From: bartb@hpfcbart.fc.hp.com (Bart Bobbit)
Subject: Re: Tasco vs. Leupold Rifle Scopes
Organization: Hewlett-Packard Fort Collins Site

Tasco scopes do have very good optics.  That's what impresses most folks
as they look through 'em.  But clear, bright, undistorted images through
the lenses are not what makes any rifle scope accurate and repeatable.
Accuracy and repeatability is a mechanical thing; the reticule must be in
the same place for each and every shot.  And that's the Tasco brand's
weak point.  Their mechanics is not quite up to the quality (accuracy and
repeatability) of Leupold scopes.  After only a few dozen rounds on heavy
recoiling rifles, Tasco scopes tend to loosen up mechanically and the
reticule will be in a different place for each shot.

This inability of Tasco scopes to be repeatable is small and may not be
noticed by most shooters.  A quarter to third MOA error is typical.   Some
may loosen up to a half MOA or more.  To a shooter who has equipment and
ability to produce quarter MOA groups through 300 yards will not accept
this level of mechanical accuracy.  Others may find it acceptable; that's
a decision one has to make for themselves.  Interestingly enough,
even the Leupold scopes used for benchrest competition are often modified
with an external device under the turret to improve the repeatability and
accuracy of the 36X target scopes in elevation; windage seems to be very
good.

I'm convinced that no rifle can be shot more accurately than the shot-to-shot
errors its sights have.  If there's a half MOA error in the sights and the
rifle/ammo combination can shoot half MOA, the best group size one can
count on is one MOA; the errors in sights and rifle/ammo add together.

BB

From: bartb@hpfcla.fc.hp.com (Bart Bobbitt)
Subject: Re: Need advice on Win. M70
Organization: Hewlett-Packard Fort Collins Site

Lloyd D Reid (reidld@ecf.toronto.edu) wrote:

: OK, you got me.  I mistakenly assumed everyone shot low drag
: ~150 grain bullets
: from 30" bbl target rifles at ~2900 fps.
: Guess I'm getting closed-minded ;-)

I wish I had a dollar for every time someone got me; I'd retire and buy
everyone on this net a firearm of their choice.

: This [40MOA] is an intersting number.  I shot this very combination at
: 700 ft elevation on a cool day (~55 F), and needed to come up
: 34 minutes from my 100 yard zero.  These 'minutes' are according
: to the graduations on my Leupold scope, which I assumed to be
: reasonable well calibrated.

Well, with due respect to Leupold, their minutes are not quite minutes.
As I remember someone who checked out a Leupold some time ago, he said
it has about 7% more movement on paper than claimed in its specs.  Thay
may be why you moved you scope up 34 MOA from 100 yards to 1000 yards.
With my Weaver T20 scope and zeroed at 100 yards with 155s at about 2900,
I need to come up about 33 MOA to zero at 1000 yards when at 5000 ft.
altitude.  At 700 ft. altitude, I'd need to come up about 37 MOA.  Having
checked my T20 and it moves exactly 1/4 inch per click per 100 yards of
range, and my software says that's what I should come up going from 100
to 1000 yards, both our come-up numbers are about right for the sights
we're using.

: Bart, are you using unconverted 'American' or 'British' or
: 'Australian' minutes (i.e., corresponding to the scale readings
: on Warner, Paramount, or Central sights)?  Or have you converted
: to true MOA?

I'm using the traditional shooter MOA; 1 MOA equals 1 inch for each hundred
yards of range.  That tracks near exactly with my Weaver T10 and T20
scopes.  With iron sights, such as my Warner, Swenson, Mo's and Redfield
Palmas, they all have 40 tpi lead screws and 3 MOA per knob revolution.
But I gotta keep in mind that my iron sight radius varies from 32 to 37
inches depending on the rifle used.  At 36 inches of sight radius, one MOA
on those sights moves bullet impact only .833 MOA on paper.

: Maybe I need to apply a 'Leupold MOA' correction
: factor to my readings?

I agree.  Clamp your scope in a vise, focus it on a ruler 50 yards away,
then crank the knobs.  For 10 MOA on the adjustments, the reticule should
move exactly 5 inches on the ruler.  But whatever it moves, you can do the
math to determine exactly what your movement per adjustment MOA is.  Then
you'll be able to convert settings to shooter MOA and calculate all the
neat stuff more accurately.

: Curiously, the Chrony ballistics program predicts 34.4 minutes
: come-up required from a 100 yard zero, when Sierra's BC of .475
: is used (I know that you favor using a set of 3 lower B.C. values
: for this bullet).

Paul Perez and I did the math and MOA stuff with iron sights for our
Paramount rifles with the 155s exiting at 2920 fps.  We went to the range
to sight in Paul's rifle after establishing a true boresight at 100 yards
(setting the group 3.9-in. below bullseye center), then set the sight's
elevation scale to zero without moving its knobs.  He came up the amount
calculated with my 155-BC numbers at our 5000-ft. altitude for 300 yards.
His first shot was a bit high; about one-quarter inch high and perfect for
windage.  That's close enough for me.  He layed there and shot a bunch of
Xes, then quit.  We next moved back to 800 yards where he put on the dope
calculated for that range.  He called his first shot an X at 9-o'clock;
and it was an X at 8-o'clock.  Paul started laughing at this exercise of
mathematical success.  He was quite pleased that his calculations were on
exactly.  I had been crossing my fingers this whole session hoping all was
correct; I guess it was.

: .....for all the types of ammo a Canadian .308 shooter is likely to
: use (155 Sierra Palma bullets, or DND 7.62 issue), 35 minutes
: of scope adjustment should suffice.

Well, it depends on the exact movement per click; scopes do vary somewhat.

: .308Win	155Palma .475	2901	-333"  = 33 MOA		93"

With my Sierra software set to BCs of .404 (>2400fps), .411 (2400-1900fps)
and .391 (<1900fps) I get a 1000-yard drop of 404 inches with 2900 fps
muzzle velocity.  This is what I used at the Nationals with three rifles
shooting 155s.  The come-up for them was about 45 to 46 MOA on the sights
whose 34 to 35 inch sight radius moved near .87 MOA on paper per MOA on
the sights.

BB