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Normal Topic Correctly fitting your scope - Part Three (Read 169 times)
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Correctly fitting your scope - Part Three
Mar 24th, 2019 at 4:25pm
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Having ensured the machining, alignment and fitment details are correct it is time to prepare the rest of the firearm.

Begin by stripping as far as you can and inspect every single part of for wear or other detectable faults which may inhibit accuracy. Replace any suspect components, clean all mating surfaces to ensure there is no movement between locating parts nor any incorrectly fitted/assembled pieces present to cause issues once the scope has been mounted.

I strongly recommend a comprehensive bedding job and even have your trigger tuned. Getting these attended to plays an important part in the mental condition you bring to your shooting techniques and there is no more influential tool in the toolbox than headspace (the shooters, not the chambered cartridge). Knowing that everything is perfect goes a long way to getting really good results during zeroing which provides a better zero. This boosts self-confidence and trust in the firearm.

You need a solid, stable, flat, well-lit work area where you can mount the firearm ready to fit the rings and then the scope. It is beyond essential that you can position the firearm so the receiver is perfectly level and vertical. This is critical and any error here will permanently affect groupings. I use a customised vice on top of a 3 axis trimmer table taken from a milling machine. This allows almost infinite adjustment on all three axes so I can get a perfect position and lock it in. On the road, I use a Tipton Ultimate Gun Vise.

I have some Torx head screws that about twice the length of the mounting screws and insert them well into the receiverís threaded holes to act as locating dowels to the rings in the next step. You need to be sure that whatever you use will allow the rings to be pressed firmly down against the receiver without fouling anywhere. At the same time, this must correctly align the rings with the mounting surface and fasteners.

Once you are happy with everything, temporarily mount the scope. Check that you can operate all controls on the scope and operate the safety, cocking, bolt etc. and that you have sufficient access the clear/ load the chamber and magazine while holding the rifle in the different firing positions you may use. Move the scope to the correct position for your eye relief and height needs then measure the gap between the objective lens housing and rifle. It should be no less than three mm. You may need to consider a different ring/ base combination if there is less than three mm clearance. Once you are satisfied that there is no impediment to using the setup and it is correctly positioned to meet your needs mark the scope (I use masking tape) to ring relationship for later assembly.

Now you need to apply an even thin coat of Gear Marking Compound to the ring bases. Offer the base(s) to the receiver being very careful to avoid any lateral movement and press down.  Carefully remove the rings and inspect the compound transfer from base to receiver surface. The transfer should show a full even and complete contact of the entire base of the ring on the surface of the receiver.  Any minor issues can be rectified using JB weld two-part epoxy.

If this does not suit, you will need to have the surface of the receiver machined to provide a perfect fit.  I cannot state strongly enough how important it is to obtain a perfect rings/base to receiver match.  This is what prevents movement in the rings which is an all too common cause of poor groups.

Once the correct base to receiver fitting is achieved it is time to mount the rings using the correct screws, a torque wrench and Loctite 222 purple thread locker.  Leave everything time to cure. (Tip: use masking tape whenever you are applying compounds to avoid messes)

Either way, I am able to lock things down in the correct alignment to fit the scope without fear of inadvertently knocking anything out of the correct position/alignment.

The next stage is lapping the rings. There is plenty of online info for this process. Be aware that minimal material removal is important. Many a set of rings have been lapped beyond usefulness as the bore has too much material removed thus preventing sufficient clamping force to be applied.

There are times that I use an oversized ring set and line them with 2 mm Sorbothane to help with eliminating torsional forces from the rings which negatively affect the mechanical accuracy and resolving power of the scope internals and the effects of resonance waves and inertia versus acceleration during recoil.

A few tips on this
1.    Buy a complete mounting/lapping kit to suit your scope tube size. That way you will have a good set of instructions and the correct tools for the job.
2.    Use Gear Marking Compound or Bearing Blue to test the fit of the rings to the scope. The rings must be fully mounted and torqued down first.
3.    Have plenty of soft rags and cleaning gear handy and allow plenty of time to do this.
4.    Use lots of masking tape to protect the firearm from the abrasive paste in the vent of spillage.
5.    Use a high-quality Epoxy Enamel spray paint to cover all exposed metal surfaces.

Videos
Whole fitting process. https://www.youtube.com/watch?v=L4oF_07X1qU
Lapping video. https://www.youtube.com/watch?v=fTIY9cZlpPs
  

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