Impossible to answer without a DETAILED DESCRIPTION OF ALL MARKINGS AND LETTERING, condition, box, papers, accessories.
You will have to call Colt to find out.
A letter from Colt will get you started.
Most gun shops. Your Iver J is in caliber 38 S&W, which is NOT .38 Special.
On line auctions.
how to breakdown and load 38 caliber iver johnson pistol?
If the pistol says 38 Super, the pistol with fire "38 Super" ammo. Most 38 Super ammo today will have +P after 38 Super. If the pistol is a modern firearm in good condition it can fire 38 Super +P rounds. However, if you pistol is 25+ years old, I suggest you having a competent Gunsmith examine the pistol to determine if it can safely fire modern "38 Super +P" ammo. (A little bit about the history of the 38 semi-auto round is below) Around the turn of the 19/20th century, Colt developed a semi auto pistol that chambered a round called the 38 ACP, (Automatic Colt Pistol). When the US Army was looking to adopt a semi auto pistol in 1910 it rejected Colt's 38 ACP. the round lacked the knock down power, but accepted Colt's 45 ACP with an improved pistol that was adopted in 1911 as the Model 1911 pistol. Colt improved it's 38 ACP in the 1920's by increasing it's pressures and chambered it's model 1911 for this round, naming it the Colt 38 Super Automatic. (The famous Tommy Gun was also chambered for the 38 Super for a short time too). Under no circumstances should pistols chambered for the old 38 ACP be fired with 38 Super ammo! Although the rounds are physically identical, they are not interchangable. the 38 Super Automatic is much more powerful. If the pistol does not specifically say 38 Super, it should not be fired with modern 38 Super ammo. If your pistol says 38 ACP, you must find ammo that is specificly made for this antique firearm, which is hard to find. If you are a skilled handloader, you can load rounds for the 38 ACP using data from reliable handloading manufacturers. Note that a standard .38 auto pistol should NOT be subjected to the increased pressures of Super .38 +P ammo.
beffore we can answer that question,we must have the code on your p-38.It may say have a ac 43.or byf 42,or cyq 44 code.this will tell what factory made your p-38 and then with the serial number we can tell what year and month it was made.
I have seen people shoot accurately at 100 yards or more with a .38 pistol. However, in general, a pistol bullet can travel, on average, about a mile.
You must call S&W to find out.
Best bet is to find a gunsmith
if you allude to 38 S&W cartridge then you will find the case is shorter then a 38 Spl. case. You can fire a 38 S&W cartridge in a 38 Special but you can't fire a 38 Special in a pistol designed for the 38 S&W cartridge.