This posting is not so much to ask for help, as it is to share my experience.  If you have had this problem and worked your way through it, I welcome your sharing your solution with me.

In November of 2001 I purchased a Bushmaster AR15 E2 M4 with the non-removable handle.  I am disabled and need all the help I can get to carry and manipulate the rifle, so I mounted a full-sized 3 X 9 scope on top of the handle, because iron sights are useless to me.  The arrangement works fine, except that the rifle groups poorly, printing mostly pairs (2-leaf cloverleafs) of holes touching in a 4- to 6-inch diameter circle. Having been shooting for over 50 years, and having owned at least 3 rifles capable of shooting into 1/4-inch all day long, I am accustomed to a high level of accuracy.  I decided long ago that most rifles can be made to shoot 5 times as accurately as most owners think they can, if the shooter does his part, and sometimes with a little detective work.

The pairs of holes tells me the rifle is capable of outstanding accuracy, even for a Bushmaster 5.56, but the large grouping area tells me something weird is wrong.  Several people examined this rifle and upon first examination, we decided the scope and mount were correctly installed and secure.  However, upon closer scrutiny, it was discovered that the scope and mount were moving ever so slightly within the U-shaped gutter on the top of the carrying handle that the mount fits in to.  I have decided that the width of the mount is just slightly to wide, although this is not visible to the eye and extremely difficult to detect because both of the outside vertical surfaces of the mount and the carrying handle gutter are at a slight angle. This is find if the angles are exactly the same, but if not, the slight difference produces enough slop to destroy good groups.  The poor design of the mount is made even more flimsy by the fact that the only means of tightening-down the scope and mount to the handle is by means of a single threaded shaft and knurled knob intended to be tightened by fingers only.  Because the mount and the handle are not permitted to engage fully by the slightly different angles of their vertical surfaces, no amount of tightening will make the attachment of the scope to the rifle completely secure and rigid, and without play.

I have been told a hundred times to trash this junk mount and get a flattop and be done with it, but I am disabled and I really need the grasp and purchase of the handle.  The rifle just doesn't seem like an AR wtihout the handle.

I am 95 percent certain I fixed the problem once and for all by cutting a couple of shims out of 0.20" flat aliminum stock and putting them between the mount and the handle on either side of the single threaded attachment machine screw and knob.   This appears to have eliminated the slop between the mount and the handle caused by the fact that the vertical surfaces of both did not engage, but merely allowed the mount to pivot on the handle where they touched.

Between my loose scope mount problem and my disability which keeps me mostly indoors, here it is 19 months after I purchased the rifle and I still don't have it sighted in.  What an aggravation.  However, I'm fairly confident that I will soon be shooting little teeny-tiny cloverleafs with my Bushmaster, as I did before with other accurate rifles.

Wish me luck !

-Beldar
([email protected])
 

Beldar

I really like these rings.  They are made by Ironsighter at http://ironsighter.com/  model 570M for $29.95.  (listed under rifle mounts) They put the center of the scope exactly where the rear peep site would be.  They also angle forward which helps get the scope where it needs to go.

I use the scope as the "handle".

[img]http://jcrisp.home.mindspring.com/_images/arRings.jpg[/img]

I have same setup (the carry-handle to weaver-base screw on mount, one thumbscrew holds it, mount rides in the carry handle groove).  I use Good Rings ($50+), and lap the rings (320 valve lapping compound), rotate steel bar same diameter as scope when rings are semi-tight, this makes for perfect alignment)

The rings should have 4 or 6 screws each.  One for each side of the base, one for each side of the upper ring (or, two for each side of the upper ring, better..)

Tighten the handle adapter block mount down good, use 'removeable' Locktite to make sure the thumbscrew doesn't come loose.

Unscrew all of the ring setscrews to a specific distance (base of head at edge of hole, or something very repeateable for all screws).  Rear Scope ring base:  Screw in right side 1 turn, left side 1 turn, repeat until they are tight.  Repeat for front ring base.  Put ring caps on around steel bar coated w/320 valve compound that is same diameter as scope (usually 1"), same procedure, tighten one side one turn, then the other.  Tighten evenly until bar it is semi snug, but moveable. The gap between the ring caps and the ring bases should be the same on all 4 parts (front, rear, left, right).  Then lap the rings (10-20 strokes, spiral motion with bar), this smooths out any imperfections and makes sure the scope is mounted truely paralell, and the rings will be in solid contact with scope.  Remove top rings, steel bar.  Clean compound from rings.  Lay scope in ring bases.  Place ring tops on top of scope, tighten each side, 1 turn at a time until _tight_ (not snap off the screw tight, but tight).

I do not mean to talk so basic about this, as it sounds like you have mounted many scopes before.  Hopefully somebody else will read this and be able to apply The Method.  I had the same problem as you (3+" groups) until I changed rings (1.5" groups) and lapped them (sub MOA groups @100yds).  Even though the scope is a bit high, but I still have the irons for backup.

Hope this helps!

-edited to remove redundancy in description, but not completely...

not all carry handle mounts are created equal. Did you buy quality or spend $6 at a gun show?

I really reccomend this brand of mount. They mount under the carry handle so the do not block the iron sights at all like the mounts you describe. They are quality all around and priced accordingly.

[url]http://www.rifletech.com/cgi-local/shop.pl/page=2fdce2.html[/url]