Hacking the Crosman Vigilante

[George Schmermund]

It came to me today that I've totally neglected the aspect of controlling the loudness of airgun reports. The topic was one of my original quests when I started this adventure and then got side tracked during the tsunami of other tests and measurements. At this point I'll just have to admit that I have no control over what I want to do next. There are many pieces to the puzzle of how airguns work, but if we keep collecting the pieces as we go I think that some of us will benefit when the dust settles. A clearer picture may then be seen. I'll just park my information here until things appear to be made from whole cloth.

Sound and vibration are next to come. Stay tuned (pun).

[George Schmermund]

I got diverted back to the electropolishing on the barrel. A discussion with my buddy Bruce got him fired up about the process, too. One of the topics was about how to build and use  a carbon fiber (CF) brush as an alternative to doing a dip bath approach. In the interim  Bruce put together a brush and brought it over to my place to test it on some SS weld coupons that he brought along for testing. I had the acid electrolyte components so we mixed them up for a test run of his CF brush  project. The results were strikingly good.

Since the electrolyte was mixed it seemed like the right time to get into the barrel treatment I had been planing. Two of the short barrel cross sections were polished using the dip method. I was able to partially dip them into the solution and just treat part of the barrel as a comparison test. The images show the transition area along with the treated and untreated areas. The photos are of a barrel section that was polished for 1 minute. The grain structure of the lands is very clearly seen. The tool marks have dissapeared.

The features in the images are quite small. The step height between grooves and lands is less than .002". The actual height is difficult to measure accurately by mechanical means. A first approximation can be guessed at with a small hole gauge, but it's still a guess. Contact measurements at this scale tend to deform the surfaces being measured and will introduce errors. I'll probably end up mounting the barrel section in a metallurgical mounting press and then use an optical micrometer to get good numbers.

In the mean time it is sufficient to see that the polishing can controllably remove surface material selectively in the range of a couple of microns. The machine marks left by the rifling tool leaves marks on top of the lands that are down in the microns range. I'll use a surface profilometer at some point to determine the real numbers. Right now I'm only interested in the grosser aspects of the polishing process.

The electrolyte mix that was used to do this work was mixed to do the best work on stainless steel. It's a very aggressive recipe to be using on what might be mild steel of the barrel. I'll do some more research and see what the best mix will be for steel barrels.

On another front, the sheet of Scotchlite 680 that was ordered has now arrived which will allow the shadowgraph experiments to proceed. I'm getting pretty excited to see the results.

As an aside, I've been working with the focus stacking software and getting better with it as I go. I'm adding a photo of a single frame of the stack of about 25 images to illustrate the power of this technique. Keep in mind that these stacks are imaging an arcing semicircle formed by the barrel.

[George Schmermund]

I've been puzzling over the best method for measuring the lands and grooves of the cross sectioned barrels. The metallurgical mount and polish technique is the best method, but it sure is time consuming. After pondering the project over a few beers it came to me that there was a linear displacement transducer instrument somewhere in one of the darker corners of the attic. Braving the darkest sanctums of my techno-repository with a flashlight, I was able to recover the device.

The virtue of this particular instrument is it's ability to make very accurate measurements down to 1 micron. What makes it different from the typical precision micrometer is the force of the probe against the anvil. The measurement specification for most micrometers requires a load force between the spindle and anvil to be .5 to 1 N. This amounts to a force of ~ 50 to 100 grams. Applying this load also requires that the spindle be rotated while applying the force. This is an undesirable situation for the measurements that I want to make. These high forces also make it difficult, if not impossible, to measure the diameter of heads and skirts of many types of pellets with any accuracy or reproducibility.

As can be seen in the photos, this linear transducer has a loading force of only 2.5 grams! The probe doesn't rotate and the anvil and probe can be customized to accommodate barrel sections, pellets, and other small featured items. 

[George Schmermund]

I've been giving some thought to valve dwell time and pellet transit time in various barrel lengths. For clarity I'd like to say that, from what I've read, it seems that in airgun vernacular the 'lock time' is the same as what I'm referring to as 'transit time'. This is a holdover from charged particle physics in my case. If the terms are not usefully interchangeable please set me straight.

Anyhow, what I've noticed in the previously posted O-scope traces is that what I thought was the first hammer bounce is more likely to be the rebound of the valve stem. The timing is consistent at very close to being 4 ms and the profile is shaped differently from the hammer strike. If this is correct it will be very useful when relating it to a pellet's transit time.

There was a comment that some of the things that I'm measuring are not generally transferable to other airgun platforms. I'm somewhat nonplussed by this comment because the measurements that I'm making can be easily rearranged to suit the requirements of other airguns. It's just a matter of choosing the right transducers and readouts to get the numbers that you want.  This brings me back to my mantra: 'Don't calculate what you can measure'. Nothing against spreadsheets, but.....

[George Schmermund]

I thought that it was time to take another look at choking a straw barrel. The last time that I played with the lathe and knurling tool on a barrel it was to confirm that the technique was viable and just used the test as an exercise in making the measurements as accurately as I could. As previously posted, the knurling worked quite well to reduce the bore diameter at the muzzle.

Since then I've read a lot of information about the the process and very little about any measured results. I've also made some dimensional measurements of the lands and groves. Considering how small the step is between the grooves and lands, I now had a target to aim for (pun) when deciding how much choke to apply. I chose 1/2 mil (0.0005") as a start. The bore was reduced from .1778" to .1773". The force involved to accomplish that was surprisingly low. At some point I should construct a micro load cell in order to attach a number to this force. All in good time. Right now I just wanted to measure the dimensional change in the bore and see the effects on a target.

Anyhow, it was finally time to test the results. I chose to do the preliminary tests with CP Destroyers and CP Pointed pellets. I already knew that the CP Pointed ones were a gross disappointment from previous tests. The Destroyers always seemed to produce favorable results in the assortment of barrels that I've used. Could a choke improve the earlier results and make the Vigilante less fussy about what its fed?

The photos show the difference between the two pellets when shot through the unchoked and choked 10" barrel. The shots were fired from 15 feet. I used each quadrant to separate the results of 10 shots per group and keep them on the same target sheet. One quadrant of the pre-choked Pointed group has only 5 shots. The test in the last quadrant of the CP Pointed choked group was not done because of low pressure.

There are a lot of other measurements still to be made, but this is where we are now. I think I see an improvement, but I'll leave that up to you guys to make further assessments.

As an aside, I'd like to add that a ten shot string with the powerlet temperature adjusted to 82º F gave an average velocity of 596.4 fps using the CP pointed pellets. I'll try boosting the temp to 85º F and see what the difference between the CP Destroyer and CP Pointed comes out to be.

[Rob M]

the results are looking very promising.. i wonder if a longer pellet would do any better

[George Schmermund]

Now that I've become so enamored with the idea of pushing pellets through barrels to test drag characteristics it seems practical to relieve the lathe from having to be tied up for the tests. I've had a universal testing machine sitting in the corner of the garage for a long time just taking up space and collecting dust. It's time has come to earn its keep. This is actually the type of machine that should be used for this type of testing and also many other tests that I'm now considering. Who knew that airguns would become this recreational?

The machine is rated at 10 kN ( one metric ton) for both compression and tension. It would be considered rather lightweight as far as universal testers go, but will work out perfectly for my airgun plans. By changing load cells it will be able to measure down into the grams region. These expanded capabilities are getting very interesting (to me).

[Rob M]

you have 1 of everything , this is crazy lol

[AmBraCol]

These expanded capabilities are getting very interesting (to me).

AND to some of us sitters-by...  What equipment do you NOT have "sitting in the corner of the garage..."?   

[George Schmermund]

I decided to put the parts together and see what the Vigilante would look like in full dress. I also wanted to have something to shoot targets with. The new knurled muzzle choke is considerably more accurate than the stock version. This is a pleasing outcome and worth the effort spent so far. There's still lots more to test and measure, but I'll get back to that soon enough.

I've left the knurled part of the barrel extending out past the housing extension. That's going to be my signature on the barrels that have been tuned and choked.   

[George Schmermund]

I've been spending some time actually shooting a couple of Vigilantes at targets. The barrel with the knurled choke seemed to work better than the non-knurled ones, but I wanted to see what the difference would be if a new barrel was crowned differently than usual. Then it could be compared to a choked one and the two methods could be compared. This test could actually be expanded because I'm using a Crosman 1077 barrel to make two new 10" barrels. The nice thing about this is being able to make two 10" muzzles from the middle of one 20" barrel. That means that the two muzzles are literally identical because they are from the same point in the middle of the parent 20" barrel.

Since the bench testing and measurements so far have not required any special need for anything more than generic pellets, I've collected only the readily available Crosman Premier tins from Amazon and Walmart. These include destroyers, pointed, and hollow points. When I'd done some target shooting in the past with these different pellets, the Vigilante showed a marked preference for the destroyers in any of the previous barrels. The pointed and hollow point pellets were consistently producing groups(?) with many flyers that made shooting them unenjoyable, to say the least. The destroyers always seem to give good results at my standard 15" target range, though even they weren't without the odd flyer.

The photo shows the results of the new muzzle crowning method. To keep the different pellets on the same target, I shoot each different type at one quadrant and then rotate the target. That way I can get at least 4 different tests on the same piece of paper and not have to re-aim the gun. Each of the 3 groups are 10 shots. That's 30 shots without a flyer!

I'm rather stunned by the results and don't really have an explanation yet. I hesitate to do the choke knurling at this point until I can determine what's really happening. The target is at the usual 15' and the gun is clamped in a vise in order to eliminate any marksmanship requirements. I readily admit to being a lousy shooter.

[Rob M]

thats really good to hear.., id love to see sight assisted 10 yrds

[George Schmermund]

The progress continues with the Vigilante hack. The results of the muzzle crown and knurled choke testing demonstrate that accuracy can be significantly improved and the number of flyers can be greatly reduced even with pellets that don't work well with the factory barrel. More testing needs to be done to find out how these improvements came about. The high speed muzzle shadowgraphs will be a great help in sorting some of these things out. I'll have to move that testing back up the list of experiments.

The barrel and housing design has stabilized for the time being and I've decided to build up some units as a direct replacement of the factory one.  These barrels can be switched over with just 1 screw. I'm listing these new type barrels on eBay if anyone is interested in acquiring one. Just look for "Vigilante upgrade".

[Rob M]

the ebay mod looks great and adresses more issues than i thought, very cool

[George Schmermund]

Now that I've been doing some actual shooting at targets it's become obvious to me that I can't hit much of anything if I use the factory sights. After buying a cheap red dot sight the possibility of being able to hit what I'm aim at seemed close at hand. The problem is that the Vigilante is made more for a tactical look than function. The barrel rail, even with the new rigid stabilization, is not designed to accept much in the way of add-on sights. Those of you that have vigilantes know how limited the top mount really is.

I decided to mill off the front sight and machine a new tactical mount that could be rigidly fixed to the rail. The new mount now allows a sight to be moved forward enough to make room for easy actuation of the barrel latch. The photos show the new arrangement on one of my testbed revolvers.

There are still plenty of things that can be done to improve the overall performance of the Vigilante. I'm glade that I've taken some time off from testing so that I can make sure the things I've been posting about have some relevance to the real world of actually using the gun for target practice.

[George Schmermund]

The the top rail was a good start in the direction of adding some form of sight, but it was left wanting. The original rail was machined from nylon (it was handy), but was a bad choice because of it's flexibility. When it was attached to the barrel housing rib and the plastic cheap sight was added, it really wasn't stable at all. The Gamo sight alone seemed to be made from recycled rubber bands. That's OK, though, I just needed a place to start.

This weekend's project was to buy a better sight and machine a new rail. The results come out much more like what I had in mind. The rail is machined out of aluminum and is much more solid. Also, the red dot scope is far superior to the first one. The Barska is still a low-end device, but will be satisfactory for the time being if it continues to work properly. Overall, the pistol is considerably stiffer than when it came out of the box. More can still be done in that direction.

I'm working on the ergonomics of this gun to make it friendlier to a guy who is a lousy shot. The next step is to add a forearm grip under the barrel housing to asset in two handed aiming. The vigilante is getting closer to becoming a carbine. Plans are in the works for a shoulder stock. 

[Rob M]

wow, this is awesome ! id love to see it as a carbine , and be equally interested in seeing what a competition pistol shooter could squeeze from this design !

[George Schmermund]

A Delrin forearm has made the vigilante a new gun and was worth the time needed to machine it. The pistol now handles unusually well with the a forward grip. The overall increase in weight, even when moving the sight all the way forward, is easily balanced without needing a sandbag or rest. When the shoulder stock is added I'll have a mini-carbine. I may finally be able to hit something that I aim at!

I originally was looking at getting a Crosman 2240 and hacking it, but I didn't want just a single shot gun. These Vigilantes are turning into the pistol I've been looking for. There's much more to do and each step forward makes it a more desirable gun for me. The next step is to cut off most of the protruding trigger and just use the seer to fire the gun as a single action only repeater. It's not going to be a 'lawyer trigger' anymore, but I'm betting that it will improve my shooting accuracy considerably.

I'd like to again say thanks to all of you who have been patiently following this project and for all of the positive and encouraging comments. I'm not much of a conversationalist in a forum venue, but I do pay attention to all of your comments and replies.

[George Schmermund]

Extra Photo.

[Rob M]

Extra Photo.

looks great , nice knurls