Extend the Range of .22 Shotshells with Reverse Paradox Tubes for a Garden Gun

Gun Watch ^ | 19 May, 2020 | Dean Weingarten

[marktwain]

In a previous article, I commented on the usefulness of .22 LR shotshells and their limited range. Their use is severely hampered by the poor patterns produced by these shotshells out of rifled barrels.

The effective range of these shells can be doubled or tripled with the use of a reverse paradox tube.

The Ball and Shot gun, more commonly known as the Paradox gun, was invented by Col. George Fosbery, VC, and patented in England in 1885. The patent was sold to Holland and Holland who marketed the guns under the Paradox name.  The idea was simple: put shallow rifling in the choke of a shotgun to spin bullets, and give decent accuracy to bullets from a shotgun bore.

The reverse paradox tube solves the opposite problem. I believe this is the first publication of the concept. Normally, smooth bore tubes work very well for shot charges, and rifled tubes very well for bullets. There are rare circumstances where a firearm is called to use both effectively.

There are dedicated Garden Guns that have smooth bores and give decent patterns with the .22 shotshells. Addition of a second smooth bore, after the .22 bore, twice the diameter of a .22, is claimed to give tighter patterns.

In 1937, Frederick J. Routledge filed a patent, which was granted in 1940, #2,185,523. He claimed doubling the bore diameter of a .22 smoothbore for about 18 inches, greatly increased the pattern density of the shot at 10 yards and further.

Several thousand of the Routledge bore guns were produced, and are said to work well. Such dedicated .22 shotguns/Garden Guns work. They are expensive, compared to a box of .22 shot. They do not work well with single bullets.

There are likely less than a hundred thousand smoothbore .22 rimfire firearms in the United States, of which perhaps 10,000 have the Routledge bores.  There are about a hundred million rifled .22 rimfire firearms in the United States. Many of those firearms are produced with a threaded barrel for muzzle attachments.

Reverse paradox tubes work well and shoot close to point of aim with rifled bullets and shot charges. If properly aligned, the bullets never touch the tube.

Adding anything to the muzzle of a rifle may change the point of impact. Firing a few shots to test the point of aim is simple.

Aluminum, steel, and pvc (polyvinyl chloride) tubes were tested. Aluminum and steel were either threaded or had an adapter machined, so as to be easily attached to the end of the barrel. Tubes of up to 1 inch inside diameter worked well. Both sch 40 and sch 20 pvc were tested.

30 inches of 3/4" sch 20 PVC and a threaded/slip coupling weigh 5.6 ounces. PVC  reverse paradox tubes work surprisingly well. The pressures out of the muzzle of a .22 LR are much lower than chamber pressures. Pressures are lowered dramatically when the gases leave  the muzzle, into the larger diameter reverse paradox tube.

The tubes double to triple the effective range of the .22 LR shotshell, compared to most rifled barrels.

The test patterns shown were shot 10 yards from the muzzle of the tube or the muzzle of the gun.  The pattern on the left has 20 pellets; the one done with the reverse paradox tube has 71 pellets. They are typical patterns. Testing showed the maximum effective range with the tube to be about 45 feet (15 yards) from the muzzle of the tube. The tube and rifle extend about five feet from the shooter's shoulder.

Sch 20 pvc is considerably lighter than sch 40 pvc. Because of the geometries involved, a thin tube is stiffer than a thick tube of the same weight. Stiffness is a desirable quality in reverse paradox tubes.

Testing for the 3/4 inch pvc showed the optimum length to be between 25 and 31 inches.  CCI 31 grain shot shells were used in the test.  Five shot averages of pellet counts inside an 8 inch circle at 45 feet (15 yards) from the muzzle of the tube were as follows:

Tube length  Pellets inside 8" circle

33 inches      39.6 pellets
30 inches      45.6 pellets
28 inches      42.6 pellets
26 inches      43.6 pellets
24 inches      38.2 pellets
22 inches      35.8 pellets
20 inches      31.8 pellets

Early comparisons of the CCI and Federal loads show patterns to be very close. 

At 45 feet, the tiny #12 pellets are near their maximum range for fatal penetration on small pests. They should be traveling a little over 600 feet per second at that range. One commentator at the shotgun world forum stated, in his experience, they were adequate for pigeons at 15 yards.

By 120 feet (40 yards) the energy of the #12 pellet has dropped to 2.3% of the energy of a common BB gun at the muzzle.  The purpose of such small shot is to prevent damage to property and persons while dispatching small pests at relatively short ranges. Pigeons or rats are about the largest pest that can be easily dispatched with the shot shells at more than 10 feet. Some shooters have reported good results for larger insect pests. They work very well inside of structures and areas where energetic shot would be inadvisable beyond 40 yards. 

Anything less than 40 pellets in an 8 inch circle leaves considerable holes for small pests. The combination of pellet count and pellet energy means 45 feet is about the maximum range for this load, with the reverse paradox tube.

The energy of the .22 LR shot cartridge is a little less than a standard velocity .22 short. The report is similarly low. This is positive for a load meant for use inside structures or with nearby neighbors.

The report of Aquila Super Colibri cartridges out of a rifle is similar to that of a BB gun.  They could be used for pests if backstops are available at short ranges. It does not take much of a backstop to stop  the Super Colibri. However, the 20 grain projectile of the Super Colibri renders it dangerous at further distances than #12 shot. A Super Colibri is unlikely to put a hole in a barn's roof, but it could break a window. A standard velocity .22 would almost always put a hole in the roof.

It is not necessary to have a threaded barrel to experiment with reverse paradox tubes. The tubes can be attached by friction, or taped onto a barrel, or non-threaded adapters can be made. Alignment of the tube with the barrel is important. A 1/8th inch misalignment at the muzzle of a 30" tube can move the center of the pattern a couple of inches at 10 yards.

Threaded barrels make the addition of reverse paradox tubes easy. Tubes can be taken off and replaced in a minute. There are cheap adapters for pvc tubes available, for nearly all threaded .22 muzzles. The adapters are sold as automotive accessories. They adapt 1/2-28 female threads to male 3/4" National Pipe Threads (NPT)  (and others). NPT threads are commonly used to attach pvc couplings.

The cost of the thread adapter and the PVC material is less than a box of shot shell ammunition.  A thread adapter can be had for about $3.50, a threaded/slip 3/4"  pvc coupling for less than a dollar, and sch 20 pvc pipe is less than $2 for ten feet, enough for four tubes! $3.50+$1+$.50=$5.00. Many people already have pvc and couplings from previous projects.  For $15, a hobbyist can purchase three thread adapters and the materiel for several reverse paradox tubes.

Thread adaptor with .22 shot cartridges for scale

The ends of reverse paradox tubes should be cut square, then deburred. A band saw worked well for cutting the ends of pvc pipe square. The end was deburring by rubbing with finger and thumb. Sandpaper can be used for those so inclined.

Sources for thread adapters:

1/2-28 x 3/4" NPT thread adapters, steel, made in the USA, for $12.99.

From Sears.com:  the adapter is out of stock.

They are available on Ebay from $3 to $10 in numerous ads.

From Ebay: Free shipping from Taiwan/Hong Kong.

Here is a 5/8-24 version for $3.29 for barrels in that thread pattern. It also offers free shipping.

If ordering from Hong-Kong/Taiwan, out of Ebay, it might be wise to order two or three adapters, because shipping may take a few weeks.  The adapters work well as thread protectors, yet cost only a third of what common thread protectors cost.

A straight tube is important. Some pvc tubes come with gentle bends acquired from transport or storage.  A friction fit to the pvc coupling works adequately, but glue could preserve proper alignment. It might be possible to adjust the alignment in the short period while pvc glue is setting up. A reference mark on the tube could help to maintain the proper alignment.  Testing showed that patterns from individual firearms can vary considerably.

It is best to shoot a test pattern or five to see how an individual rifle does with a reverse paradox tube.  Because the patterns are small, users need to know if the tube is patterning to point of aim.

The light weight of the reverse paradox tube makes the rifle easy to handle. The length of the rifle, with tube mounted, takes a little practice. Striking the muzzle of the tube on door frames or bushes is likely to affect the alignment. It is not as awkward as it might appear. Many muzzle loaders were of similar lengths, overall.

Experimental set up with pvc tube marked for cutting.

While performing these tests, there were tantalizing indicators better performance might be possible. The pvc tube delivers cylinder bore performance. Improved cylinder performance would add enough pellets at 15 yards to fill holes in the existing patterns.

Investigation of those possibilities awaits future articles.

The cost to thread the barrel of a .22 at the factory is minimal, probably less than a dollar.  The usefulness of muzzle accessories means more manufacturers will be offering models with threaded barrels in the future. 

All safety measures must be observed. Ammoland and the author publish the information for academic interest, and cannot assume any responsibility for actions taken by readers.

©2020 by Dean Weingarten: Permission to share is granted when this notice and link are included.

Gun Watch

[Beagle8U]

“I experimented with shooting through shotgun barrels with chokes. I only looked at 20 and 12 gauge barrels.”

You were shooting 22 cal shot through shotgun barrels?

I’m not understanding what you are saying.

[Beagle8U]

“On a good day chokes don’t matter, and on a bad day chokes don’t help.”...said no trap shooter...ever.

[Beagle8U]

“You might want to consider the Cutts Compensator which was very popular with skeet shooters from the 30’s onward as an external jug choke.”

Kinda hard to find one in 22 cal.

[Tijeras_Slim]

You have to pick an appropriate one, true. But over thinking selection in sporting and changing them at every station is counter productive.

[marktwain]

I always liked the cutts and the PolyChoke.

I have some really nice shotguns at great prices because they had PolyChokes.

[Tijeras_Slim]

I like polys more than cutts. Although the .410 cutts is a nifty little item.

[redfreedom]

The box says:

Federal Premium
410 Handgun
410 2 1/2 In Buckshot
4 Pellets - 000 Buck
Muz Vel 850 FPS
Personal Defense

And they are steel.

The problem with the round steel ball is they do not do a quick kill, unless you get a brain shot. As with lead, they do not tumble, fragment or mushroom which all causes more damage, thus a quicker kill.

I’ve been killing these critters for years, and a conventional bullet will put them to sleep in short order, usually taking no longer than a few minutes.

My most memorable shot was with an open sight SKS at about a hundred yards. When hit the critter convulsed so quickly it came out of the water about two feet with parts flying in every direction. The main carcass sank. The larger parts remained afloat for a short time, then a large fish (probably northern pike) started gulping them down.

[marktwain]

And they are steel.

Why do you believe they are steel?

Did you do a magnet test?

The Federal website shows them as lead.

[marktwain]

You were shooting 22 cal shot through shotgun barrels?

I’m not understanding what you are saying.

It is not hard to do with a .22 adapter.

[marktwain]

I like polys more than cutts. Although the .410 cutts is a nifty little item.

I grew up oggling both in the catalogs and gun magazines.

I never was predjudiced against them.

Some people judge everything by appearances.

I love the way they look.

[Tijeras_Slim]

They do increase muzzle awareness for many shooters.

[marktwain]

Were any Routledge guns made with reverse paradox barrels?

I have not heard of any that were a combination of rifled followed by smoothbore.

[Beagle8U]

OK, you were using a 22 cal adapter in a shotgun barrel, which wouldn’t be a smooth transition to the choke.

You need to make something to screw unto a 22 cal that you could drill out to 22 cal bore and then bore a jug choke in that.

It needs to start at 22 cal bore, to taper, to jug, to taper back to 22 bore.

[Beagle8U]

Trap shooting is pretty much full choke for everyone. A few use mod and some x full.

[marktwain]

It needs to start at 22 cal bore, to taper, to jug, to taper back to 22 bore.

Great. Go for it.

I find it an interesting idea.

[marktwain]

Tijeras_Slim: Did anyone use chokes on the Mosquito matches?

Were any shown that outperformed the Routledge bore?

First thing is to find, is if anyone already did the experiment.

[Beagle8U]

If I still had access to a lathe I would make one for you.

[marktwain]

I have considered making one, but my machining skills are small, my time limited, as is my access to a lathe, and the indications are it would not work from a rifled bore.

The dimensions which might be optimum are unknown.

Another reason I have not worked harder or found someone to make one is the patterns I am seeing with the reverse paradox tubes, are nearly optimum for the effective range of #12 shot.

[Tijeras_Slim]

The Routledge bore is a constant diameter countersink from the muzzle back about 18”. I doubt anyone has added constriction to a .22 smoothbore, given the small shot charge and limited distance they’re used.

I did manage to break a skeet low house 1 with one when it sailed by about 12 feet away.

[Beagle8U]

Well, I was a tool and die maker that has done quite a bit of gunsmithing.

I could make one easy if I had a lathe.