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| Extrusion |
 Posted: 10/21/2006 11:29 AM Post subject: Question about barrel length |
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Sergeant First Class
Joined: 29 Sep 2006
Posts: 147
72.81 Spud Bux
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| i made my first over under pneumatic a few days ago and i must say it it awsome but i think the barell may be a tad to long the chamber is 28" long and 2" wide the barrel i have been using is 54 inches of 1/2" solid black iron...very heavy not i do have a peice of 30" long black iron barrel wich is much much lighter and i want to use it but wich would be better for all around performance and power the 54" long barrel or the 30" long i tried to ggdt my gun but i couldnt figure out the valve and all and it said "Barrel choking flow" and "Barrel unecicarily long" what does this mean? |
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| joannaardway |
| Posted: 10/21/2006 12:24 PM Post subject: |
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Brigadier General
Joined: 09 Oct 2006
Posts: 961
115.90 Spud Bux
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When GGDT says "Barrel excessively long" it means that a vacuum has formed behind your projectile.
When it says "barrel choking flow" it means that the total flow from your valve(s) is higher than the barrel can support - you have possibly got the wrong numbers for your valve in that case.
What is your valve? Someone will know the appropriate figures to sort it out to get you the right results. |
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| Extrusion |
| Posted: 10/21/2006 12:53 PM Post subject: |
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Sergeant First Class
Joined: 29 Sep 2006
Posts: 147
72.81 Spud Bux
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| my valve is a 1/2" ball valve and i have no ideo how to put it in GGDT and when i think ive got it close it say the projectile only got like 100 fps wich i know is way wrong lol. |
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| POS |
| Posted: 10/21/2006 15:17 PM Post subject: |
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Major
Joined: 14 Sep 2006
Posts: 395
264.52 Spud Bux
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| barrel choaking flow isn't that bad. I get the same message when I calculate the speed of the projectile and barrel of a smaller diameter than the valve. No woeries about that one. What wories me, is the other message. It indeed creates a vacuum, slowing your bullet down at the end of the barrel, due to lack of pressurized air. You should make the barrel shorter !! |
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| Extrusion |
| Posted: 10/21/2006 16:19 PM Post subject: |
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Sergeant First Class
Joined: 29 Sep 2006
Posts: 147
72.81 Spud Bux
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but how much shorter i only have 2 choices a 30" barrel and a 54" barrel i just shot 2 ball berrings into the same tree at the same psi but different barrel and they both went 1 1/2" or so into the tree wich really amazed me lol 1 1/2" into a hard tree thats harsh lol but what i need is someone to GGDT my gun for me because i have no idea how to for the person that does they get 50 spud bucks 
Specs:
First Barrel 54" long 1/2" wide
Second barrel 30" long 1/2" wide
Chamber 28" long 2" wide
Valve 1/2" ball valve |
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| POS |
| Posted: 10/22/2006 3:03 AM Post subject: |
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Major
Joined: 14 Sep 2006
Posts: 395
264.52 Spud Bux
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50 ? Nice, But a bit hard, since you only have 10 bux  |
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| MrCrowley |
| Posted: 10/22/2006 3:49 AM Post subject: |
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Blizzard of Ozz
Joined: 23 Jun 2006
Posts: 6137
3165.90 Spud Bux
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1:go to the ggdt website it has info on all the errors
2:why can't you cut the 54" barrel to a shorter length? |
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| Extrusion |
| Posted: 10/22/2006 12:08 PM Post subject: |
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Sergeant First Class
Joined: 29 Sep 2006
Posts: 147
72.81 Spud Bux
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| yeah i decided to just go ahead and buy the signature ability and i dont have anything to cut a iron barrel with lol |
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| boilingleadbath |
| Posted: 10/22/2006 19:08 PM Post subject: |
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Moderator
Joined: 12 Mar 2005
Posts: 1647
5491.22 Spud Bux
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I'm running a generic valve, 100 ms opening time, .5" porting, at 70% flow:
Running out of air is not an issue, even running at 3 PSI.
Flow choking is not an issue
muzzel velocity is ~ 300 fps with a 7 gram projectile @ 100 psi from a 54" barrel.
The 30" barrel gives you 225 fps with the same conditions. |
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| Extrusion |
| Posted: 10/23/2006 16:02 PM Post subject: |
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Sergeant First Class
Joined: 29 Sep 2006
Posts: 147
72.81 Spud Bux
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| Thanks blb is the reason im getting such low fps because of the valve? im pretty sure thats it lol. |
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| boilingleadbath |
| Posted: 10/24/2006 12:55 PM Post subject: |
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Moderator
Joined: 12 Mar 2005
Posts: 1647
5491.22 Spud Bux
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Yes, the valve is really limetting preformance; barrel pressure never exceeded ~20 psi, IIRC.
I'd expect an enormous improvement if you used a 1" sprinkler. (which acctualy has a bit more flow [~25% more] than your barrel can use, but a 3/4" would limmet preformance... so I'd pay the extra couple dollars and get the more effective product. |
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| Extrusion |
| Posted: 10/24/2006 13:00 PM Post subject: |
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Sergeant First Class
Joined: 29 Sep 2006
Posts: 147
72.81 Spud Bux
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| boilingleadbath wrote: | Yes, the valve is really limetting preformance; barrel pressure never exceeded ~20 psi, IIRC.
I'd expect an enormous improvement if you used a 1" sprinkler. (which acctualy has a bit more flow [~25% more] than your barrel can use, but a 3/4" would limmet preformance... so I'd pay the extra couple dollars and get the more effective product. |
Yes i did ggdt on a modded 1" spinkler valve on my gun and i got around 554 fps!! as opposed to the 300 with the ball valve talk about a HUGE increase in performance! |
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