 fills I believe.

Also my settings on the magnetospeed have changed, I use sensitivity setting "HI 1" which is the middle sensitivity setting - which also means that the magnetospeed should/might work with the .257's out there.

Daystate has an air rifle that has a built in chronograph in the moderator/silencer, Air Wolf MVT. However, on small calibers such as .177 and .22, there is little lead dust, which mean the chronographs optical "eyes" don't get very dirty/need to be cleaned very often. If the same concept would be used in a Texan shroud, every few shots you'd have to stop and clean off the lead dust from the "eyes". Since the magnetospeed uses magnetic detection to pick up the projectile/velocity, it seems having a magnetospeed built into a shroud/moderator for the Texan might not face the same problems or maybe will just need to be wiped off after every 100 shots or so.
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 13, 2018, 03:18:53 PM
Some LEDs blink, just like a fluorescent, and that causes errors.... Other LEDs work fine.... Good old fashioned incandescent lights always work.... You need two, one over each sensor....

Bob
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 16, 2018, 07:48:51 PM
Just an update on where things are at:
The barrel tension system showed significant improvement over the stock Texan barrel.
When shooting 130 yards at my friends farm, the Texan shot 0.8" groups. However the Texan was sitting in a bench rest type gun rest. It was my friends gun rest and I don't know the brand/model but the Texan was secured to the rest, aligned with the target then we used clamps to keep the gun rest from moving on the heavy table. All I had to do was touch the trigger. I only shot Aeromagnum 109 grain HP's during this test and I admit I did not clean the barrel previously after shooting a good bit of the Hunters Supply 154 grain ammo. The Aeromagnums chrono'd 1030 fps.

The next day I went to gun range to test the Texan some more. This time I was shooting both High Arc 111 grain ammo and the Aeromagnum 109 grain ammo and I was sitting on a bench and shooting off the bipod. Out of 10 shots, only 4 or so would group tight (sub .75") then the rest would form a 2" group. Needless to say I was very disappointed.
I came to the conclusion that the Texan is very hold sensitive. From the moment you pull the trigger to the time the pellet leaves the barrel is significantly longer than a power burner. It's similar to archery, after hitting the release, you need to make sure you follow through with the shot. Knowing this, I still was unable to get better groups. From what I've read about the .257's out there, the Airforce platform has significant flex and a stock such as the mad dog stock has been reviewed to fix the issue.

I've already made a custom barrel tension setup, so I think I will go with the route of making a light aluminum frame which will hopefully stiffen the Texan, replace the tank mounted butt plate and finally add a mono pod.
Title: Re: .308 Texan titanium barrel tension
Post by: Monkeydad1969 on March 16, 2018, 11:57:57 PM
Eagerly awaiting your results.

Joe
Title: Re: .308 Texan titanium barrel tension
Post by: Alan on March 17, 2018, 03:47:55 AM
Group consistency is highly reliant on the way a weapon is held.

Years ago, I was fairly good friends with Tom Brown, who used to do the ballistic and pressure testing for Hodgdons. From him, I learned that group size sometimes enlarged when shot from a machine rest which seems counterintuitive. And from my own experience of recent, my WAR Cobra shoots higher groups when supported by my bean bag rest, compared to using the bipod and rear rest—a reasonable and intuitive conclusion.

In your case, I suspect with more range time, you'll find a rest scenario when will maintain good groups. Of course, tuning is also as issue, just like it is for powder burners. And by the way, no matter how it was held, ≈3/4 inch groups at 130 yards is nothing to sneeze at!!
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 17, 2018, 08:19:57 AM
Good results, but it sounds like possibly your rock solid barrel is moving around in the frame, relative to the scope....

Bob
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 17, 2018, 09:36:44 AM
Bob,

I'll see if I can get better pictures of the Texans barrel assembly. There is no way the barrel can move, it it rock solid and held in place with 9 set screws. Also the Texan wouldn't have grouped a .8" CTC 10 shot group at 130 yards if the barrel assembly was moving relative to the scope. The tension assembly mates with the receiver for 8-9 inches (I don't know exact measurement off the top of my head) and acts like a large 1 piece bushing with a length of 8-9 inches.

Everyone else, this is a few pics of my shot groups using a bipod off a bench.
Title: Re: .308 Texan titanium barrel tension
Post by: rsterne on March 17, 2018, 09:53:12 AM
Sorry, I didn't realize your tensioning sleeve went inside the receiver.... must have required extensive machining for that?....

Bob
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 19, 2018, 03:32:51 PM
Bob,

I know you're Canadian but don't feel the need to apologize!

Pretty much on a stock Texan, the barrel has 2 bushings. Each bushing has a 4 holes and 1 tapped hole for a setscrew to secure the bushing to the barrel. The set screws from the Texan frame/receiver go through the holes in the bushing and set against the barrel. The bushings have a 1" OD and have an ID of 0.675. The bushings are first slid onto the barrel, then each are held in place by 1 set screw to keep the bushings from moving. Once to two bushings are secured on the barrel, the barrel/bushings are slid into the front of the Texans frame/receiver. Once in the holes in the bushings align with the tapped holes in the Texans frame/receiver. Then a total of 8 set screws are screwed into place and the Texans barrel is secured.
So to sum it up, on a stock Texan (Condor, Talon etc) the setscrews in the frame/receiver push against the barrel (but not the bushings), however, in return the bushings are pushed against the Texan frame/receiver.

On top of the set screws that hold the barrel in place, behind each bushing there is a retaining ring that seats on a groove in the barrel. Set screws provide great hold to gradual thrust/torque but can slip during an impact style force - like the kind produced by the Texans recoil. These are also used to align the bushings in the right spot on the barrel.

The bushings have to be located in the center of the barrel as behind them is the hammer/spring assembly - so the barrel is only supported in the center - leaving the ends vulnerable to vibrations. 

A modification people seem to have been making to the Condor and Talon is to make a single piece bushing. This way there is more contact area against the bushing/receiver as well as the barrel and the bushings to better support the barrel. Using a 1 piece bushing requires the removal of the first retaining ring. I will say that since the Texans recoil significantly more than its little siblings and the impact force generated by the Texans recoil is distributed among both the first and second retaining ring - I can't say for sure or not if only one will be fine.

So my design goes like this:
I removed the rear bushings retaining ring (the bushing closest to the Texans tank). I cut a much deeper groove in the barrel where the rear retaining ring originally was. Then I put my split ring in the groove and then retaining cup holds the split ring halve together. Since the split ring would be taking the compression force of the titanium tube, it would have to take a lot of load - as well as it has to withstand the impact force of the Texans recoil. A normal retaining ring or set screws would not have been sufficient at all. I actually turned a piece of mild steel to 0.670 and tried different things before carving into the Texans barrel. 
The retaining cup was press fit over the split ring, it's very tight/semi permanent. Combined with the friction produced by the force of the retaining cup against the split ring, there is no chance of the barrel rotating in relative to the retaining cup - so no set screw was needed to hold it in place.
Since the titanium tube has an OD of 1", it acts as one large bushing.
However I did drill bottomed holes (not through) in the retaining cup. This allows the rear 4 set screws that secure the Texan frame/receiver to prevent the new barrel assembly from moving due to the impact forces generated by the Texans recoil.

The barrel is only under tension from where the stock rear bushing was to the muzzle and does not reduce harmonics/vibrations prior to the assembly. However I see it like this: take a garden hose for example, the water goes where the end is pointed regardless if the hose is coiled up prior end of it. So even though I cannot reduce the barrels harmonics from the loading tray to the barrel tension assembly, I don't think it really matters all that much.

Make sense?
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on March 19, 2018, 03:47:27 PM
last few details:

There is no front bushing, the other end of the titanium tube is supported at the end of the muzzle.
There are no modifications done to the Texans frame/receiver - so this assembly can be dropped into anyone's .308 Texan.
The set screws that secured the frame to the front bushing/barrel seat against the titanium tube.
The set screw that held the end cap/cover thing on is also seated against the titanium tube.
A total of 9 set screws hold the new barrel assembly in place.
Title: Re: .308 Texan titanium barrel tension
Post by: rcpro88 on April 03, 2018, 02:55:17 PM
Check for my post called .308 Texan Exoskeleton Stock for build details/updates. I will post the results of the titanium barrel tensioning assembly once the stock is done. I will post them here. 
Title: Re: .308 Texan titanium barrel tension
Post by: Monkeydad1969 on April 04, 2018, 05:24:59 AM
I will definitely check out your new post.

Joe