Author Topic: High velocity POI vs Low velocity POI (Read 1078 times)

AtlLaw · « **on:** February 17, 2012, 04:45:13 AM »

Being a simple person I don't have any problem accepting the "low velocity = more time in the barrel = higher point of impact" hypothesis. (Theory #1) But being really simple I also accept the "higher velocity = flatter trajectory = higher point of impact" theory. (Theory #2) I just can't equate the two in my mind. $:-\$

Example - sighting in of my 45 Colt. I used slow, cast (250 gr.) bullets, ones I had loaded with a light charge of Unique for my SAA's, to get on paper. At 50 yards they hit really low. Matter of fact I ran out of elevation getting them off the ground and onto the target.

Thinking of Theory #1, I had just about decided I was going to have to replace the front sight. Hi-ebber, and day always be a hi-ebber, I decided to give my 250 gr. hunting load a try. It carried a healthy charge of 2400.

When I cranked off the first one it almost went OVER the target!

Hence the faster load shot way higher then the slower load ala Theory #2.

How can you predict who gonna do what?

Seems to me that there needs to be a range to target factor figured into these theories. $:-\$

r29l20 · « **Reply #1 on:** February 17, 2012, 04:58:15 AM »

I'd be neet to see the actual muzzle lift and bullet path through a slow motion camera.

thejanitor · « **Reply #2 on:** February 17, 2012, 05:43:14 AM »

My thought would be #2 = higher farther out due to rainbow of slower #1 It did seem weird to me when we started Trail boss loads in the 45-70, but I left it there and accepted it without any extra thinking..... Works for me. Too much thinking just gets me into trouble. thejanitor

smokehouserex · « **Reply #3 on:** February 17, 2012, 05:45:08 AM »

Hey AtlLaw:

I had always thought according to your theory, slower=more arc thus higher POI, faster=flatter with less arc,lower POI, but never gave it a lot of thought, just thought......and didn't pursue any other conclusion. When the question came up here, I heard another explanation for it. I don't know which is correct but have seen OAL effect POI as well. I have experienced that Longer rds. raise POI with everything else being the same, just my opinion, so???
From now on I will know what I believe after I see a gun locked down firmly so it cannot move and test fired for a final conclusion, until then or a better test is done, I"ll just say I don't know.

Have you ever shot at the River Bend Gun Club just out of Atl?
HM

thejanitor · « **Reply #4 on:** February 17, 2012, 05:50:19 AM »

Quote from: thejanitor on February 17, 2012, 05:43:14 AM

My thought would be #2 = higher farther out due to rainbow of slower #1 It did seem weird to me when we started Trail boss loads in the 45-70, but I left it there and accepted it without any extra thinking..... Works for me. Too much thinking just gets me into trouble.
But we did sight the open sights for TB and the scope for hunting loads- and found like you the elevation was not user friendly for the 405 gr bullet TB load at 100 yds so if we were to want to use the sights for both loads we would be having problems. We just took off the scope for TB close up, plinking and re-zerod the scope for hunting season..... Maybe not the simple solution but it worked for our need.
thejanitor

cwlongshot · « **Reply #5 on:** February 17, 2012, 05:52:31 AM »

Richard, Oh but there is more....

(BTW I subscribe to theory #1 )

Along the same lines/thinking, longer time in the tube. Think follow thru... Not as huge in rifle but immense in pistols.

IF you remember I shoot bullseye, summer outdoors and winter indoors, 50' to 50 yards. In that discipline, follow thru is a huge part of shooting "X"'s. Drop your hand and you just shot a 9 or 8 instead of a X...
Now try a AIR PISTOL match!!!! You can push a pellet Right off the target!! Simply because your projectile is traveling 4-500 fps VS 900-1000 fps for the 22! Even outdoors shooting three gun matches. My 38 loads run just over 600 fps while my 45 loads are about 750 fps. If you don't learn follow thru you don't shoot competitive scores...

Any excessive movement will effect a slow moving bullet more than a speedy one .

CW

trotterlg · « **Reply #6 on:** February 17, 2012, 05:59:16 AM »

You need to try the experment with simular loads and the same bullet. Try loading a few rounds, some with 15% less powder and the same bullet, when you shoot them you will find the ones loaded 15% lower will hit higher on the target. Larry

gstewart44 · « **Reply #7 on:** February 17, 2012, 06:06:12 AM »

The design of the SAA grip will account for a bit of the change as well. In a lowvelocity/low recoil round, it is quite easy to keep the muzzle from climbing. To use Richards "hi-ebber" when the highvelocity/highrecoil interacts with the SAA plow handle the resultant vectors necessarily push the muzzle up. The greater the recoil the faster and higher the muzzle climb.

AtlLaw · « **Reply #8 on:** February 17, 2012, 06:28:37 AM »

oops! Need to clarify that!

Thanks Gregg!

I was shooting my 45 Colt Handi Rifle. The cast bullets were "cowboy" equivalent loads that I shoot in my SAA's.

And that's a good idea Larry!

Just a few rounds would be a better indicator then my statistically insignificant and meaningless experiments usually are. $:-\$ I think I'll try that after I stick a scope on that thing for next deer season!

gstewart44 · « **Reply #9 on:** February 17, 2012, 06:35:16 AM »

Guess the same principle will apply to the short rifle to a lesser degree...depending on the drop in the comb of the stock (Think PA longrifle vs a modern AR variant).

AtlLaw · « **Reply #10 on:** February 17, 2012, 06:49:28 AM »

Quote from: thejanitor on February 17, 2012, 05:43:14 AM

I left it there and accepted it without any extra thinking..... Works for me. Too much thinking just gets me into trouble.

Ain't dat da trufe! But I keep wondering about stuff. $:-\$ next thing ya know I'm knee deep in sumpin...

Quote from: smokehouserex on February 17, 2012, 05:45:08 AM

Have you ever shot at the River Bend Gun Club just out of Atl?

HM I've been a member at RiverBend for some years now. The number of times I can get up there a year certainly don't justify the amount of the yearly dues, but without the membership any range time would be difficult. $:-\$

AtlLaw · « **Reply #11 on:** February 17, 2012, 06:52:42 AM »

okay, okay, okay... $:-\$ You guys are making my head hurt again...

Ten Ring · « **Reply #12 on:** February 17, 2012, 07:29:26 AM »

Atlaw you need to retire to your man cave and work on some shims,I'm sure the answer will come to you.
Jim

moorepower · « **Reply #13 on:** February 17, 2012, 07:32:11 AM »

Shoot both at 10 yds and I think you will discover that gravity has more effect on a slow heavy bullet at 50yds. and velocity will overcome gravity at that distance. Would you ask the same question if you were shooting a 180 grain .308 and 150 grain .300 WBY at 200 yds.? It is all gravity.

AtlLaw · « **Reply #14 on:** February 17, 2012, 07:43:27 AM »

Quote from: Ten Ring on February 17, 2012, 07:29:26 AM

you need to retire to your man cave and work on some shims,

Would that I could jimbo... $:-\$ My cardiologist told me to cut down on my drinkin so I can't work through my six-pack of shim material a night like I useta could.

The quest for knowledge has many hindrances.

Quote from: moorepower on February 17, 2012, 07:32:11 AM

It is all gravity.

Ah-ha! Another element I hadn't thought of!

So you ascribe to theory # 2, right?

STUMPJMPR · « **Reply #15 on:** February 17, 2012, 07:50:02 AM »

New theory. Your barrel whips around when fired from the bullet traveling down the barrel. This has been proven. If the bullet exits when the barrel is at its low point then the bullet hits low. If it is at its high point it hits high.

PaJohn · « **Reply #16 on:** February 17, 2012, 09:35:56 AM »

Gravity's affects don't vary with speed. A bullet moving one foot per second has the same gravitational pull toward the center of the earth as one moving 1000 f.p.s. The faster bullet just covers more lateral distance. There isn't enough aerodynamic lift like that generated on a wing to have an affect. The bullet begins to drop as soon as it leaves the barrel. We adjust our sites to tilt the gun up or down to have the vertical drop and horizontal distance traveled intersect at the target.

moorepower · « **Reply #17 on:** February 17, 2012, 11:43:24 AM »

I subscribe to both 1 and 2. Ok Pa I understand gravity is a constant, but a bullet is traveling more feet in the same amount of time, so per the same measured distance, given the same weight and b.c. the slower bullet will drop faster because gravity will pull each bullet down the same distance per measurement of time ish. The slower bullet shot at a close range target, say 10 yds. away will exit the barrel latter in the guns reaction to the force "muzzle whip" of recoil. The gun barrel will move more reacting to the slower bullet than the faster bullet, before each leave the barrel.

mechanic · « **Reply #18 on:** February 17, 2012, 03:27:31 PM »

If I remember my physics....and I don't most of the time....a bullet dropped at a height of 4', and a bullet fired parallel to the ground from 4' will both hit the ground at the same time. Of course the latter will be harder to find.....

I've heard this debated several times, and now it's become something that I think about from time to time....causing my wife to say..."what are you thinking about so hard?" If I tell her the truth, she will say I need to see a shrink, I'm too fixated on this gun stuff...If I say "aw nothing" she will pester me to death until I can think of something worthwhile that I might have been thinking of....

Never mind.

Will a true physics guru respond on this so I can quit thinking about it?

Mr Atlaw, I think this gets confusing when you try to add in all the factors, and the unknown human elements...

Ben

RaySendero · « **Reply #19 on:** February 17, 2012, 04:14:55 PM »

Quote from: AtlLaw on February 17, 2012, 04:45:13 AM

.....

Seems to me that there needs to be a range to target factor figured into these theories.

AtlLaw,

All but one of my rifles will shoot higher off a bench rest to 100 yards as:
1) the bullet weight is increased with the same velocity or
2) as velocity is increased with the same bullet weight.

However, the degree to which this POI will happen varies a lot from one rifle to another.

smokehouserex · « **Reply #20 on:** February 17, 2012, 04:15:07 PM »

Well Mr. AtlLaw:

I don't think you are a simple person as stated previously, this is a very complicated/complex can of worms that you opened. Physics even. LOL But I hope to learn which is correct by the time it's completed, or locked, I hope it doesn't get too wild as some have. If it does then we will need your expertise to get them straightened out. HA HA At least not any GIANT or red print as of yet!

A very good post, I am enjoying the various opinions, maybe a fact or two are included as well.

I was wondering if a Range master was still at the club, his name is Homer, don't remember his Sir Name, Big man and easy going, probably around 70 yrs. of age. Ran the centerfire benchrest shoots in the 70's. I know it's a stretch, ,,,just wondering?

?
thanks
HM

jeepmann1948 · « **Reply #21 on:** February 18, 2012, 12:18:35 AM »

Well this is making my heard hurt too, Atlaw.
The mere mention of Physics brings back memories long ago of a Gentleman trying to keep me awake while he was boring me to sleep with monotone lectures.
Which by the way were not about girls or hot rods (my primary intrest of the time)
I just subscribe to theory number 1 and go back to dreaming of girls and hot rods

AtlLaw · « **Reply #22 on:** February 18, 2012, 04:54:20 AM »

Okay, I been reading and thinking and thinking and reading... $:-\$ Not a good thing to be doing on a Saturday morning when the sun is shinning and the birds are singing.

But let me see if I understand this so far.

Scenario: I have sighted in my rifle with the bottom charge listed in the manual. Velocity should only go up from there as I search for the load that delivers the optimum combination of velocity and accuracy. I am using the same bullet and powder in all loads.

To say with any degree of certainty that the next load tried, containing an increase of one gr. of propellant, will hit the target higher or lower then the base group, I must consider:

Interior ballistics;
Exterior ballistics; and
Newton's Law,
all viewed in the defining light of the Laws of Physics. Is that right?

Is it possible that one can occasionally be to curious about how things work or why things happen?

moorepower · « **Reply #23 on:** February 18, 2012, 05:34:25 AM »

Mechanic, thats what I tried to say.
Ray, are you holding the fore end tight or riding the bags?
Atlaw, you only really know what the gun likes when you work up the load. Start low and shoot 5 shot groups working up .3 grains at a time till you get to max load, or you are happy with the load, which often for me on a rifle seems to be around .3-.9 grains before max. One barrel may not like the same powder/primer combo as another. Statistically a 3 shot group is not enough to really tell you how the guns shoots, but in a hunting rifle seems to be adequate.

RaySendero · « **Reply #24 on:** February 18, 2012, 09:43:01 AM »

Quote from: moorepower on February 18, 2012, 05:34:25 AM

.....
Ray, are you holding the fore end tight or riding the bags?
.....

I hold the forearm on the bags.

blind ear · « **Reply #25 on:** February 19, 2012, 03:34:55 AM »

Well, we dun switched from "figgerin" to "fisics", I'll let you guys handle this one. ear

Goatwhiskers · « **Reply #26 on:** February 19, 2012, 04:59:25 AM »

All this makes me recall the old adage: "Want to be cruel to someone? Make 'em think." Have an nice day. Goat