From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: [HI-PWR] Loads, Powder Lots, & Testing
Organization: Hewlett-Packard Fort Collins Site

Doug White (gwhite@ll.mit.edu) wrote:

: My concern was just how tightly one can shoot with iron sights.  Someone
: told me that the human eye can only resolve to about 1 MOA.  This could
: be in error, and it could be that 'pin-hole' effect of a peep sight will
: reduce this.

There's not a big difference between how well one can shoot with aperture
compared to scope sights in the competitive shooting discipline.  Remember
that the rifle can be held just as steady with either type of sight.  So,
the difference is how well one can call their shots.  With a scope, it's
easy to call within 1/16th MOA or thereabouts with a scope.  As the
human eye resolves about 1/4th MOA (good vision, corrected with glasses
or not), that's about as close as one can call their shots with aperture
sights.  Good prone shooters have about a 1/2 MOA wobble area on the
target and will call 95% of their shots in an area no bigger than
about 3/4ths to 1 MOA on the target.  In the less stable positions, the
wobble area will be bigger, but the calls should be just as accurate and
they indeed can be; if your eyes are open when the rifle fires.

Many years ago, an old man told me that if a rifle shooter needed a bench
to sight in a rifle, that shooter was not a good, nor even an average shot.
It took me a while, but I finally figured out what he was talking about.

: I've got a Warner rear sight with an adjustable iris aperture, and I'm
: using a clear disk w/conical hole aperture in the front.  On sunny days,
: I've been closing the rear most of the way down, and I'm using the 2nd
: smallest front aperture I've got.  Are there any nuances to the use of
: these gadgets I should be aware of to minimize my sighting error?

Some rules of thumb regarding front apertures.........
Clear plastic/acrylic front apertures are great for indoor smallbore where
there's no rain drops around to get on them and mask your target number.
If you do use 'em outside, be sure the large diameter side is towards the
target; if they're in backwards, the black ring won't be as black.

The size of your holding, or wobble area defines the smallest aperture
you should use.  If your hold lets the bullseye appear to touch the edge,
the aperture is too small and it will encourage jerking when the sight
picture looks perfect.

Usually, the approx. size is what appears to be about twice the bullseye
diameter.  The only way you will know what is best for you is to use the
size you shoot the best scores with.  It's better to use one too big than
too small.

As for the rear iris, it should be large enough to get sharp edge definition
on the aperture.  If it is closed down enough to where while looking through
it, a gray area appears in its middle, that's too far; your eye will strain
to get enought light.  Nobody shoots better than they can see.

: As far as calling my shots, I can certainly tell (shooting offhand) the
: difference between a 6 o'clock 10 and an X, but I'm not sure I can tell
: the difference between a 6 o'clock X and a 3 o'clock X, which is about
: 7/8th MOA.  Maybe I can call tighter from prone or a rest.  I've been
: shooting offhand almost exclusively, so I haven't had much experience
: with a stabler position.

Here's way to learn how much bullseye displacement in the front aperture
is worth.  Spear a white piece of paper with a pencil, then put that
pencil down your rifle's muzzle.  Put a black dot on the paper with something
so it aligns well with the sight axis.  If that dot can be made to appear
the same size as a 6 MOA bull for highpower short/mid range, 4.5 MOA bull
for highpower 1000 yards, or an 8 MOA bull for smallbore, your're in.
Look through the sights with that dot aligned with them after adjusting
them to get a well centered dot in the front aperture, move your rear
sight 1/2 MOA up and 1/2 MOA right.  The dot will now appear just like
the bullseye does when the rifle's aimed at 1:30 deep in the 10 ring.
If you make a dummy target with 1/4 MOA grid lines on it, you can tell
where the rifle will be aimed with a given number of clicks off center.
Note what the sight picture looks like for each rear sight offset.  It
won't take long for you to learn how much off-center the bullseye is for
a shot to be called anyplace very accurately inside the 9 ring.  You could
anchor your rifle in a vise, then tape a dot on the wall aligned with the
sight axis, too.  And you could print out with your computer a series of
black dots of different sizes, then measure the front aperture's height
above bore axis so you would know where to spear the white paper with the
pencil.  You may need to put tape on the pencil to wedge it tight in the
muzzle.  A little math could be used to determine exactly the dot's size
for the few inches it will be in front of the front aperture.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Losing it at 600.
Organization: Hewlett-Packard Fort Collins Site

Christopher Morton (cmort@ncoast.org) wrote:

: As quoted from <C5G7Fx.EBH@fc.hp.com> by bartb@hpfcla.fc.hp.com (Bart
: Bobbitt):

: # This is an old shooter's tale.  The only time the position of the sun can
: # make a difference is when using an unshielded post front sight.  And the
: # sides of the post visible to the shooter are slightly round.  With this
: # type of post front sight, the center of the visible post can appear off
: # to the side away from the sun; the rifle tends to shoot into the sun.  But
: # it only effects windage and seldom more than a half minute.  With covered
: # aperature front sights, this doesn't happen.

: The US ARMY MTU disagrees.  At least they disagree sufficiently to teach
: "light's up, sights up" at SAFS-Rifle.  They did for the last two years
: too.  Doesn't mean that they're right.  Doesn't mean they're wrong
: either.  Does the USAMTU at Benning have an internet account...? :)

You're talking about elevation changes.  I was talking about windage
changes.  You're right about the elevation changes.  That happens when
the light intensity goes from low to high and the shooter's eye iris
gets smaller.  When that happens, the aiming bull appears larger and
the front sight post will still appear the same size, but when touching
the bottom of the apparently larger bullseye, the shots will go low.
In darker (dimmer?) light, the eye's iris gets larger and the bullseye
appears smaller causing the front sight post to be closer to the center
of the bullseye; the shots go higher.  The `light's up; sight's up'
rule of thumb is very correct for post front sights whether they are
hooded or not.  Typical correction varies from a quarter to almost a
full minute elevation change depending on the person's eyes and light
condition changes as well as atmospheric conditions.  When aperture
front sights are used, this doesn't apply; the bullseye centers in the
round aperture regardless of how big it appears, but the aperture size
might need to be changed to allow a better sight picture.

So, you're right and so is the USA MTU.  Years ago when I taught some of
the SAFS at the Nationals, I would explain this situation to new shooters.
Some believed it; others didn't.


BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: New Rifle Advice
Organization: Hewlett-Packard Fort Collins Site

I [Bart Bobbitt (bartb@hpfcla.fc.hp.com)] wrote these words:

: For sights, the Warner is the only rear sight made in this country that
: holds zero, has no backlash or lost motion, and has enough windage adjustment
: to cope with hurricane-speed winds.

....and now I'm gonna eat 'em; without condiments to improve the flavor!!!!

Mo DeFina (Mo's Competitor Supplies, Brookfield, CT) has a new competition
rear sight out.  I just saw one this weekend that's about a year old.  Note
that this in not his huge, heavy, flat-slabbed thing he's had for several
years.  Instead, it is a lighter one that is much better made.  I guess he's
had this sight for about a year or so; don't know why I've not seen one until
today.

It mounts on a horizontally-ribbed base much like the great sight from down
under in Australia, the Central sight.  The elevation arm is split like
the Central sight, but is twice as big dimensionally.  Its windage arm is
the same size material and has over 40 MOA of adjustments either size of
its mechanical zero; great for use on a .308 Win. Palma rifle in a hurricane.

The scales are easy to read, too.  With its lead screws at 40 TPI, one turn
on an adjustment knob gives three MOA of change.  His earlier sight had 36 TPI
lead screws and that caused problems when sight dope from its user was passed
on the the next shooter in a team match who used a 40 TPI lead-screwed sight;
the next shooter was always 10% short of having the correct sight settings.

Although the lead screws are smaller in diameter than Warners, they have
plenty of thread engagement with both elevation and windage blocks they move.
And these adjustment blocks are properly clamped onto the lead screws.  No
preload springs are needed to eliminate backlash.  They aren't likely to shoot
loose.

Adjustment blocks ride on hardened steel, tiny square guides about an inch
long.  These guides are held in a V-groove and work very nicely.  It is sure
an inexpensive approach to making a repeatable rear sight.  Turning the knobs
presents a smooth, even tension throughout the adjustment range.  Deep grooves
on the knob's inside let the detent ball click softly into place.  There's no
binding whatsoever.

My only dislike of this sight is the adjustment knobs are not marked in any
way; no full MOA numbers (0, 1 and 2) nor half or quarter MOA lines.  The
only indicator is a red dot on the inside boss of each lead screw; it's hard
to see if turned away from where you look at the sight from.  But putting
some white stuff at the zero point on each knob helps.  If you're really good,
you could put a tiny chunk of white china marker lead at the quarter MOA
points, a bigger one at the half, then big ones at the full MOA points.  It
helps to be able to read your sight settings when you need to know where
they're at.

Threaded for Gehmann and other European-thread apertures, it will no doubt be
popular.  Thread adaptors are available to use the USA standard apertures.
Bases are available for popular target rifle actions.  One nice thing about
it is that when used for short ranges, the elevation arm can be moved down
on the ribbed rear sight base so the elevation knob on the top won't be so
high as to bumb against the bill or your shooting cap during recoil before the
bullet exits the muzzle causing a bad shot; like into the 9 ring!!!!

Mo DeFina sells these for about $175; bases cost about $25.  I now think
Alan Warner finally has a competitor for his great, aluminum-bodied, very-well
made and extremely repeatable rear sight.  Plus, Warner's cost $330 for the
standard No. 1; $350 for the No. 2 with the longer windage arm.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: New Rifle Advice
Organization: Hewlett-Packard Fort Collins Site

Stefan (smpod@mars.lerc.nasa.gov) wrote:

: Except for the Redfield Palma, this is the cheapest new sight on the market!

: Maybe I should get one before the price goes up with demand ;-)

If you're talking about getting a Redfield Palma sight, its two elevation gib
lock screws replaced with longer ones, then the sight properly retighened
and adjusted for zero backlash.  Then lock nuts need to be put on these gib
screws to keep 'em in place.  Otherwise, as the Palma comes from the Redfield
factory, the elevation gib screws will loosen up in a couple hundered rounds
and the sight will have at least one MOA of slop in it.  Having reworked
dozens of Palma sights for folks, it's sad that Redfield has ignored my
suggestions years ago to put longer elevation gib screws with lock nuts on
them so they will stay in place and not shoot loose.  Otherwise, the Palma
is a good sight for use up through 600 yards.

BB