hello all I am new to this site,

well i am trying to trade some stuff for a 300 blackout AR pistol and want to use the upper from the 300 and put it on my 9mm SBR. Can i remove the pins that hold the magazine block on the 9mm and replace it's upper with the 300 blackout upper? would there be any other parts that would need to be replaced? would it  be something i can change back and forth easily at the range?

you should be able to remove the pins for the block and use a standard AR mag. I dont know if colt uses the longer last round hold open, that may be an issue.

I'm not sure, as I sold my colt, but you may have to change to a standard buffer if there is one of the longer/heavier 9mm buffers in it.

the only other thing I can think of may be the take down pin size if you are using an older lower.

this is all speculation on my part though, as I dont have your lower and upper in front of me to disassemble and look at.

If the mag block is held in by roll pins, I would NOT recommend changing it very often because each time willo wear out the aluminum receiver a little more (could eventually cause functional problems). Better to buy a top-install drop-in mag block (I have the Hahn) which goes in and out without tools. This would allow you to switch to any AR15 upper (9mm, 5.56, .300 etc.) in less than a minute with no tools just by adding or removing the block.

The only other change might be the hammer - I believe a 9mm hammer will not work with other calibers. A rounded AR15 hammer (M16 hammer with tail cut off) would work for all calibers if you ramp the 9mm bolt.

thanks for the information, i am glad that i  have that option when i find an another upper.

thanks, I was emailed  this from AzCDL on some house bills going on in your state

HB 2376 would allow law enforcement officers, when contacting anyone possessing a firearm, to make a non-professional assessment of their mental state, and if, in their sole discretion, they determine that person may be a danger to themselves or others, seize their firearms, and request they be carted off for a court-ordered mental evaluation. This is an awful lot of power to hand someone who might disagree with your fundamental belief system. After all, if you believe you have the right to have the means to defend yourself, you must be crazy – right? That certainly appears to be what the sponsors of this bill believe

HB 2380 is the ultimate slap in the face to law-abiding gun owners. It would abolish Constitutional Carry. Only criminals would have the freedom to carry when and where they desired without government permission. Or, maybe that was the intent of this legislation

there are others