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View Full Version : For Dawson adj sights for Glocks, what height front blade for 17L?

C0untZer0
June 23, 2011, 07:56 AM
Does anyone know what height front blade is necesary for the Dawson adjustable sights for the front blade on a Glock 17L?

I have heard of people having problems shooting high with the .285 on their G34 and not being able to crank the rear sight down any further.

Dawson puts out this formula for determining necesary change in front hight:

Sight Radius x Impact Distance / Target Distance = Sight Height Change

http://www.dawsonprecision.com/images/Instructions/FrontSightHeight.pdf

I am thinking that the longer sight radius on the 17L should mean that it can utilize a slightly shorter front blade than the G34 (not sure of my math)

But my basic question is if the .300 front sight will work with the G17L - meaning, it will give me enough room to adjust the rear sight to POA and not bottom out and run out of room.

GURU1911
June 23, 2011, 08:47 AM
Easy fix count-zero:

1. Install new adj. Rear sight & new .300" front sight on slide.
2. Lower rear sight elevation as low as possible.
3. Measure height of rear sight from bottom of slide.
4. Measure height of front sight from bottom of slide.
5. Subtract the difference between the two sights.
6. Mount slide in milling machine vise & mill the difference from the height of the front sight. You want the height of both sights to be equal.
7. All vertical adjustments in elevation will raise bullet impact.

Guru1911

C0untZer0
June 23, 2011, 10:03 AM
No No No No No

I don't want to mill anything - I'm not a miller.

I want to just use a tiny screwdriver and turn a screw...

I know the Dawson .285 front sight shoots high on the G34, and after users have cranked their rear sights all the way down as low as they can go - they are still shooting about 2" high at 25 yards

So according to the formula, if they are shooting 2" high at 25 yards (900 inches), with a G34 which has a sight radius of 7.56" they need a front blade .021" taller than the .285 That would mean they actually need to increase the height of the blade by .0168" they would need a .3018" blade in the front.

Dawson makes a .300 which is probably close enough.

The shorter the sight radius, the greater the angle between line of site and bullet trajectory - but instead of imagining the curved trajectory just use a straight line from muzzle to target. The longer the sight radius the less the angle and therefore the distance that the bullet strike is off POA/Line of sight is less. So, with a .285" sight if our line of sight was 7.56" and the bullet is hitting 2" high at 25 yards or 900 inches, theorteically if we had a barrel 25 yards long / 900 inches, with a .285" tall site, at 25 yard/900 we would onlt be .285" high on POA - that would be like sticking the barrel right up to the paper target and firing.

So I am saying that with the longer sight radius of the 17L - if I were using the .285 tall front site, with the rear cranked down all the way, it probably would not shoot 2" high at 25 yards - probably something less than that.

Ugh.. I have to solve that equation for Impact Distance.

Sight Radius x Impact Distance / Target Distance = Sight Height Change

My math teachers always told me I would need math later on in life and I always thought they were full of it.:(

GURU1911
June 23, 2011, 12:40 PM
If i have offended you with my reply to your question, i apologize. However, my method does work. Have used it many times with great success, when installing novak or bomar sights on 1911 slides. If you do not have access to a milling machine, a swiss fine-cut mill file & a dremel tool with a fine abrasive drum tip, & some cold blue will work also.

Guru1911

Jim Watson
June 23, 2011, 01:03 PM
Barrel time and recoil might mean the 17L would not shoot just where predicted by trigonometry.

If you don't want to use GURU's method (which really works with a plain blade, not so well with fibre optic or tritium) then:

1. Put on the adjustable rear, leave the stock front.
2. Shoot the gun and calculate the correction required to get within the rear's range of adjustment.
3. Buy the front providing the nearest to that change.

C0untZer0
June 23, 2011, 01:51 PM
I'm not offended, I appreciate any info any one offers. I just can't mill anything - that's way over my head.

On the Glock forum someone with this problem fixed it by milling their rear Dawson sights.

I should have said that this is the fiber optic front.

I guess my fear is if I purchase too tall of a front blade, the rears are not going to be able to adjust up enough to make it shoot POA, if I buy a too-short front blade the rears can't crank down enough (as is the case with a few people posting about their G34s shooting high with Dawson .285 fronts.

Dawson goes from .300 to .315 fronts for the fiber optics.