I have an Olympic Arms CAR-15 (fixed A2 buttstock, A2 sights, regular-contour stainless barrel) that I really like and plan to keep (simple).  I recently decided to get the barrel threaded for a Phantom FH and since I plan on removing the barrel myself, have been thinking of the virtues of the flat top receiver once the barrel is back from the smith.  

I have a few questions:

1). I’ve noticed that in order to clear the front sight block when using any scope on a flat top receiver (A3 style), risers must be used.  What’s the difference in height between most of these risers/mounts as compared to the fixed carry handles?  Are the flat top receivers specifically suited for a particular type sight?  I mostly use the A2 sights, which I find fantastic, but in the future may want to add something like a X32 or smaller scope or reflex-type sight.  

2) What’s available in a non-flip, removable, rear sight base that I can transfer my A2 sight parts to?  Doesn’t have to be fancy, just simple and rugged (estimated cost and source would be nice).

3)What’s the difference between an M4 type feed ramp built onto the receiver vs. a regular feed ramp (which I probably have)?  Is it like the FAL “unibrow” vs. two scallops?

4) Also, does anyone know of a good source for Olympic Arms flat top upper receivers?  I’ve seen a number of vendors here selling various brands but no Olympics.

5) Lastly, What type receiver or barrel clamp should I get, where, and how much?  I'll be using a friend's work bench, vise, etc.

I thoroughly enjoyed the thread with pics, you guys have some serious ARs!!!

TIA,
MG-70

Too many questions... brain overload...

Anyway, I only know the answers to a few of these.

1) No riser is necessary, as the focal length of the scope is WAY past the FSB, and you never even see it as a shadow in most scopes.  You can hold your finger over the end of the scope, and you never even see your finger.  The worst that happens is that you get a small shadow and/or the amount of light entering the scope is reduced.  The FSB on ARs is so far out that the light thing and shadow are not an issue.  Most of us simply use a riser to get quick detach capability (to use our expensive BUISs) or to get the scope up high enough so it is more comfortable to use (the eye bell of the scope can get too low to the stock and/or can make pulling the charging handle harder if it isn't on a riser).

2) No idea why anyone would sell a stripped BUIS or where to get one.

3) M4 ramps are made for greater reliability during full auto firing and higher gas pressures like the M4 has.  The extended feed ramps (all the way into the receiver) allow the bullet nose to hit a little lower and still feed into the chamber without jamming.

STANDARD


M4


4) Olympic probably uses the same uppers all the other manufacturers use (e.g., Alcoa forges, Anchor Harvey forges, Cardinal forges, and Cerro forges).  I doubt anyone would actually sell "Olympic" uppers, since many folks (not me) think Olympic is of lesser quality than the other guys.  I love my Plinker Plus upper, so I have to disagree with them.  Any flat-top that isn't marked with a different manufacturer's mark (like the RRA and LMT ones) would fit and pass for an Olympic flat top upper.

5) You can get the Bushmaster action block, but lots of folks seem to like the DPMS Panther Claw better.  Prices vary all over the place, but the Bushmaster is usually a little cheaper.  There ARE other styles, and they all seem to get good reviews, but the DPMS and BM are the two I see people talking about most.  You can check MidwayUSA, CheaperThanDirt, Brownells (have their own type, as a matter of fact), and more for current prices.  I haven't bought one yet, as I keep buying my uppers already assembled.

ETA: As far as "flat top or not" goes, I would say if you plan to use a scope a lot, go for the flat top.  It's more stable and isn't so high up like carry handle mounts that you have to have a cheek riser to use it comfortably.  If you don't plan to use a scope much, the built-in carry handles (A1 and A2 uppers) are much better, IMO.  The detachable carry handles are heavy and are too skinny for my big hands (the sight is at the same height as an A1/A2, but the attachment base and screws take up part of the hand room in the handle).  I got an A3 upper rifle w/detachable carry handle first, then got an A1 (the Plinker Plus) upper later.  I much prefer the A1 upper to the A3, but the A3 rifle is used with a scope, so I have to put up with it to get the lower scope mount.  Just keep in mind that there is no way to comfortably use a scope AND a BUIS at the same time with an A3 upper (even risers can't get scopes high enough to clear the iron sights without making the scope too high to be comfortable).  Plus, if you want that BUIS to be useable, you'll need some way to get that scope off quickly (thus, the QD scope riser most of us use).

Shameless post of my two ARs:

Thank you both for the answers and pics (feed ramps and rifles!)!  A couple more…

1. The Olympic bbls don’t have the extension but they’re still compatible with the M4 uppers, correct? (they just won’t benefit from the modification).

2. Any idea what an Olympic Arms A2 receiver and sight w/forward assist and port cover in Like New condition are worth?

TIA,
MG-70