BBT Bigbore Benchrest Build
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BBT Bigbore Benchrest Build
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Topic: BBT Bigbore Benchrest Build (Read 854 times))
Erik Green
Shooter
Posts: 11
Real Name: Erik
BBT Bigbore Benchrest Build
«
on:
September 23, 2017, 03:57:53 AM »
I have a machine shop...............
I have a fulltime job.......
I already have too many projects started..... and un-finished!
One more cannot hurt.......
Inspired by Bob's Monocoque gun and a nice piece of thick walled Titanium tube I found at a good price I started designing.
I have been puttering in CAD the last 3-4 months and have a pretty good idea of what I'd like to do.
This first post is a request for input from Bob et-al on what they think my numbers might be able to produce.
I have access to clean 4400psi bulk nitrogen and will be building a booster to get into the 5000psi range.
So:
I will be running the gun regulated.
Bobs Boattail 155gr. .308
36" .308 barrel with 10" twist. Much of the initial design intent is to minimize the length of the transfer port.
The plenum chamber will be the butt of the gun so the valve is reversed allowing the transfer port to run up and forward into the barrel hopefully at a 45 degree angle.
Reservoir -- 1.5" diameter .084" wall grade 9 3al-2.5v 105ksi yield strength. Plus 2 layers of .013" Carbon Fibre
Vol=1030cc
Plenum -- 2" dia .160" wall steel
Vol=250cc
Sykes SS valve
Everyone is welcome to analyze.
Erik
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Great Falls, MT
dyotat100
Expert
Posts: 1095
Re: BBT Bigbore Benchrest Build
«
Reply #1 on:
September 23, 2017, 08:26:20 AM »
What pressure are you going to regulate it at?
2" .160" steel? What kind?
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rsterne
Member 2000+fps Club
Bob and Lloyd
GTA Senior Contributor
Posts: 26925
GTA Forums Person of the Year 2017
Real Name: Bob
Re: BBT Bigbore Benchrest Build
«
Reply #2 on:
September 23, 2017, 12:19:00 PM »
Yes, those are the questions I would have asked.... I know nothing about using carbon fibre to reinforce a titanium tube.... Even if you could use it to increase the hoop strength of the tubing, it wouldn't do anything for the tension loads where you attach the ends, I think an all-metal solution, so that the yield and UTS are Omni-directional, would be a better solution, or at least one you could get advice on.... For the plenum, you might consider using a commercially available bottle.... The 13 CI, 3000 psi one might be a bit small on plenum for best efficiency, but if you can stay to 3000 psi regulated you might consider it.... A larger diameter, higher pressure bottle might give you more flexibility in design....
As to the pressure required, a .308 cal, 155 gr. bullet has an SD of 0.233.... Just based on that, with a 36" barrel, you will need nearly 3000 psi to reach 950 fps with full bore-area porting.... While my "lofty goal" spreadsheet say you might do that at maximum power with about 200 psi less than that, it is always better to allow for tuning the gun down to reduce air use, report, and recoil.... You can, of course, trade off a shorter barrel against a higher pressure to achieve your FPE goal.... I would not limit the design to using 3000 psi regulated, in case you need more pressure to get the velocity you want in an efficient manner.... or end up wanting to use a heavier bullet or shorter barrel....
I love the concept drawing.... Good Luck....
Bob
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Coalmont, BC, Canada
🇺🇦
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since! 🇺🇦
Airsenal:
1750 CO2 Carbine, .177 Uber-Pumper, .22 Uber-Carbine, .25 Discovery, 2260 PCP 8-shot Carbine, 2260 HPA (37 FPE), 2560 HPA (52 FPE), XS-60c HPA in .30 cal (90 FPE), .22 cal QB79 HPA, Disco Doubles in .22, .25 & .30 cal, "Hayabusa" Custom PCP Project (Mk.I is .22 & .25 cal regulated; Mk.II is .224, .257, 7mm, .308 & .357; Mk.III is .410 shotgun and .458 cal), .257 "Monocoque" Benchrest PCP, .172/6mm Regulated PCP and .224/.257 Unregulated, Three regulated BRods in .25 cal (70 FPE), .30 cal (100 FPE) & .35 cal (145 FPE), .257 Condor (180 FPE).
sixshootertexan
Expert
Posts: 1835
yes
Real Name: Ricky B
Re: BBT Bigbore Benchrest Build
«
Reply #3 on:
September 23, 2017, 09:30:00 PM »
Pretty cool think I've seen something like that before. What kind of FPS are you looking for?
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Magnolia,TX
CCS 2300, CCS 2400, Custom Built Regulated .25, Custom Built PRod Clone, .308 Bullet shooter, XS46U .177, 850 Hammerli, Custom Built Regulated .177, Benjamin 392, Crosman 2200
MJP
Member 4400+Fpe Club
GTA Senior Contributor
Posts: 2136
I'll make it real. For me.
Real Name: Marko
Re: BBT Bigbore Benchrest Build
«
Reply #4 on:
September 24, 2017, 04:18:18 AM »
Nice drawing, and good idea on the valve.
For benchrest, why so much reservoir? Shooting tethered is the usual way of BR.
Like Bob already stated, the carbon doesn't add strength to the tank, you cant get it to enclose the whole cylinder.
Be sure to do all the math right and use atleast 3:1 safety margin on your calculations. 5000psi is a lot of force.
Waiting to see how she turns out.
Marko
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Finland
Impossible just takes a little bit longer to achieve.
If an engineer is not presented with a suitable problem, they will create their own!
Erik Green
Shooter
Posts: 11
Real Name: Erik
Re: BBT Bigbore Benchrest Build
«
Reply #5 on:
September 24, 2017, 06:43:41 PM »
I had forgotten that my actual measured wall thickness on the Ti CWSR tubing is .093"-.094". Giving me some safety wiggle room. My intention will be to hunt with the gun as well so will not always tether. Doubt it will be fun to pack any long distance but gophers are a penny a dozen here in Montana.
I intend to go 3X factor of safety. Aiming for 5000psi reservoir and regulating down to whatever works best once its finished.
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Great Falls, MT
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BBT Bigbore Benchrest Build