Convert 9mm to .300 blk

[Sdl]

I want to convert my 10.5 9mm upper to a 10.5 .300 blackout. I think I can still use the same gas system. Swap the barrel and BCG. Add a new buffer and I’ll be good to go. Am I correct on this? Thanks for any help.

[jtallen83]

Have you thought of just building another upper? The cost will not be that much different by the time you swap out parts. 

[dpete]

^^^ This. 

[shooterrex]

Your 9mm should be blowback and not even have a gas system.

9mm buffer is way longer than milspec.

9mm buffer spring is usually stronger than milspec.

If you built a different upper you would still need to change the spring and buffer.

[MikedaddyH]

You are all forgetting the lower...  Glock Mag Lower vs. AR15 Lower

[shooterrex]

My 9mm used an AR-15 lower.

Mean arms endomags.

[DNP]

1 hour ago, shooterrex said:

My 9mm used an AR-15 lower.

Mean arms endomags.

Same here. I used a little different upper though. 

[98Z5V]

CMMG Banshee uses AR15 lowers, AND AR15 mags, with mag kits to convert the mags.  I hate to tell Rob, but those things run like a striped-ass ape.

We need to know more about the 9mm gun that this guy has, before we can make anymore recommendations, or critiques. 

14 hours ago, Sdl said:

I want to convert my 10.5 9mm upper to a 10.5 .300 blackout.

Then give up all the deails on your 9mm.  We cannot go forward with information, until you do that.  Descriptions are mandatory, pics are almost necessary.  Otherwise, we're just pissin' in the wind here, in this thread..