Integral 22 bolt action question

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John A.
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Integral 22 bolt action question

Post by John A. »

Once I get my permission slip back from the ATF, I plan to make an integrally suppressed bolt action.

While most integral rimfires are similar, mine would probably be nearest to the Gemtech Mist 22 design. Though obviously not exactly. Nor do I want it exactly like it.

Baffles will be a pin/welded monocore to avoid 2 stamping the gun.

My barrel will be ~ 12.5". Once the monocore is perm. attached will be about 17.5" overall.

I have read that gemtech no longer ports their barrels. Something about many folks complaining that they can't get their tube off to clean under there.

While I don't initially plan to port off enough gas that supers will drop below sub, I do want to port some of the gas because it'll make it more quiet. And if finding ammo becomes problematic again long term, I could always open the port(s) up more later on if I have to. But for the time being, I have about a case of subs I want to shoot up before going ape-googly with the mill and drop my velocity too much.

I plan to make a long rear endcap that the outer tube will (barely) slide over and use two O rings on the OD of the barrel and slide the barrel sleeve/suppressor tube over the barrel and tension and seat it using the front endcap which is male threaded to screw into the front of the monocore to cam the tube that way. It should all but eliminate thread leading while sealing the rear portion off.

I am going to taper the rear endcap and the butt of the suppressor tube so once the front endcap is tensioned in place, the joint should seal pretty well. kind of like an opposing angle self centering taper cut.

Also, I plan to notch the rear of the monocore to allow some of the gas to travel back over the barrel as a reflex can too. There is just so much area over the barrel, I want to utilize it as much as possible, aside from the barrel ports.

Which brings me to a question.

Would it sound better if I separated the area over the barrel into 2 chambers by using a thin divider essentially separating the barrel ports from the reflex chamber? Or just leave the entire barrel sleeve/suppressor tube open and pack it with copper mesh?

I'm not convinced that with 22 subs that there would be enough gas ported out over the barrel to fill the tube, and then bleed into the expansion chamber. The barrel OD is around .620", and the ID of the barrel sleeve will be .995"ish. I would think that it would take a lot of gas and pressure to fill that up. I'm just not convinced that a 22 would need to divide the large space over the barrel.
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Re: Integral 22 bolt action question

Post by ECCO Machine »

Porting is definitely still worthwhile. I don't use any packing on mine or any segregation between the ported section and the monocore, and it's firing pin click quiet. 10.5" of barrel with a dozen and a half 1/16" ports and 10" of monocore.
John A. wrote: The barrel OD is around .620", and the ID of the barrel sleeve will be .995"ish. I would think that it would take a lot of gas and pressure to fill that up. I'm just not convinced that a 22 would need to divide the large space over the barrel.
Turn that barrel down to gain volume and shed weight. With no internal image hosting here and no good external hosts since photobucket's cash grab, I don't really post photos, but basically I turned the barrel down from the receiver to the thread tenon shoulder. It's .500 for a bit over an inch from the receiver, then stepped down to .400. Over that .500" section is the aluminum sleeve that is the rear cap, but slotted and relieved for the mounting screw stud dovetailed to the barrel (it was an old Western Field model 45). Just forward of that, the sleeve is solid and a snug fit to the carbon fiber tube (23mm ID x 25mm OD), which extends all the way to the front. The snout of the monocore is male threaded 3/4-28 x .250 with a knurled threaded collar to secure it. I do not use any O-rings, just not necessary with rimfire, especially when dealing with so much internal volume.

The end result is a stupid quiet rifle that weighs just 4.3 lbs with it's original wood stock, including the TRS-25 optic.

The tube can be a bit stubborn if I leave it on there too long, but as long as it's taken off every two or three hundred rounds, the monocore scrapes the crap off sufficiently with no need for chemicals or scrubbing.
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John A.
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Re: Integral 22 bolt action question

Post by John A. »

Thanks for the reply. This is fun just thinking of all the things I can do to it. Blank canvas.

I've been on this merry-go-round enough to know not to get aggravated waiting on the paperwork to come back, but I'm chomping at the bit to get started making chips.

I didn't think 22 would have enough gas to make a divider in there, but I wanted to ask to see what everyone else has done.

I know that Doc Dater did divide his old 77/22's, though he may had done it more for reinforcing the tube than anything. I don't know.

What kind of velocity are you getting using so many ports?

Drop supers down to sub?

Did you essentially start porting between the rear cap and move to the back of the monocore? Or port in patterns around the circumference of the barrel?

Did that many ports affect your accuracy negatively? Do they lead up pretty bad?

Sorry for all the questions. Just trying to learn what I can in advance.

I had thought about making one 3/32 port about 3.5 inches from the chamber and another at 4". Shoot for velocity after drilling each one so I don't drop too much from standard subs. Drill more if I want/need to.

Like I said, I wasn't going to drop supers down to sub at this time, I was just wondering how you did yours to figure out how I'm going to move forward eventually.
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Re: Integral 22 bolt action question

Post by T-Rex »

Gemtech stopped porting, not because it didn't work, but due to end-users not cleaning frequently enough and resulting in a stuck outer tube. I believe it was 2 ports, 180* degrees from one another, approximately 2" from chamber end.

Have you thought of integrating the clamshell design into your build? It doesn't need to have a thick tube wall, but will help with outer tube removal.

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Do you shoot mostly the same 22lr ammunition? If so, trying to tune for that may yield more satisfying results.

Thompson and YHM both have the monocore as the removable part. Maybe something to that?
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John A.
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Re: Integral 22 bolt action question

Post by John A. »

Yeah, I thought it had to do with complaints about removing the tube. Am curious of the diameter of the port though.

I have considered a couple of ideas.

1. clamshell

2. Diverter

I will need to explain the diverter.

Since the rear endcap has to be used, I thought about making it long enough to cover the ports, and hollow out much of the inside of it so the gasses/etc would collect on the inner wall of the rear endcap rather than the inner wall of the suppressor tube/barrel sleeve.

Could pretty easily clean it out occasionally with a small wire brush.

Clamshell would likely be the easiest to do.
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John A.
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Re: Integral 22 bolt action question

Post by John A. »

Ecco, since you said you didn't use packing, have you noticed any extra sound from the ported jets coming into contact with the inside of your tube?

What about erosion from the ports?
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Re: Integral 22 bolt action question

Post by a_canadian »

John A. wrote:Since the rear endcap has to be used, I thought about making it long enough to cover the ports, and hollow out much of the inside of it so the gasses/etc would collect on the inner wall of the rear endcap rather than the inner wall of the suppressor tube/barrel sleeve.
I really like that. You could leave maybe a 0.10" radius gap at the front edge of the rear cap, make the rear cap seriously long for the hollowed-out portion, say 3" long then the flange almost closing off that volume but still big enough to allow fairly rapid gas expansion into the remaining forward portion of the chamber. Leave the wall of this extended rear cap chamber thick-ish, maybe 0.070" or so to allow for many cases of ammo without eroding through it (if aluminum). Maybe even fin it, as in cut a series of chambers back there with thin walls, sort of a reverse radiator kind of thing to absorb and confuse gas flow and noise echo. Wouldn't have to be too complicated, maybe just one extra flange placed directly in line with the ports so as to break that fastest-expanding gas into fore and aft streams. Cool idea.
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John A.
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Re: Integral 22 bolt action question

Post by John A. »

I hadn't thought about the radiator ridges inside. It would be pretty simple to counterbore a bunch of them while it's chucked up in the lathe.

Or, a guy could make a large internal thread on the interior. That would actually increase the surface area of the tube while keeping it as short as you could and would disrupt the gas too.

I don't pretend to know whether that would make anything more quiet or not though. But would spend a lot more time standing over the lathe :lol:
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Re: Integral 22 bolt action question

Post by fishman »

Acme thread might be a good idea. Very high surface area
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Re: Integral 22 bolt action question

Post by a_canadian »

That's even cooler! Use acme threads for the outer tube and just extend them for the inside length of the rear cap, almost to the reduced diameter flange. Faster and more reliable thread for removing and cleaning, and simplifies it to a single threading operation. Then just permanently adhere the plug into the normally threaded outside tube and it'll be cleanable from the front, with a push rod able to come in from the back to push cleaning rags out.
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Re: Integral 22 bolt action question

Post by T-Rex »

Do you guys think a 22lr is going to produce enough heat to make the effort worth while?
I can put a good amount of 22 through my AR reflex build before it even gets too "warm".

Also, I would assume it definitely works on centerfire as the OSS system is pretty much based on this technology.

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Re: Integral 22 bolt action question

Post by a_canadian »

I wouldn't expect significant heat absorption. Rather the point of surface shaping would be to cause sound waves to break up into more complex patterns, bringing out destructive interference and reducing output noise.
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