trapdoor front sight math help...

[rpludwig]

Trapdoor, shooting mild smokeless (30g H4198 under 350g cast .459), shooting high as expected...installed an extra high front sight which needs to be cut down. Want it on @ 100yds., but can only shoot @ 50yds where I am at.

So, with new x-tall frt sight installed it is shooting 8" low @ 50 (as expected).

doing the math, sight radius of 27.375 x 8" / 1800" = .1217
thus, if I wanted it ON @ 50, I would need to cut the sight down .1217"

That said, not knowing the trajectory of this round, is there a way to calculate the adjustment for 100yds without shooting it @ 100yds? Or is it simply half .1217 (.06085) since the distance is doubled???

Thx in advance,
Ron

[Scharfschuetze]

I'll make the assumption that you are shooting a 405 to 420 grain boolit and duplicating the old "infantry" load of 1,300 fps. Using that as a base line, you'll have a mid range trajectory at 50 yards of about .7 inches or 1.4 MOA to zero at 100 yards.

Given that, you'll need to raise your current impact point by about 9.2" at 50 yards or 18.4 MOA. With my math, that means a reduction of about .140" (rounded to the nearest thousandth) to your front sight to get on at 100 yards.

[Mk42gunner]

Best to find a hundred yard range for absolute zeroing.

I would take some of the front sight off, but not all, until I actually got to shoot it at the desired range.

Robert

[pietro]

.

Brownell's sight height calculator (google) can be useful - but it's calculations are based on the zeroing error @ 100yds.

http://www.brownells.com/GunTech/Sight_Height_Calculator/detail.htm?lid=13186


.

[rpludwig]

Gents...thanks for the replys...all good advice.

Managed to get it back home and on the 100yd mark just now.

It's shooting 36" low at 100 with this load (30g H4198 under 350g .459 cast boolit). Don't have a chrono, but manuals show it ~1250-1300fps.

By my math:

36" x 27.375" /3600" = .27375"

Thus, looks like the front sight needs to be cut down ~ 1/4", I'll err on the conservative side and take off about 3/16" and test again...easy to cut down, hard to put back!

Plz correct me if I have some wrong assumptions here!

Thx again!

Ron

[Scharfschuetze]

I think that you're on the right track. Slow and careful is the solution when filing front sights down.