.30 Vulcan2 Tactic - Power Plenum

Jump to latest Follow Reply
Centercut

Centercut

Member
Jun 9, 2017
7,651
1
4,467
People's Republic of California (PRC)
open.spotify.com
1580662667_17336105855e36ff8b2e7225.94876850_651CFDA6-C337-4FEA-80D4-07C44D6B827A.jpeg


I bought a “well used” .30 Vulcan2 Tactic last year to use in RMAC 2020 Precision Marksman and Speed Challenges, because I used my .22 Cricket mini last year with 18.1 gr. JSB and the wind hold off was too much for some of the stages. Plus for some stages there is an advantage to using a larger diameter pellet.

My issue with the Vulcan2 was that although accurate, it only got two mags (9 shot mags) per 250 bar fill shooting 44.75 JSB at 885 FPS. This was prior to any work on the gun. Turns out it needed a good tune badly, reg pressure was at 155 bar, valve spring retainer was off the threads and free floating in the valve house, and the barrel was actually rusty internally. Despite all of the above, it still shot 1.5 inch groups at 100 yards. Not bad...

First to scrub the barrel and remove any rust, then JB bore paste to mirror finish. Next rebuild gun with all new orings and adjust valve spring tension properly, then tune the gun to shoot 860 FPS. Efficiency went up as expected, but still got only 25 shots on reg plus two accurate shots off reg. So now up to three mags from 250 bar fill. 

1580661919_11332481025e36fc9fe3a4a0.20162214_23928660-1654-48FC-B0C3-7C5553D8F1A0.jpeg


It turns out I had a spare power plenum from one of my Cricket tunes. {Power Plenums are nothing new}. I knew that this would increase efficiency and also allow me to lower my reg pressure at least 15 bar. The plenum screwed right into the air tube like it was made for it. Unfortunately the valve house would not screw all the way in to the plenum. So I sent the valve house and plenum to John Hagan for some minor machining and also to make a 1.5 inch extension for the barrel shroud (thanks John!). Plus, I ordered a Huma, not because it’s any better than the stock reg but because the internal plenum is about 1/2 inch longer due to the Huma reg compact size. 

1580662300_780812795e36fe1c639565.13610488_F9EC2BB7-3EA4-4111-A4B2-30C8ED608449.jpeg


1580662345_5770880525e36fe49984db6.38391833_5381C7D1-9C3D-467E-955D-EAC0E9ECF60D.jpeg


I set the Huma at 140 bar, and reassembled. I’ve only shot a few shots over the chrony, but it plateau’d at 890 FPS and I set the speed at 875 FPS. The HST adjust is almost at minimum tension and the gun feels and sounds much more effortless than before. Once I get the stock back from hydro dip I’ll run some shot strings and shoot some 100 yard groups. I’m expecting over 30 shots per 250 bar fill at 875 FPS, and MOA at 100 yards. We’ll see... more to follow in a couple of weeks.
 
If I'm doing the math right. You'll need to lower your regulator setting down to 127bar to get pellet speed of 875 with the 500mm barrel. And the shot count for 300cc tank at 875 should be very close to 29 shoots. I hope your new combined plenum is a is 76cc or larger.

Knowing your gun had a smaller plenum and now you'll be able to run a lower regulator setting. I'm expecting your hammer is probably going to be to heavy. It may be in your best interest to research lighter hammer springs or taking weight off your existing hammer. Your new regulator setting is about 6% lower. My guess you'll need to lower your hammer weight by ad least 6%. You may get lucking and A.T. Just turned the spring down tight for the .30. There may be adjustment in the original spring. 
 
Upvote 0
Appreciate the advice @mrshosted You shot a .25 Vulcan Tactic at EBR so I’m sure you’re familiar with AGT airguns.
Standard .30 cal Vulcan2 plenum to start. About 30mm diameter tube. Valve house plus stock inner plenum about 2 inches. I added 1/2 inch to inner and about 1 1/2 inches add on exterior plenum. Its almost double what the stock plenum space is. I’ve added similar to 3 or 4 Crickets in the past so I had an idea what to expect. We’ve been doing this for years with Cricket and EDGun. Those exterior plenums can be added in series if desired like Derrick @zx10wall did to his .25 Taipan Veteran on another recent post. He used 3 and his plenum is huge. At least the size of the new PP on Impact. 

Like I said, I set the reg to just under 140 bar (stock is 155, about 11% lower). The Hammer spring tension is so light I thought I’d need a weaker spring but it’s ok setting to 875 FPS. Plateau was just over 890 FPS. HST is backed out almost all the way. Cocking was always smooth and easy now even more so. 
 
Upvote 0
I sorry, I dont know where 6% came from. Your regulator will 18% lower at 127. From the description you've described your plenum to have a 26mm (1.02inch) inside diemeter and height of 2 inches which is 8.06 square inches or 20cc if you doubled it's 40cc (just estimating on the size and cc using your description) . I sounds like your on par for 140bar at 875, I'm looking forward to reading about your experience.

IMHO, you could really benefit from a larger plenum. Derrick@Azx10wall plenum did he say how much it added. The 44.75 gr pellet is a massive piece of lead. All my calculations where with a 76cc plenum with a 500mm barrel. I'd expect another 15bar drop in regular set point. Giving you the regulator set point of 127B 
 
Upvote 0
Thanks. 40cc total plenum is a good estimate. It gets to a point of decreasing returns since most calculations don’t factor in port size, length and flow restriction. (How far valve opens and flow path). My goal was to maximize efficiency within reason. Power is not a concern since 44.75 JSB are most accurate between 860 and 890 FPS, and I’m aiming for accuracy not power. Could I add another plenum? Easily in minutes. But the extra length requires another longer adaptor for the shroud and the gun is a good length the way it is. I originally thought about doing this mod to my .25 Vulcan Tactic Gen4 to shoot .25 heavies, but the magazines are so much better on the Vulcan2, and can be changed out much faster. Bottom line, sometimes enough is good enough. ;)
 
Upvote 0
So, the gun has one plenum added, and I did shot a string this past weekend on Sunday. Still don't have to stock back from hydro dip so no accuracy testing yet.

Well, I set the reg. for approx. 139 bar, plateau at 890 to 895 FPS, and the HST for a speed of 875 FPS. This is not my final pellet speed, and I plan to take it down to about 855 to 860 FPS and that's where it'll stay once I have everything set. The gun is more accurate at the lower speed with the 44.75 JSB. 

Initial gun setting - reg. at 155 bar, pellet speed at 895 FPS, 18 shots per 250 bar fill. (two 9 shot magazines)

Now: reg. set at 139 bar, one "Cricket" power plenum installed with Huma reg., pellet speed set to 875 FPS. 28 shots on reg. and two more shots before speed drops under 860 FPS, so 30 shots from 250 bar fill. Valve house port opened up and polished, valve spring retainer set for tighter valve action than stock.

1581382184_4412628745e41fa2887dab2.11372547_C3775198-4EDF-4FF7-9AD0-B9DAA78929B1.jpeg
1581382185_16592371465e41fa296972c4.20559896_C72D1627-D93D-4EF5-B4C4-AC23D0075AD5.jpeg



Future: next weekend I will add one more Power Plenum. I’ll use a .30 Tanto in place of the .30 Tatsu so that it fits and I won’t need the adaptor. I'll set the reg. at about 129 to 130 bar, hopefully the plateau will be around 875 to 880 FPS, and I can set the pellet speed with HST to about 855 to 860 FPS. This should give me about FOUR mags (36 shots) from a 250 bar fill with 44.75 JSB at desired speed. 

This is DOUBLE the shot count from when I got the gun (used). Also, I will shoot some 100 yard groups to see if I have MOA at 100 yards or not. I hope so since I plan to use this gun at RMAC in June for the Precision Marksman and Speed Challenges...
 
Upvote 0
Your results are looking good. Where is the hammer spring set at? With the two extra plenums spacers how big is your plenum now? It nice you able to slow down the pellet some over your first plan and gain keep the accuracy. I'm a big fan of the 860 fps with the 44.75 gr pellets. It's increasing your shot count to a nice 4 mags AKA 36 shoots. I alwise like when it works out magazine even. It sure make it easy to keep track of your bottle pressure.
 
Upvote 0
Still trying to tune this. With the lower reg. pressure I need more valve spring tension to get the proper efficiency (with significantly less than design reg. pressure, it takes more valve spring to shut the valve quickly after hammer strike). As it is now, it doesn't feel or sound right, and efficiency didn't improve with the additional power plenum. And of course now that I've taken it apart and put it back together ten or more times I've developed a slow leak somewhere, probably the firing valve. Its always something. ;( I'd estimate that I have about 60cc plenum volume now (for reference, the new Impact Power Plenum is 54cc), with reg. set right under 130 bar at about 128 to 129 bar. 
 
Upvote 0
It's sounding a bit blur bee. The valve dwell time is to high. Your pellet is almost out of the barrel when the valve closes. Adding more spring behind the valve is the same as removing hammer, try a lighter hammer spring. You could try cutting a coil off the hammer spring. Or adding a spacer under the valve spring. I have faith you'll find the snappy pop your looking for. 60cc on the plenum is out standing!! I have a filling this is going to be your new favorite.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu