Hello ladies and gentleman I have just purchased my first ar.  I however have a few questions i was hoping perhaps some of the more experienced members could help me with.  My rifle is an essential arms built rifle, on the lower it says mod j 15 f cal. 223/556 and serial number.  It is my understanding that that specifies the caliber of rounds the magwell is made to accept as it is the lower.  My real question (unless im wrong about the writing on the lower in wich case please correct me)  is what is the barrel chambered for .223rem or true .556 military?  I have read the sticky and tried to educate myself however my efforts have been futile.  Pertanent info.  the only markings i can see on the barrel are are M1S 1-9.  I am led to believe that this is a 1 in 9  twist  stainless barrel however no chamber is mentioned.  Should i just take it to a gunsmith and pay him to insert go no go gauges or is it common knowledge that a noob liike myself doesnt know?  Thankyou for the help if it is possible.

The go-no go gages won't tell you if it's a 5.56 or .223 chamber. The difference is in the "throat" of the chamber. The only way to find out would be to have a 'smith make a chamber cast and measure it. Another thing would be to use .223 Remington ammo only and then you wouldn't have to worry about it. You may call Model 1 Sales and ask them. They machined the barrel.

ty for youre time sir i will give them a call cant believe i did not think of that doooooooooh
to anyone else who may have this question in the future the lady on the phone said unless specified .556 or hc it is chambered for .223 only.