BC of 51 gr ammo .25

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Hello to all im interested to know bc for this bullet
I do not have material to test. Only one chrony
And no bullet yet

Many thanks in advance
Thierry

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[thierryaudibert]

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thank you teemu for your answer, by the way here i do not find barrel with fast twist rate in .25 (6.35) caliber airgun

lothar walther airgun barrel are 0.248 land and 0.254 groove in 17.7 :1 twist rate  (same than mine)

in firearms barrel i find only 0.250 land and 0.257 groove in 28″ in 10:1 twist rate, i think is a bit faster than needed but maybe i’m wrong
by the way if i put this barrel i must take a .257 mold (and of course a strong valve)
but for valve isn’t a problem my condor go to gunsmith for optimisation.

or simply try to find a mold who make shorter bullets  (i try later to remove gas check on bullet to test shorter ammo

[teemuParticipant]

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You can also try find other barrel manufacturers… But those could be little bit expensive. It is up to You how much money You like to spend. Better quality cost more…   Last barrel blank which I bought cost me 495€….

[denisbeaudryParticipant]

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Thierry,
Can you post a pic of a bullet loaded into the breech then pushed back out? Also are you certain you cut all the choke off the barrel ? You never know it might be barrel harmonics causing the issue . I’ve read that the barrels on the airforce guns tend to flex quite a bit.

[thierryaudibert]

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Denis i understand what you talking about, but if barrel not correct why  at 10m for example i put all in same hole?
i suppose is the speed the problem the bullet do not stabilise correctly
what do you think about?

following one bullet of each (.250 and 253) and i see a groove on the boat tail isn’t good no?
the problem appear on both bullet one groove seem to mark the boat tail

[denisbeaudryParticipant]

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Looks like you may have found the problem . I don’t know why you would have rifling marks on the tail . 😮 . Your barrel is the same spec as I am using and many others. It should measure very close to ..255 ” I got a measurement of ..2552 from my barrel today consistently . The last time out shooting I sized my bullets to .2541 ” and was getting better . That’s .0012 smaller than bore . Your .250 is probably too undersized. Is there any type of leade cut into your barrel , it may be that your not getting the bullets in the bore square ? Not sure maybe one of the experts will chime in here.
I hope to get out shooting tomorrow if the weather cooperates . Got lots of testing to do. Bonne chance mon ami.

[rsterneParticipant]

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I don’t actually see any marks on the drive band from it being larger than the groove diameter of the barrel in either photo…. I would therefore think that starting with the larger size and experimenting with different sizing bushing would be the best bet….

I have no idea why one groove would be damaging the boattail, as it is smaller than the center portion of the bullet…. Perhaps that is being damaged when you push it backwards out of the breech?…. Polishing the chamber might help…. I would certainly examine the chamber with a high magnification and try and determine what is going on with that one land….

Bob

[thierryaudibert]

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i do not push back i push all long the barrel and exit bullet by the mouth of barrel

try to push at half barrel and push back to see if problem occur at the mouth of barrel (bad unchoking process maybe)
but strange problem appear on my krall with original 6.35 barrel non chocked

thank you for your help

et bonne séance de tir Denis

[denisbeaudryParticipant]

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Is it possible that the chamber was cut offset from the rest of the barrel . If the barrel was spun in a lathe to cut the “leade/chamber” and the bore was not perfectly centred from the initial machining . When you push a bullet in ,it would almost have to go around a corner before straightening out. I’ve looked at LW barrels, Hatsan barrels and some cheap crosmans , none of them had a straight bore through . You could see it was offset by eye .

[thierryaudibert]

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i just cleaned the barrel again,
push a bullet half the barrel and push back the groove on the tail appear again

it seem is not the choke

[Author]

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