Should front/rear sight be same height?

[Zak Smith]

On a 1911, should the plane defined by the top of the front and rear sights be parallel to the top of the slide, when the pistol shoots to POA at 7 yards?

On my Dan Wesson Patriot, it seems to shoot to the top edge of the front sight only when the rear adjustable sight is cranked way up, at about 0.05" higher than the front sight.

When a 1911 is locked up, is the barrel parallel to the top of the slide? If so, shouldn't the tops of the front & rear sights be the same height off the top of the slide?

thanks
Zak

 

[BigG]

I can't answer your question but I know that the sights on any gun are not parallel to the bore axis because the line of sight is a straight line whereas the bullet path is a parabolic curve. Therefore, the bullet is either going up or coming down to meet the point of aim. HTH

 

[Zak Smith]

BigG,

At close enough range - like 7 yards, the trajectory will only diverge from the straight-line path by a few tenths of an inch, not the 2.5" I'm seeing here.

-z

 

[BigG]

Zak, figure this: your bullet will cut the line of sight at two places; the first as the bullet ascends to meet the line of sight near the muzzle and the second the range where the gun is zeroed for. On a 1911 type the sight line is probably a half inch above the bore axis, therefore, in this case, the bullet has to angle up a half inch to intersect the sight line the first time.

I don't want to give you a lot of hassle but there are a lot of pistol errors that a shooter can make with a 45 Auto. If you are sure that no shooter induced error is taking place then your sights are definitely questionable if it's 2 1/2" high at 7 yds.

Another thing: most target shooters hold a six oclock hold where the bullseye looks like a lollypop on top of the front sight. This is about 4" above line of sight at the target distance (50 feet or 25 yards). HTH

 

[Handy]

Zak,

On 1911s especially, there is no direct relationship between the top of the slide and the barrel. So no, the sights shouldn't be parallel.

1911s with fitted barrels and long links can be so out of parallel with the slide that new sights and a new, higher firing pin hole is necessary.

I don't think the ballistics question is all that important. Between 1 and 25 yards, there isn't much of an arc.

Of the guns I can think of that keep the barrel and slide pretty parallel, the sights are about the same height (Glock, P7, etc.)

 

[Zak Smith]

I understand external ballistics of this situation.

 _BC_ _MV_         0       5      10      15      20      25      30 | YARDS
0.205  850 >   -0.50   -0.57   -0.79   -1.07   -1.55   -2.04   -2.63 | > Sierra 230gr FMJ

This describes a 230gr FMJ with BC 0.205 fired at 850. The pistol is set up with the sights 0.5" above the bore centerline, and the sights are parallel to that bore centerline - the bullet vector and the sight plane start parallel.

As expected, at x=0, the bullet it at -0.5, and then it starts dropping: about 0.5" to 15 yards, then another 1.54" to 25 yards. Since it started off 0.5" below the POA, it's at about 1" low at 15 yards, and about 2" low at 25 yards.

At 7 yards, with parallel sights and bore centerline, the POI would be about 0.64" below the POA.

Now if you sight in the pistol for 15 yards, there will be an angle between the bore centerline and the sight line. The trajectory will be this:

0.205  850 >   -0.43   -0.19   -0.03   -0.00   -0.10   -0.29   -0.66 | > Sierra 230gr FMJ

In other words, POI = POA at 15 yards (by definition), and POI is no more than 0.5" below POA from the muzzle to 15 yards. The top of the bullet's curve is at approximately 14 yards, where it is just fractionally over the POA.

What I noticed was that the POI was about 3" under the POI (as defined by the top edge of the front sight, with the tops of all the sights in line). I then cranked up the rear Bomar-clone quite a bit, until it was within about 0.5" of POA.

It is possible that I'm pulling the shots down, but I think I'm not. With the exception of called flyers, I can get about a 1" edge-to-edge group at 7 yards - it was just low. I also shoot my CZ-75B-SA right to POA with no problem.

thanks
Zak

 

[Zak Smith]

Handy,

Thanks. I am not well versed in the mechanics of the 1911 yet.

-z

 

[Zak Smith]

BigG,

I forgot to respond to one of your points:

Another thing: most target shooters hold a six oclock hold where the bullseye looks like a lollypop on top of the front sight. This is about 4" above line of sight at the target distance (50 feet or 25 yards). HTH

Here's a trajectory that supports that POA/POI (for the 25 yard case):

 _BC_ _MV_         0      25      50      75     100 | YARDS
0.205  850 >   -0.24    4.04    5.42    3.54   -1.41 | > Sierra 230gr FMJ

If it's sighted in (second zero, "coming down") at about 94 yards, it will be 4" above POA (going up) at 25 yards. This will obviously require the rear sight to be much, much higher than would be to be sighted in at 15 yards.

In particular, if the barrel were parallel to the slide, then a 15 yard zero would require about a 0.111-degree inclination, while the 94-yard zero would require about a 0.384-degree inclination.

-z