Figuring how much to raise front sight

[brstevns]

OK I am confuse. I have a rifle that is putting its rounds 17 inch high at 25 yards. How do I figure how much to build up the front sight? Would not FPS of the bullet figure into the picture?

[lefty o]

.001"=1" at 100yds, so devide by 4 at 25yds. yes bullet weight and velocity factor in, in how the gun recoils and this can affect POI, etc. recommend settling on a load before permanently altering sights.

[JSnover]

The velocity would figure into it but at 25 yards you'd have to shoot them r e a l l y s l o w to take 17" off the trajectory.
There's a simple formula for that somewhere but it depends on the sight radius.

[NavyVet1959]

The velocity would figure into it but at 25 yards you'd have to shoot them r e a l l y s l o w to take 17" off the trajectory.
There's a simple formula for that somewhere but it depends on the sight radius.

Yep... Basic high school trigonometry... Just keep your units consistent...

Let's assume a 16" sight radius and that you are wanting a change in the point of impact of 17" at 25 yard.

Well, first, 25 yards is going to be 900"

Let's also assume that the 25 yards is measured from the rear sight for simplicity in the calculations.

Now, you *could* do it by calculating the angle between the height of the existing front and rear sights and then calculating the new angle needed to change the bullet impact by the desired amount, but a much easier way is just to use it as proportions.

Think of it this way:

17" is to 900" as x is to 16"

Or mathematically:

17/900 = x/16
>> x = 16 * 17 / 900
>> x = 0.3022"

Now, if you really want to get picky, this is not a perfect way of doing it since a bullet travels a curved path. But for most of the shooting we do, it's close enough. If you were doing artillery, then you might need to use a different formula. Remember, when you are shooting at very steep angles, an increase in the angle *can* result in a decrease in range.

[Hick]

Do the calculation like Navy Vet says. The velocity aspect matters most if you have a very wide range (such as shooting CB at 1000 fps and jacketed at 2500 fps). I do that, and had to experiment to find the happy medium where I could raise my rear sight enough to get the slow ones on target, but still lower my rear sight enough to get the higher velocity ones also on target.

[brstevns]

Trying to get a old 303 British Martini sighted in. Was using some loads with a 200 gr bullet near the 1800 fps mark. Billet hitting about 17 high at 25 yards, So if I am reading and figuring correctly we are talking raising the front sight almost 1/3 0f a inch? Was planning on building it up with jb weld so as not to damage the rifle.

[NavyVet1959]

Yep... That is what the numbers say... What is your sight radius?

Got a laser bore sighter?

17" off at 25 yds seems a bit of a large discrepancy... Especially 17" low... If it was 17" high, then it is just sighted in for a much longer range.

[bdicki]

http://www.brownells.com/userdocs/Miscellaneous/sightCorrection_F2.swf

[brstevns]

Yep... That is what the numbers say... What is your sight radius?

Got a laser bore sighter?

17" off at 25 yds seems a bit of a large discrepancy... Especially 17" low... If it was 17" high, then it is just sighted in for a much longer range.
Yes it was 17 inches high at 25. Would like to sight it in for 100

[gnoahhh]

Something's rotten in Denmark. 1800fps isn't that drastic a difference from the arsenal loads of that period for it to be off 17" at 25 yards. The numbers don't lie, and having to add 3/10" to the front sight sounds bizarre. Did someone file the front sight down to a nubbin? Something blocking the rear sight from going any lower? Original sights or not?

[NavyVet1959]

Yes it was 17 inches high at 25. Would like to sight it in for 100

OK... Must have had a brain fart... Was thinking that you said it was 17" low when I posted my 2nd post in this thread... Still, the magnitude of the sight change is the same, just a difference of whether you shorten it or increase it. :)

Adding height to a front sight is better than having to remove it. You can always try attaching a piece of zinc or lead around the front sight and then filing it down to a new front sight to gets an idea of whether it is going to work for you. When you get something that you like, redo it with a more permanent method.

To determine bullet drop over distance, you need to know the time it takes for the bullet to travel that distance. For a given muzzle velocity, this can vary somewhat due to the ballistic coefficient of the bullet in question. For this discussion, let's assume that it still is going 1800 fps at 100 yds.

The distance an object drops with respect to gravity is defined by:

d = 1/2 * g * t2

Where g is the acceleration due to gravity. This varies from the equator to the poles, so let's just use an average of 32.2 ft/sec2.

For 100 yds and 1800 fps, we're talking about 1/6th of a second travel time.

d = 1/2 * 32.2 * (1/6)2

d = 0.44722 ft = 5.3667"

On the other hand, if it had decelerated to 1000 fps at the 100 yd mark, then the bullet would have an average velocity over the distance of 1400 fps. This would mean it took 0.21429 sec to get to the target.

d = 1/2 * 32.2 * (0.21429)2

d = 0.7393 ft = 8.87143"

Hope this helps...

[NavyVet1959]

Something's rotten in Denmark.

I think they call it "Surströmming"... :)


1800fps isn't that drastic a difference from the arsenal loads of that period for it to be off 17" at 25 yards. The numbers don't lie, and having to add 3/10" to the front sight sounds bizarre. Did someone file the front sight down to a nubbin? Something blocking the rear sight from going any lower? Original sights or not?

Yeah, I thought it a bit strange also... I would put a laser bore sighter on it and mount the rifle so that it couldn't move so that I could take a closer look at where the bore was pointing vs what the shooter was seeing in the sight picture. Take the human out of the equation as much as possible.

[brstevns]

Something's rotten in Denmark. 1800fps isn't that drastic a difference from the arsenal loads of that period for it to be off 17" at 25 yards. The numbers don't lie, and having to add 3/10" to the front sight sounds bizarre. Did someone file the front sight down to a nubbin? Something blocking the rear sight from going any lower? Original sights or not?

Well , that is all I can say. Cousin and I were firing it from a bench with the issued sights. We were both hitting between 16-17 high at 25 yards. Going to add some soft solder to the front blade and file it down before trying anything else. Like I said I do not wish to do any damage to the rifle.

[Tenbender]

Duh , Way above my pay scale.

[NavyVet1959]

Well , that is all I can say. Cousin and I were firing it from a bench with the issued sights. We were both hitting between 16-17 high at 25 yards. Going to add some soft solder to the front blade and file it down before trying anything else. Like I said I do not wish to do any damage to the rifle.

Good plan. Don't make a change that you can't easily reverse unless you've done this a lot and are REALLY SURE what you need to do.

Lead... Hot melt glue... Even wood... All of them can work to give you a base to use with a temporary sight.

[country gent]

While not disputing your results is there something else affecting this also. Alot of single shot rifles are susecptable to pressures excerted when holding. Being on the high point of a harmonics node can affect impact also. 17" high at 25 yds is alot. Is the forearm pulling the barrel down? SLing tension can do this also. Is the bbarrel straight and true? The laser bore sighter may help find the issue. A taller front sight can eb made up, building up JB weld .300 tall that thin will be fragile to say the least. Soldering a piece on it may be better. .302 is just shy of 5/16" Thats alot of added hieght, depending on the existing front sight you front blade will end up close to 1/2" tall. I would put it at 100 yds and see what it does there also before modifying changing alot.

[brstevns]

Need to play with it more before doing anything, just reporting where it is shooting for 2 different shooters. Does anyone know what the correct height of the front sight should be for a Martini Henry Carbine in 303 british ? At least I would have something to go by.

[pietro]

Cousin and I were firing it from a bench with the issued sights.

We were both hitting between 16-17 high at 25 yards.

Going to add some soft solder to the front blade and file it down before trying anything else.




What sort of rifle is it ? . [smilie=1:

Before you add solder to the front sight blade, a better option for determining if a different front sight is needed would be to temporarily hot glue a thin rod (plastic ?) vertically to the front sight, which rod could then be cut down for zeroing.

FWIW, a hard front bench rest will cause just about any rifle to throw shots higher than normally. 8-)

OTOH, it also sorta sounds like you & your cousin may be experiencing a little slippage of the buttplate under recoil - it wouldn't take very much downward slippage to throw the shots off that far.


.

[brstevns]

[QUOTE=pietro;3763761]What sort of rifle is it ? . [smilie=1:

Before you add solder to the front sight blade, a better option for determining is a different front sight is needed would be to temporarily hot glue a thin rod (plastic ?) vertically to the front sight, which rod could then be cut down for zeroing.

FWIW, a hard front bench rest will cause just about any rifle to throw shots higher than normally. 8-)

OTOH, it also sorta sounds like you & your cousin may be experiencing a little slippage of the buttplate under recoil - it wouldn't take very much downward slippage to throw the shots off that far.


.[/QUOTEIt is a Martini Henry Kabul 303 carbine. I believe a Ior II model
Thanks for the using a plastic rod idea. Neat trick never thought of doing it that way.

[brstevns]

Here is a link to the one I have .http://castboolits.gunloads.com/showthread.php?255247-Kabul-Arsenal-303-Martini

Was making nice groups , just so high!!!

[NavyVet1959]

You might want to try this ballistic calculator and plug in a few what-if type numbers to get an idea of what range your rifle might have been signed in at.

http://gundata.org/ballistic-calculator

Rough guess is might be sighted in for 300+ yds.

[NavyVet1959]

Here's a better ballistic calculator that will allow you to play with the ballistic coefficient, current sight zero, distance from bore to sight, and such:

http://www.hornady.com/ballistics-resource/ballistics-calculator

You should be able to plug in some values into it and determine what distance the current sights might be set for.

Assuming 1800 fps, a 0.370 ballistic coefficient, a 200 gr bullet, and 1" between bore and sight, it looks like it is currently zeroed for 755 yds.

If this is right, it means that at 100 yds, you'll be 66.3" high and at 425 yds, 174.1" high.

Measure your actual distance between the bore and the sight and put in your bullet's ballistic coefficient and see what you come up with.

Maximum range using that calculator is 2000 yds, so if you're curious about what .303 British used as artillery would do... :)

[brstevns]

Here's a better ballistic calculator that will allow you to play with the ballistic coefficient, current sight zero, distance from bore to sight, and such:

http://www.hornady.com/ballistics-resource/ballistics-calculator

You should be able to plug in some values into it and determine what distance the current sights might be set for.

Assuming 1800 fps, a 0.370 ballistic coefficient, a 200 gr bullet, and 1" between bore and sight, it looks like it is currently zeroed for 755 yds.

If this is right, it means that at 100 yds, you'll be 66.3" high and at 425 yds, 174.1" high.

Measure your actual distance between the bore and the sight and put in your bullet's ballistic coefficient and see what you come up with.

Maximum range using that calculator is 2000 yds, so if you're curious about what .303 British used as artillery would do... :)

Thanks