GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Topic started by: skorec on December 04, 2017, 09:24:29 AM
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We know that for 1cm inaccuracy at 100m we need only 0,05 mm muzzle barrel deflection.
That means that at the end of receiver is it less then 0,005mm.
1. How to reach so little deflection without using some glue between the receiver and barrel ?
2. Which are differences at muzzle barrel ( 500 x 15mm ) deflections causing by different temperature ?
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We know that for 1cm inaccuracy at 100m we need only 0,05 mm muzzle barrel deflection.
That means that at the end of receiver is it less then 0,005mm.
1. How to reach so little deflection without using some glue between the receiver and barrel ?
2. Which are differences at muzzle barrel ( 500 x 15mm ) deflections causing by different temperature ?
Now there's an idea for test, unless someone has been-there-done-that: shoot a set, then lay a warm hand on one side of the barrel for a bit and shoot another set. After a cool down (15 to 30 minutes), repeat the two sets, but this time warm the other side of the barrel.
I remember seeing a product a guy here in SC was doing. It was essentially a sleeve over the barrel that I think was supposed to make it really stiff and cut down the barrel vibrations during a shot.
In a similar, but cheaper vein, do you know how they damp vibrations on sheet metal panels and component housings? Spray the backside with tar, rubber, or some sort of liner. In other equipment, they take that a step further and glue (with a thick glue layer) another sheet of metal. The metal isn't there to stiffen so much as to work with the damping material to dissipate the energy of the vibrations.
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Ever wonder how much a steel barrel bends due to it's own weight?.... I ran the calculations for a .25 cal. with 1/2" OD that was free floating with 24" unsupported and it bends downwards about 0.020" (1/2mm) at the muzzle.... That is about 3" at 100 yards.... Increasing the OD to 3/4", even though it increases the stiffness of the barrel by 5 times, only cuts the deflection in half, because the barrel weighs 2.66 times as much.... Using a CF sleeve to increase the barrel to 3/4" OD, however, would reduce the deflection to about 1/4 as much, because it is the same stiffness of the steel barrel, but only half the total weight....
Just a piece of trivia, but since a barrel tends to straighten out (ie the muzzle rises) during the shot, you can see where part of the vibration cycle comes from....
Bob
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Cross over post.
This may seem weird...but am an old guy, so a lot of stuff we do/say seems weird...but hang in there, there is a point to all this.
(Besides...what good is getting old if you can't bore younger folks with stuff that they THINK has no relevance?)
May be totally wrong...but it's been on my mind when talking about barrel flex/vibration/ barrel bands/ airgun accuracy
Was a transition in centerfire bench rest in the mid to late 1960's.
First: "They" started offering modern high power/bench rest type scopes. Those old Litchert, Unertl, Lyamn Super Target spot external adjusting scopew were way long...really heavy...and had some attachement issues becasue of it.
Attachment issues? These scopes were made to slide back and forth in their mounts...and often one mount was on the barrel and one mount on the breech. With heavy recoil rifles (like 30-06's) there was no return spring, so when they slid (OK..the rifle recoiled back and the scope stayed still) you could still use them with .300H&H mag recoil as even with 7/8" of eye relieve, it never would smack you in the face.
The "in" guys (the top benchesters of the area) couldn't wait to get ride of the long heavy scopes. Were weight limits, and ever ounce saved in scope weight could be put into stuff that mattered more.
(and ok...up into the early to 1970's, could pick up those great out of favor scopes for cheap...and as a young guy, that's just what I did.)
Give 8-9 ounces more weight so to play with, they put it into the action and the barrel. Specifially, an action that was suited in length to the short bench cartridges of the time (so no excess length...and another weight savings)...a kind of bare-minimum sythetic stock (another weight savings), and one heck of a big fat short barrel.
Certainly those big fat barrels were free floated...but they also had big fat barrel shanks threaded and tensioned into big fat recievers.
Were also short barrels...for the same thickness, being short has some beneifits for accuracy.
(About this time, feel into a long barrled Win. 75 (.22LR) that had two click adjustable screws in the fore end. These bore directly onto the barrel and sullied contact/tension. Could move the POI all over the place by using those two tension adjustments...but if you got it "even" in tension and matched to the best ammo, it would shoot great...at least until the next lot number of ammo.
In airgun terms...don't think that this year's JSB's are going to be exactly the same as next year's JSB's).
And it worked....and continues to work with a weight savings in one area being used in another (more important) area.
So THEIR solution seems to be a very solid action, minmum length and weight, minimum scope weight (but still a top-line scope with repeatable adjustments), and as stiff a barrel as you can get away with.
So...if I got to build a bench rest, one-off, airgun...I dont doubt a sleaved barrel could help with weight....but I'd SPEND that weight with a larger action/more firm/threaded barrel-reciever attachement.
Bad news is that us po'folks have to live with what's offered, or what can be easily modded.
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Cross over post.
:'(
I wanted only notice how important is join between barrel and receiver.
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I am planning to add also some stiffening chunk se the picture.
https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=133591.0;attach=207804;image (https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=133591.0;attach=207804;image)
https://www.gatewaytoairguns.org/GTA/index.php?topic=133591.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=133591.0)
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Cross over post.
:'(
I wanted only notice how important is join between barrel and receiver.
......................
I am planning to add also some stiffening chunk se the picture.
https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=133591.0;attach=207804;image (https://www.gatewaytoairguns.org/GTA/index.php?action=dlattach;topic=133591.0;attach=207804;image)
https://www.gatewaytoairguns.org/GTA/index.php?topic=133591.0 (https://www.gatewaytoairguns.org/GTA/index.php?topic=133591.0)
It's not only the barrel attachment but also the breech material that counts. Those Evanix clones use rather soft aluminium for breech and at least Evanix has relatively sloppy tolerances for barrel and air tube attachment. If you do that breech extension you could add a dovetail on top that's on level with breech dovetail and use a rail to further support/connect it at the breech.
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rkr ,
Adding also dovetail is good idea . Thanks .
Also I am thinking which plastic tightening have I add between barrel and breech .
It should be detachable.
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A while ago I picked up a Schultz and Larsen M33 .22lr target barrel (# 5405 puts it in late 40's) some throat erosion but overall in pretty good shape...
I am leaning towards making a 2500-2700 psi Disco tube with a Baker .5" breech on a riser... Basically try to solve the prob by hanging the power plant off the ~28" long by .91 od barrel rather than vise-versa.. ;) hopefully can get to it within the next year or so...
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A while ago I picked up a Schultz and Larsen M33 .22lr target barrel (# 5405 puts it in late 40's) some throat erosion but overall in pretty good shape...
I am leaning towards making a 2500-2700 psi Disco tube with a Baker .5" breech on a riser... Basically try to solve the prob by hanging the power plant off the ~28" long by .91 od barrel rather than vise-versa.. ;) hopefully can get to it within the next year or so...
I've been thinking of that approach as well. Add scope rail that's attached to the barrel. The question is how to attach the barrel to the stock? Support at both ends or bed in some 10cm at the breech end or something else ...
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The 6mm Lead Sleds in PB Benchrest (600 yd) usually have the scope mounted on the barrel.... and often the action machined out of the barrel as well, making it all one piece....
Bob
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May by two of weaver barrel can be fixed direct to barrel.
I believe that it can solve factory inaccuracy of lot of BullpUp s.
https://www.aliexpress.com/item/Universal-Adjustable-Rail-20mm-Picatinny-Weaver-Barrel-Mount-Adapter-for-Scope-Flashlight-Laser-VEB97-P/32516692291.html?spm=2114.search0104.3.91.rGU1lC&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10065_5000015_10151_10344_10068_10345_10342_10325_10343_10546_10340_10341_10548_5130015_10541_10084_10083_10307_10303_10539_5080015_10312_10059_10313_10314_10534_100031_10604_10603_10103_10605_10594_5060015_10596_10142_10107,searchweb201603_33,ppcSwitch_2&algo_expid=6ec6101f-e670-4d23-bda4-61eb33215087-11&algo_pvid=6ec6101f-e670-4d23-bda4-61eb33215087&rmStoreLevelAB=3 (https://www.aliexpress.com/item/Universal-Adjustable-Rail-20mm-Picatinny-Weaver-Barrel-Mount-Adapter-for-Scope-Flashlight-Laser-VEB97-P/32516692291.html?spm=2114.search0104.3.91.rGU1lC&ws_ab_test=searchweb0_0,searchweb201602_2_10152_10065_5000015_10151_10344_10068_10345_10342_10325_10343_10546_10340_10341_10548_5130015_10541_10084_10083_10307_10303_10539_5080015_10312_10059_10313_10314_10534_100031_10604_10603_10103_10605_10594_5060015_10596_10142_10107,searchweb201603_33,ppcSwitch_2&algo_expid=6ec6101f-e670-4d23-bda4-61eb33215087-11&algo_pvid=6ec6101f-e670-4d23-bda4-61eb33215087&rmStoreLevelAB=3)
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Gunsmiths sometimes attach scope bases directly to the barrel on PBs.... As long as the barrel is thick enough, it is not a problem.... The scope bases are usually a SINGLE groove Picatinny (Weaver) mount, and are positioned for a particular scope ring position and spacing.... as the mounting holes for them are drilled and tapped directly into the barrel....
Bob
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YES SINGLE groove Picatinny (Weaver) mount screwed/fixed direct to the barrel will be much better.
I am just now thinking about two screw which fixed the barrel inside breech. They are obviously M5 screws and if you look on the area where they really touch barrel you may see that touching area is less then 2 square mm .
May be some fitting/adjusting of screw in to barrel dints can increase the touching area and so decrease barrel deflection. I don’t now.