I can sort of understand using chamber inserts to allow one shotgun to use several guages of shells, because the same smooth barrel should work with all. But I have been reading about the same type of insert in rifles and pistols, which seems odd given the role of barrel rifling with solid slugs.

What is up with this?

I've wondered about that too. One application that I can think of is placing a long rifled insert into one barrel of a shotgun so you could have a deer rifle/shotgun combo. You could also make a cape gun or a double rifle out of a shotgun for a small fraction of the price of a real one. Because ot the way double barrels are set, aiming such an altered shotgun as a rifle would be a real challenge, and would probably require a scope and a bead. Some states require trappers to carry a .22, but some trappers would rather have a shotgun. To avoid lugging two guns, they can make a combo from an inexpensive double barreled shotgun with a .22 rifled insert in one barrel for $90. Many cartridges use a bullet that is nearly identical in diameter to other cartridges. You could use a chamber insert to adapt a magnum rifle to shoot a much cheaper standard round for plinking. You could also ressurect some old military guns with a chamber insert. Accuracy could suffer, sometimes the inserts get jammed in and require a gunsmith to remove, and copper/lead fouling and excess barrel wear can result. A person would really have to know what they are doing (not me) to avoid damaging their gun at worst, or just wasting money at best. I have found that if I save my money, I can always squeeze one more gun into the locker. Since you can buy a new .20ga/.22 combo gun for around $350, I'll pass on barrel inserts.

Some are the same diameter, but more powder. For instance: in a .357, you can shoot either .38 OR .357-the diameter of the round is the same, the charge is just bigger for the .357. However, you cannot shoot a .357 in a .38 chambered pistol, due to the added stress & longer cartridge of the .357. Same with .22 & .223. You can get conversion kits for AR type rifles that replace the bolt & you can effectively fire .22 out of it (with special magazines as well). The neck diameter is the same-the .223 is simply longer, and more powerful.
There are conversion kits for some pistols as well-it is simply a matter of replacing the barrel. I have read elsewhere of people doing a 9mm to .45 conversion on pistols, but have no first hand experience with that.

It's not common and it doesn't work very well.

I've read about the US Navy using a sleeve insert during the 1960's to shoot .308 ammunition in their M1 Garand rifles which normally use .30-06 ammo. The .308 uses the same projectile as .30-06 but the case is shorter hence the sleeve.

Sleeves came out of the rifles at random inconvenient times. Eventually Navy went to the M-14 which is a .308 (7.62 NATO) rifle so no sleeving required. (then they moved on to the M-16)

Semi-auto pistols wouldn't be sleeved but an entire barrel change is very simple. I have a Glock 22 (in .40S&W) that can be converted to 9mm by changing barrel and using different magazines.

Gun stuff isn't all that difficult. You could probably find more than you want to know at http://www.thefiringline.com/forums/index.php
and
http://www.thehighroad.org/index.php
to name just 2 very good "gun boards."

Where I saw the inserts were on ranges where they were using .22 in 7.62 for training.
I was told the lower recoil made it easier for new shooters to get used to the rifles and that it made it easier for the instructors to correct things like flinching.

I thought they were really just trying to save the ammo cost. That counts for a lot in my opinion.
.22 long rifle is about 5 dollars for a box of 50 and my 30-06 costs about 50 dollars for a box of 20 shells.
A day at the range can easily see a brick (500 rds) of .22 gone.

Also by using the .22 instead of the 7.62 they were able to set their range up inside an auditorium so they were able to practice even when the weather was bad.

I didn't think much of the inserts for accuracy. If you were doing it for survival you might be better just getting a light .22 rifle.

Flinching can only really be corrected by proper instruction-my experience is that, if you go from a low to a high caliber, they will still flinch-not the first shot, but every one after that. And, going from high to low caliber, the same thing happens initially-you compensate for the expected kick. Even experienced shooters do this-maybe not to the extent that other would, but, it does happen. Your body simply gets used to one thing, and reacts the same in a similar condition ( the rifle or pistol doesnt change, just the caliber).
Shooting .22 conversion kits do have benefits though-primarily, its a cheap way to shoot! But, you will not get the same ballistics as a full powered round. The basics will be the same, yes-but shot placement will be completely different. But, you can practice mechanics, VERY cheaply-offhand shooting, transition drills, reloads, malfunctions, and, well, you just plain get to be a lead farmer . Nothing wrong with a day at the range!

Seems to me that the benefit of chamber sleeving 7.62 down to .22 would be about the same as dry firing. The grouping of the .22 rounds would be sloppy at best (the bullet wouldn't be engaging the rifling - just rattling its way down the barrel).

If it's a barrel & chamber sleeving then ... maybe. (is that even done?) A conversion kit would make the most sense to me.

My experience as a Range Officer for an indoor pistol range is that people need lots of .22 practice (myself included) to keep from developing a flinch or to beat it back down when it develops. You can shoot a LOT of .22 for the cost of most centerfire ammo.

So, am I correct that chamber inserts for shotguns would allow a 12 guage 3 inch magnum to use 20 guage and 410 guage shells. How about slugs shells with chamber inserts?

Is it correct that such a shotgun already allows use of all other 12 guage shells without an insert?

Am I correct that a single-shot or bolt-action rifle in .223 could use chamber inserts for .22 LR or .22 ammunition, or any other rimfire ammunition with the same bullet diameter?

Do I correctly understand that use of chamber inserts in lager caliber rifles follow the same principle regarding bullet diameter, and that using chamber inserts for much smaller ammunition would tend to less reliable shot placement and lead to quicker barrel fouling?

And are there chamber inserts or equivalents for single-shot or revolver-style pistols?

Edit: http://www.mcace.com/adapters.htm

http://www.mcace.com/shotguninserts.htm


My interest is to be able to use the widest range of ammunition with each gun.

Modern shotgun chambers come in 2 3/4", 3" and 3 1/2"
Some older ones may have shorter chambers.
While you can shoot a 3" shell in a 3 1/2" chamber, you can
not do the reverse.

If a bullet or slug doesn't ride on the sides of the
barrel, be it rifled or not, accuracy will be terrible.

22 rimfire has a different bullet diameter than 223 Rem.
so shooting 22 rimfire in a 223 would give poor performance.

Also any long jump to the rifling by the bullet can decrease
accuracy in most cases.

Since 12 gauge ammo is usually cheaper than smaller gauges
and chamber inserts don't work well with rifled guns, I prefer
to handload to get both reduced and full power loads
for each firearm.

Another option might be to look into switch barrel guns.
From the same stock and action you could shoot any combination
of gauges or calibers by switching barrels.

A new barrel for a handi rifle could cost the same as some
of the fancier shotgun chamber inserts.

I think a couple of things need to be clarified. I don't think the terminology has been officially agreed upon so these are my estimations of what is going on:

A chamber insert is a piece that converts a firearm's chamber, either permanently of semi-permanently, to fire a similar sized cartridge. The most common, and possibly the most successful is the small ring that allows a .308 cartridge to be fired out of a rifle designed around the 30-06 cartridge. How successful this device is depends on how well it is made and if you desire it to be converted back or permanent. The best, most reliable, are those very tightly machined of quality steel that are designed to be installed once and stay. These may incorporate an interference fit that locks them in permanently. Others are designed to be removed.

There are a slew of other that operate on the same principle of allowing a firearm designed for a larger shell to fire a smaller on as long as both have relatively the came bore size.

http://www.mcace.com/adapters.htm


The second item is a sub-caliber sleeve. This is essentially a small rifle barrel. A chamber designed to take a cartridge and a short barrel of six or eight inches is typical. These allow break-action, single shot, large-bore center-fire rifles and shotguns to fire a smaller cartridge. Generally the barrel assembly is centered in the bore of the shotgun with a spacer of O-ring.

http://www.mcace.com/shotguninserts.htm

http://www.mcace.com/rifleinserts.html

The third is the cartridge adapter. This is a hollow shell of a larger cartridge that holds a smaller cartridge. This hollow shell typically allows the smaller shell to be loaded into a magazine, handled by the firearm and, perhaps, ejected. The adapter shell is then typically retrieved and reused.

The most common seems to be a shell adapter that allows a firearm designed to shoot 5.56mm cartridges to fire .22LR cartridges. I have read that some firearms can be cycled by the .22LR shell. Most ARs seem to require manually working the action. Accuracy is reported to be good as both the 5.56mm and .22 use the same bore diameter.

There are also ones that allow smaller bore size shotgun shells to fire out of a larger bore. Reports are that there is less loss of velocity than might be expected but that groups are variable.

There are also shell adapters that allow a larger shell to fire a smaller one that doesn't share bore diameter. Like a .22LR in a 30-06. Some of these seem to have a short, all of half an inch, barrel stub. I would expect that accuracy would be quite poor but one report was that it was surprisingly good and acceptable for short range hunting of small game and plinking.

http://store.dinaarms.com/product_p/12ga22lr.htm

There is necessarily a good bit of overlap in terminology. Is a cartridge adapter that has a stub barrel a sub-caliber sleeve?