Over-boring a .22lr barrel

Tolerent

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I have a .22LR Ruger 10/22 rifle that I want to convert to shoot standard ammunition subsonic. A standard barrel would accomplish this somewhere between 4" and 5" long. Cutting the barrel to less than 16" creates a SBR which is a big hassle. I am considering using a long piloted bit to overbore the forward 12" of my standard 16.5" barrel.

Challenges I am considering:
  • Long Piloted bits are not as available as I had hoped.
  • I worry that turbulent gasses passing the bullet in the over-bored barrel will contribute to projectile instability.
  • Thinking of over-boring the entire barrel and inserting a 4.5" liner with a 9" twist on the chamber end to mitigate the line above.
  • I did note the rules for target rifle competition specifically allow for barrels that are not rifled full length and wonder what they had in mind.
  • Worried that any crown recessed 12" will be difficult to properly dress.
  • Wondering as dirty as .22LR ammunition is if cleaning the fore-bore will be problematic.
  • Still anticipating threading muzzle 1/2x28. I see some 9mm threaded 1/2x28 so think an 8mm over-bore will be easy to accommodate.
Looking for perspective from those with more experience in such machining challenges as well as ballistic and maintenance considerations.
 

MontanaLon

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The unthreaded portion of barrel in match guns is called a bloop tube and primarily is there to lengthen sight radius.

It would be tough to crown the muzzle with it recessed inside the barrel.

Easier route would be to cut barrel to length and then use a tube for the extension and pin and weld in place. That way it is legal length but has none of the drawbacks you mentioned.

Over boring and still threading the barrel is probably a bad idea. At least as far as using it with a suppressor. Too much travel to avoid Murphy and baffle strikes.
 
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Tolerent

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If I was to cut to 4.5" then thread for the extension it might be challenging to retain 16" of a 16.5" initial length. I guess the threads would not need be very long if welding it all back together. If I weld it I would definitely need to re-finish the weld bead better than my current abilities.

I might be inclined to run the piloted overbore bit to take material out incrementally and test for crown problems. If I am able to get a reasonable crown most of the time I imagine I would be willing to test results at 5" and progress in small increments if accuracy was problematic. More so If I concluded I needed a 9" twist liner.

is 12" of 8mm diameter bloop tube likely to be deleterious to 5.56mm projectile stability at 16" (or 9") twist? I always assumed bloop tubes were much larger diameter.

Regarding baffle strikes: I see your point. Probably would need to use a 9mm suppressor design if attempting to suppress something 12" from the end of the effective barrel.
 
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Capt45

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Couldn't you pick up a used 10-22 barrel to screw onto your stub (4.5") barrel?
 

MontanaLon

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Bloop tubes for centerfires are usually same outside diameter or larger than the barrel because the iron sight mounts are like scope rings on the barrel.

If it were me I would use a different material for the tube. Aluminum would be a choice but welding it may be more difficult with it in contact with steel. I don't do welding yet.

Threading the stub and then the barrel extension would be likely to shorten the total below 16". Plus there is so many possibilities with a length of .22 barrel.
 

Tolerent

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Couldn't you pick up a used 10-22 barrel to screw onto your stub (4.5") barrel?
My original idea was to use a salvage 10/22 barrel the inside would still need to be bored out to avoid conflict between any tiny offset or rifling alignment if I grabbed a barrel for part of the project. I could find an 18"+ barrel but I don't value the existing barrel as much as the effort to change it out on the received. I figure if I ruin the barrel it is one I was not going to otherwise use anyway.
 

Tolerent

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Because they think it is all Eley TenX judging by the price.
The cheapest subsonic ammo I see is twice the price of Federal bulk ammo. I shoot a lot and want to eventually form 1 a suppressor. I imagine that is going to be applied for about 2 weeks after I get the lathe and by the time it is approved I will have the skill to build it. After I receive the form 1 approval and build the suppressor and have adapted a few firearms to mount it on I would primarily target shoot with firearms adapted to subsonic performance with bulk ammo.
 

MontanaLon

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Welding and gun barrels don't go together. The weld will pull the barrel, it will not be straight.
It's been done for years. Drill a hole through muzzle device into barrel but short of bore. Insert a pin into the hole and weld the pin in place. Usually everything is steel, barrel, muzzle device and pin, but I think if you used an aluminum pin and an aluminum tube it could work. The weld doesn't have to connect the barrel and pin physically, just make it so the pin cannot be removed without grinding off the weld.
 

38super

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Welding will affect hoop stress. If a barrel muzzle is welded, back bore past the weld area.
 

Tolerent

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Welding will affect hoop stress. If a barrel muzzle is welded, back bore past the weld area.
I wonder how hoop stress even on a massive centerfire would compare near the muzzle to down the bore a ways. I'm not capable of doing the calculations but we are talking about a .22LR. My muzzle on the barrel in question is beefier than the chamber on my SR22 pistol which would have perhaps more pressure by some margin. Looking at the barrel I can't really see a lighter barrel muzzle on the 10/22 than on some of my .223 with 10 times the kinetic energy.

That blurted out... I would want to be conservative and avoiding stress risers does seem to be a safer path.
 

Tozguy

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Use epoxy instead of weld. My approach would be to cut the barrel to length and crown it for durability. Fit a long aluminum tube over the whole barrel and epoxy it in place. Provide for a means of aligning the tube to the bore by sighting through the barrel while the epoxy cures. The bullet will start falling as it exits the rifling so the id of the aluminum tube must be generous. Worse if the rifle is not held well by the shooter. If the bullet touches the tube in any scenario accuracy will be horribly dangerous.
Its an interesting exercise but it would be so much simpler to buy subsonic ammo. I have used some Remington subsonic that was reasonably priced.
 

Tolerent

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Use epoxy instead of weld. My approach would be to cut the barrel to length and crown it for durability. Fit a long aluminum tube over the whole barrel and epoxy it in place. Provide for a means of aligning the tube to the bore by sighting through the barrel while the epoxy cures. The bullet will start falling as it exits the rifling so the id of the aluminum tube must be generous. Worse if the rifle is not held well by the shooter. If the bullet touches the tube in any scenario accuracy will be horribly dangerous.
Its an interesting exercise but it would be so much simpler to buy subsonic ammo. I have used some Remington subsonic that was reasonably priced.
I love the thought process of sleeving the barrel full length. This is a contoured barrel so a bit more difficult but still sleeving a bit similar to a morse taper fit seems doable. Especially with a thin epoxy bond layer.
Regarding the barrel jump while firing: the projectile is traveling between 960 and 1060 fps with one exception for the 90 rounds I tested from a similar 4.5" barrel from a charger pistol (that was not extended) with my bulk ammo. Adding 12" is not going to be twice as bad as adding a suppressor and those often come with only .03 overbore so any barrel sleeve strike would be unlikely at an overbore of .06 and if there was a sleeve strike it would really be mild rub and not a hard contact. A non event in regards to mechanical safety. The only concern would be the same concern I would have from any sudden barrel deflection while discharging the firearm.

Couple edits:
1. the 4.5" barrel on my charger pistol leaves about 3" of foregrip without a barrel resting on it. Really dangerous. I am installing linear compensator on those 3" as a guard to keep my fingers out of the path of bullets. Really dangerous with unutilized foregrip. I am needing to upsize the chase in the foregrip to allow for the compensator as my charger came OEM with a contoured barrel. Lots of sanding.
2. See the post below.
 
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seasicksteve

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Epoxy = Felony . If an extension is added to bring a short barrel to legal length it will need to be blind pinned with a weld over the pin or permanently attached by welding or brazing. Low temp solder also will not satisfy ATF. Get a tax stamp and make it an sbr
 

Tolerent

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Epoxy = Felony . If an extension is added to bring a short barrel to legal length it will need to be blind pinned with a weld over the pin or permanently attached by welding or brazing. Low temp solder also will not satisfy ATF. Get a tax stamp and make it an sbr
Hence my interest in maintaining the original barrel length. My $200 stamp is going to be attached to a suppressor I can mount on any of my threaded .22 barrels rather than the barrel length of one SBR where having a shorter barrel is not important to me.
 
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FanMan

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If you're worried about crowning the muzzle end of the rifling portion deep down inside, DIxie Gun Works sells .22 barrel liners in various lengths. Bore the entire barrel 5/16", cut the liner to the desired length and crown its muzzle end as desired, and solder or epoxy the liner in place.
 

Tolerent

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If you're worried about crowning the muzzle end of the rifling portion deep down inside, DIxie Gun Works sells .22 barrel liners in various lengths. Bore the entire barrel 5/16", cut the liner to the desired length and crown its muzzle end as desired, and solder or epoxy the liner in place.
I anticipate this could be my final solution. Before getting this far though I plan to let the bored to muzzle crown demonstrate for itself whether or not I can rely on it without drilling out the last 4.5" and installing a partial liner.
 

Tozguy

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A non event in regards to mechanical safety. The only concern would be the same concern I would have from any sudden barrel deflection while discharging the firearm.
The bullet hitting any part of the rifle unintentionally after exiting the rifling would be a ricochet in my books. Not the same as normal muzzle jump from recoil. Either one has an effect on accuracy but in this scenario the internal 'ricochet' would make the bullet's flight unpredictable and therefor out of control and therefor dangerous.
 

Tolerent

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The bullet hitting any part of the rifle unintentionally after exiting the rifling would be a ricochet in my books. Not the same as normal muzzle jump from recoil. Either one has an effect on accuracy but in this scenario the internal 'ricochet' would make the bullet's flight unpredictable and therefor out of control and therefor dangerous.
I don't want to get in a dispute with your engineering judgement. I ask you consider:
  • How a soft lead bullet like a .22LR might act differently than a hard bullet like a bimetal bullet.
  • How a rub on a smooth surface at a slight angle might act differently than a harsher angled impact.
  • Why threaded barrel bb/pellet guns are oversized to the steel bbs, and how a steel bb rattling down such a barrel is not considered unpredictable. If you sandbag such a rifled pellet gun and shoot a few dozen shots you might discern as I have that the bbs spiral out of the barrel along the grooving and form a neat doughnut pattern providing you with a clear ability to count barrel rifling twist grooves.
  • Why service proven suppressor designs have often such narrow design clearances between baffle and flight path.
  • What historical outcomes of baffle strikes are related to trajectory and how a baffle strike is a greater or lesser concern than a smooth barrel rub.
  • How much your firearms deflect when you shoot on a gusty day or even when not sandbagged and braced on a good day and at what point you consider your target shooting to be unpredictable and dangerous.
I am really preferring to consider the matter from a more comprehensive perspective than just what feels dangerous to one or more individuals. I am looking for perspectives based on engineering and experience.
 

Tolerent

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Only one cat. But, It is our next door neighbor's and I would not risk the repercussions.
If I wanted the cat gone I would use a Havahart trap and drop the cat off at the animal shelter.
We lived in Hawaii for 6 years... It might be a good thing I did not have a quiet .22 over there. We had easily a few hundred feral cats within a half mile of us. Gun laws in Hawaii are pretty challenging.

Maybe that's why they have so many feral cats. To be fair, we had a lot more specialty restaurants in that area than we have here and I have full confidence they were not tapping the cat supply. No one tapped the Pidgeon supply there either. Well... the cats tapped the Pidgeon supply. The cats, mongoose and rats pretty much left each other alone.
 
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hardcorps

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You may try drilling a small hole perpendicular to the bore just ahead of the chamber. Do it on the bottom and have it vent into the stock. It's messy but can tame the high velocity ammo. Haven't done this with a carbine but have with a few Ruger MKII pistols.
Or, get a Ruger Charger with one of those sketchy "pistol braces".
 

hardcorps

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..for that matter you could drill many vent holes, like compensator ports, wherever you want. You'd have to experiment with placement, size, and number of holes. At least 10-22 takeoff barrels are inexpensive.
 

Tolerent

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The reason I am shortening the barrel is to be effective with a suppressor.
How does the porting affect the sound signature of the firearm?
What size hole is small? I think 1/16" is about as small as I have drill bits for. Not sure I can drill that small a hole in a barrel without breaking the bits.
I suppose I could fill the barrel with a Cerro safe plug and drill a bunch of "Small" holes. Then melt out the plug.
I wonder if a 1/16" hole is likely to plug or neck down with crud over time while venting dirty high pressure gas repeatedly?
 

hardcorps

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A hole just forward of the chamber vents pressure.
Before you try anything, though, have you tried your suppressor without barrel mods?
A good, modern suppressor works quite well, even with bulk high velocity ammo.
 

hardcorps

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Not mine, but:
"
"The other answers have adequately covered the fact that simply drilling holes will make the weapon’s report louder, but I’m going to add a bit about a more obscure technique that involves porting a barrel to decrease velocity.

A standard suppressor will not have any meaningful effect on the velocity of a bullet, all it does is corral the escaping gasses to reduce the report. If the bullet leaves the muzzle at a supersonic velocity, it will make a sonic ‘crack’ sound as long as it is moving faster than the speed of sound. This sonic crack is usually eliminated by using subsonic ammunition, but a downside of this is that now you have different ammunition types for the same round and therefore conflicting logistical systems.

With the Heckler & Koch MP5SD(SD stands for Schalldämpfer, German for suppressor) , HK wanted a way to make the 9x19mm Parabellum round* subsonic without using specialty ammunition. Their solution was to port the barrel down its entire length so that the gas pressure was reduced during firing. This causes a lower force on the bullet and lower acceleration, leading to a reduced muzzle velocity. The gas vented from these ports is captured in an aluminum sleeve around the barrel and allowed to slowly escape. The forward portion of the barrel has baffles like a traditional suppressor to help slow the expansion of the hot gas.

*Standard 9x19mm loads have velocities around 400 m/s out of the MP5’s 225mm barrel. The speed of sound at sea level is only 343 m/s, meaning that a standard MP5 shooting 9x19mm ball ammo will be significantly supersonic. The MP5SD shows muzzle velocity decreases of 16 to 26% compared to a standard MP5, giving the MP5SD a muzzle velocity between 336 and 296m/s.

Below is an early diagram of the MP5SD barrel, showing the ported section to slow the bullet and the baffled section to slow the escaping gas (the barrel in the diagram is pointing left)."
 

DangerZone

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If you are going to all this trouble, you could form 1 the entire gun and create an integrally suppressed barrel with porting down the barrel as the above poster mentioned. Or you could go one step further and just buy an integrally suppressed barrel for your 10/22. What you are looking to do seems needlessly over complex and just trouble waiting to happen. I haven't looked into many integral barrels, but I imagine a few are set up to reduce velocity as you are looking for. You could also look into using wipes for your rifle. they are a legal minefield, but it's possible. With the work you are already proposing, wipes would be a far easier course of action. and if you use something the size of a 9mm suppressor on a .22 I think you'd be far better off just keeping the .22 supersonic through a .22 suppressor.
 
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