[curator]

I finally got to a 100 yard range with my 4095 classic. Per previous thread here
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I made a DIY rail-over-irons adapter and put a cheap red-dot on it. Zeroed it as best I could off-hand standing at 18 yards, and there it sat for a few months. Here's the result at 100 yards without touching the sights:
]http://i902.photobucket.com/albums/ac222/museummaster/IMG_1293.jpg]
I made a DIY rail-over-irons adapter and put a cheap red-dot on it. Zeroed it as best I could off-hand standing at 18 yards, and there it sat for a few months. Here's the result at 100 yards without touching the sights:

I shot 20 rounds with irons (all in the lower right quadrant), and 40 rounds with the red-dot (I counted 38 or 39 in the upper right quadrant). Ammo was 180 gr Blazer aluminum. Had my first malf early (stove pipe), which may have been because I was shooting seated and had the mag resting on the table.

The red-dot has a fairly substantial standoff distance above the barrel, and zeroing it at 18 yards almost certainly puts the red-dot sight axis crossing the bullet path at a fairly significant angle. I'm pretty sure this is why the red-dot group cluster about 10" above the iron sight "group."

The "groups," if you can call them that, have about 80% inside 6". Some of that is undoubtedly me, as I wasn't using a rest (other than right elbow on the table). I should run the geometry calculations to see if the 10" offset between groups is consistent with the difference in standoff of the irons and the red-dot.


Conclusion is that a decent group can be shot with .40S&W at 100 yards, but might not be accurate enough for hunting. I have no idea what the ballistics are at that range, , but it doesn't seem that bullet drop is a huge factor.

[builditbigger]

I would re site it for 50 or 75 yards, then try the 100 again, that seems to be the best ranges to set mine at. You might get a tighter and more consistent grouping.

[curator]

No doubt. Unfortunately, unless the range has a spare target stand they'll let me haul out, my choices are 25 yds or 100. Doing the math now on sight axes and barrel axis + bullet drop (assuming 1100 fps). I'll likely try to find zero at 25 yds with a calculated offset for 50. With no spotting scope, I'll at least be able to see the hits at 25 yds. :-[

[ArmyCWO]

Was there not something on this forum indicating that if sighted in at 25 yards, it drops back in at about 100 yards or am I mistaken.

Mr. Mac

[curator]

It depends on the sight standoff distance. A rough measurement shows the iron sights to be about 1-3/4" above the barrel axis. On mine, the red dot is about 3-3/4" above. Assume the gun is clamped in a vise to hit the bullseye at 25 yds, and both sights are then adjusted to this POI. The bullet will approach the sight line for the irons at a shallower angle than it does the red dot sight line. Since the sight lines are different (irons above the red dot line after 25 yds). Any shot aimed with the red dot will hit higher at distances beyond 25 than if aimed with irons.

[Yeoldetool]

3.75" above the bore is ALOT. Not cheek weld......chin weld. Meh, if it works for you...

[nclpta]

decent grouping, but i would still adjust both because i am certain you can get a better group.

[curator]

decent grouping, but i would still adjust both because i am certain you can get a better group.

I'm blaming it on the ammo . . . :devilsidesmile:

[Yeoldetool]

Definately not the ammo. :cantlook: If you're getting groups like that at 100yds, you could get them all in the black with proper sight alignment.

[curator]

Well, if it's not the ammo, then it must be the barrel getting hot (40 rds in ~10 min)? Couldn't possibly be me . . . . :-[

Point taken, Y.O.T., and thanks. The red dot could be limited by its size though. It's a Tasco with I think a nominal 4 MOA dot. Whatever it is, the dot pretty much covers the black at 100 yds. Next time out, I'll zero both at 25 yds first.

Army CWO: It depends on rear sight standoff, distance from sight to muzzle, and muzzle velocity. With stock irons on a classic and 1100 fps, a zero at 25 is a zero at 50 yds. Higher velocities would move the second zero out further. Here is the math on bullet drop, assuming a constant 1100 fps velocity. Best combination seems to be zeroing my reddot at 50 yds and irons at 25. Turns out for the irons, the sight position is almost identical for 25 and 50, since the bullet drop arc just touches (but does not cross) the iron's sight axis if zeroed at 40 yds. Here are the results for POI vs. POA

distance BUIS Reddot
(yds) @25 @50
10 -0.8" -2.4"
15 -0.5" -1.8"
20 -0.2" -1.4"
30 +0.1" -0.6"
50 0.0" 0.0"
75 -1.9" -0.8"
100 -5.5" -3.1"

where "-" means POI below POA.

If anybody has chrono results or calculations for bullet velocity vs. distance, I'd happily redo the POI/POA calculations, as I'm sure velocity on a FNFMJ 0.40 round is dropping off fairly fast, even for 180 gr wt.