Author Topic: Increasing the height of the front bead?  (Read 387 times)

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Offline kombi1976

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Increasing the height of the front bead?
« on: November 01, 2005, 03:04:52 AM »
I'm not sure if this is the right forum but here goes.
I have a Martini Cadet rifle that has been sporterised and re-barrelled & chambered from .310 Cadet to 25-20.
The rear sights are excellent.
While they're basically a notched-V they have both elevation and windage adjustment and the increments are very small.
Even the front bead is perfect as it sits right in the rear V well.
BUT a .310 Cadet, which these sights were designed for, shoots a 110gn cast bullet at 1500fps and a 120gn jacketted at 1250fps.
The 25-20 can push a 60gn at around 2100fps, a 75gn at just under 1900fps and an 87gn at about 1650fps.
So for obvious reasons it's shooting 5" high at 25yds and over a foot high at 100yds! :(
If I use reduced cast loads I can keep it in check but that kinda takes the fun out of using a 25-20 in the first place.
The flatter trajectory is, after all, the reason.
So can anyone recommend a suitable increase to make the rear sight function?
Is there a particular model of rifle that has a front sight that could be fitted to it to achieve this?
I know that fitting a scope is the easy way out but frankly I like the idea of this staying open sighted and after a scope rail, 'smithing and suitable rings I'm still up for a reasonable amount for a scope.
8)

Cheers & God Bless

.22lr ~ 22 Hornet ~ 25-20 ~ 303/25 ~ 7mm-08 ~ 303 British ~ 310 Cadet ~ 9.3x62 ~ 450/400 NE 3"

Offline RonF

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Increasing the height of the front bead?
« Reply #1 on: November 01, 2005, 05:25:28 AM »
You need a higher front sight.  If the one you have is dovetailed in, then you should be able to get a taller replacement.  To find the height increase you need, measure the distance between your front and rear sights in inches.  Call this D.  Then the ADDITIONAL front sight height you need is given by

x = 5D/900.

This assumes you want to lower it 5" at 25 yards.  If 5" isn't right, then change the 5 in the equation to what ever amount you want to lower the point of impact.  

Hope this helps you.

RonF

Offline gunnut69

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Increasing the height of the front bead?
« Reply #2 on: November 01, 2005, 09:09:08 AM »
Measure the distance in inches between the front and rear sight; the nearest ¼” (.25”) is good enough.
Multiply the number of inches between the sights (the sight radius) times .0012, times the number of inches you need to move the group at 25 yards.  The multiplier is  .0006 for 50 yards and .0003 for a 100 yard correction.  I had this sent to me and it is the simplest way I've found and it works!
gunnut69--
The 2nd amendment to the constitution of the United States of America-
"A well regulated militia, being necessary to the security of a free state, the right of the people to keep and bear arms, shall not be infringed."

Offline kombi1976

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Increasing the height of the front bead?
« Reply #3 on: November 01, 2005, 01:11:56 PM »
Thanks Ron and Gunnut.
I'll work it out and apply the necessary changes. :grin:
I'll keep you posted on the results. :wink:
8)

Cheers & God Bless

.22lr ~ 22 Hornet ~ 25-20 ~ 303/25 ~ 7mm-08 ~ 303 British ~ 310 Cadet ~ 9.3x62 ~ 450/400 NE 3"