Fixed Sight Geometry

[41rem]

Have had a few fixed sight handguns over the years where the point of impact was so far off I considered it ridiculous. Was using the standard bullet weight for caliber and usually start a new gun at 50 feet, then move out to 25 yards.

A one offender I remember was a Para Ordinance P-13 that shot 18" high with 230 ball ammo.

What gives, can't a manufacturer figure out how to at least get them close to POl?


41

 

[ND shooter]

Good question. And what are options to fix?

 

[41rem]

On that P-13 I had a gunsmith mill a slot in the slide & install a taller front sight

 

[358WCF]

Got a new Rock Island officer's model 1911 for the female offspring last year. Basically it's a pretty decent piece, shoots nice little groups, but they're about 5-6" low at 10 paces with the factory sights. Factory or handloads no real change. More than one person shot it with same results. Thinking it's the wrong ft. sight? Shorter barrel/slide, maybe needs different front sight than the 5" with no elevation adjust on the rear sight?

Planning to try 185s. If that doesn't work, will touch front sight to the bench grinder a wee bit, then go to the range one day with a pile of ammo & a bastard file to finish the job. Wishing I'd paid better attention in math class. Meanwhile, the Crimson Trace laser in replacement grips is right on the money. Nicer grips too. If it works out I may keep it & find her something else.

 

[Syncrowave]

Those 1911 shorties get right snappy, and if 230gr standard ball prints 5-6" low, I suspect 185s will shoot quite a bit lower (assuming they're faster)...

 

[358WCF]

Those 1911 shorties get right snappy, and if 230gr standard ball prints 5-6" low, I suspect 185s will shoot quite a bit lower (assuming they're faster)...

You're probably right. It's worth 5 rounds to see what happens. The kid has smaller hands so she may choose 185s or 200s to use. Then it's the file & touch up all over again if there's a big difference... or install a different sight. I may take the coward's way out & contact Rock Island.

 

[Syncrowave]

I may take the coward's way out & contact Rock Island.

That's where I would start ... after shooting it myself to make sure she isn't limpwristing it.
45ACP is a handful in a shorty, IMHO. Heck, it's a handful in a 5" 1911.

Wishing I'd paid better attention in math class.

You can use trig, or just use proportional triangles.

[A = The amount you need to shorten the front post, in inches] / [B = Sight radius in inches] = [C = How far you need to raise the group, in inches] / [D = Distance between muzzle and target, in inches]
A/B = C/D
Since AD = CB then A = CB / D

Using your numbers and mine with a lot of guessing:
5.5" low at 10 paces (290 inches)
I'm guessing sight radius on an officer's 1911 = 3.5"
A = 5.5" x 3.5" / 290" = 0.066" = 66 mils
I would try lowering your front post by 40 mils, then shoot and see what you got. Then use a file to sneak up on it.
I'd key front post height to standard ball 230gr @ 830 f/s ammo. Otherwise, it's anybody's guess what you did.

 

[Steve Donlon]

I sent one back that was shooting low and they just put a lower front sight on. No big deal.

 

[ELR LVR]

Have had a few fixed sight handguns over the years where the point of impact was so far off I considered it ridiculous. Was using the standard bullet weight for caliber and usually start a new gun at 50 feet, then move out to 25 yards.

A one offender I remember was a Para Ordinance P-13 that shot 18" high with 230 ball ammo.

What gives, can't a manufacturer figure out how to at least get them close to POl?


41

You file the front sight down if it's shooting low
If shooting High, change the front sight to a taller blade, Then file to perfection
---
Or use adjustable sights

 

[358WCF]

That's where I would start ... after shooting it myself to make sure she isn't limpwristing it.
45ACP is a handful in a shorty, IMHO. Heck, it's a handful in a 5" 1911.



You can use trig, or just use proportional triangles.

[A = The amount you need to shorten the front post, in inches] / [B = Sight radius in inches] = [C = How far you need to raise the group, in inches] / [D = Distance between muzzle and target, in inches]
A/B = C/D
Since AD = CB then A = CB / D

Using your numbers and mine with a lot of guessing:
5.5" low at 10 paces (290 inches)
I'm guessing sight radius on an officer's 1911 = 3.5"
A = 5.5" x 3.5" / 290" = 0.066" = 66 mils
I would try lowering your front post by 40 mils, then shoot and see what you got. Then use a file to sneak up on it.
I'd key front post height to standard ball 230gr @ 830 f/s ammo. Otherwise, it's anybody's guess what you did.

Another 15 thumbs up for adding the equation. Algebra 2 was was "higher math". That was 50 years ago & it's all a distant memory. The sight radius is c. 5.5" from rear edge of front sight to rear edge of rear sight, so using your equation it looks like a BCH over 1/10". Will try to contact Rock Island before starting the grind. If no joy will attempt field surgery. Thanks again.

 

[Hal]

ELV

You move the back sight the way you want the group to move.
The front sight, you move the opposite direction, as you want the group to move.

Hal

 

[Springer2]

I wanted to have one Tupperware pistol to use for classes. I got a great deal on a XD9 Tactical but it shot way high. I did not use it much except for classes so I just held low at 25 yards and thought I would contact Springfield about it later. As luck would have it, I attended a conference and vendors put up some door prizes where I won a set of Trijicon night sights for a handgun of my choice. I got the sights for the XD and ever since then, that XD is right on accurate. Clearly the wrong height sights were on it from the factory.

 

[ELR LVR]

ELV

You move the back sight the way you want the group to move.
The front sight, you move the opposite direction, as you want the group to move.

Hal

That's correct
I said the same thing just a different way, for the guy to be able to correct the problem
If shooting High, the front blade is too low, which makes the barrel aim high
Hence, needing a Taller front blade, to make the barrel aim lower
if your rear sight is adjusted as far as it can go, the only other option is getting a taller front blade
then modify the front blade to have POI = POA
---
This is if...a guy is lining up the top of front blade to top of rear sight window.
Filing the front blade lower, raises the barrel, hence, raises point of impact
---
Extreme example:
if you had a 5 foot high front blade, you would be aiming into the ground in front of your feet
needing the file the front blade down to raise POI
---
I merely assumed by process of elimination that if the guy had adjustables, he would not be posting
If a guy does not have adjustable sights, this is how you correct it
many people don't know ....they need to file the front blade
in extreme cases, some even bend the barrel into a curve slightly using a press
I would much rather mess with the blade