It's been a few months since I posted here, so it's good to be back.  Having got that out of the way, I've got some questions about a .45 build I'm thinking of starting up.  I'm planning on using the eagerly awaited CavArms aluminum lower with a Hahn block and grease gun mags.  I'm considering getting an Olympic upper, and that's where the question comes in.  If I'm reading their online catalog correctly it looks like I can order one with an 11.5" barrel, and that sounds good to me.  If I decide to go this route, does this mean that I'll be registering the lower as an SBR when I get around to ordering it, or registering the upper, or what?

I'd also be interested in hearing from other people out there who have similar builds, short-barreled or not.  If the SBR route winds up being too much hassle I'm still pretty certain I'll proceedwith the 16" barrel, and I was wondering if people had any hints or tips for me as I go forward with this build.

Thanks in advance!

You register the lower, not the upper. I have no experience, however, with .45 uppers.

It sounds like the Cav Arms aluminum lower may take a while to get to market. And when it does you would have to go through the whole NFA process to SBR it which can take several months.

That being the case you could use a Cav Arms polymer lower with GG mags or a standard lower with the converted Uzi mag until the Cav Arms aluminum lower gets here. Just don't use a short barreled upper until you do the paperwork.

I have a Oly uppper and as well as I remember it was fun to shoot. I sent it off to have an integral suppressor installed and paid the money to SBR the lower at the same time. The last time I got to shoot it was in November. Hopefully the NFA transfer will be completed in the next month or two.

I never thought it would take a year to do all that. I am sure that it will be worth it but damn it will soon be a year.

It may take you even longer to do what you want if you wait for the Cav Arms aluminum lower.

Good luck and have fun.

I have a .45 upper SBR (at least my Class III guy has it).  I've been waiting about 4 months for the paperwork to clear.  I have shot it on several occasions and it's quite fun.  The only problem is getting high cap uzi mags at a reasonable price.  

I've put about 200 rounds through the gun w/ no failures even through the break in perios.  My set up has a 6.5 inch barrell and a gse lower. eotech scope.  It's a great step and it doesn't miss.  I reload my own ammo so my per round price is about that of factory 9's.  I like the bigger punch of the .45.  If I can learn to post pictures I would be glad to show it off.  I've read some bad posts about oly arms but I cannot comment on that however I'm quite glad I made the purchase.
Ken

I have an Oly .45 setup on a Cav arms lower using the M3 mags.   Mine's waiting to be integrally suppressed if my damned form 4 ever clears.   The tube is at my dealer and it will be final assembled once the paper is good.   This way I still get to shoot my upper unsupressed while I wait.   I'd suggest buying a good low mileage upper off the EE.   You can use it with a standard Cavarms lower while awaiting their aluminum setup.   All the other stuff will swap to the new aluminum lower when it becomes available.   After you do a form 1 you can cut the barrel and install it on your new aluminum lower.    I plan to build a second .45 once the aluminum comes out.   I'll probably go to a 5-6" bbl and short FF handguard.   The barrel will be as short as possible and still get a sight tower on past the HG and a short stubby FS.   I'll probably use a pistol suppressor on that rig.    The .45 SBR is a nice idea, it's probably going to be the most practical AR shorty caliber as you dont need high velocity to be effective.   Of course mine will probably never see any more serious use than punching steel or the unlucky jackrabbit.  

Cool, thanks to everyone for all the helpful replies.  I guess right now I'm thinking about going ahead with the Cav lower and a regular length upper, then when the aluminum lower gets here I can decide if I want to proceed with the paperwork hassle for a SBR and/or suppressor setup.  Time to go hunt the EE for a used upper, I guess...