Probably because your mate is not cleaning it like you are.
I know you say it is not a cleaning issue but my experience is different. With thick SS barrels from reputable manufacturers fouling interfere's with MPI more than heat, unless you leave the next cartridge in a hot chamber to heat-up like an oven. The popular 'first cold bore' should really be called 'first clean bore' shot. Having shot for a number of years in F Class competition I can tell you that lubricity of the barrel influences MPI as much (if not more) as heat. As for heat, this comes from two actions; how the barrel warps when heated, but also how long you leave the cartridge in the chamber before pulling the trigger. Heat is compounded in an AR as it automatically feeds the next round in to the 'oven' where it acts as a heat-sink at the worse possible time, within a second of the last round fired. If the outside of your barrel feels warm to touch imagine how hot the powder is inside the next round sitting waiting to be fired. No doubt a few on this forum have seen machine guns get so hot it 'cooks-off' the next round and you get a runnaway gun.
In a bolt gun shooters tend to feed the cartridge in only when it is nearly time to shoot. Those mindful of hot chambers temperatures will deliberately leave the bolts open to facilitate air-flow through the barrel to cool it quicker. May as well do this in an AR if you are not in a situation requiring the gun to be at instant.
Back to fouling. In precision bolt-guns where variables such a cleaning and heating are more evident I shoot 1 MOA low when the barrel has been normally cleaned and then prepped for shooting, and 1.5MOA low when the barrel has been properly cleaned. Every 100rds it gets a full service with copper cleaning, compared to the normal fouling brushwork. Some shooters use the two or three sighters in a match as 'fouling' shots, deliberately paying minimal attention to where the shot goes knowing that these will print differently and for fear of 'chasing the spotter' (adjusting your windage and elevation based on the previous round). In an AR I often fire the first two rounds in quick succession into the butts to foul the barrel...plus it feels good for some reason...
Don't forget, whether it is fouling or heating causing your first shot to be low this will be compounded by your systems ability to group. For example, if your gun shoots 1.5MOA then expect every shot to land anywhere within a 1.5MOA circle, the MPI of which will be 1.5" low on the first shot. So, at 100yards you might find that sometimes the shot will be actually right on the aiming mark as the two variables negate each other, yet it is still being influenced by either fouling or cold barrel. And sometimes it will be a full 3" low as both variables compound each other.
I know of some shooters who prepare for a match by deliberately not cleaning the gun going into the match. It is not a widespread practise and if it were so successful it would be.
My point is, if it is the first couple of shots from a cold AR the heat will change the MPI the least of your total shooting session/string. But... at the start the lubricity of the barrel will have changed the most throughout your shot string. Fouling affects the start of your shooting session, whereas heat affects the end of your shooting session.
(I assume your 1.5" is at 100yds, so 1.4MOA)
I know you say it is not a cleaning issue but my experience is different. With thick SS barrels from reputable manufacturers fouling interfere's with MPI more than heat, unless you leave the next cartridge in a hot chamber to heat-up like an oven. The popular 'first cold bore' should really be called 'first clean bore' shot. Having shot for a number of years in F Class competition I can tell you that lubricity of the barrel influences MPI as much (if not more) as heat. As for heat, this comes from two actions; how the barrel warps when heated, but also how long you leave the cartridge in the chamber before pulling the trigger. Heat is compounded in an AR as it automatically feeds the next round in to the 'oven' where it acts as a heat-sink at the worse possible time, within a second of the last round fired. If the outside of your barrel feels warm to touch imagine how hot the powder is inside the next round sitting waiting to be fired. No doubt a few on this forum have seen machine guns get so hot it 'cooks-off' the next round and you get a runnaway gun.
In a bolt gun shooters tend to feed the cartridge in only when it is nearly time to shoot. Those mindful of hot chambers temperatures will deliberately leave the bolts open to facilitate air-flow through the barrel to cool it quicker. May as well do this in an AR if you are not in a situation requiring the gun to be at instant.
Back to fouling. In precision bolt-guns where variables such a cleaning and heating are more evident I shoot 1 MOA low when the barrel has been normally cleaned and then prepped for shooting, and 1.5MOA low when the barrel has been properly cleaned. Every 100rds it gets a full service with copper cleaning, compared to the normal fouling brushwork. Some shooters use the two or three sighters in a match as 'fouling' shots, deliberately paying minimal attention to where the shot goes knowing that these will print differently and for fear of 'chasing the spotter' (adjusting your windage and elevation based on the previous round). In an AR I often fire the first two rounds in quick succession into the butts to foul the barrel...plus it feels good for some reason...
Don't forget, whether it is fouling or heating causing your first shot to be low this will be compounded by your systems ability to group. For example, if your gun shoots 1.5MOA then expect every shot to land anywhere within a 1.5MOA circle, the MPI of which will be 1.5" low on the first shot. So, at 100yards you might find that sometimes the shot will be actually right on the aiming mark as the two variables negate each other, yet it is still being influenced by either fouling or cold barrel. And sometimes it will be a full 3" low as both variables compound each other.
I know of some shooters who prepare for a match by deliberately not cleaning the gun going into the match. It is not a widespread practise and if it were so successful it would be.
My point is, if it is the first couple of shots from a cold AR the heat will change the MPI the least of your total shooting session/string. But... at the start the lubricity of the barrel will have changed the most throughout your shot string. Fouling affects the start of your shooting session, whereas heat affects the end of your shooting session.
(I assume your 1.5" is at 100yds, so 1.4MOA)