Optimum velocity for 25 and 50 yds?

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Optimum velocity for 25 and 50 yds?

Post by beeser on Mon Sep 01, 2014 9:08 am

Is there an initial optimum velocity where the bullet is at the same elevation in its parabolic path at 25 and 50 yds?

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Re: Optimum velocity for 25 and 50 yds?

Post by Rob Kovach on Mon Sep 01, 2014 9:15 am

No.  Every barrel has variations that makes a barrel shoot a particular combination better than another so achieving a particular velocity is irrelevant. All that matters is the size of the group, so starting with a known popular combination and testing with other similar combinations, different crimps will reveal what your gun likes.

If you get lucky, the load that your gun likes will have the same scope settings from 50 to 25 yards.  It's more important to make ammo that your gun shoots tight groups for.

Adjusting sights is ok.

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Re: Optimum velocity for 25 and 50 yds?

Post by dronning on Mon Sep 01, 2014 9:45 am

Basically if you get the bullet going about 1200 fps it is essentially flat (not really) but close enough to stay in the X ring - about a 3/4" drop.


More than you wanted to know below and none of this even takes into consideration what bullet or what your gun can shoot accurately with reasonable recoil.

It's complicated:
What distance you sight the gun in has a huge impact.  What is your sight to bore distance ie iron sights will be different than a frame mounted optic.  You would have different answers if the line of sight through the optic was 2" off the bore verses 1/2".  To get a bullet to pass through the X at 25 and fall back down to the X at 50 it would be going pretty slow.  So accuracy would be a huge issue with some bullets.

examples:
1200 fps 1.5" sight to bore distance zeroed @ 50yds.  You would only be 0.1" difference at 25.

Same gun with 1.5" sight to bore distance and different bullet speed @ 800fps zeroed @ 50.   You would have a 1" @ 25

Same bullet @ 800 fps, different gun with a 1/2" sight to bore distance zeroed at 50. You would have a 1.5" difference @ 25 

The numbers completely change if you zero at 25yds.

- Dave


Last edited by dronning on Mon Sep 01, 2014 9:51 am; edited 1 time in total (Reason for editing : clarity)

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Re: Optimum velocity for 25 and 50 yds?

Post by beeser on Mon Sep 01, 2014 10:14 am

All interesting stuff members.  Thanks for your thoughts and explanations!  My questions were prompted by what I thought was a morning epiphany as to why the word zero is used for the center of a target while also thinking of member Ghillieman's latest comment in the Equipment Discussion section.  There are of course two solutions to every quadratic equation (zeros) but in talking about zeroing a gun we're probably only talking about the shape of the bullseye.  LAM

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Re: Optimum velocity for 25 and 50 yds?

Post by Ghillieman on Mon Sep 01, 2014 10:59 am

I have a high red dot, and I'm sure that angle has something to do with it, but my 200 SWC's @ 830fps have the same 25/50 zero. It's convenient.

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Re: Optimum velocity for 25 and 50 yds?

Post by Rob Kovach on Mon Sep 01, 2014 11:07 am

What is your powder charge and crimp for that round?

My 200gr LSWCs over 3.8gr BE .468 crimp have the same zero for 25/50 yards also.  It's the same with my red dot and my iron sights with a line of white hold.

It IS convenient!

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Re: Optimum velocity for 25 and 50 yds?

Post by beeser on Mon Sep 01, 2014 11:18 am

Rob Kovach wrote:What is your powder charge and crimp for that round?
Ditto on your question to member Ghillieman.

Just curious though, have you tried 185 gr. LSWC bullets?  Why if not?

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Re: Optimum velocity for 25 and 50 yds?

Post by Ghillieman on Mon Sep 01, 2014 2:58 pm

That round is 4.5 WST pushing a Lee 200 SWC I cast, crimp is .467. That was a practice load for my hardball gun. This wadgun is still new to me, but the load is accurate in it. Looking at 185gr molds for a casting session this fall.

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Re: Optimum velocity for 25 and 50 yds?

Post by Rob Kovach on Mon Sep 01, 2014 7:00 pm

When I shoot 185gr bullets--either jacketed or LSWC, I end up needing 3 clicks down when going from 50 yards to 25yd.

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Re: Optimum velocity for 25 and 50 yds?

Post by inthebeech on Mon Sep 01, 2014 10:28 pm

I have to go UP with the rear when going from 50 to 25.  I'm thinking it has something to do with muzzle flip having more effect on trajectory at the longer distance.

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Re: Optimum velocity for 25 and 50 yds?

Post by Rob Kovach on Mon Sep 01, 2014 10:51 pm

It wouldn't be muzzle flip.  The bullet is gone before recoil starts making the gun move.  It could just be the load, your barrel, and your sights and perhaps your bullet is at the top of its arc when it gets to the 50.

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Re: Optimum velocity for 25 and 50 yds?

Post by Sa-tevp on Tue Sep 02, 2014 8:58 am

inthebeech wrote:I have to go UP with the rear when going from 50 to 25.  I'm thinking it has something to do with muzzle flip having more effect on trajectory at the longer distance.

I've been meaning to ask about this too as I sorted out my 45. Iron sights on a SA RO, NSK 185 JHP and my 25 yard zero is two clicks UP from my 50 yard zero (30 clicks out). Could still be a grip nut issue in my case.

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Re: Optimum velocity for 25 and 50 yds?

Post by GrumpyOldMan on Tue Sep 02, 2014 9:34 am

Rob Kovach wrote:It wouldn't be muzzle flip.  The bullet is gone before recoil starts making the gun move.  It could just be the load, your barrel, and your sights and perhaps your bullet is at the top of its arc when it gets to the 50.
Nope.

The bullet might be gone before you perceive the gun moving, but recoil dynamics have a known, proven, and sometimes quantifiable and predictable effect on bullet impact.

Take an iron sight revolver zeroed for 25 or 50 yards and unload it. Maybe leave the cylinder unlatched if the next step works. Put it upside-down on a tabletop, resting on the sights. Look again to ensure it's unloaded (I look at the rear of the cylinder for case rims). Walk around and peek down the muzzle and move your eye around until the firing pin hole is centered in the bore.

You will see that the bore is pointed "up" compared to the alignment of the sights, which = DOWN from the line of sight when in the normal firing position. 

That's why if I start to relax my grip with the .45 during a string of 50-yard slow fire, my group center (loosely defined!) can drift up into the top of the 8 ring. Less resistance to the recoil movement during the "bore time" of the bullet = handgun rotates more UP = bullet leaves barrel when it it pointed higher on the target.

Consistency is the key here. Accuracy fundamental #1, hold the gun the same way for every shot.

For centered zero at two distances, the closer one with the bullet on the way up and intercepting the line of sight, and the other crossing back down, as pointed out above, the distance of your line of sight above the bore has an effect. The OP's reasoning is sound and the question is a good one. The answer is, "it depends, and it is possible". However, no one I know has deliberately tweaked velocity and/or sight height to achieve this effect. When it happens, it us usually one of life's happy accidents while seeking the desired load accuracy.

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Re: Optimum velocity for 25 and 50 yds?

Post by Ghillieman on Tue Sep 02, 2014 10:00 am

If you are adjusting the sights UP, instead of down, from 50 to 25, you could try slowing down the bullets velocity to put more curve in its trajectory. Fine tuning that might allow you to have one zero for both distances. Be careful you don't degrade accuracy and function.

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Re: Optimum velocity for 25 and 50 yds?

Post by RJP on Sun Sep 14, 2014 2:52 pm

beeser,

Many years ago I did this (same point of bullet impact)with my .45. What I did was use iron sights and a sub-6 hold on the target. The black area of a 25 yard target is 2 & 5/8 inches from the center to the bottom of the black. For a 50 yard target the distance is 3 & 7/8 inches from the center to the bottom of the black. The difference is 1 & 1/4 inches. This accounts for most of the trajectory curve.

On my .45, the top of the iron sights was 7/8 inches above the center of the bore.  With ammo going about 800 fps, I did not have to adjust sights from 25 to 50 yards. The sights were zeroed (point of impact) for 80 yards.

All this really depends on a consistent firm hold if it going to work for you. And of course, if you are using a center hold, it will not work at all.

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Re: Optimum velocity for 25 and 50 yds?

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