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Topics - rsterne

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1
OFF TOPIC / Snowman Alert !!!
« on: February 04, 2018, 03:31:22 PM »
It’s been snowing all night.  So the morning goes like this;
 
8:00   I made a snowman.
 
8:10   A feminist passed by and asked me why I didn’t make a snow woman.
 
8:15   So, I made a snow woman.
 
8:17   The nanny of the neighbors complained about the snow woman's voluptuous chest.
 
8:20   The gay couple living nearby grumbled that it could have been two snowmen instead.
 
8:25   The vegans at No. 12 complained about the carrot nose, as veggies are food and not to decorate snow figures with.
 
8:28   I am being called a racist because the snow couple is white.
 
8:31   The Muslim gent across the road wants the snow woman to wear a headscarf.
 
8:40   Someone calls the cops who show up to see what’s going on.
 
8:42   I am told that the broomstick of the snowman needs to be removed because it could be used as a deadly weapon. Things get worse after I mutter : "Yeah, if it's up your ass"
 
8:45  Local TV news crew shows up.  I am asked if I know the difference between snowmen and snow-women?  I reply, "Snowballs" and am called a sexist.
 
8:52   My phone is seized and thoroughly checked while I am being blindfolded and flown to the police station in a helicopter.
 
9:00   I'm on the news as a suspected terrorist bent on stirring up trouble during this difficult weather.
 
9:10   I am asked if I have any accomplices.
 
9:29   A little known jihadist group has claimed it was their plot.
 
Moral: There is no moral to this story. It’s just the Country we live in today!

Bob

2
Airgun Ammo / .30 cal Heavy Pellet from NOE - IN THE STORE
« on: December 28, 2017, 08:03:43 PM »
NOE has decided to take my revised pellet design to Group Buy in .30 cal.... http://noebulletmolds.com/smf/index.php/topic,2360.0.html



It will be available only in their "RG" base pin system, and 3 sets of pins of different depths will be supplied.... allowing you to cast 3 different weights, of 59, 62 and 66 gr. (shown).... The moulds are a nose pour design.... Please note that the skirt is 0.308", but the head is 0.300", just like JSBs.... The length will fit in the AirGunLab modified MRod magazines, and Flex mags....

2 and 4 cavity moulds will be available, in brass or aluminum.... Those signing up will get a 15% discount upon production.... 10 orders are required before the tooling will be made....

Bob

3
There were a couple of perfect sized boxes under the tree this morning, and I was hopeful they contained what I wanted.... Here is what my darling wife gave me....



It's a .22 cal Beeman Chief PCP, and the scope is a BSA 4-14 x 44 FFP Side Focus with 30mm tube and extended MilDot reticle.... The scope looks a bit big mounted on that gun, but it will be going on my new 6mm PCP project gun anyways.... It is my first FFP scope, and it will be interesting how I get along with that concept.... I stole a scope from my Hatsan AT-44 Long before I gave it to my son for Christmas (and replaced it with a Leapers 4-16 x 50 AO).... The scope from the Hatsan will be going on the new .257 PCP project I am working on concurrently with the 6mm.... It is an older Hawke 6-18 x 44 AO with an SR12 Reticle.... Both scopes should be good for up to 150 yards or beyond, which will be appropriate for the new guns....

The plan for the Chief is to shoot it as is to get a baseline with a bunch of pellets.... and then tear it apart and see what magic I can work on it.... I don't even know when that will happen, maybe not until next winter.... it will depend on how long my current projects take to complete.... Oh, and I finally found some of the new .22 cal Redesigned JSB 25.4 gr. Exact Monster pellets, they will arrive after Christmas.... I'm hopeful I can tune up the Chief to make good use of them, if they prove to be accurate in it.... If not, then I'm sure the 18.1 gr. Heavies will do a stellar job.... Incidently, the Chief weighs 6.75 lbs. naked, and 8.5 lbs. with that big scope on it....  8)

Ahhhhhhh it should be a very good year....   :o

Bob

4
Airgun Ammo / Inventory Run - 63 gr. FN in .257 cal at NOE - In Store
« on: December 09, 2017, 06:30:46 PM »
This bullet is being discussed as a possible Inventory Run....  http://noebulletmolds.com/smf/index.php/topic,2339.0.html



It is a shortened version of the 260-85-FN but currently out of stock in the NOE Store.... If 5 guys are interested, it should move up to an Inventory Run.... IIRC, Doug Noble and Cedric both used this bullet before they moved on to heavier ones in more powerful guns.... No reason it can't have a Lyman style HP pin in one cavity....

Bob

5
Ask Bob / MOVED: Walkthrough on tuning a pcp and huma reg.
« on: December 06, 2017, 06:31:28 PM »
This topic has been moved to PCP, C02, and Helium Powered Airguns.

http://airgunguild.com/index.php?topic=2290.0

I don't have one of these PCPs, you may have better luck there....

Bob

6
Airgun Ammo / NOE Year End Mould Sale
« on: December 01, 2017, 01:00:14 PM »
From now until Friday Dec. 8, there is a 20% discount on all moulds not previously ordered....  http://noebulletmolds.com/NV/

Bob

7
The Garage / Converting an Atlas 12" x 36" Lathe for Metric Threading
« on: November 24, 2017, 02:30:38 PM »
I have a 40ish year old Atlas 12 x 36 Lathe with the Quick Change Gear Box, and of course it only does Imperial threads, from 4 to 120 TPI.... A couple of weeks ago, I found out on the Internet that by replacing two gears you can do all the common Metric threads from 0.5 mm to 6 mm pitch, and keep the Imperial threading capability from 8 to 120 TPI, all you lose is the coarse threads, which I never need.... I ordered the gears through Amazon, and for about $100 got the 44T and 52T change gears I needed to perform this conversion.... They are Boston Gears # GB44B and GB52B.... direct replacements for the Atlas change gears....



Here is the original setup.... The gears are covered in a very sticky black grease called "Keystone No. 29".... which is the most tenacious grease, made for open gears, you can imagine.... Get it on your hands, and everything you touch turns black.... The good thing about this stuff is that it stays put, and doesn't need replacing, I have never touched the grease in 40 years, all I do is the regular oiling of the pivot points and shafts....



Note the twinned 48T idlers, it is those we will replace.... Above and to the left of them is a "sliding gear" (shown in the usual "OUT" position) which is engaged with a 16T driving gear activated by the tumbler gears for forward-neutral-reverse of the lead screw.... That 16T gear is twinned with a 32T behind it (with a guard between), both rotating at the same speed, on a double-keyed hub, just like the 48T idlers, which also rotate together.... This setup does all the Imperial threads from 8 to 120 TPI.... If you move the slider to the "IN" position, to engage the 32T driving gear, the lead screw turns twice as fast, giving the ability to do threads from 4 to 7.5 TPI.... It is those coarse threads I will be giving up.... The first step is to drop the sliding gear down and move it out of the way and remove the twin 48T idlers and the shaft they rotate on....



I slid the double-keyed hub part way out of the gears so that you can see it.... It causes the two gears to rotate together on the flanged bushing below the gears, which is held in place by the adjusting bolt and nut.... The bolt slides in a slot to allow the mesh between the idler and the input gears of the QCGB to be adjusted.... The thick washer goes on the outside of the gears, and when the nut is tightened the flanged bushing is held in place, and the gears, on that double-keyed hub, rotate on it.... I smeared a thin film of the #29 grease on the sides of the new gears, lubed the double-keyed hub inside and out with Moly grease, and slid it into place, then lubed the flanged bushing with Moly grease and slid it inside the hub with the flange on the bushing against the inside of the 44T gear.... This places the 44T on the inside, acting as a spacer for the 52T gear, but they will rotate at the same speed, locked together by the double-keyed hub.... The thick washer goes on the outside, under the nut, with a dab of Moly grease on the inside surface....



I reinstalled the idler assembly by sliding the bolt head into the adjusting slot, and slid it over so that the new 52T idler gear was in mesh with the input gears of the QCGB.... It is important to adjust the mesh of the gears so that there is just a bit of "backlash" between then.... not tight, but not too loose either.... just a bit of rattle between them is the correct setting.... Once you have the correct mesh, then tighten up the nut on the shaft to hold the flanged bushing in place.... The gears, on their double-keyed hub, will rotate on that bushing.... Note that in the photos below I haven't yet gooped up the teeth of the gears with the Keystone #29, I brushed that on after adjusting the mesh and taking the photos.... I didn't want that sticky mess all over my camera....



The next step is to slide the hub for the sliding gear over towards the idlers and adjust the mesh between the slider and the 52T idler and retighten the nut to hold the slider in place.... You then swing the sliding gear adjusting assembly upwards to engage with the 16T drive gear, check for proper mesh, and tighten the hand lever to hold it in place.... With the gears adjusted in this way, you are set up for Imperial threading, exactly the same as before, and the TPI chart on the front of the QCGB is correct for all threads from 8 to 120 TPI, and the 9 feed rates.... The fact that you changed from a 48T idler to a 52T idler makes NO difference to the gear ratios.... In a spur gear train, only the size of the first and last gear matter, the others only change the direction.... NOTE that in this position, the new 44T gear is not in mesh with any others.... it is acting only as a spacer for the 52T idler gear....

To change over for Metric threading, all that is required is to move the sliding gear to the "IN" position, and readjust both gear meshes....



In the "IN" position, the sliding gear will engage with the new 44T idler, which is smaller, so you will have to loosen the nut on the shaft of the sliding gear and move it in towards the idler.... NOTE this is different from the original setup where both idlers were 48T, so you didn't have to readjust the position of the slider relative to the idler.... Adjust the mesh, tighten the nut to hold the slider in place on the lever, and swing the lever up to engage the slider with the 32T drive gear (instead of the 16T).... Adjust the mesh, and tighten the hand lever.... The lathe is now setup for Metric threading, and you can no longer use the threading chart on the QCGB.... you need the one below....



The upper part of the chart, in black, are the Metric thread pitches (in mm) now available.... There are a few lesser used Metric pitches which you can do while in the Imperial mode, and those are show in red.... They aren't perfect, but are close enough (within 0.8%) unless you are making a very long thread.... You can approximate 1.6 mm, 0.8 mm, 0.7 mm, 0.45 mm, 0.4 mm and 0.35 mm pitches by using the 16, 32, 36, 56, 64 and 72 TPI settings respectively.... Those were available before, you probably just didn't know it....

So how does this work?.... Well, it speeds up the lead screw.... Using the inner 32T drive gear doubles it to start with.... The key is the two new gears, pinned together on that double keyed hub, so that they rotate at the same speed.... When you move the slider to the "IN" position, and engage it with the new 44T idler, it turns the 52T gear at the same speed.... This speeds up the input gear for the QCGB by 52 / 44, which is 1.181818 times.... then multiply by 2, and you get 2.363636 times as fast for the lead screw as in Imperial mode.... If you select the 60 TPI position in the QCGB, you end up with 60 / 2.363636 = 25.385 TPI.... almost exactly a 1 mm pitch.... When you try and cut a 1 mm pitch thread, you are actually cutting one that is 1.0006 mm pitch.... In 10 threads, the total error is only 0.0002".... ie negligible....

I hope any of you that have an old Atlas 12" with the Quick Change Gear Box may find this "How-To" article useful.... I can't take credit for it, but it sure works well.... One other thing to be aware of is that your threading dial is now pretty much worthless, since it is intended for Imperial threading.... About the only way you can use it would be to always use the number 1 position, and ALSO make sure that your carriage is in the SAME position when you engage the half nuts.... If you have a reversing motor, you can leave the half-nuts engaged all the time, and reverse out of the thread, of course.... The other alternative is to leave the half-nuts engaged and turn the spindle by hand with a hand crank, like this.... NOTE make sure you unplug the lathe from the wall before inserting the handle for safety....



I know it is counter-intuitive to use a power tool by hand.... but when threading up to a shoulder, or other critical work.... it sure reduces the pucker-factor.... The crank is pretty simple, it grips the inside of the spindle bore with a mechanism similar to a bicycle seat post.... You tighten the bolt with a 9/16" socket through the center of the chuck, before inserting your work....



Once again, I can't take credit for this idea.... This one came from Lloyd Sikes, and many thanks to him, I have used it a LOT....

Bob

8
There have been many discussions about downrange ballistics, and since Helium has come on the scene, we now can play with velocities that were unheard of not that long ago.... I have done up some charts to compare what happens with a 100 gr. bullet with a BC of 0.200, compared to a 200 gr. bullet with a BC of 0.400.... The caliber is irrelevant, as long as it is constant, but because of the weights chosen, it might help if you think about a .308 cal powered by Helium for the higher velocities (or by air for the lower ones).... I used the G1 Ballistics Model, so think of these as flat-based Spitzers.... The BC is the important number, along with the muzzle velocity....

If you shoot a 100 gr. bullet at 1500 fps, that is 500 FPE, and if you double the bullet weight, about the best you might expect is about 1100 fps, which is 537 FPE.... Conversely, if you tune the gun to shoot a 200 gr. at 500 fps, you might hit around 700 fps with a 100 gr.... That is why the charts for the light bullet use a range of MVs from 700-1500 fps.... while the charts for the heavy bullet show a range of 500-1100 fps.... I am simply trying to get a valid comparison between a light bullet driven fast and a heavy bullet driven at just slightly higher FPE, just as you might achieve in reality.... Anyways, here are the charts for what is happening at 200 yards downrange in a 10 mph crosswind....



Note that even starting at 1500 fps, the bullet is subsonic at 200 yards (it has lost 450 fps).... and has lost just over half it's energy.... However, if you start it at only 1000 fps, it has only lost 150 fps, and retains over 70% of it's energy....



In the second chart, the bullet drops about twice as far starting at 1000 fps than it does at 1500 fps (80" instead of 40").... but it only has about 10" of drift instead of 15"....



By comparison, the heavy bullet (with it's superior BC) retains 79% of its energy starting at 1100 fps, and 86% starting at 900.... It has only lost about 120 fps when starting at 1100 fps, and only about 80 fps if launched at 900....



In the last chart, you will note that for a given muzzle velocity, the heavier bullet, with its superior BC, has a flatter trajectory compared to the lighter bullet in the second chart.... In fact, if you compare the heavy bullet at 950 fps to the light one at 1000 fps, they have the same drop.... and the heavy bullet has 5" of drift, compared to 10" for the light one....

My personal preference is to use whatever bullet your gun will shoot in the 900-1000 fps range.... I know that some prefer a lighter bullet moving faster, and that's fine too.... All I am trying to convey here is what happens if you take that into the Supersonic range, where the drag dominates bullet performance.... Yes, you can get a flatter trajectory, as after all, velocity is the dominant factor in determining that.... much moreso than the BC.... There are compromises to be made, however.... and hopefully the above will give you something to ponder to determine what those are....

Bob


9
This is a project I have been developing on the GTA for a while now.... Here is a rough drawing of the concept, which is to mount two empty 88 gr. CO2 cylinders under a QB78 main tube, reversed back towards the trigger group.... This will provide a nice wide base to the forearm for shooting off bags on a bench.... A pair of cylinders weigh 1 lb. 9 oz. and they each have an internal volume of 121 cc....



Well I finally got some shop time today, and I decided to work on the tank block to mount two 88gr. CO2 cylinders reversed under a QB78 main tube.... Using the previously posted drawing as a basis, I produced the following....



The upper hole is tapped 1/4" NPT for a threaded stub that will mount the block to the front of a QB78 main tube, retained using the original threaded CO2 cap.... You can see the two air passages crossing in the bottom of the hole.... They were drilled with a #21 drill (0.159"), which is the tap drill size for a 10-32 screw.... The total area of the two passages is equal to a 0.225" hole, so a similar size hole will be drilled through the 1/4" NPT stub to feed air into the QB78 tube.... Since that is larger than anything that would be used for the exhaust port, that means the entire 290+ cc's will be available to the valve....



There is an 11/32" hole drilled through in line with each 88 gr. cylinder, and that is tapped from the front 1/8" NPT for a gauge and a male Foster fill fitting.... The air passages will be plugged with low-profile 10-32 SHCSs, sealed with a #008 O-ring in the 5/16" recesses milled in the lower corners of the block.... At the moment the holes for the 88 gr. cylinders are only milled 1/2" diameter and 3/4" deep.... I will be centering each hole in a 4-jaw chuck in my lathe to machine the O-ring groove, and drill and tap the portion outboard of the O-ring to 16 mm x 1.5 mm to accept the cylinders....

The block weighs 5 oz., so the completed weight with the stub and the two cylinders should be just under 2 lbs.... The stock will have to be shortened a bit, so the total weight increase will be less than that.... I plan an operating pressure of 1800 psi maximum, in keeping with what CO2 can reach at 120*F, and because that is the MSWP of CO2 cylinders....

Bob

10
Sold Items / Wanted QB78 Tube and Front Cap - Got It !
« on: November 19, 2017, 11:42:25 AM »
For an experimental project, I need a QB78 tube and the front cap that threads over it and retains the CO2 plug.... If you have one you wish to donate, please PM me....

Looks like I have one coming.... Thanks for looking....


Bob

11
Airgun Ammo / .225 cal 35 gr. RF & HP at NOE
« on: November 19, 2017, 08:54:52 AM »
New Group Buy at NOE for a 35 gr. GC bullet in .225 cal, and also a smooth sided 37 gr. version.... both with a Lyman HP pin available in one cavity.... http://noebulletmolds.com/smf/index.php/topic,2298.0.html

Bob


12
Airgun Ammo / Need BBT HP Moulds?
« on: November 13, 2017, 08:32:34 AM »
The NOE Store has sold out of the HP versions of the .22 and .25 cal Bob's Boattail Moulds with a Lyman HP pin in one cavity.... If you are interested in seeing an inventory run, please post in this thread....  http://noebulletmolds.com/smf/index.php/topic,2316.0.html

Please state the size(s) that you are interested in....

Bob

13
OFF TOPIC / We Will Remember Them
« on: November 11, 2017, 08:09:30 AM »
High Flight

John Gillespie Magee, Jr

Oh! I have slipped the surly bonds of earth,
 And danced the skies on laughter-silvered wings;
 Sunward I've climbed, and joined the tumbling mirth
 Of sun-split clouds, --and done a hundred things
 You have not dreamed of --Wheeled and soared and swung
 High in the sunlit silence. Hov'ring there
 I've chased the shouting wind along, and flung
 My eager craft through footless halls of air...
 Up, up the long, delirious, burning blue
 I've topped the wind-swept heights with easy grace
 Where never lark or even eagle flew --
And, while with silent lifting mind I've trod
 The high untrespassed sanctity of space,
 Put out my hand, and touched the face of God.

In memory of F.L. John Sterne, D.F.C.... and all those who paid the ultimate sacrifice.... We Will Remember Them !!!

Bob

14
Airgun Ammo / .308 cal 106 gr. Airgun Bullet at NOE
« on: November 06, 2017, 06:28:22 PM »
Brand new design I didn't even know about, now in the store....

http://noebulletmolds.com/NV/index.php?cPath=30_515

RG2 and RG4 moulds available, they come with flat nose (106 gr.), cup point, and hollow point pins (100 gr.)....

Bob

15
Ask Bob / How Barrel Harmonics Can Affect POI
« on: November 06, 2017, 03:30:41 PM »
There have been some recent discussions about the use of Harmonic Barrel Tuners to dial in a PCP for a given pellet and velocity.... Here are some generic charts showing what happens when the pellet arrives at the muzzle of a barrel that is vibrating in the vertical plane.... The first chart shows an example of the angle the muzzle is pointing, relative to the boreline at rest when the trigger is pulled.... I drew the chart so that a pellet travelling at 900 fps would arrive at the muzzle at the point where the barrel is at its highest.... with that being a bit over 2 MOA (it might be more or less, depending on barrel stiffness)....



You would think that would be the worst possible case, because the barrel is the furthest from its position at rest.... but in fact it is pausing at that moment, because is it reversing direction.... In the second chart (a detailed view of the last peak in Chart 1), each dot represents the time the pellet arrives at the muzzle, with a dot every 10 fps from 800 to 1000 fps.... 900 fps is at the peak, because I chose the vibration frequency to make it so.... You will note that there is hardly any difference in the angle the pellet leaves the barrel for quite a large ES either side of 900 fps.... That intuitively might tell you that is the optimum velocity for a barrel vibrating at this frequency.... However, that is incorrect also....



The next chart shows the POI of the pellet (I chose a BC of 0.036 to get these numbers at the various velocities).... If the gun is sighted in at 100 yards when the velocity is 900 fps, then at 800 fps it hits about 6.5" low, and at 1000 fps about 4.2" high.... At 800 fps, a 20 fps ES changes the POI about 1.5".... At 900 fps, it makes about a 1.0" difference.... and at 1000 fps, that 2% ES changes the POI only about 0.7"....



When you combine the flatter trajectory of faster shots with the angle of the muzzle at the instant the pellet leaves the barrel.... you get an interesting result, as shown below (gun again sighted in at 900 fps at 100 yds.).... The slower pellets (eg. @ 800 fps), arriving after the peak of the barrel vibration, shoot lower on the target.... but the faster (1000 fps) pellets, arriving when the barrel is still travelling upwards, ALSO shoot lower on the target.... This increases the vertical dispersion for pellets travelling slower, and decreases it for pellets travelling faster.... Now, for that same 20 fps ES, pellets at 800 fps have vertical stringing of 2.1" (instead of 1.5").... those at 900 fps are still about 1.0".... but pellets at 1000 fps, with that same 2% ES, only have a vertical stringing of less than 0.3" (instead of 0.7")....



It is important that you do not interpret this to mean that faster is always better.... The concept I want you to understand is that by using a movable weight (or changing a weight) attached to the muzzle, you can change the frequency at which the barrel vibrates.... If you want to shoot at 900 fps, then you want the barrel to be on the upswing, but nearing the top of it's movement, when the slowest pellet arrives at the muzzle.... This adjustment is arrived at by trial and error, but can reduce the vertical dispersion of your groups once you find it....

Think about it this way.... The slowest pellet in your shot string arrives at the muzzle when the barrel is nearing the highest point on the swing, but still on the way up.... It is launched on a higher angle, but going slower, drops more.... Conversely, the fastest pellet arrives earlier in the vibration cycle, when the barrel isn't pointing quite as high, but going faster, drops less.... The combination of these factors can reduce the vertical stringing of the shots when they impact a target downrange.... I hope this explanation helps you understand the merits of tuning the harmonics of your barrel for the velocity you are using....

Bob

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