Power Plenum ~ Taipan Veteran

[mtnGhost]

I see what you mean about the valve spring. Bummer, I wanted to test with something stronger, but all my springs are going to be the same or slightly weaker. 

Anyways I'm glad that I took it apart. There was surface rust that I had to clean up on the valve pin and the hammer. My barrel also had some surface rust when I got it, but I spent a bunch of time polishing with jewelers compound from 7.5 down to 0.25 microns lol

Has anyone tried double stacking plenums in front of the reg? I have a second one that I'm tempted to test after ai get my Koi.

The more plenum the better. The only reason not to have more is for those going for a low power tune, like under 20 FPE. You’ll just have a longish tube but I’d like to see your results. In fact, I'm going to do the same. Thanks.

Aesthetically it would work with the Koi, but thr Tanto would probably make the barrel and air tube look perfect. I don't think the Tanto is going to work though, I don't mind the air tube length with one plenum extension, but two would expose the muzzle blast beyond my comfort level.

What do you mean about the muzzle blast and the Tanto? I have my .25 Vet Long rocking 63.8 FPE with a Tanto attached.

~4.6" of the air tube extending beyond the barrel (2 plenum extensions and without a DonnyFL moderator that is)

 

[zx10wall]

I’ve got another power plenum on the way. This .25 Long has become an experiment of the sorts Actually all my PCPs really are a product of my tweaking. 

E, warm me up a 600 mm STX for her

 

[mtnGhost]

I’ve got another power plenum on the way. This .25 Long has become an experiment of the sorts

Actually all my PCPs really are a product of my tweaking. 

E, warm me up a 600 mm STX for her

Would love to see a photo from Ernest on the breech for the STX. I'm super tempted to turn some STX barrel adapters on my lathe to see where the power is at with 600mm and 700mm barrels. I might even thread the 30" TJ blank I have in .30 caliber for fun, but I need to get more steel rods to make a new pellet probes. I ruined the 29" TJ that I made for my MKII when part of the probe I made broke off in the breech and really f'd up the bore. I don't plan on going through that again - that blank took me forever to setup  

This Koi added some length to my Standard lol, but man is it quiet!!! 

 

[zx10wall]

Cool. Yep, a second plenum would be nice with the Koi. Is that an old Eddy soft case back there? 

 

[mtnGhost]

Cool. Yep, a second plenum would be nice with the Koi. Is that an old Eddy soft case back there?

Yeah. The zippers busted off both of the ones I have for my Matador and Lelya. Thin metal 

 

[mtnGhost]

I am still bugging out on how quiet this Taipan is with the Koi on it. At 48FPE (28.5gr) it is quieter than my 600mm Crown with the Sumo with the 24gr Varmint Knockers at 45FPE. I'm just hoping that it's accurate without funky POI shifts at long range. Opted for the .25 Koi though, so I don't think the moderator will be a problem.

Hopefully someone can chime in with the Tanto at higher power. I'd love to know how it sounds compared with the Koi. I might wait until after the weekend to install the second plenum extension, I have a narrow window for target shooting this weekend and need to collect some data before I mod it further. Overall, I think the power output is promising so far, given the short 460mm barrel  

 

[zx10wall]

I am still bugging out on how quiet this Taipan is with the Koi on it. At 48FPE (28.5gr) it is quieter than my 600mm Crown with the Sumo with the 24gr Varmint Knockers at 45FPE. I'm just hoping that it's accurate without funky POI shifts at long range. Opted for the .25 Koi though, so I don't think the moderator will be a problem.

Hopefully someone can chime in with the Tanto at higher power. I'd love to know how it sounds compared with the Koi. I might wait until after the weekend to install the second plenum extension, I have a narrow window for target shooting this weekend and need to collect some data before I mod it further. Overall, I think the power output is promising so far, given the short 460mm barrel  

With my .25 Long, believe is or not, the addition of the Tanto is all I feel I need. It greatly reduces the bark.

 

[mtnGhost]

I believe you. I ordered one from Donny today (sticking with .25 for my .22).

I'm quite honestly afraid to install this second plenum, because I will probably want the power potential of them both, full time. The problem with that is length - one of my main build parameters for this was keeping it as short as possible

Tons of wind and rain are forecasted here this weekend, so I will probably wind up testing the dual plenums tonight or tomorrow.

 

[mtnGhost]

Yeah.. no. Too damn long now

 

[mtnGhost]

With two plenums I'm maxed at 50FPE with the JSB Redesigned Monsters at 949fps. Thr FX chrono says I lost power with 33gr (805fps) and with my target ammo, the 28.5gr NSAs at 840fps. I haven't touched my reg, it's still around 145bar.

I don't think I need more VDT with this short barrel. I'm going to try dropping pressure down to 130bar and see what happens. I don't care for the length now at all

 

[zx10wall]

It’s not bad bro. You need to fab up some goodies to facilitate using a 600mm STX. Your barrel is the limiting factor!

 

[mtnGhost]

It’s not bad bro. You need to fab up some goodies to facilitate using a 600mm STX. Your barrel is the limiting factor!

Yeah dude, I can imagine this thing with a 700mm barrel on it. Pushing Impact territory!  

 

[zx10wall]

It’s not bad bro. You need to fab up some goodies to facilitate using a 600mm STX. Your barrel is the limiting factor!

Yeah dude, I can imagine this thing with a 700mm barrel on it. Pushing Impact territory!

Why not?!? Trade that backpack for a guitar pack

 

[Bigragu]

Yeah.. no. Too damn long now

That doesn’t look bad at all. If I hadn’t been following this tread I’d say it looks factory.

 

[zx10wall]

Doubled my power plenum pleasure as well now. It immediately jumped another 15 fps at the same HST and reg setting ~ sending King Heavies at 935 fps now. Will test shot count and accuracy later today.

 

[mtnGhost]

Doubled my power plenum pleasure as well now. It immediately jumped another 15 fps at the same HST and reg setting ~ sending King Heavies at 935 fps now. Will test shot count and accuracy later today.

Looks good. Interested in seeing your accuracy results and shot count now

I'm going to hunt down some springs today for the factory valve and play around with heavier and lighter setups. I plan to follow Ernest's suit and turn out some POM-H bushings for the hammer, but I'm also thinking about testing a lighter spring with some brass bushings in different sizes (slid over the rear of the hammer) to act as a weight. There may be some advantages to increasing the weight with all this plenum volume. I'm looking for another 4-5FPE with this barrel before I can get on with my life haha

 

[zx10wall]

Here’s a my string:

Created: 01/04/20 09:33 PM
Description: .25 Veteran Long x2 Plenum
Notes 1: 
Notes 2: 
Distance to Chrono(FT): 1.00
Ballistic Coefficient: 0.046
Bullet Weight(gr): 33.95
Temp: 49 °F
BP: 1027.87 inHg
Altitude: 120.00
# FPS FT-LBS PF
34 935 65.91 31.74
33 931 65.35 31.61
32 934 65.77 31.71
31 928 64.93 31.51
30 935 65.91 31.74
29 928 64.93 31.51
28 932 65.49 31.64
27 927 64.79 31.47
26 931 65.35 31.61
25 935 65.91 31.74
24 934 65.77 31.71
23 936 66.06 31.78
22 930 65.21 31.57
21 938 66.34 31.85
20 940 66.62 31.91
19 928 64.93 31.51
18 934 65.77 31.71
17 928 64.93 31.51
16 931 65.35 31.61
15 929 65.07 31.54
14 930 65.21 31.57
13 928 64.93 31.51
12 932 65.49 31.64
11 930 65.21 31.57
10 935 65.91 31.74
9 930 65.21 31.57
8 935 65.91 31.74
7 931 65.35 31.61
6 938 66.34 31.85
5 929 65.07 31.54
4 933 65.63 31.68
3 932 65.49 31.64
2 933 65.63 31.68
1 930 65.21 31.57
Average: 932.1 FPS
SD: 3.3 FPS
Min: 927 FPS
Max: 940 FPS
Spread: 13 FPS
True MV: 934 FPS

From here, it will get another 4 good but slowly descending shots. This string was taken inside using lights. It is not 49 degrees inside but is about 70 degrees. 

Accuracy is okay but leaves something to be desired at 100 yards. I may be over speeding the pellet and need to slow it down. I’ll continue to play with her. 

 

[mtnGhost]

That is very respectable, very nice!!! Yeah those 34gr never flew well for me over 930, I think that is just the nature of the beast.

I have mine apart again as I write this. I had spent a few hours playing with springs, making acetyl bushings, et al and got real good data on the hammer and valve. Then, as I'm trying to figure out where the bottlenecks are I measure my brass transfer port and saw this..

I took for granted that it was ~5.5mm. My seat is 7.62mm, so I'm probably going to drill it out with a 7/32 and see what happens. I'm not toonworried about the seat, but if need to make a larger one, I'll just make one.

PS - has anyone measure their port in the .25's?

 

[zx10wall]

I haven’t measured valve port but will next time I’m in there. Side note; the refresh rate (shot to shot plenum recharge) on this setup is about 15 seconds. Shooting it faster gives a much poorer SD and ES. 

 

[mtnGhost]

I haven’t measured valve port but will next time I’m in there. Side note; the refresh rate (shot to shot plenum recharge) on this setup is about 15 seconds. Shooting it faster gives a much poorer SD and ES.

It's around 10s for mine.i took the little fill limiter screw out of the top of my Huma reg though. That is with the Huma right? Have you chrono'd any heavy slugs with it yet? Would love to know what the max FPE is in your .25

Bah, this has been a slow marathon getting this one setup. I bored out my brass TP to 5.53mm, thought it was all good and had air dumping down the barrel. Had to resurface a flat on the face to get it sealing again. 

Anyways, I got all of 10fps out of that mod from where it was before for 959fps max. I had dropped my reg pressure down to around 142bar prior and tested a new spring and bushing. Cocking is like cutting warm butter, but with the larger port I earned a benefit of using even lighter tension. When I shoot the monsters, it sounds like 400fps when it's actually 900-915

Hoping it's accurate. Dumping rain here again tomorrow, but I'm a soldier so I gotta get out and test it