Saturday, November 3, 2012

Practice Makes Perfect, I Hope

The Nikon scope that I ordered for this AR-15 project will not arrive until Tuesday or Wednesday, but I'm going to get in some more practice with this funky BSA scope that I found in a packing box.

This is a BSA Platinum 6-24x44 scope with a 1" tube and mildot reticle. And today's exercise is to get it mounted, levelled and boresighted on the AR-15. I'm going to use Burris Signature Zee rings - I'm sold on the things - with the concentric inserts. Those are the inserts that come with the package; the eccentric inserts are sold separately - for $16 per ring!

I adjusted the scope with the bathroom mirror method again so that it was optically centered.

The first step is to level the gun, so on go the Wheeler bubble levels. Looks level to me!

The AR-15 flat-top has a good-sized flat just behind the Picatinny rail. This accomodates the Starrett machinist's level nicely. But notice that the bubble here is all the way to the left.


When in doubt, always believe the more expensive piece of gear, so we level the gun to put the Starrett bubble in the center, and re-adjust the Wheeler to agree.

Here's the Starrett with the bubble in the center. It's hard to get it there and harder to keep it there.

The Burris ring is a tight fit on the rail - in fact it won't fit at all. Notice the little cut in the ring's base, next to my thumb? That's the "Zee" that you find in the Burris rings for the Weaver-style base.

So we just get out the old pry-bar (Stanley screwdriver) and gently open up the "Zee". The rings are steel and do not yield easily; it took me seven attempts to open it enough to slide it on the rail.

And then whaddaya think happened? Yup, these (medium) rings are too low for the 44mm bell of the scope. In this photo, the bell of the scope is resting on the handguard, and the tube of the scope hasn't touched the ring yet.

But I was once a Boy Scout, and I was prepared with a set of high rings, seen here. Of course, that meant opening up the "Zee" on yet another set of rings, yadda-yadda.

I set the rings exactly 4 inches apart and tightened them down to 20 in-lb, while pressing them forward against the rail. These are 1" rings and the bases use straight-slotted screws! Caramba! Interestingly, Burris 30mm rings use Torx screws at the base. Wonder why?

You can see the lower ring inserts in place here; they resemble big-end bearings on a crankshaft.

And here is our old nemesis, Mr. Boresighter. Everything still looks level, but we have been tugging and pulling and torquing on the gun a bit, and this is our last chance to check the levelling before we put the ring caps on. So we check one more time with the Starrett level and it's off half a bubble. So we level the gun again and tweak the Wheeler level to match.

Torquing down the rings. Moving in a criss-cross pattern, one quarter turn for each screw. Checking the scope to see that it's level in the collimator. Checking the bubble level. Then another round of quarter turns until the wrench clicks at 20 in-lb. Several times I felt a slight "give" as I turned a screw; I think this may have been the plastic insert being pushed into place by the pressure of the steel ring.

Here's the view. It was just fiendishly difficult to get a good snapshot with this scope. But what you see here, even though it looks off-axis, is what I saw with my eye: nicely level, one unit to the right and 3.5 units high.

And here's the final assembly. The feeler gauge says that the scope is 0.077" above the handguard. Is that too close?

All done and ready to be put away.

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