I am working on a project upper for .300 AAC Blackout and in the process of doing research I found this at Brownell's. I like the idea of being able to change barrels (and bolt if need be) so can simply buy a few more parts and have another caliber available. Have any of you ever used one of these to build an upper assembly? I am also considering a few non-swappable upper/rail forend combos, notably the VLTOR VIS polylithic upper, and the MEGA ARMS - AR-15/M16 MEGALITHIC UPPER RECEIVER are also candidates. If you have any experience building up an upper assembly from one of these I'd like to have your opinions about them.

I really like the swap barrel design, (the idea of caliber changing appeals to me), but I also like the other monolithic system rails. I am planning on doing more research before I choose, so please tell me what your impressions are of these upper receiver solutions. I feel that accuracy will be greater with the VLTOR and MEGA Arms systems, so I'd like to have the benefit of others experiences with all of these - or perhaps a suggestion for some other solutions I haven't found yet.

There are so many choices - and I can't buy all of them...
or can I?????

Zero5Delta

Here are a couple of options along the same lines, one is slightly cheaper, the other (that's looks comparable) is significantly cheaper

Neither are exactly "monolithic", but they are both "quick change"

MGI quick change upper


Tac2 discreet carry

The Tac2 lets you for a carbine into a standard briefcase,
If you but this one, but or use your own briefcase, as the one they sell is a piece of crap

Both systems can be found through other source for less than the manufacturers want.

One of my friends went with the Dolos system, it works pretty well, I'm going to use it too.



https://www.coppercustom.com/shop/parts-kits/dolos-ar15-quick-change-barrel-system/