9x18 mak is bigger in diameter then 9x19 para or .380acp(it is shorter then 9x19 and longer then the 9x17,or .380).Not by much,but it does create issues with finding decent loads for 9x18,which,interestingly,is sort of the intent of the Soviets when they adopted it (some say).
The 9x18 is,if I remember correctly, 0.363-0.365" in diameter.9 para and .380 are .355.
I don't think this has much to do with performance,but I do think it has everything to do with keeping your enemies from being able to use captured ammo in his weapons.
The Soviet Union has always done weird stuff to make their strategic commodities incompatible with pretty much the rest of the world.
Stuff like making their railways a bit wider so it made using trains a little more difficult to move men and material during WW2.
Anyhow,9x18,in my opinion,is not a *bad* cartridge,its relatively powerful when you consider that its designed to work in blow back weapons of modest size.
Ballistics wise,it tends to perform like .380 acp,not 9x19 parabellum.Like the .380,many of the JHP loads that are available tend to perform sub-par to the FBI guidelines everyone is so fond of,with expanded projectiles rarely meeting the 12" mark in ballistics gelatin tests.
However,the purpose of JHP's is to limit penetration.
If you want penetration- ball,of course,penetrates much better.
The only drawback I can see is that because of its intentional design making it just a hair bigger then 0.355,along with -mostly- somewhat anachronistic weapons chambered for it and available to private citizens,its less of a concern for ammunition manufacturers to market their best lines is this caliber.
I say "anachronistic" because why would someone want an all steel,thus heavy,weapon chambered in such a mild cartridge,if they can have a 9mm para in something almost a full pound lighter?
Some people just like the guns.
Some actually require a lower powered round in a heavier weapon because for one reason or another they are recoil sensitive.
But for the most part,9x18 chambered guns have become the realm of collectors.
So the ammo companies just don't push out as many new designs in this caliber as they do in the more popular ones.
Personally,I'd like to see MP-448 'Skyph'
pistols imported,which are basically polymer framed,high cap,"modernized" Makarovs.
Such a weapon could breathe new life into the 9x18 cartridge for self defense.
9x19 Parabellum was designed as a sort of stop gap measure by Georg Luger for his famous Luger pistol.Originally chambered for the 7.65×21mm Parabellum,it was found to be lacking in ballistic power.
Because it was created by Luger,SAAMI calls it 9x19 Luger.
Being derived from the 7.65x21mm Parabellum,some call it the 9x19 Parabellum.
Its the same thing.
The only relevant differences today are SAAMI spec and CIP spec differences,as well as the NATO version.
SAAMI is the American version,and here you'll find the higher pressure +p,+p+ etc designations.
CIP is European and some say is loaded hotter then the standard (non +p) SAAMI stuff.If I remember correctly,CIP does not have any "+p" designations.Usually,CIP loaded ammo seems to be on a par with SAAMI +P.
The NATO 9x19 is the standard load for NATO alliance armies.It is almost as potent as a SAAMI spec +p,but not quite.It is almost always found in 124gr or thereabouts weight.
I do not believe I've ever heard of NATO loads being made with anything but military type ammunition,the only available load to us mere mundanes being FMJ.(You can't have armor piercing handgun ammo,and I don't think I've ever seen 9x19 NATO JHP.)
European nations making 9x19 ammo to CIP spec do not produce as wide a variety of JHP as American manufacturers,working with SAAMI spec, do.
Alot of the SAAMI spec standard (non +p) ball,used mostly for plinking and target practice,is very weak contrasted to SAAMI +P, CIP spec, and NATO; which is,I believe,where 9x19 parabellum has derived a good bit of its reputation as a poor street performer.
Gang bangers and other assorted miscreants usually use the weapons and ammunition they can easily get their hands on,9x19 pistols being largely available weapons in America,coupled with cheap SAAMI spec plinking/target ammo available at wal mart,has,IMHO,skewed any attempt at using "street statistics" to judge the 9x19.
That being said,good ammunition is easily available and for those that do their homework the 9x19 is no slouch.
Personally,I like to use CIP spec ball for serious practice as its cheaper then similar power SAMMI,and good American SAAMI spec +p or +p+ for the "heavy lifting".Standard SAAMI spec ball is fine for plinking.
I would not feel undergunned with CIP spec ball,or NATO ball,but standard SAAMI spec ball....well...........that stuff is for shooting at bottles.
Good SAAMI spec modern design JHP usually gives nothing to bigger cartridges when it comes to terminal performance.
My favorite is anything in +p 124 gr loads with a good JHP.
There are in fact other 9mm chamberings out there.Its really quite a long list,from other 9x18 rounds like the 9x18 Police and 9x18 Ultra,to 9x23 cartridges like the Largo and Steyer.
Theres even the 9x21,created by IMI (Israeli Military Industries) for nations where military service calibers are not allowed to be owned by mundanes.
Its supposed to perform just like 9x19 Parabellum in all other respects.
Anyway,make sure you use the proper ammunition for your weapon
If you don't know what your buying,ask for help from someone who does.