So,

In my haste over the past few months I've managed to collect what amounts to 3 full lowers.  I have 1 Spike and 2 Aeros, with standard LPK's.  The Spikes is fitted with OD green Sig Stock and Grip.  The Aeros's don't have any stocks.

What I'm thinking about doing, is turning the Spikes OD Green into a 300blk rifle, because I don't own that caliber.   I have also considered doing a 25-45 Sharps.

With the 2 Aeros, I'm considering doing 1 as a pistol.  I don't have one and think its something I should own.  I've also considered doing 1 as a pistol and then getting the other done as a form 1 SBR, but I'm torn.

Anyone got any suggestions or thoughts?  I'm very open.  I don't want to dump a ton of money into them, but I'm not completely opposed if its awesome LOL

Build a 7.62X39

I'd never considered 7.62.  I thought I remembered their being issues with BCG and extractions.

I'd go with a Grendel. As soon as I can scrape up the funds, I'll be adding one to the family.

Okay, so I built one as an AR Pistol in 5.56.  I still have the other 2 that I need to do and I have the money finally.  I've been looking at doing 7.62, but finding a BCG is proving to be a huge pain.  I've been looking at Radical Firearms version if anyone is familiar.  

The other one I still haven't decided.  I thought about 300blk, but its basically just 7.62.  I've considered 458 and .50 Beo.  

I know someone mentioned Grendal, but I'm not super sure about that cartridge.

Grendel is an awesome cartridge. It's very proven in an AR platform and is one of, if not the best, all around hunting cartridge for AR's.

6.5 if you're into precision long range shooting and hunting. 7.62x39 if you are into hunting and just cheap high quantity shooting at closer ranges. 300, IMO, is only useful with a silencer. Expensive hard to find ammo. Easily confused with 5.56 at the range=KABOOM! Ballistics no better than 7.62x39. the subs only have energy in the 45acp range.
If you want to build a 7.62, I've had great luck with AIM BCGs and CPD mags. I've used barrels from PSA, Radical (extension came off, but after I got it fixed it seems fine), another PSA, ESS solutions (m4 barrel that sportsmans guide sells) and my next build has a faxon barrel. With this combos I've never had to do anything with the LPK or anything. I normally run a heavier buffer and extra power spring, but they all functioned with carbine buffers, I just like to fine tune them.

The 7.62 vs 300blk was my exact thought.  The 7.62 is VASTLY cheaper.  I have 2 6.5CM and a 270 and 300WM if I decide I wanna shoot distance.

These issues are exactly why I didn't build a 7.62, So by the sound of it you have found solutions to feed and ejection issues associated with the 7.62 versions??!!! If so 7.62 will be my next build!

If you reload a 300blk SBR would be pretty cool. If my state allowed SBR's that would be my next gun.

As I understand it, its mostly magazine and proper BCG that cause the issues.   I'll let you know how it shakes out.  I've got another 5.56 and 7.62 upper on the way.  As well as a M5 lower from Aero.  I have a problem LOL