Accidentally finding the magic- .30 Vulcan2 Tactic

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Centercut

Centercut

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Jun 9, 2017
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So today I was shooting my .30 Vulcan2 Tactic, trying to practice at various yardages. FYI, I bought the gun (very) used, and it was shooting just under 900 FPS with 44.75 pellets. Unfortunately it only got about 18 shots on reg at that power. 

So I rebuilt and tuned the gun, and tried various reg pressures and pellet speeds, plus valve spring tensions. I wanted to get it shooting accurately but still get three magazines (27 shot) per 250 bar fill. I got the tune to that point at a reg pressure between 145 and 150 bar, and 860 FPS with the 44.75 grain pellets. When shooting it comes off the reg right about 25 to 26 shots but still maintains POI at 70 yards for a couple more shots. So today, here is a typical 5 shot group at 67 yards. 

1577668582_17901667125e094fe63ac751.29786273_9E388942-E43B-4A35-822D-9CB81E6E95C3.jpeg


Well after shooting one group and hearing the gun come off reg, I decided to shoot one more group. Obviously the pellet speed was slightly lowering (I tune so that the gun shoots a shot or two when off reg at normal speed or slightly less then lowers slowly for another 2 or 3 shots). So for these 5 shots I’d estimate a pellets speed less than 860 FPS and about 835 to 845 FPS. I didn’t have my Chrony available. Here’s that group. 

1577668825_5510931145e0950d9e48fd6.67201039_A861108E-9F9B-4C36-B326-0E8CBF3AE4D2.jpeg


I was onto something. Totally by dumb luck. So I filled the gun back to about 160 bar and shot a few until I heard it come off reg. Then I shot this 5 shot group. 

1577668959_11794743795e09515fa40e80.95869425_6F2CA9A1-3D27-47DE-92B6-8380216A3782.jpeg


Damn! I stumbled on the ideal speed for the 44.75 pellets in the .30 Vulcan2 Tactic by coincidence. That above group is 5 shots at 67 yards. Next step is to tune the gun for 840 FPS and test it again. I plan to use it for RMAC Speed and PRS Challenges. I’d use it for NRL-22 also but nothing within a 3 hour drive each way from San Diego. 
 
Very nice group. I would think for a 30cal that the trajectory would be a rainbow at 830fps? Would like to see what it does at 100 at the holdover.
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Not as much as you might think or that would make any significant difference at 100 yards. At 840 FPS zero at 50 yards the holdover is 4.0 MIL. At 890 FPS which is a more common speed, with 50 yard zero the holdover is 3.6 MIL. Or about a 2 inch difference. 
 
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Centercut,

You need to measure the speed when you are going out of regulator because you might be shooting faster than when on regulator if the HST is too low for the regulator pressure.

If your HST is balanced with the regulator pressure your next few shots will maintain the same speed and if your HST is too high for the regulator pressure then your velocity after dropping regulator will decrease. In your scenario I think you adjusted the HST too low to get high shot count and after dropping regulator the next few shots will travel faster to then have a dramatic drop in speed. It will be awesome to do this test with a chronny and see exactly what is the speed that is giving those tight groups.
 
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Orion, thanks. The reason I said what I did is because I have shot over the Chrony in the exact situation I mention, so I know almost exactly what happens when it comes off reg. One or two shots at near reg speed, then slowly decreasing shot speed. So it looks like this. 

On Reg 860, 855, 858, 854, 857, etc

Off Reg, 854, 851, 845, 841, 836, etc. 

This has been done over and over again during the tuning of the gun. It never goes up after coming off reg, I don’t tune my guns that way. It is inefficient and inaccurate to tune your gun like that. The shots I took were from the off reg numbers. I just didn’t have the Chrony with me to confirm exactly but I’m 99% sure the numbers were close to the above both times I did it (the 2nd and 3rd groups). Thanks for the input. 
 
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It seems that you are truly inspired to turn old airguns into real shooters 
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. Nice job .

By the way , how would you compare the Vulcan Tactic .30 to the FX Crown .30 . I've hesitated between both , finally got the Crown ; very good gun but a bit cumbersome with a moderator. If the Vulcan is as accurate as the Crown ….mmmhhh , i'll maybe go for one.
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Well, the gun isn’t that old, it was made in 2018. But it was pretty trashed when I bought it, rust inside barrel, valve coming apart, tune way off... It just took some time to get it back in shape and properly tuned.
Yes, it is as accurate as the Crown. It is heavier, kinda like an Eddy R5M. Trigger is very good, smooth cocking. However I think you’d be happier with an Uragan. It’s also an AGT gun, but lighter and with double the shot count. Same trigger same barrel, same accuracy. IMHO. 
 
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Orion, thanks. The reason I said what I did is because I have shot over the Chrony in the exact situation I mention, so I know almost exactly what happens when it comes off reg. One or two shots at near reg speed, then slowly decreasing shot speed. So it looks like this. 

On Reg 860, 855, 858, 854, 857, etc

Off Reg, 854, 851, 845, 841, 836, etc. 

This has been done over and over again during the tuning of the gun. It never goes up after coming off reg, I don’t tune my guns that way. It is inefficient and inaccurate to tune your gun like that. The shots I took were from the off reg numbers. I just didn’t have the Chrony with me to confirm exactly but I’m 99% sure the numbers were close to the above both times I did it (the 2nd and 3rd groups). Thanks for the input.
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Oh great, I missed the part you mentioned that. I agree with you, tuning that way is inefficient. I'm glad you found this and even more you are sharing! 
 
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As an example of the wrong tune, I have a gun right now (won't mention model) that shoots about 860 through about 40 shots. Then it comes off reg and gives me about 6 shots @ 890, then down. So that means the spring is way low for the reg or that the reg is way too high for the speeds I want.

Also, I found that when this gun goes off the reg and I get those few shots around 890, it is far more accurate at that speed. The problem is, this gun only gets about 40 shots set like it is. If I increase the speed to 890 to get the accuracy, I may get fewer shots. But then if it is tuned correctly, the shot count may increase. We won't know until it gets the wrenches :)

Crusher


 
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