Add Mid-length carbine upper to existing RRA 20" match AR

[QTHNH]

I am looking for a sanity check on my plan. I am looking to buy components to allow me to switch my AR15 between match upper components and carbine length components. (I use the match configuration for informal club competitions, and I am not competing in any regional competitions FWIW.)

I have a RRA LAR-15 20" NM A4. I am looking to add a mid-length carbine upper group to use with the existing RRA lower. I am consider buying a BCM M4 16" Upper Receiver Group, and reusing the RRA bolt carrier group and charging handle.

Do you see any concerns in mating the BCM upper with my existing RRA lower?
Is there any reason to separately acquire the BCM BCG and charging handle, as I am assuming I will reuse the RRA components when swapping?

Thanks in advance for any advice.

 

[MACGYVR]

Just buy a complete upper and you can swap all day long with the push of a pin.

 

[KMM696]

My concern with your plan (and it's a small one) is the bolt. I prefer to not swap bolts between barrels, since the bolt and barrel extension will wear into each other. Swapping that bolt around may cause accelerated wear that I'd prefer to avoid. I do not claim that you have to worry about this - I'm sure that any combination of in-spec bolt and extension that passes a headspace check will run just fine. It may only be inside my head that this is something to consider.

I'm not concerned about the carrier or charging handle - much looser tolerances on both of those. I started AR15s with the one lower and multiple upper theory, too. That didn't last long for me - nothing gets swapped anymore, they multiplied like rabbits in the safe.

 

[mac1911]

im may be wrong but is the bolt not "fitted" to match the barrel on the Nation Match model ? Im not sure how much fitting goes into the RRA NM model vs a mil spec production model. I can tell you that my RRA NM feels and sounds smoother than my mil spec RRR a2 upper.
For what you save by swapping BCG and Charge handle it may be even less to just buy a mil spec BCG and charge handle.