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Old June 25, 2001, 08:54 AM   #1
swampy
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Selecting load components to raise point of impact???

I want to build a load to raise the point of impact. What are the component (powder speed and/or bullet weight) considerations involved? The pistol is a CZ75Mil (9mm)with fixed three dot sights. I've only shot three commercial loads in it for three different points of impact. S. African 115 gr FMJ PMP shot several inches low at 15 yards. PMC 124 gr FMJ shot approximately 1" below the white dot on the front post. Winchester 115 gr FMJ white box shot to the point of the white dot on the front sight. As to the amount of muzzle flip, the S. African was very little, the PMC was more and the Winchester had the most. I am guessing that a 115 grain bullet driven at higher velocity would raise the point of impact. The increase in muzzle flip compensates for the higher speed of the bullet and quicker exit from the muzzle?? Thanks
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Old June 25, 2001, 09:12 AM   #2
BigG
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Heavier bullet will raise point of impact all other things being equal. Try 147 grain.
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Old June 25, 2001, 11:27 PM   #3
Bill Adair
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Swampy,

Is your rear sight a dove tailed blade? If so, you should contact the CZ importer, your dealer, or a gunsmith, to see if optional blades (higher) are available.

Many fixed sight handguns have optional sight parts, for just such problems.

A last resort, would be to file your front sight blade down, and touch it up with cold blue, or a permanent black marker pen.

If you want to try raising your POI, use heavier bullets at lower velocity, but watch for problems cycling the action. The best you will probably get with load changes, is an inch or two at 50 feet.

Bill
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Old June 26, 2001, 07:31 AM   #4
renaissance7697
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Big G & Bill Adair

"To raise the POI > use heavier bullets and lower velocity."

Is it "Weight" or "Velocity" that does the trick?

For example; will less powder with the same weight bullet raise the point of impact?
will same charge, but heavier bullet do the same
or
Is it a combination that has to be arrived at by trial and error


Is the Physics of it:
Lower velocity = More time in barrel = Greater lift to trajectory caused by muzzel flip.
with
A heavier bullet (all other things being equal) yielding a lower velocity.

The "Cowboys" who have to deal with fixed sights
Have a theory about adjusting POI both in elevation AND azimuth by varying the load..
I cant recall how it goes though.

Can you offer any advice on that?
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Old June 26, 2001, 12:19 PM   #5
BigG
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This is a S.W.A.G., but, I think you got it here:
Quote:
Is the Physics of it: Lower velocity = More time in barrel = Greater lift to trajectory caused by muzzel flip. with A heavier bullet (all other things being equal) yielding a lower velocity.
My feeling is that the gun has more time to recoil before the bullet leaves the bbl, ergo, the shots print higher with heavier ammo. These are ball loads I'm talking about, so both would be full powered.

One of the scientific minded members might be able to give you a mathematical reason why, I can't. I just go by my observations.
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o "In the beginning of a change, the patriot is a scarce man brave, hated, and scorned. When his cause succeeds, however, the timid join him, for then it costs nothing to be a patriot." Mark Twain

o "They have gun control in Cuba. They have universal health care in Cuba. So why do they want to come here?" Paul Harvey

o TODAY WE CARVE OUT OUR OWN OMENS! Leonidas, Thermopylae, 480 BC
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Old June 26, 2001, 03:17 PM   #6
Bill Adair
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(Emailed to renaissance earlier)

My understanding is as you stated, that it's a combination of dwell time in the barrel, and of course recoil, which effects barrel rise.

The heavier bullet produces heavier recoil, and accelerates slower, thus leaving the barrel later.

I'm going through this exercise with a S&W K frame 9mm revolver (model 547), with fixed sights, which was shooting about 3" low at 30'. It was apparently regulated for 147gr bullets, which were the preferred police load when the gun was produced.

I suspect the slower 147gr bullet may shoot higher, but also drops faster, so any rise due to heavier/slower bullets at 25 feet, may be lost at 50 feet? Testing so far has been inconclusive, as I tried them at different distances, on different shooting ranges.

Hope to get to the range this week to do some more testing.

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Old June 26, 2001, 03:37 PM   #7
BigG
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Bill: IIRC my Luger was regulated dead on at 50' with 115 grain ball. When I switched to 147 grain ball it printed about 3 inches higher at the same distance.

I believe my Glock 19 does the same but my memory is fading.
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o "The Earth is degenerating today. Bribery and corruption abound. Children no longer obey their parents, every man wants to write a book, and it is evident that the end of the world is fast approaching." Assyrian tablet, c. 2800 BC

o "In the beginning of a change, the patriot is a scarce man brave, hated, and scorned. When his cause succeeds, however, the timid join him, for then it costs nothing to be a patriot." Mark Twain

o "They have gun control in Cuba. They have universal health care in Cuba. So why do they want to come here?" Paul Harvey

o TODAY WE CARVE OUT OUR OWN OMENS! Leonidas, Thermopylae, 480 BC
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Old June 27, 2001, 02:55 PM   #8
Bill Adair
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BigG,

That's about what I would expect, and am hoping to see. Thanks for the info.

No range time today, as it's raining again.

Bill
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Old June 27, 2001, 06:05 PM   #9
Hutch
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Bill, the drop of 'most any bullet from 25 feet to 50 feet is virtually negligible. Depending on the height of the front sight, the bullet may actually still be rising at 25 ft, if that's your zero.
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Old June 27, 2001, 09:29 PM   #10
Bill Adair
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Hutch,

That's true with most factory ammo, but the slower heavier bullet loads I'm testing, may have a sharper ballistic curve than faster lighter bullets.

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