Time to file rear sight?

[Maestro]

I've found a load that my .50 flinter seems to like...
70 gr. 2F Swiss
.490 round ball
.018 pillow tick patch / Wonderlube
...and I've been getting good groups at 25 (holes touching) and 50 (1-2 inch) yards - BUT... I'm consistently 3 inches high at 25 yds. and 5-6 inches high at 50 yards.
So... today I got to spend the entire afternoon at the range and decided to see where it prints at 100 yards - 6-7 inches high! Does this sound logical? Is it time to start filing my rear sight down to zero in around 25 yds. so it's back on at around 75 yds.? My main shooting objective is hunting and, although I can always hold low, this seems a little extreme - not to mention if I want to beef up the load a little. Also, I don't anticipate taking 100+ yd. shots (t least this year, I'm not ready for that). Any suggestions? Thanks in advance!

 

[walruskid1]

personal opinion - zero it at 50 yds, little high at 25 - little low at 100.

 

[Zonie]

Your gun is sighted in for about 125 yards.

I came to this conclusion by making some guesses.

The powder load you are using will give about 1550 FPS velocity (based on the measuerd velocity of my .50 with a 70 grain charge.)

Plugging the velocity into my Ballistics program for round balls, and guessing at the zeroed range I found:
If the gun was sighted in at 120 yards the gun would be 3 inches high at 25 yards, 5.6 inches high at 50 yards, 3.9 inches high at 100 yards and zero at 120 yards.

If it was sighted in at 125 yards it would be 3.3 inches high at 25 yards, 6.1 inches high at 50 yards, 4.9 inches high at 100 and zero at 125.

If it was sighted in at 130 yards, it would be 3.5 inches high at 25 yards, 6.6 inches high at 50 yards, 6.0 inches high at 100 and zero at 130.

Because the 100 yard number doesn't agree with what your seeing (7 inches high) I have to cover my but by saying some of that may be caused by sighting error. NO, Not your error, the guns. :grin

 

[TANSTAAFL]

If for hunting, work out desired load, determine max range, zero for point of aim, it won't be high by much at any distance in betwixt, and a only a little low at 10-15 yards over.

Bob Spencer lays it out in much better detail here:
[url] http://members.aye.net/~bspen/trajectories.html[/url]

 

[Dave K]

Well, if he left the charge where it is, but adjusted his sights so that it was flat on at 100yds. What would it be at 50yds and 25yds.?

 

[Dave K]

Tanstaalf, you are faster than me! :grin:

 

[Zonie]

I should have mentioned that my 1550 FPS was using FFFg. FFg gives a little lower velocity.

If the load was more of a hunting load, say 100 grains of FFg under the .490 dia ball, the Lyman book says the velocity would be about 1622 FPS out of a 24 inch barrel with a 1:48 twist.

If the gun was zeroed at 50 yards, the hits would be:
25 yards=+0.2, 50=0.0, 75=-2.2, 100=-6.8

If the gun was zeroed at 75 yards the hits would be:
25 yards=+0.9, 50=+1.5, 75=0.0, 100=-3.9

If the gun was zeroed at 100 yards the hits would be:
25 yards=+1.9, 50=+3.4, 75=+2.9, 100=0.0

If the gun was a Lyman GPR with a 32 inch barrel with a 1:60 twist, the 100 grain load of FFg would give a velocity of about 1840 FPS.
With this load you could expect the following:

Zeroed at 50 yards:
25 yards=+0.1, 50=0.0, 75=-1.8, 100=-5.7

Zeroed at 75 yards:
25 yards=+0.6, 50=+1.1, 75=0.0, 100=-3.4

Zeroed at 100 yards:
25=+1.5, 50=+2.8, 75=+2.5, 100=0.0

 

[TANSTAAFL]

Not by much. :winking:

 

[Slamfire]

I think I'd work on determining your hunting load first, heavier loads tend to shoot a bit lower, due to less time in the barrel while the recoil develops. :hmm: