So, I have a stripped RRA lower that I am going to transmogrify (finally!) into a 9mm AR.

-I just ordered a Hahn block from Ameetec.
-I plan on ordering a complete 9mm upper from Adco.
-It seems they also have the 9mm hammers in stock, so I'll get one from Adco.
-Some generic LPK from someone for the rest of the bits.
-Mags from CDNN. A few Colt, and some range-beater Promags.

What I still need:

-From my understanding, I need a 9mm bolt catch to make proper use of the Hahn/Colt mag bolt hold open. Who has these?

-I also need a 9mm buffer. Adco lists them as out of stock; Anyone have another source?

Thanks in advance!

The 9mm bolt catch is only needed with the standard top load block.  The bottom load and the dedicated top load blocks use the standard 5.56mm bolt catch.

As far as the 9mm buffer, Adco has a good price.  If you have a dealer account with Brownell's, I believe they are the same price or slightly less.

9mm bolt catch & buffer -  Garrison Manufacturing Inc.

Quoted: The 9mm bolt catch is only needed with the standard top load block.  The bottom load and the dedicated top load blocks use the standard 5.56mm bolt catch.

Sounds like Tomislav have this one here.  For $25 more you could have gotten a dedicated adapter and not worry about a 9mm bolt catch.  If you can, buy an extra bolt catch.  Mine broke on me last weekend, after 2K rounds.

Quoted: The 9mm bolt catch is only needed with the standard top load block.  The bottom load and the dedicated top load blocks use the standard 5.56mm bolt catch.

And the bolt hold open function still works? I was under the impression that i needed a 9mm BC to do that...

ETA: The block I ordered is the 'Hahn 9mm Dedicated Mag Block Adaptor'

Do the RRA mag blocks need the 9mm bolt catch?

Quoted: Quoted: The 9mm bolt catch is only needed with the standard top load block.  The bottom load and the dedicated top load blocks use the standard 5.56mm bolt catch. And the bolt hold open function still works? I was under the impression that i needed a 9mm BC to do that... ETA: The block I ordered is the 'Hahn 9mm Dedicated Mag Block Adaptor'

You should really check with whoever you ordered the block from to confirm what you ordered and what they intend to send you.  BHO works with the dedicated top load or the bottom load block using the standard bolt catch.  With the regular top load block, you must use a 9mm bolt catch for BHO on the last round.

Quoted: You should really check with whoever you ordered the block from to confirm what you ordered and what they intend to send you.

As stated above:

ETA: The block I ordered is the 'Hahn 9mm Dedicated Mag Block Adaptor'