I have your basic A3 flattop and a Burris 2 - 7X variable for mounting.  Roughly, how high up do you normally set these optics, especially for target, prone shooting?  I have medium ht rings, do I need the Bushie 'risers' for another 1/2"?  thanx
billy

I don't claim to be an expert, so take this for what it's worth.  I would say it's a personal thing, and what fits your shooting style.

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Here is my 24" gun.  It has Leupold QRW High rings and a Bushnell 3200 Elite 10x40.  I found it didn't sit far enough forward to suit me, and I added the GG&G GS-1 rail.  Set it up a little higher, but moved it forward where I wanted it too.

To be honest, I haven't shot it enough to know how it feels.  I think it might be a little high, but manageable.  And when I learned to shoot an AR in the Marine Corps, I shot it with my nose to the charging handle.  Thus the need to move that scope forward.  It's all about how you shoot and how it feels to you.

1.40" from top of rail to center of scope is the norm.  This usually requires Extra High rings from most vendors.  Getting the scope far enough forward for proper eye relief is usually a problem with many optics.  That's why the LaRue mounts are so great.... they give you proper height and eye relief.

The Armalite 1-piece is another option.  About half the price of the LaRue and very solid, but not quite as much eye relief, and not as fast to mount and dismount.

A one-piece like the LaRue or Armalite has the plus of simplicity, fewer connections between receiver and scope, and no ring alignment issues.

An extended riser rail with regular rings is more flexible, but has more connections for tolerance stackup and more possible looseness/failure points, and can give even more eye relief, depending on the length of the rail.  Most people need the eyepiece of the scope in front of the charging handle, which usually requires an extended rail.

LaRue SPR:
stores.homestead.com/Laruetactical/Detail.bok?no=30
SPR with even more eye relief:
stores.homestead.com/Laruetactical/Detail.bok?no=40



Armalite 1-piece:
www.armalite.com/sales/catalog/components/mounts_rings.htm

its all personal preference, everyone has a diff cheekweld.  irons are 1.3" above the rail, thats what i prefer.  most larues are 1.5" above the rail i believe.  i shoot ntch, so i run a riser/extender and low/med rings depending on scope dia.

ihave a dpms flattop and i used the bushmaster risers with med. weaver rings and a 4 x fixed scope.you can't use the nose to the carry handle hold as tought in the service but it does work well for me

Quoted: ihave a dpms flattop and i used the bushmaster risers with med. weaver rings and a 4 x fixed scope.you can't use the nose to the carry handle hold as tought in the service but it does work well for me

these allow you to mount the scope more forward.  yankeehill.bizland.com/store/product260.html

THANKS FOR THE INFO.

Irons have aperture about 1.4" above the top of the rail.  I use the Armalite one-piece on a 4-16x and it puts the center about 1.25" above the rail which works fine for that.  Eye relief is no problem with it.  I have a Simmons (I think) 2-7x in some rings that are the same height.  A little short on the eye relief at 7x without the offset, but workable.  I don't put my nose all the way to the charging handle though.  

If you're measuring the rings in the store look for 3/4" from top of rail to the bottom of the scope tube.  That'll give you the height you need, but if you can have someone help you position the scope with you looking through it, do it, because you might need the offset to get the right eye relief.