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Normal Topic Correctly fitting your scope - part one (Read 1585 times)
50BMG
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Correctly fitting your scope - part one
Sep 10th, 2018 at 2:50am
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Optical sights or scope mounting is something not often done at all well. The brand, cost or type of firearm, sight or mounts does not offer any guarantee. Who built the firearm or who mounted the sight is also no guarantee that it will have all been done correctly. Every manufacturer, gunsmith etc. has a bad day from time to time.

Just this week I was asked to help with a perceived rifle accuracy problem. The .338 rifle intended for 2000 plus metre target shooting was about as high end as you could imagine. It wore the absolute best of everything and cost in excess of 10K. The scope was one of the biggest names in the business and close to 6K. The builder was someone who enjoys huge respect and an envious reputation in NZ.  In the end, the problem was a fairly common one. The machine screw holes drilled and tapped into the receiver were about .15mm too shallow for the standard 8 x 40 screws used to mount the sight. This meant that when correctly torqued, the mounts were not able to achieve the required clamping force to ensure the sight remained fixed in a stable, consistent position.

On the surface simply shortening the screws seems like a good easy way to resolve the issue. Not so fast…the size of the screws is usually fairly carefully calculated. The manufacturer/designer of an optic mount takes into account the weight of the sight, weight, centre of gravity, recoil velocity, inertia to estimate total moment of force (leverage) the sight creates on the screws during firing with any likely calibre the sight may be used with.  They usually consider the need for restraint to avoid removing unnecessary material from receivers so as not to unduly weaken them. As a rule, the size and material of the supplied screws is the safe minimum to ensure trouble-free and durable service. Shortening screws can reduce the mechanical load holding ability of them while the heat in cutting screws can reduce the physical properties of the metal rendering them no longer fit for purpose.

Another common issue is that screw holes, mounting surfaces, internal ring surfaces etc are incorrectly aligned and when used cause a misalignment of sight and bore axes. Worse still scope rings can be so far out of alignment with each other they stress the tube and inhibit or damage internal mechanisms.  These are manufacturing issues and need to be checked for before you commence mounting the sight.

Think about the meticulous effort that goes into building true ¼ MOA firearm or for that matter what expertise, care and skill it takes just to have your favourite rifle action “trued” and re-barreled. Why would you not take this degree of care to get the sight mounted? Trouble is, this happens all too often. It is usually caused by ignorance but in some cases, I believe there is a high degree of carelessness in this area for whatever reason. Ignorance perhaps? Go back to my example above.  $16K of the best of the best totally stuffed up due to carelessness.

But to be fair, I would say that incorrectly aligned reticles, improperly positioned ocular lenses and incorrectly torqued fasteners are the biggest cause of problems. I have found setups where 30mm rings have been used for 1-inch tubes. This was achieved by grinding back the caps until a clamping force could be obtained. Not at all good as it distorted the tube and absolutely wrecked the scopes tracking accuracy.

So it does require a bit of essential equipment to mount an optical sight. You need a vernier calliper, micrometer, rule, engineers chalk, bearing blue/ gear paint or similar, thread gauges, torque wrench, selection of levels, cant gauge can be useful, a suitable gun vice to hold the firearm level and vertical, the correct drivers for all screws, nuts etc. correct grades of thread lockers, alignment bars, lapping bars and paste, assortment of cleaners, rags, good lighting as a start. You will also need a place and time where you can work uninterrupted. A notebook is always good.

You can mount a scope with far less. You can also use the cheapest over the counter ammo you can find for your ¼ MOA rifle but you probably wouldn’t. You might choose to fit a $200.00 scope on your brand new custom built 1500m steel ringer but not likely. So take time, get the right gear to correctly mount your sight and then enjoy the benefits.

Next post in this series will cover preparing the receiver and rings.
  

"The brave few are Freedoms rampart for the many"  "Otherwise protect your freedoms or you will surely lose them"
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Trout
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Re: Correctly fitting your scope - part one
Reply #1 - Sep 18th, 2018 at 7:27am
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Hi 50BMG,
I read all your posts with interest.Iv learnt a little on the way.Iv only had two 308s in my 15yrs of huniting.But both good out to 600yds target shooting.But 400yds on deer my limit for the clean kill on deer.
I put a little zeiss on my TX3.I practise a lot of cold bore shots at 200yds.I put a 3/8 white dote on black sheet of A4 paper.Im queit happy to hit the white dot 2 out of 3 shots.Have soft rippon  flags up for detecting wind.No wind near perfect condition on a coldish morning,keeps barrel cold as well.
H C and i use to practice on rabbits down our local river yrs ago as the sun was setting on their eyes.Anything from 400 to 500 yds was fear game shooting of the bonnet of our truck.As we called it,gentlmans sport.
Iv rambled on enough,keep up the good write ups and hope your shooting range school works out for you.
Trout Smiley
  

Shot a few deer,caugth some big trout and salmon
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tinass
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Re: Correctly fitting your scope - part one
Reply #2 - Sep 18th, 2018 at 8:04am
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I look forward to the next post regarding this, cheers for all the posts 50BMG.
  
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Oscar
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Re: Correctly fitting your scope - part one
Reply #3 - Sep 18th, 2018 at 8:49am
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Cheers. Look forward to reading. Be interested to see what you consider the 'bare minimum' eg for a rifle used only for hunting within Point Blank Range
  

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Re: Correctly fitting your scope - part one
Reply #4 - Sep 18th, 2018 at 9:18pm
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Oscar wrote on Sep 18th, 2018 at 8:49am:
Cheers. Look forward to reading. Be interested to see what you consider the 'bare minimum' eg for a rifle used only for hunting within Point Blank Range

Hi Oscar,
I know you asking BMG 50 the above,but my T3x 308 is zeroed at 200yds and only has a 4 inch drop at 275 yds,useing Hornady SSTs 150gr.I think the best ammo off the shelf for energy and flat shooting.So my tika is pretty good for a light rifle to carry around shoot out to 275yds.300yds is 6.5 inchs of drop.
The zeiss scope has a Z6 retical on it,so 1st dot down=300yds if I use it,2nd dot=400yds,3rd dot=500yds and 4 dot=600yds.
Iv practice of lot on the 3rd and 4 th dot at 500yds,600yds,very accurate scope.I work at night so going to the range just out of Tekapo mid week,easy for me in the best weather conditions,when the lake is reflecting the skys in it=no wind.
I only shoot about 4 deer a year and a few roos.Each deer = 60rds down range a yr or more.All fun tho. Grin
  

Shot a few deer,caugth some big trout and salmon
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Re: Correctly fitting your scope - part one
Reply #5 - Oct 26th, 2018 at 5:29am
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Oscar

In my view, the minimum is whatever you need to achieve a securely mounted optic which is concentric to the rifle bore axis that reliably holds zero. I do not see any difference between mounting at long range optic or a holographic combat sight.  The basics do not change.
  

"The brave few are Freedoms rampart for the many"  "Otherwise protect your freedoms or you will surely lose them"
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