Hacking the Crosman Vigilante



Author Topic: Hacking the Crosman Vigilante  (Read 12519 times - 3 votes) 
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Offline George Schmermund

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Re: Hacking the Crosman Vigilante
« Reply #260 on: November 22, 2017, 10:28:31 PM »
I spent some more time machining the 6 shot clips today and the new reamer is working perfectly. With the new fixturing in the mill the precision of the drilling and reaming has been improved. The improved clip alignment with the forcing cone has now increased the muzzle velocity to run fairly steady between 350 and 375 fps @ ~ 80 F with rapid cycling. This isn't really great performance in the overall scheme of things, but it's an improvement. I'm going to order some longer barrels from Crosman and see where things get to before hacking the powerplant.

« Last Edit: November 22, 2017, 10:30:04 PM by George Schmermund »
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Offline Rob M

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Re: Hacking the Crosman Vigilante
« Reply #261 on: November 23, 2017, 01:08:12 AM »
looking very nice.. at some point , the barrel length will outweigh the available gas.. But when that is , who knows.. I'm guessing a 14 inch barrel would be a great starting point , and even the 10.3 incher would in theory get  you over 400 fps.
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Offline George Schmermund

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Re: Hacking the Crosman Vigilante
« Reply #262 on: December 06, 2017, 10:53:26 PM »
Now that I've started the Vigilante .22 cal project it's obvious that I'll need to get more gas into the valve section. At the moment it seems reasonable to increase the volume of the valve and to enlarge the transfer ports. It all looks pretty straight forward with some simple machining.

The volume of the valve can be increased about 20% initially by machining some grooves into the inside wall of the valve body. The wall thickness is nominally 0.100" thick. By cutting some grooves into the inner wall and leaving some space between the groves I should be able to leave small sections of full wall thickness that will act as sort of inverse barrel hoops to deal with the pressure.

The photos show the setup to measure the inside wall uniformity and also the wall thickness. I'm using a Starrett back plunger dial indicator arrangement for the lathe measurement. It's virtues are that it's an easy measurement and it can reach further into the valve cylinder than the typical test indicator. It also gives me reliable axial alignment for setting up the grove cutting tool.
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Offline Rob M

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Re: Hacking the Crosman Vigilante
« Reply #263 on: December 06, 2017, 11:11:27 PM »
very nice setup ! looking forward to the gains produced !
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Offline WhatUPSbox?

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Re: Hacking the Crosman Vigilante
« Reply #264 on: December 07, 2017, 02:35:33 AM »
The full thickness section barrel hoops will not help with the axial strength of the valve wall if you thin it too much in the grooves. May be worth running some quick numbers to make sure you have sufficient margin.
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Offline George Schmermund

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Re: Hacking the Crosman Vigilante
« Reply #265 on: December 08, 2017, 04:00:27 PM »
Assuming that the valve casting material is ZAMAK 3 (a safe bet) and using Barlow's Formula, the burst strength of the valve walls when thinned to .035" should be in excess of 3000 PSI near room temp. This would be without any internal hoops. I don't plan on the working pressure getting above 1000 PSI.

The longitudinal forces at 1000 PSI have a safety factor of at least 10 under worst case conditions.
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Offline George Schmermund

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Re: Hacking the Crosman Vigilante
« Reply #266 on: December 10, 2017, 07:42:51 PM »
Up until now I've been using split ball bore gages to measure the effects of muzzle treatments and general small hole dimensions. The down side of these instruments is that they require a transfer measurement to get the numbers. This method will allow for only one static measurement at a time. This makes probing the bore at more than one place slow and tedious. Also, the radius of each 1/2 ball is generally too large to get a measurement down to the bottom of the grooves in the rifling so you're left with only the bore diameter at the lands.

I've just acquired a dial type bore gage that uses a different technique. It's a vintage Federal Products instrument that makes dynamic measurements as you continuously probe around in the private parts of a bore. It will reach in 2 1/2" and reads directly to 0.0001" It can easily be interpolated to 1/2 of a tenth. There are 12 probes that come with the set and each probe has a range of 0.008". The full range on this set is from 0.122" to 0.250". This will cover the barrel bore diameters of interest to me now. The use of setting rings is a big help in setting and calibrating the probes, but a good micrometer can also be used, thought it does make for an awkward measurement.

Besides the dynamic reading capability, I like the radius difference between the larger and longer fixed anvil and the smaller radius of the moving ball anvil. The ball can get down into the bottom of the grooves and the longer fixed anvil can straddle the grooves while staying on the faces of the lands. This allows accurate step height measurements of the rifling.

The photos show the basic arrangement of the instrument.
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Offline George Schmermund

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Re: Hacking the Crosman Vigilante
« Reply #267 on: Today at 10:11:49 PM »
The project to expand the volume of the valve by removing material from the ID of the valve body seemed pretty straight forward. The calculations indicate that the remaining wall thickness was safe at typical operating pressures. The problem with the approach of removing material is that I can't put the material back in if need be. After studying the situation through the lens of a few extra beers the solution came to me in the form of another one of my visions.

I'll make an adjustable volume by adding an appendage to the side of the valve body that can be exchanged for different sizes as needed. There's quite a bit of room between the pistol frame halves to accommodate these extra volumes. Starting with a piece of 1/4" 12L14 steel rod, I'll bore out a blind hole to some yet to be determined ID. The open end can then be threaded to 1/4"- 40. The valve wall can be threaded to match. Loctite red can them be used to seal the threads. Using the same threading arrangement will allow the change of appendage volumes without having to do any more machining on the valve body.

The photo shows the basic tooling needed to accomplish the task.

 
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How do you word it... "Air Guns" or "AirGuns"?