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Feet per second spread

Discussion in 'Anything Airgun Related' started by buffy vampire slayer, Aug 17, 2014.

  1. buffy vampire slayer

    buffy vampire slayer LOW BELLEND THRESHOLD

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    right guys,
    my first question and I hope you guys can help.
    I have a .22 FAC thoeben crusader gas ram.
    these guns are FAC rated from the factory and it will not hold a consistant zero.
    thought it was the scope or mounts so have tried several combinations with the same result.
    what would you expect the extreme 10 shot FPS spread to be at around 800 FPS using 16 grn pellets?
    I put the gun over the chrono on Friday and the extreme spread was 68 FPS from 844 to 776.
    did again this morning and the extreme spread was 45 FPS from 810 to 765.
    this gun is still under warranty.
    what do you think?
    I know what I think but just need comfirmation.
    cheers boys.
     
  2. cloverleaf

    cloverleaf Honorary Member

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    Given the savage accelerations that can be encountered in Gas Ram guns (especially FAC rated variants :eek:) my first thought would have been the 'scope too.

    The firing characteristics also tend to make the guns unforgiving and hold sensitive in my experience (lovers of the ram will doubtless be along shortly to disagree).

    As I think you already know a spread of 68ft/s about a mean of around 800ft/s is pretty sodding terrible (around 8.5% :eek:) so this is bound to have something to do with the accuracy issues you're experiencing. It may be that the "fast" firing cycle is exacerbating the effect of this velocity spread by exaggerating the difference in muzzle position with respect to pellet exit.

    I've noticed rammed guns seem to be less capable of holding consistant velocity figures than springers - in terms of shot-shot consistency as well as over longer periods of time with temperature variation (both through use and changes in ambient). IIRC the last HW90 I tested gave around 20ft/s spread - can't remember which calibre it was though (probably .22 so this equates to about 3-4% spread).

    Not sure about the warranty now Theoben are defunct - if you've got chance to get shot I'd grab it with both hands - I doubt the capability of rammed guns at the best of times; pushing them to FAC levels just makes their negative traits worse IMO and certainly doesn't allow them to make use of the potentially extended range associated with higher muzzle energies.

    If you must keep the gun it's probably worth investigating the piston head and ram seal (making sure they're in good nick and correctly lubed) however I think these problems are inherent to the gas ram system so at best I doubt you'll completely sort the issues you're having.

    Other possibilities might be a poor / inconsistant barrel lockup or loose / stroking mod, but I reckon you're on the right path - good luck getting it sorted :)
     
    Last edited: Aug 17, 2014
  3. sharpsman

    sharpsman Pro Poster

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    It may be worth while trying different pellets as some are not happy being launched at warp factor 5 and can distort off the initial air blast,a friend had an elimanator and it would only shoot Bisley magnums accurately anything else was hopeless.
     
  4. buffy vampire slayer

    buffy vampire slayer LOW BELLEND THRESHOLD

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    firstly,
    the warranty is with the gun dealer who I bought it from so this is not an issue.
    secondly,
    the pellets I am using are the same ones my FAC rapid mk2 (sold it now) was pushing down the barrel at 36 ft/lbs so I doubt the pellets are the problem.
    thirdly,
    the barrel lock up and all the other stuff,o-ring muzzle seal etc that can be seen on a external examination are all good.

    thanks for the input guys:cool:
     
    Last edited: Aug 17, 2014
  5. sharpsman

    sharpsman Pro Poster

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    t he delivery of the air is done in a more violent way in springers and gas rams than in pnuematics.
     
  6. Jackroadkill

    Jackroadkill Donator

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    Wish I could disagree with you, but you're right. I have an Eliminator running at 21fpe, which is about as high as it will go without becoming overly jumpy and (as you say) hold sensitive.

    I don't know if the Crusader was originally intended to operate at FAC power levels; the Eliminator only really manages it due to being a big, heavy rifle and it really needs the shooter to show it who's boss. The above quoted spread in the velocities suggests that the zero problems aren't with the scope and mounts, though, so I think there may be problems with the seals or the ram itself, or perhaps with the pellets.

    A bit of research (http://www.gunmart.net/gun_review/theoben_crusader_vs._theoben_eliminator) suggests that Theoben themselves recommend a light (in FAC terms) pellet, but I have to say that with my Eliminator it seems to be Bisley Magnums or nothing; lighter pellets just get spat everywhere, in addition to the energy falling. I don't know whether conventional wisdom regarding springers developing more power with lighter pellets extends to gas rams, but in my rifle the opposite is certainly true.

    As much as I hate to say it, the OP's best option may be either to substantially drop the power or go back to the dealer with the rifle and see if they can get any joy.
     
    Last edited: Aug 17, 2014
  7. terry1001

    terry1001 Major Poster

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    I would consider the spread of velocity, even the lower figure, to be excessive and it will cause groups to open up simply due to the size of variation.
    As to whether or not it's a characteristic of the specific gun or gas ram rifles in general I don't know but surely the point of a fac rated rifle is to extend your shooting range and if there is a lack of accuracy then you can't do this.
    I would be inclined to try some different pellets, just in case, as this is quick and easy to do. If you're not happy with the way it shoots then it's probably a good idea to return it to the dealer and buy something different, once doubts start to creep in your confidence in using it will dissappear.
    If the ram can be adjusted for different pressures it could be worth lowering it a bit to see what happens and then raise it to see what happenns and how it shoots as you increase the power but if it were me I would return it and get something else.
     
  8. engraver

    engraver Keyboard Hero

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    I would give the valve a tap with a flat punch to let some air out all you need is a toffee hammer.

    Then try to cock the gun the same speed every time, I once read about a guy with an slr who could get way different fps when cocking it fast compared to slow.

    It was a complicated theory but easily demonstrated over a chrono.

    Ive had gasrams that were dead accurate but all over the place over a chrono, and others that were very consistent ie fenman, similar power with lots of various pellets.

    Like said the power just exaggerates the systems inconsistencies, but its worth dropping it bit by bit, and try cocking it fast and consistently, it wont cost anything to try.

    But I once got a Theoben grand prix many years ago that shot a bit harsh, and in those days I didn't have a chrono, whilst shooting it one day the scopes crosshairs snapped, so I took it to the gunshop and asked for them to put it over the chrono, it was 17 ft/ibs!:eek: but they sold it me so they dropped it to 11 ft/ibs when I took it out it was like a different rifle, solid clunk, smooth as silk and very consistent and accurate at that.

    So point is, don't give up on the gun yet it may not have any catastrophic internals, best thing to do is keep tapping the valve and shooting 5 or 6 shots to get an idea, Im sure you will hit the guns natural frequency.
     
  9. dave goodall

    dave goodall Donator

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    Have u cleaned out he barrel recently also check out breech seal try h&n or crosman prems what theoben recomended and aim for 18 ftlb -20 ftlb

    http://www.theoben.nl/attachment.php?aid=1838


    Tbh tho there are alot better sub 12ftlb springers out there what will out shoot any the gasram modes esp the fac versions for accuracy power isnt everything by far
     
    Last edited: Aug 17, 2014
  10. buffy vampire slayer

    buffy vampire slayer LOW BELLEND THRESHOLD

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    on the flat part on the top of the breach it is embossed "CRUSADER FAC .22 CAL"
    the problem I have got really is that this gun was sold to me,with a warranty,said to be running at 24 ft/lbs,which at 840 fps with 16 grn pellets it is.
    now if I start messing with the ram pressure for instance it may invalidate the said warranty.
    like one of you kind gents has said,I now lack confidence in this gun except at short ranges as I have no idea which aim point to use.
    the shop is closed Monday,but I think I'll take it back tomorrow,get my dosh back,get it taken off my ticket,put in for another authority to possess and do what I should have done in the first place!
    buy another rapid
     
  11. dave goodall

    dave goodall Donator

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    U no it makes sense mate thats why gasrams are now obcelete theoben usa wont touch them part from the slr and i think once they sell out of bits they,ll end there only goid thing about theoben gasrams is that they were all built in the uk from scratch no farmed out parts but that will also be the demise of them buy a rapid a true fac king i too was taken by tne theoben bug and tried all the gasrams all were crap apart from the tanus like most things made in the uk the first modes were great then asteady slow decline why they thought a fac gun would be great in gasram is behond me wen sub 12 guns dont work unless around 10 ftlb atvb dave
     
    Last edited: Aug 18, 2014
  12. buffy vampire slayer

    buffy vampire slayer LOW BELLEND THRESHOLD

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    spoken to west yorks firearms licencing and to get this gun taken off my ticket and replaced with the authority to purchase THE SAME TYPE AND CALIBRE GUN they estimate a turn round time of 4 to 6 weeks.:eek::down:
    that really is some $hit service if it does take that long:(
     
  13. engraver

    engraver Keyboard Hero

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    If your replacing it bud, go down the Rapid route again, cant beat them on ticket.
     
  14. 177

    177 Donator

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    You can always buy a suitable gun if one comes up and have it held by an RFD (or the seller, by arrangement) until your ticket is sorted.

    My uncle had an Eliminator years ago which was about the most hold sensitive rife I have ever shot. Before that he had a Webley Patriot (remember those ? :) ) which wasn't quite so bad for hold sensitivity but its perceived recoil was horrific, so less prone to hold error and more prone to jumping about like a fresh caught trout :rolleyes:

    Good luck finding a resolution.
     
  15. buffy vampire slayer

    buffy vampire slayer LOW BELLEND THRESHOLD

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    well the gun went back to the dealer yesterday and he was more than happy to either fix it or give me my money back:up::cool:
    so I took the latter.
    sending my ticket in shortly along with the transfer paperwork and a request for the authority to possess the same .22 cal and mod putting back on.
    so I`ll be in the hunt for a rapid (again) as I`m now off rammers for life
     
  16. terry1001

    terry1001 Major Poster

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    Probaly the best thing to do, shame you've got to wait so long for the variation.
     

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