GTA
General Discussion To Gateway To Airguns => Back Room => : ribbonstone February 06, 2007, 10:07:53 AM
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...finding out cost me a donated chronograph.
Was thinking about my back yard guns and how they've done what I need inside the range they get used in (25-30yards max.). So was working backwards to find what vel. the favored combination of rifle and pellet was delivering at 30yards.
(In case you are wondering, so long as it delivered 5-6 foot pounds at 30 yards and would group uner 1", was doing fine for any backyard pest, including squirrels.)
Lots of testing this afternoon...63degrees/ +7feet elevation. Crosman figures not far off the published mark for stock valve and 24" barrel or 14" barrel (2260 from Cooked Barn but with stock valving and a 2300 from the Crosman custom shop). Daisy 22SG a good bit slower than advertized, but equal to the published "real world" speeds. Tuned QB79 still where I left it (had smoothed it and done most of the simple tunes, but then DECREASED hammer spring and slightly increased valve spring to get it back down to the 650fps area).
Got some figures for some old original Sherian Cylinderical slugs...the ones without the waist...15.8gr. average weight. With 595fps at 5feet and 542fps at 90feet, it worked out to a BC of .0377...which is more impressive than any of the current pellets tried so far.
So i decided to try to get the figures from the 2260 fr the Logun "Penetrators"...evidently the muzzle brake's set screws had gotten loose...pellet "tinged" the brake..centered the Chrony.
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Dont tell me that guy, I just got mine today, trying to figure it out, probably just me. :o Ed
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Well..lost my unit in Katrina, and this one was donated to me by a buddy....it started off life as a rebuilt unit (they sold/sell the rebuilt units for soemthing like $50) and he'd been using it for a few years as a back-up.
My original unit had a 3/8" Lexan plate mounted on an angle ahread of the unit...would defelct any error shots (and for the years I owned it, never did ding that plate other than in testing it to see if it would deflect a pellet). Yeah...the little rectangle of lexan would get frosted and hard to see through, so you'd have to replace it now and again. The donor unit was bare-naked in front and that tumbling pellet hit the LED screeen about dead middle.
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Go figure, once the sheilds were down it takes one in the heart. Things gotta get better and the lexan sheild IS a great idea. Sorry for the loss. Ed
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Trick seems to be to angle the shield DOWN rather than up...just large enough to protect the box. Makes it easier to see throught, less sky/light refelction.
BTW...might be worth it to buy some small dimeter wooden dowel to replace the metal legs that hold up the shield...if you intend any long range shooting (which seems to be when most of them get killed). A 1/8" wooden dowl will break if you hit it...the steel rod will crack the sky screen housing if its struck.
Will proably just buy another rebuilt unit if they are still offered...otherwise, a new basic unit (I don't mind crunching he numbers back at home).
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Thank's for the info on that. Question: how far back can you shoot from and get a good reading. Ed
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If you can get the pellet over the screens, even at 100yards, it will work...but mostly I'll shoot at 2yards, taking the time to line the 'graph up so I can also shoot for group at the same time. Inexpensive camara tripod is a big help (don't need one of the expensive ones for this).
If you ae nervous about hitting the chronograph, set a paper target up next to the 'graph...shoot it to find out how much LOW the rifle will print (will generally print low at close-close ranges due to the height of the scope over the bore).
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THANK'S RIBBONSTONE. Ed
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Hey, Ed, I chronied my 350 at 30 yards last fall, needed both muzzle and donwnrange velocity for my ballistic software. Considering your shooting ability, you shouldn't have anything to worry about.
Dave
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Maby if I stick some bunny ears on it I'll feel more at home hehe. Don't want to shoot it , don,t think it would tast that good. :o Ed