Sighting a rifle scope: the theory

Pinecone · May 28, 2018

Then use a smaller vital area. If you can only hold a 2 inch group at the MPBR, then decrease the vital area by 2".

Yes, the shooter has to do their part. But MPBR works as advertised.

ras_oscar · May 28, 2018

To answer the questions posed above:

1. The reticle it BDC. It has circles and dots from the center cross hairs extending down the vertical axis. My understanding is the circles are 100 yard increments beginning at 200, and the dots midway between are 50 yard increments.

2. I have never been hunting. I have never served in the military. I have always had great respect for those with the skills to pick up an accurate weapon and engage a target at distance. The need for reasoning and mental calculation appeals to my engineering personality. It's the same reason I enjoy reloading. I have thus far reloaded only pistol rounds. I am accumulating the equipment and studying the process of reloading rifle rounds, which I understand has several important differences. The range presently available to me is limited to 200 yards. Once I become proficient at that distance I plan to seek longer ranges.

3. I would consider myself proficient at a given distance if I could consistently place rounds within a 4" group

4. Please confirm that the holdover dots are only accurate with the scope at full zoom. The scope is 4-14, and thus far I have been using it at the lower end of that range. The scope is second focal pane, IE the dots do not change size when I zoom in or out.

5. What is "magic BB"?

danb · May 28, 2018

ras_oscar said:
To answer the questions posed above:

1. The reticle it BDC. It has circles and dots from the center cross hairs extending down the vertical axis. My understanding is the circles are 100 yard increments beginning at 200, and the dots midway between are 50 yard increments.

2. I have never been hunting. I have never served in the military. I have always had great respect for those with the skills to pick up an accurate weapon and engage a target at distance. The need for reasoning and mental calculation appeals to my engineering personality. It's the same reason I enjoy reloading. I have thus far reloaded only pistol rounds. I am accumulating the equipment and studying the process of reloading rifle rounds, which I understand has several important differences. The range presently available to me is limited to 200 yards. Once I become proficient at that distance I plan to seek longer ranges.

3. I would consider myself proficient at a given distance if I could consistently place rounds within a 4" group

4. Please confirm that the holdover dots are only accurate with the scope at full zoom. The scope is 4-14, and thus far I have been using it at the lower end of that range. The scope is second focal pane, I E the dots do not change size when I zoom in or out.

5. What is "magic BB"?

For #1 and #4, IIRC you have the Nikon P308 4-16x42.

The reticle chart is below. With customary toe. So for example the first dot "F" is 8" per 100yds at 4x zoom (16
" at 200yds), but 2" per 100yds at 16x. At 10x zoom, it would be 1/2 way (5"). Note that they tell you the diameter of the dots and circles as well. F is basically covers a 4" circle at 100yds on 4x zoom.

My advice, given #3 is as outrider said above: sight in 1-1.5" high at 100yds. Go to the 200yd range and adjust accordingly. At 10x on the 200 yds range you will be a bit above the first circle F (depending what load you are shooting and what your barrel length is).

Biggfoot44 · May 28, 2018

Magic BB = Originally a millitary expression , sometimes also Golden BB. Referes to in a situation of widely scattered projectiles/ fragments/ whatever, unlikely for any of them to actually hit anyone/ anthing , one of them by pure happenstance hits a small , etrememel vital target.

Example in waterfowl context . Billy Bob takes a shot at goose 200yds away with #2's . By pure happenstance, one pellet hits the goose in the eye, and into the brain . Really bad luck for the goose, but by no means does that make 200yd shots at geese a wise or effective strategy .

Biggfoot44 · May 28, 2018

So far I have been discussing in the context of zeroing with regards to a conventional plain 'ol crosshair . ( Not a bad set up , with a reasonably flat shooting ctg, will suffice for 90% of hunters for 90% of available shots . Yes, arbitrary percents , but reasonably close to reality .)

If the scope has BDC features designed for specific load or class of load, follow the mfg charts . Use a grain of salt, and verify the POI at various distences to verify . Or ignore the BDC features, and only use the basic crosshair,if that suits your needs.

**********

And indeed it is cognizent for the shooter/ hunter to realistically know their capabilities of precision with their rifle, from real world shooting positions . That is the limiting factor for ethical hunting, even if the rifle is theoretically capable of farther .

Not to put the OP on the spot , I'll speak theoretically.

If a person is reasonably confident of 4in circle @ 100yds , zero so crosshairs are in lower part of your group, and limit to 150yd shots.

If person is reasonably confident of 4in circle @ 200yds , zero more or less at 200yds , and limit to 250 ( or bit less depending on exact load or ctg . This level will suffice for vast majority of hunting for deer in east coast , unless you deliberty seek out diagonally across a 400ac field, or lengthwise down a power line .)

If person is reasonably confident of 4in circle @ 300yds , high five yourself , and delve into your trajectory compensating scope of preference .

Major03 · May 29, 2018

In regards to BDC's...I personally don't care for them. They are specific to one load, and barrel length. Change the variables, and the point of impact changes. Does it change enough for you to care? That's a subjective call...but for me, I don't like them.

I'd rather have a reticle with either mil-dots or stadia lines and calculate the drop.

Like Bigfoot says...if you choose to use a BDC verify the yardage PER LOAD. If you shoot more than one type of load, repeat.

gtodave · May 29, 2018

outrider58 said:
I keep 99.9% of my hunting rifles 'zeroed' 1 inch high at 100yds.

You have 700+ hunting rifles? Cool :thumbsup:

davsco · May 29, 2018

so with a bdc reticle, zero it at their recommended distance (should be either 100 or 200 yds). then just shoot it from 50 yards on out in 50 yard increments and see where you're hitting vs where you're holding. just as an example, when you use your 400 yard hold, you may be hitting 6" low. now maybe if you use your 450 yard dot, you're bang on at 400. just need to write all that down, where you're holding vs where you're hitting. now you know where to hold for what distance you're shooting.

outrider58 · May 29, 2018

gtodave said:
You have 700+ hunting rifles? Cool

...and one pistol.

Sent from my SM-G965U using Tapatalk

Pinecone · May 29, 2018

davsco said:
so with a bdc reticle, zero it at their recommended distance (should be either 100 or 200 yds). then just shoot it from 50 yards on out in 50 yard increments and see where you're hitting vs where you're holding. just as an example, when you use your 400 yard hold, you may be hitting 6" low. now maybe if you use your 450 yard dot, you're bang on at 400. just need to write all that down, where you're holding vs where you're hitting. now you know where to hold for what distance you're shooting.

Or ignore the BDC reticle and either turn the knobs, or set a zero based on MPBR.

dreadpirate · May 29, 2018

outrider58 said:
...and one pistol.

Sent from my SM-G965U using Tapatalk

Ok - now I have to ask; what is the zero for the 0.1% case?

Biggfoot44 · May 29, 2018

I don't know Outriders 0.1% , but for me pistol cal carbines , things of nominal " black powder velocity " , and shotgun slugs, get zeroed 1.5in high @ 50yds .

outrider58 · May 30, 2018

dreadpirate said:
Ok - now I have to ask; what is the zero for the 0.1% case?

100yds dead center.

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Pinecone · May 31, 2018

You can use the ballistic calculator to do a MPBR for a pistol caliber also.

For Hornady Critical Defense 9mm 115 grain, using the 4" barrel velocity (just to run something), it works out to MPBR of 137 yards for a 10" vital area (+/-5"), with a zero range of 116 yards.

Or sight in at 2.6 inches high at 100 yards.

Biggfoot44 · May 31, 2018

Oh , pistols , that's easy .

Sight in 1.5in high @ 25yds.

Magnum revolvers, full 10mm , light & hot 9mm, etc will be dead on at +/- 75yds , 3-4in low at 100yds . Beyond 100yds test yourself specific load and your ability to hit under field conditions .

.38spl , .45acp, 147gr 9mm , etc , will be dead on at +/- 50yds , 3-4in low 75yds . At 100yds if they are shooting at you , aim for throat to hit more or less center of mass. If Bambi is standing more than 75yds , either stalk closer, or he gets to walk away .

Mini14tac · Jun 2, 2018

Another article I just received.

http://blog.cheaperthandirt.com/pro...dfEtp&sc_llid=1517569&sc_eh=6d1684242b63ea6c1

Sighting a rifle scope: the theory

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