smooth bore pen gun - 25 acp

[BCJ]

I'm in need of a new project and am out of things to suppress. I have been thinking about just making a smooth bore 25 acp pen gun. I need help to figure out the correct bore diameter to use so that I don't spike the pressure by making it too tight or lose pressure by making it too loose.

The bullet diameter is .251; I was planning on making the bore diameter match at .251 so there is friction to create the seal but not too small to spike the pressure. If it were rifled the bore would be .243 and the groove would be .250. Knowing that should I plan a smooth bore to be .250"

Thanks

[Bendersquint]

I'm in need of a new project and am out of things to suppress. I have been thinking about just making a smooth bore 25 acp pen gun. I need help to figure out the correct bore diameter to use so that I don't spike the pressure by making it too tight or lose pressure by making it too loose.

The bullet diameter is .251; I was planning on making the bore diameter match at .251 so there is friction to create the seal but not too small to spike the pressure. If it were rifled the bore would be .243 and the groove would be .250. Knowing that should I plan a smooth bore to be .250"

Thanks

Why are you not using a barrel?

[BCJ]

Barrels for .251 seem to be harder to find unless a buy a full blank or get a barrel liner. I only plan on the barrel being 2" long so a blank seems like a waste unless I can find a piece of drop.
I'd be happy to buy a piece of drop if anyone has one. Otherwise for the range of a pen gun a smooth bore doesn't seem terrible. I want a centerfire round to keep things simple with a breach and centered firing pin

I built a flashlight looking AOW a while back for 38 short colt but basically had the bullet even with the end of the barrel so it was basically just a chamber. I did an offset bore 22 lr barrel also but just left it smooth for the barrel. I might go back and use a section of barrel liner for the 22 barrel in the flashlight.

[Tony M.]

Glad to see some interest in AOW's here. I've got a smoothbore .25 and the bore is indeed .250. I've shot it with .251 and .252 bullets and it's just fine.

I'm thinking about having a rifled barrel made as a replacement. No particular reason beyond "I can".

[mpallett]

I "might" have something you can use. I'll look around.

[BCJ]

Glad to see some interest in AOW's here. I've got a smoothbore .25 and the bore is indeed .250. I've shot it with .251 and .252 bullets and it's just fine.

I'm thinking about having a rifled barrel made as a replacement. No particular reason beyond "I can".

Thanks for the feed back and confirming what I thought. At minimum I plan to make an additional barrel for the flashlight gun in 25acp. My pen gun may just end up being a 22 lr with offset floating firing pin.

I "might" have something you can use. I'll look around.

Thanks

[Gunfixr]

Check Numrich. I ordered some .25acp barrels for Ravens, Davis's, or some other cheap pistols to do something just like this for a customer.

They were like $20 or something. All chambered and ready to go, about 7/16" OD at the chamber, 2' or 2 1/2" long.


Here ya go, Jennings barrel, .25acp. Part # 1395700, $26.

[BCJ]

approved form 1 = a stainless steel pen gun. I ended up going 22LR
All parts were made from scratch (other than two springs). I made an offset captured firing pin and striker assembly. Barrel is 416 stainless from a green mountain blank, everything else is 304 stainless. I still need to blast the whole thing for a nice finish.


Ready to fire



Offset firing pin

[quietoldfart]

Hey now, that is a fun little thing! Bet it'll sting a bit on firing though. Have you tested it yet? Looks small enough that shooting your own finger(s) off might be a concern... hm, if I were in a position to make something like that I might consider going to a 3/4" diameter (yours looks like 0.50", maybe 4.5" long with the bolt not extended?) and threading the front end, using about a 4" long thin walled tube with half a dozen micro K baffles in it. Just use something like a CCI Quiet or Gemtech Silencer Subsonic and you might have a very quiet little package. Okay, so it'd be about 8.5" x 0.75", but still pocketable more or less. If need be cut the suppressor portion down to 3", but then there won't be much reduction in blast left. Perhaps a longer barrel then and only 2 or 3 K baffles in front with much of the body being thinned enough to make over-the-barrel volume helpful in absorbing the initial blast... Such a project does get a tinkerer thinking! Nice work.

[BCJ]

Its five inches long so there's enough to hold onto without having fingers on the barrel. I've put three rounds through it so far just to test it out. Its fun to shoot and being all stainless it weighs enough to counter the little 22 round.

If not for the price of stamps I'd make a small flashlight gun with built in suppressor.

[srs]

I'm guessing that a suppressed pen gun would be a two stamp item?

[quietoldfart]

Yes, I suppose you fellows' stamp collecting hobby can become expensive. Thank you for sharing the project with us all. Might I ask for a sketch showing the interior workings in cross-section? I'm a bit puzzled by the small hole near the firing pin for example. I really enjoy the simplicity of the trigger mechanism, quite ingenious.

[BCJ]

The firing pin is just a short piece of drill rod with a cut out it in so it is captured by a pin (the pin is in return captured by to collar).
You can see the offset bore for the firing pin here and the small hole for the retainer pin cut through he threads.


This is the firing pin. Its a piece of drill rod with a cutout for the capture pin


The striker can be see here, it is centered in the receiver


Anything that I couldn't make on a lathe had to be hand filed from key stock or flatbar.

[quietoldfart]

Again, simple inside as it is outside. A nicely reliable mechanism, easy to work on if need be. Very good sir.

[BCJ]

Again, simple inside as it is outside. A nicely reliable mechanism, easy to work on if need be. Very good sir.

Thanks

[GHEN]

This is a great thread!

Thanks all for sharing.

GHEN

[quietoldfart]

This project of yours, BCJ, it stuck in my head. Couldn't shake it. And so, you know the thing about idle hands... I've gone ahead and done a bit of experimenting. My first prototype was based on a 6" length of airgun barrel in .22", bored out to be a slightly sloppy fit for .22lr. I pressed this into a 3/4" aluminum tube 12" long and drilled and pinned it in a couple of places after turning a 1/2" section at the breech end down and threading it for the rear cap. Long story short, it's a 14" long integrally suppressed .22lr 'wand' gun. The familiar key ring to pull back and cock the sear. A simple external trigger and sear. Very manual, just the one spring to smack the hammer into the firing pin. It works, is quite surprisingly quiet considering it's just a stack of slightly cone-formed washers with thin steel tube spacers, but it's awkward and silly and I'll not post a picture as it's embarrassing.

#2 worked out quite a bit better. Another section of airgun barrel, this one threaded at both ends so I can thread on a suppressor and at the back for the trigger/sear mechanism. It uses a floating firing pin set into a slot down one side of a bolt, retained there by a tiny magnet inlaid into the bolt and a small cap brazed to the rear of the pin. It's about 6" long overall, a bit awkward to cock, but it works. Again nothing quite worth showing off but a good learning platform to get me ready for #3.

#3 is starting to look like something worth sharing:


And here's a 25 image slide show displaying the various components etc:

http://s1319.photobucket.com/user/quiet ... deshow/pen

Can't seem to sort the pictures in the order of the build though they're named sequentially, but oh well, the idea should come across. It's 5.4" long (haven't yet found a pen tip to mount in the front, but it'll still be under 6" with a cap) and 0.55" diameter. The trigger/sear saddle is brazed into place then finished. Trigger/sear arm is O1 tool steel, which I managed to snap in the vise when almost done so I just brazed that back together, tested, found strong enough and used anyway. The two springs give enough push to the hollow hammer to make it fire reliably. The body is made from a Chinese (Industry Brand) airgun barrel, this time bored out just barely big enough to fire subsonics, safely, so there is a trace of the airgun rifling left intact which does score the .22lr lead neatly if not deeply when pushing a round through manually. I'm going to make a bigger knob for the bolt as the small round headed bolt is a bit painful to push back. I will make something large enough to be tightened into place by hand, as I want this to be a tool-free gun for maintenance. The back cap comes off by first cocking the sear, then pressing it further still into the hole to extend the trigger spring, plucking that spring off the small retaining pin, then pressing the trigger to bring the sear tip up just barely clearing the barrel for unscrewing.

The spring under the trigger is compressed most of the time, so pushing the bolt back drops the sear pin into the space ahead of the hammer (the head of the firing pin separates the hammer and bolt by about 0.10") just as the bolt maximally compresses the two springs. A cartridge drops in easily, if barely - I wanted to keep the slot as short as practical. There's about 2" total of barrel including the breech portion which is drilled out a bit larger to be an easy but not too large fit. No extractor, so I made a little steel push rod in a plastic knob to get brass out if it gets stuck.

It fires nicely. This one's a gift, so I didn't thread it as the recipient wants something which looks at least somewhat like an actual pen. I'll be bluing it this week.

I've some other projects to get back to so no more pen guns for a little while, but it's such a fun sort of project and really not very difficult to shoot. I'll try to find an old proper .22lr barrel for whatever's next. I expect something similar to #3, but threaded at the front for a small suppressor with some K baffles, and a screwed-on pen tip of course, with cap.

[quietoldfart]

Here's the finished pen gun, blued this evening with Outers Gun Blue. Came out more brown than I was expecting, which is good as I'd hoped for a brown just expected more of a cold grey-blue. Before doing that I was concerned about the firing pin strike area at the breech, as when dry firing without brass in the chamber it tended to peen badly. I decided to drill it with a flat-ended twist drill then set in a 3mm wide bearing from a bicycle chain, a Sedis Sport to be exact, and solder that into place. Had to ream the inside diameter with a diamond burr in a Dremel tool first to fit cartridges comfortably. Then just pressed it into the hole and soldered and it works flawlessly now. The bearing steel is too hard to dent, and so long as the owner doesn't dry fire too often without brass or a snap cap in place it should last a very long time.

[quietoldfart]

Here I go again, shamelessly bumping an old thread in the name of... well, completeness I suppose, not vanity, as I've been working on an ultra-lightweight .22lr takedown rifle and have not taken the time yet to work on the next edition of the pen gun. This pictures simply illustrates the very last changes to my second edition. I brazed a pocket clip onto the cap, and fitted a more compact, sensible trigger mechanism to the body. I can make it much more sleek for the next version. No need to have the trigger/sear sticking out so far. and the pocket clip will be bolted into place, as I'll plan ahead and leave enough thickness for drilling and threading. But this one works well one-handed, both cocking and de-cocking.

[rockman96]

I'd forgotten this thread... What you've built here is very cool. Can't wait to see the new design.

Are you free to do this sort of thing at will in France, or do you have to go through a process like we do here? Just curious.

[quietoldfart]

Not exactly free to do things at will. There are some rather complex regulations in place, especially around transport. As the laws are somewhat... circuitous, to say the least, I occasionally engage the assistance of an attorney to keep things sorted. For my semi-automatic pistol, for example, there was a psychological/medical evaluation as well as a requisite course of study and examinations, a permit process, as well as membership in a sporting club. It may have helped that I purchased that pistol and magazines from a senior gendarme of my acquaintance. For single shot rimfire weapons there is less legal concern. In the name of keeping my life simpler I choose not to shoot anything larger than .22lr. Besides which, larger calibre arms tend to be noisier, something to which I am averse. Of course concealed carrying of any sort of firearm is off the books, requiring a legal 3-ring circus of applications and testing and excuse-making, not something I wish to engage in nor for which I feel any need. There is a maximum of 12 firearms permitted for a civilian, and ammunition stores may not exceed a certain number of rounds per weapon type. Though complex and at moments troubling, these minor difficulties pale in comparison to the often nonsensical regulations in my native UK, especially those around pistol use.

[Capt. Link.]

It seams the MAC Stinger is not dead.I'm pissed I missed this post as I have a few short barrel stubs and would have been happy to supply a barrel.Anyone up to a .357 sig Stinger or a 40 S&W. I'll ship as far as France if you pay for shipping and its legal.The last pistol is a WW2 throw away.The one built on the knife mat not be a AOW but a non NFA pistol!
Here's some eye candy for inspiration.

[quietoldfart]

An interesting collection of examples Capt., thank you! I'm not able to discern the mechanism of the 'syringe' model, have you any thoughts on how it functions?

And thank you for your generous offer. Fortunately, the barrel I acquired for my take down rifle project will provide material for the next pen gun, still leaving enough after that for one more. I'm using just 10" of a 1:16 Winchester .22" barrel and so have 10" more left over. Should provide a bit better accuracy than those I've made based on air rifle barrels and had to slightly ream to allow safe passage of the lead - airgun barrels being slightly under-sized for the same nominal calibre. The outside diameter of this remainder tapers from 0.675" to 0.575", leaving a lot of thickness for me to really think about other options in the designing. One thing I'd like to try is a push-through stop for the bolt rather than a dogleg cut. This would keep the appearance much simpler, allowing for a simple oblong loading slot. There could even be a secondary hole for this push-rod with a button head, allowing for retaining the bolt open against spring pressure. Neither of these holes would need to run to the outside as there's so much steel, allowing each to be drilled slightly shy of the outer diameter thereby keeping the far side intact. And I'll be able to drill and tap the back end for a simple plug for spring insertion, no need for a thin-walled external cap. This allows for a much larger spring, so ample power for assuring a shot every time.