andyfr1968 772 Posted January 31, 2011 Report Share Posted January 31, 2011 Hi folks. Right then, this is an odd one...... A few months ago, my mate Paul who I shoot with sometimes gave me back my old Lightning he'd been useing after he'd bought himself an HW90 in .22. He wanted a .177 and as it happened, I'd still got the .177 barrel from my own 90 before I fitted a .20 barrel a couple of years back. It was a pellet fussy little sod when I had it and out of the few pellets it grouped very well with were H and N Baracuds or Bisley Mags (same things...). Anyway, I gave him what was left of the tin of Baracuds I'd been useing before I swapped barrels for him to use. His 90 would do no better than a 2 inch group at 30 yards when fitted with my old barrel where as when it was fitted to my own gun's action, it was pretty much pellet on pellet Same tin of pellets... After trying a few different brands out, we settled on AA Fields which were again more or less pellet on pellet but again, when that barrel was fitted to my own action, it didn't like them.... What the hell's going on there then??? I'm at a total loss to work this one out Any ideas anyone??? Cheers. Quote Link to post
venomviper 129 Posted January 31, 2011 Report Share Posted January 31, 2011 hi ya buddy would it be the cylinder as for a gas rammer 177 to .20 or 22 would change the power as well would you need to re-gas the ram ? ? or it could be size of the cylinder ? even down to the shims as well buddy have you tried that to ? different alinement of the barrel ? sorry i cant help ya buddy shay Quote Link to post
andyfr1968 772 Posted January 31, 2011 Author Report Share Posted January 31, 2011 Hi, Shay. When we changed to the smaller caliber the gun was down on power as expected so we had to put a little more pressure in the ram to compensate. The only other thing that's changed is the mod so I'm wondering if there's some wierd harmonics thing going on. I've never had anything like this before Cheers. Quote Link to post
rossi_j 99 Posted January 31, 2011 Report Share Posted January 31, 2011 Strange, maybe a difference in power, thats my stab in the dark, I have no idea sounds very strange, hope someone comes up with something. .atb. .ste. Quote Link to post
venomviper 129 Posted January 31, 2011 Report Share Posted January 31, 2011 maybe the mod is untrue to the barrel buddy ?????? its a bit of a mind f--k aint it pal has the barrel been chopped and re-threaded ? as a friend of mine had his barrel chopped and re-threaded and after couldnt get a good group at all i hope you find out what it is buddy and please let me know what it turns out to be shay Quote Link to post
andyfr1968 772 Posted January 31, 2011 Author Report Share Posted January 31, 2011 (edited) Thanks Shay and Ste. The power's been set to a little over 11 which was as it was on my own 90. I have a Chrony and access to a pump to set it up. The gun is now grouping very well with the AAs and also with Loguns 9.5 grains. It's just odd that when that barrel was fitted to my gun, it didn't like either of those but loved the Mags/Barras.... Edit... No Shay, the barrel's not been altered in any way, the only change's are the action and the mod.... Edited February 1, 2011 by andyfr1968 Quote Link to post
ghillies 209 Posted February 1, 2011 Report Share Posted February 1, 2011 porthole prob/port seal, piston caps gone or maybe the actual pistons dodgy? or even the springs gone. Quote Link to post
Whitey1234 1 Posted February 1, 2011 Report Share Posted February 1, 2011 remove as many variables as you can. you said the barrel was the same but the action and the mod were different. so the barrel was grouping well on your original gun. put the barrel on your original gun and check it's still grouping well. now try the combo with the new mod on see if it still groups well. now change the barrel onto the new gun without the mod. what does it do? now reintroduce the mod on the new gun. what does it do now? should tell you which bit to be looking at for the issue with a bit of luck. Quote Link to post
andyfr1968 772 Posted February 1, 2011 Author Report Share Posted February 1, 2011 Thanks for the replys, lads. There's no fault with the gun, it's just a really odd illustration as to how airguns can be fussy about ammo 'cos for whatever reason, it's clearly more than just a barrel issue in this case. The barrel shoots differently when it's changed from my gun to his. Wierd.... Quote Link to post
ghillies 209 Posted February 1, 2011 Report Share Posted February 1, 2011 porthole....piston cap. Quote Link to post
andyfr1968 772 Posted February 1, 2011 Author Report Share Posted February 1, 2011 On 01/02/2011 at 23:13, ghillies said: porthole....piston cap. I've got to be honest, Alex, I don't quite follow you there... Quote Link to post
ghillies 209 Posted February 2, 2011 Report Share Posted February 2, 2011 (edited) the porthole cant just be any old shape and size, someimes one gets miss shaped, or was never right in the first place, it affects the air flow from the pison chamber to the barrel, if its foo barred theres various amounts rabdomly going through so any pellet would be inacurate, or at least far less than it could be. sometimes on breack barrels the seal goes or wears and just seeps random amounts of air.. the piston cap is the 'washer' on the piston that seals down the tube, if that goes, which they all do sooner or later, then seaps randomly naffing up consistancy. (warn washers on a break barral let the barrel move in the groove..thats anothe acuracy killer) just a thought. if the barrel was bad on both guns, i'd have asked if the barrel had been cut down, usualy peeps get a little too clever, the barrel has to be at certain legths to let the lands work properly, and the crown takes affect too (the flat end shape where the barrels cut or the end the pellet comes out) that buggers acvuracy up. Edited February 2, 2011 by ghillies Quote Link to post
andyfr1968 772 Posted February 2, 2011 Author Report Share Posted February 2, 2011 Ah, right, I see what you're saying No it's not that, the barrel when it's fitted to either gun shoots fine, the strange thing is that it shoots well but with different pellets. EG, when it's on my action it shoots best with Baracudas but not too well with the AA Fields but when it's on my mate's action it's the other way around, great groups with the AA's but rubbish with Baracudas It really is an odd one, both guns have been tested on my Chrony and there's on consistancy issues with either action. I guess I'll just put it down to being one of those things. I've never given any real credability to the theory of barrel harmonics on airguns 'cos of the power when compared to CF guns but I really can't think of anything else..... Cheers. Quote Link to post
ghillies 209 Posted February 2, 2011 Report Share Posted February 2, 2011 (edited) yup the porthole diference then lol...seems a really minour issue but at velosity etc that miniscule hole shape/size puts a diferent 'presure' into the pellet, ish. a .22 port hole isnt the same as a .177.... edit in. venturi flows in mecanics, cant remember any particulars at the moment but as presure changes through shapes they resualt in diferent flow rates etc...eather by volume or velosity but the 'weight' of it or 'momenum' of it (for want of words) changes. as the pellet travels up the barrel its 'weighted' diferently, similar in lose turms to a head on colision and a glancing head on colision. they both have the same weight and velosity ' in the basic maths but the glance is far worse because of centrapedal forses of 'other' directions' that effect the ocupents and structral damages..in a metoforic sence like. add in frictions, direction of travel and presure changes etc etc theres a lot of little deviants that add up to a really big crash lol. or another way of putting it, the center of balance changes in its'energy' as it travels effecing every other factor...(like rubbing a cheese grater at diferent angle..) in short it effects the pellets start and 'angle of momentom' so minutly changes the friction rates of travel with the 'momentim' or 'kinetic' energy..changes the pellet for want of words... Edited February 2, 2011 by ghillies Quote Link to post
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.