Why Can't I Get the FPS Out of My 30 cal Impact

Forums PCP Airguns PCP Airgun – Discussion Why Can't I Get the FPS Out of My 30 cal Impact

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    AirgunBill
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    This topic was touched upon in my hunting post about shooting snapping turtles with the purchase of my new 30 cal barrel kit. I stated that I was shooting the JSB 44.75 grain at 840 fps but that was on power wheel setting #5 but on Max I do get about 870 fps and on max pw get about 814 fps for the 50 VK's. Posters commented this was pretty slow for the set-up I have. This initial tune however was more for shooting the JSB's at about 840 fps for accuracy. I do want to get the VK 50's going at about 900 fps which I am pretty sure will require more reg . pressure so I went out this afternoon to try to get a that tune for the VK 50's. I set the valve on line 4 which is 10.85 mm, the reg was on 130 bar and the hammer spacing was at 15.30 mm and the power wheel on max.. I then shot three Vk's to get a base line and got about 840 fps. ( for each setting I was shooting three to five slugs across the FX Radar which was missing a lot of reading today grrr. ) I raise the reg to 135 and the velocity dropped to 820 so I knew I needed more hammer pre-load and adjusted the hammer space to 14.40 mm and that got me to 840 fps. I then raise the reg pressure to 140 bar and got 833 fps. I then turned up the hammer pre-load which maxed out at  14.22 mm and fps  did not improve. So my question is how are you guys getting these high fps with your rigs. I installed the power plenum kit with the supplied parts. Do I need a heavier hammer and or go back to the older springs. I would appreciated some advice and ideas. Bill

     

    • This topic was modified 6 months ago by AirgunBill.
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    Theman406
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    What hammer spring are you using? Old or new?

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    AirgunBill
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    Theman406

    What hammer spring are you using? Old or new?

    New one. Do you have experience with using the old hammer spring and what was the difference. Bill

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    ackuric
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    Set of calipers and this website would tell you the difference.

    https://www.acxesspring.com/compression-spring-rate.html

     

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    biohazardman
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    From what I have read you need to use the old spring, longer one, for max power.

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    Jayson
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    Couple of things to look at, first of all, the new spring with pp will push the 44 jsb 920 no problem, (assuming 700 mm)second, check the probe spacing, some people mess that up and your restricted, all it takes is the bolt linkage to turn one time when disassembled, next, do not jump from 135 to 140, that’s a big jump and I’m guessing you were already over, slow down and go 1 bar at a time, also, 4-5 shots after reg adjust to settle before you do anything, last, be careful about thinking your gauge is accurate and you can copy what other people are doing and telling you, I have a lot of Fx guns and I would be crazy if I told you half of the gauges were accurate, several are 20 bar off, no big deal, they are consistently 20 bar off, roll with it, they are for reference only, the chrony data and your target tell all! Good luck👍🏻

     

     

     

     

     

     

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    IraLite
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    I don't have experience with the new power plenums but I heard you can obtain faster speeds without high reg pressure. I don't think at 140bar you'll even notice the need for my hammer weight or different spring. Have you tried higher reg pressures like 160bar?

    Also whats the length of your barrel?

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    ShootStr8
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    AirgunBill

    This topic was touched upon in my hunting post about shooting snapping turtles with the purchase of my new 30 cal barrel kit. I stated that I was shooting the JSB 44.75 grain at 840 fps but that was on power wheel setting #5 but on Max I do get about 870 fps and on max pw get about 814 fps for the 50 VK's. Posters commented this was pretty slow for the set-up I have. This initial tune however was more for shooting the JSB's at about 840 fps for accuracy. I do want to get the VK 50's going at about 900 fps which I am pretty sure will require more reg . pressure so I went out this afternoon to try to get a that tune for the VK 50's. I set the valve on line 4 which is 10.85 mm, the reg was on 130 bar and the hammer spacing was at 15.30 mm and the power wheel on max.. I then shot three Vk's to get a base line and got about 840 fps. ( for each setting I was shooting three to five slugs across the FX Radar which was missing a lot of reading today grrr. ) I raise the reg to 135 and the velocity dropped to 820 so I knew I needed more hammer pre-load and adjusted the hammer space to 14.40 mm and that got me to 840 fps. I then raise the reg pressure to 140 bar and got 833 fps. I then turned up the hammer pre-load which maxed out at  14.22 mm and fps  did not improve. So my question is how are you guys getting these high fps with your rigs. I installed the power plenum kit with the supplied parts. Do I need a heavier hammer and or go back to the older springs. I would appreciated some advice and ideas. Bill

     

    Are you shooting at high altitude by any chance?

    Faulty Chronograph? Got a buddy with another one to test it?

    50gr at 840fps is 78fpe. Thats the quoted value according to FX Website for an Impact Mk2 (w/ power plenum).

    Are you using a 700mm barrel?

    • This reply was modified 5 months ago by ShootStr8.
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    mtnGhost
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    I would also make sure that your reg gauge is accurate. You should also be able to gauge velocity by zeroing at some predefined distance and then checking the drop at 100.

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    AirgunBill
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    Okay I did a video of me trying to tune the Impact 30 cal again for more fps. I state the settings I made using the calipers and used the FX Radar and a Shooting Chrony to show resulting fps. I continued to up regulator pressure from 125 bar on the reg gauge in 5 bar increments and once above 130 bar I got no increase in fps. It is like there is not enough hammer weight and or spring pre-load to open the valve. Like I stated before this was a .22 cal before I added the Power Plenum and 30 cal kit with transfer port and pellet probe opened up by SPAW. The video is long at about 20 minutes but if you fast forward to the 15 min. point I show the written results. I also had the thought that starting with max hammer tension that maybe the valve does not have enough time to open up and use all the air in the plenum. The truth is I don't know the sequence and how all the parts function. If people are getting higher fps than me with this set-up I must have the tune out of adjustment. Bill

    PS this is a 700 mm barrel kit

     

     

     

    • This reply was modified 5 months ago by AirgunBill.
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    jking
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    Bill, could the FX chronograph be giving some faulty readings if the dopler was being interfered with the other chrony in front of it? 

    jking

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    AirgunBill
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    jking

    Bill, could the FX chronograph be giving some faulty readings if the dopler was being interfered with the other chrony in front of it? 

    jking

    I guess that is possible but the readings of the FX Radar test today at the starting settings mirror what I was getting in the testing I did without using the Chrony the other day. Thanks for the idea and I will have to try again with just the FX Radar to see. Bill

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    IraLite
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    @AiirgunBill your starting with the valve adjustment knob on line 4 right? You mentioned the FPS doesn't increase after 130bar, sounds like its stuck in efficiency mode.

    LOL, or you messed something up when you installed the PP.

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    triggertreat
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    Delete

     

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    Chuck26287
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    I think there is a small change that FX made that is getting overlooked by most of us.  There are two general types of Impacts with Power Plenums out there… those where the PP was installed by FX (either bought new with the power plenum installed when the gun was originally manufactured at the factory, or those that were sent back to FX to have the PP upgrade installed), and those that were upgraded to the PP by the owners who just purchased the PP kit and installed it themselves.

    A common opinion is that when you install the PP yourself, you need to use the original 57mm hammer spring to avoid the lower velocities that most people are reporting after installing the power plenum with the 52mm hammer spring that comes with the PP kit.  This is a perfectly viable solution to the condition of running out of hammer spring tension preload at the hammer spring tension adjuster.  After all, if you cannot add any more hammer spring preload tension, and the hammer is not opening valve enough to obtain the higher velocities, you have to increase the hammer striking energy another way… and the easiest way is to use the original spring which had more power when an equal amount of preload was applied by the hammer spring tension adjuster.

    Using the 57mm hammer spring is one solution to the problem, but I think FX implemented another method, but it was not part of the PP kit.  Generally speaking (I'm sure it's possible some of the very first ones out the door from FX may not have had the change, so I'm speaking "generally" here), the Impacts with PPs coming from FX (factory builds or FX upgrades) are coming to customers/owners with a 16mm Hammer Spring Tension Adjuster (HSTA) slider.  This was changed from the original 18mm slider that pretty much all guns in the field had when the PPs started shipping for the DIY owner installed upgrades.  So, if your PP was installed in the field after the PP was announced and started shipping from FX, it was installed on a gun having an 18mm HSTA slider vs the 16mm slider the FX installed PP guns were shipping with.  The 16mm slider gives you an additional 2mm of HSTA preload adjustment before the HSTA maxes out, achieving a lot of what you achieve by using the 57mm hammer spring… more energy from the hammer strike.

    I think this is why we are seeing a lot of people who have owner-installed PPs using the 57mm spring, or using the 52mm spring from the kit, then commenting about unexpectedly low velocities, and inability to achieve the higher velocities.  If they have an 18mm slider installed, they have 2mm less HSTA preload available to them than the factory PP models have.  This is why the 52mm spring is fine for the factory install versions of the PP models, and as such, is included in the PP kit.  Unfortunately, the 16mm HSTA slider is not part of the PP kit, so a field install is not the same as a factory built PP model unless you change your slider to the 16mm version as well.  It would be really nice if this 16mm slider was included with the PP kit.  Maybe it is not, because every field upgrade already has a 57mm hammer spring available if needed.

    Just my thoughts after my experience with this issue.  I have field-upgraded 4 of our 5 Impacts, and I saw the same thing the OP in this thread is experiencing.  I then CNC trimmed my 18mm sliders to 16mm sliders, and now have no problems achieving higher velocities if using higher regulator pressures and going into that extra 2mm of adjustment now available to me (using the 52mm kit spring).

    Does this seem to make sense?

    • This reply was modified 5 months ago by Chuck26287.
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    AirgunBill
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    Chuck I do indeed have the 18mm HSTA so that sounds like that could be the problem. Before I read your post I had some other ideas which I thought might be a problem. First someone had mentioned maybe the probe might not be in the right position blocking some of the air flow. When I took apart the Impact I did not change the cocking bar spacing. When I did put everything back together the distance from the rear of the probe to the rear plate was within specs. I bought the 30 cal. barrel kit from SPAW and they opened up the ports so I think they would have done it with the correct tolerances. The area I did have a question about was the the C1 hammerseat. Some installation videos have people adding the lock tight valve rod threads and then tightening the C1 hammerseat down tight which I did, the same way Ernest Rowe does. However Kral's video says the end of the hammerseat should protrude from 6mm to 6.5mm from the front barrel support face. When I did it with that dimension the hammerseat did not bottom out of tight. When I first installed the valve adjuster out to 6.00 mm it looked like the hammerseat would spin. In the end I just cinched the hammerseat down tight and let it sit overnight to let the Locktite cure.With the hammerseat cinched down it protrude about 5.85 mm as I remember. Could not having the hammerseat end being out the 6.00 mm to 6.5 mm have something to do with the valve not being able to open enough for total air transfer. Thanks so much first for you post and what do you think about the hammerseat distance. Bill

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    AirgunBill
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    Okay just took my Impact apart to put back in the OEM 57 mm hammer spring. Funny how simple and less intimating taking it apart it is the next time. Anyway before taking the hammer seat off I measured how far it protruded out from the barrel support face and it was 5.20 mm. I installed the original 57 mm hammer spring in and with the valve seal hand seated without compressing the spring it now sits out 7.75 mm or 2.55 mm more of compression I assume. So at this point I am going to wait for some comments from you guys before I Locktite the hammer seat back on and put the Impact back together. Hoping this will give my the fps the Power Plenum is supposed to be capable. Bill

    • This reply was modified 5 months ago by AirgunBill.
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    Chuck26287
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    Bill… I originally set the hammer stop to the 6mm spec.  It was also not bottomed out and snugged.  I ended up doing as you did, and leaving it a little less than 6mm, but snug.

    My logic on this was it should not have the affect of decreasing the velocity for two reasons…

    First, the hammer should be hitting the stop with a miniscule amount more energy when the stop is closer to the cocked hammer when it fires.  For instance, with yours set to 5.85mm, the stop is 0.15mm closer to the cocked hammer than when it is set to 6.0mm.  When the hammer fires, the hammer spring actively accelerates the hammer toward the stop.  Once the hammer spring has fully expanded and is no longer actively pushing on and accelerating the hammer, it starts free-sliding down the rod.  The physics are undeniable… once the hammer has no propulsive force behind it and it is free-sliding down the rod under its own inertia, it IMMEDIATELY begins to lose energy and slow down from drag.  The same as how a pellet immediately starts slowing down after leaving the end of the barrel, and loosing the propulsion of the air behind it.  Based on this, the less distance the hammer has to travel before it hits the stop, the more energy it will have when it hits it.

    Second, positioning the hammer stop 0.15mm closer to the hammer also positions it 0.15mm farther from the Valve Stem Adjuster knob.   This basically allows the valve spring to decompress by 0.15mm, which is same as backing the VSA knob back out 0.15mm.

    I have no idea whether this 0.15mm difference is significant enough to cause any significant increase in velocity, but it clearly shouldn't be considered as a possible cause of lower velocities.

    My guess, and I do mean guess, would be the 6.0-6.5mm spec is left over from when they wanted the end of the hammer stop a specific distance from the rubber ball of the original VSA mechanism.

    For now, if I were you, I would look at your current conditions where your velocities topped out.  Once thing to try is back your VSA out to where the knob just conceals the o-ring on the knob receiver.  This new valve adjustment system starts applying valve-restricting force to the valve stem as soon as the valve spring starts compressing against the hammer stop.  The four lines are left over from the rubber ball method, and are not necessarily an accurate representation of the effective range of adjustment with the new VSA mechanics.  With the rubber ball method, placing the knob just past the fourth line usually removed all restriction from the VSA.  Not so with the new spring method.

    At this point, ask yourself if another two mm of HSTA preload would get you the increase in useful regulator range and velocities you are aiming for.  My guess would be yes.

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    Chuck26287
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    AirgunBill

    Okay just took my Impact apart to put back in the OEM 57 mm hammer spring. Funny how simple and less intimating taking it apart it is the next time. Anyway before taking the hammer seat off I measured how far it protruded out from the barrel support face and it was 5.20 mm. I installed the original 57 mm hammer spring in and with the valve seal hand seated without compressing the spring it now sits out 7.75 mm or 2.55 mm more of compression I assume. So at this point I am going to wait for some comments from you guys before I Locktite the hammer seat back on and put the Impact back together. Hoping this will give my the fps the Power Plenum is supposed to be capable. Bill

    If you can't modify your 18mm slider to 16mm, you are doing all you can do with what you have by using the 57mm hammer spring.  Perfectly good resolution.  I was primarily trying to offer an explanation of why many of us who installed our own PPs have seen lower velocities than expected with the PP kit 52mm spring.  The 57mm hammer spring will get you to the velocities you want as well.

    I'm confused about the new measurement of 7.75mm.  If you had the hammer stop screwed back onto the rod to the same point where it bottomed out on the threads, the overall valve to hammer stop tip length of the rod should be the same as it was before.  If this is the case, the valve could not have been seated when you measured 7.75mm.

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    AirgunBill
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    Chuck26287

    AirgunBill

    Okay just took my Impact apart to put back in the OEM 57 mm hammer spring. Funny how simple and less intimating taking it apart it is the next time. Anyway before taking the hammer seat off I measured how far it protruded out from the barrel support face and it was 5.20 mm. I installed the original 57 mm hammer spring in and with the valve seal hand seated without compressing the spring it now sits out 7.75 mm or 2.55 mm more of compression I assume. So at this point I am going to wait for some comments from you guys before I Locktite the hammer seat back on and put the Impact back together. Hoping this will give my the fps the Power Plenum is supposed to be capable. Bill

    If you can't modify your 18mm slider to 16mm, you are doing all you can do with what you have by using the 57mm hammer spring.  Perfectly good resolution.  I was primarily trying to offer an explanation of why many of us who installed our own PPs have seen lower velocities than expected with the PP kit 52mm spring.  The 57mm hammer spring will get you to the velocities you want as well.

    I'm confused about the new measurement of 7.75mm.  If you had the hammer stop screwed back onto the rod to the same point where it bottomed out on the threads, the overall valve to hammer stop tip length of the rod should be the same as it was before.  If this is the case, the valve could not have been seated when you measured 7.75mm.

    Chuck at this point I have not been able to digest the information/explanation in your previous post. Maybe at some point I will get my head around the function aspect. I too was wondering about the way the hammer stop stuck out to 7.75 mm. I pushed the valve rod in till it stopped but there was spring compression if I pressed harder. The only part I replaced was the OEM 57 mm spring. Also when I screwed the valve stop housing in it had the spring /extra length resistance when. I don't know how I could of put things out of order but I did put the rifle back to together and locktited the hammer stop. I was going to wait till tomorrow to let the locktite set-up. The rifle cocks normally but maybe I should take it back apart now and check it out again. The hammer stop was definitely bottomed out when tighten. I don't know if the spring could of hung up on a guide or not seated fully in a housing. I will take it apart now as you say it should not stick out. Bill

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