Variations in velocity on POI

[rwsmith]

Another thread got me to thinking. What is the difference between the points of impact of two bullets with a velocity range of 925 fps and 975 fps or 50 fps . Say you are loading to get 950 fps with a 158 gr. .38 cal SWC but variations between cartridges cause differences. (I'm not a statistician) Using my handy dandy online ballistics calculator I find that the fastest bullet will go about .75" high at 50 yards and the slowest would go .75 low at 50 yards. To a competitive shooter that sound like a lot. To me, not so much.

You who load for serious accuracy, how wide is the range in velocities in a batch of ammo?

[Protocall_Design]

If you are able to shoot 1-1/2" groups at 50 yards, you are good to go for most types of matches. 1" groups at 50 yd. are considered about as good as you are likely to get out of a high end custom revolver or semi-auto pistol.

[Calliope]

Does the ballistics calculator take into account the slight change of angle in a real world gun? The slower round spends just a little more time in the barrel, so it launches at a slightly higher angle, compensating a little for it's slower speed.
I dunno, just a theory.
Besides, a 50 fps spread is easily beatable with sorted brass, consistent charges, quality bullets.

[Twoboxer]

Originally Posted by rwsmith

. . .Using my handy dandy online ballistics calculator I find that the fastest bullet will go about .75" high at 50 yards and the slowest would go .75 low at 50 yards.. . .

You who load for serious accuracy, how wide is the range in velocities in a batch of ammo?

As Calliope said, that doesn't account for the extremely high likelihood that the slower bullet will have a higher launch point due to being launched later in the recoil.

As for your second question, I'm not surprised by an ES of 50 in a test group . . . but I don't load or shoot pistol for serious accuracy at distance.

[arjay]

Playing around with a 44 some years ago the difference between 700 fps and 1100 fps seemed to be about 3" at 25 paces

[Nevada Ed]

Back in the 70's and 80's I did a lot of reloading and 50 and 100
yard shooting with a 6" 357 S&W Magnum M19.

I used 125 and 158 JSP and 158 WC lead bullets in my outings
with W231, Green Dot, Unique and Blue Dot as my main powders.
They all did their thing and all had a certain bullet and fps that
they did well with but I also learned what a fast and slow powder
can do with the type of recoil along with how the bullet can not
only change its fps but also its POI on the target, at those ranges.

I learned that sometimes not the hottest or fastest load is the best
for accuracy as well as a load that is in the starting blocks and
can not hold a steady ES.

These loads were used on Metal Pigs and I know that you stated 38.......
but the reason I chose the 357, was because of the hold over needed at 100 yards
for the 38 special and the minimum energy that hits the dirt
10-15 yards short of the target with iron sights.

Since you are just going to 50 yards, the 38 special will work but
you might try a RN and a SWC lead out to see if one works better in your revolver.
Each with a fast and a slow powder.
Red Dot to Unique & HS-6 will get you 900fps with a 6" 38 K frame
which is plenty for target work, maybe even 866?

You have shot a lead 158gr bullet at 950+ fps out of a 38 special revolver , right?

Good luck.

Some 158 lead try outs before I had a chrony; ( 15 yds. )

[Regaj]

Back in the day, we'd load up pressure (ladder) series' and then carefully and painstakingly send those downrange to paper. What we were looking for was that load in the series where the groups tightened up. More often than not, we'd find it.

We could, and often did, estimate the velocity of those loads. But it was a pretty rough business... simply extrapolating from the information we could glean from the several loading manuals we had.

Nowadays, of course, we are blessed with affordable chronographs. We tend to focus on the absolute velocity numbers we get from our loads. But just as important are the standard deviation (SD) numbers we see across a load.

I'd bet dollars to donuts that if I were to replicate all those pressure series' from years ago, and lit them off in front of my LabRadar... I'd find a very strong correlation between small SD and the 'most accurate' load that I eventually chose.

Which is a long-way-around-the-barn way of saying, yeah, velocity variation matters. Both for accuracy and POI.

Velocity is the sexy part of handloading. But standard deviation is really where the rubber meets the road.

[rwsmith]

Realistically, I could make really sloppy ammo and at 50 yards the gun would shoot far better than I could.

I'll letcha know in about 10 years if I can shoot a 1" group at 50 yards.

[fredj338]

There is actually no drop diff in ammo that is 50fps slower or faster. Most shooter can't hold 1" @ 50y even off a bench.

[Joe4d]

if you are getting 50 fps swings you are using the wrong components, or wrong loading techniques. I expect single digit SD from my loads and I dont really sort my brass beyond,, humm looks good, and humm looks bad.
But as stated, nowadays I cant even see a 50 yard target, if only miss by .75 I'm pretty happy.

[Nevada Ed]

"I'll letcha know in about 10 years if I can shoot a 1" group at 50 yards. ".............

Hay give me a break.
I might not be here in four years........

the way I talk about my wife's cooking!!

[fredj338]

Originally Posted by Twoboxer

As Calliope said, that doesn't account for the extremely high likelihood that the slower bullet will have a higher launch point due to being launched later in the recoil.

As for your second question, I'm not surprised by an ES of 50 in a test group . . . but I don't load or shoot pistol for serious accuracy at distance.

I hear this bbl time thing as acounting for diff bullet impact, but I have be er seen it personnaly in my own shooting from 7-220y with any handgun. I have seen heavier bullets shoot high & lighter bullets shoot low, but imo, that is recoil driven. Extreme example, run a 185gr 45 @ 1000fps & a 300gr @ the same vel. Same bbl time, the 300gr will always shoot higher.

[Wise_A]

There's very little correlation between 50-yard accuracy and consistent velocities in handgun ammunition. FPS almost never comes up in Bullseye forum discussions of ammo, except when different folks note that their most accurate loads tend to be around one velocity or another with a given bullet (185-grain JHP or 200-grain LSWC), regardless of the powder used.

[SMSgt]

When shooting becomes a scientific/higher-math problem, I'll find something else fun to do.

[Twoboxer]

Originally Posted by fredj338

I hear this bbl time thing as acounting for diff bullet impact, but I have be er seen it personnaly in my own shooting from 7-220y with any handgun. I have seen heavier bullets shoot high & kighter bullets shoot low, but imo, that is recoil driven. Extreme example, run a 185gr 45 @ 1000fos & a 300gr @ the same vel. Same bbl time, the 300gr will always shoot higher.

That's exactly what we are - or at least I am - saying. The heavier bullet produces more recoil, raising the launch angle, producing a higher POI at typical pistol ranges. This occurs despite the fact that gravity must make it drop further than the faster bullet . . . assuming reasonably equivalent BCs lol.

It has nothing to do with the time each bullet spends in the barrel . . . it's just how the bore axis is angled at launch.

So your "extreme example" actually proves the point.

Ballistics programs calculate trajectories as if the barrel is "strapped down", ie, exactly at the same angle regardless of MV or recoil. So the trajectory they will calculate - the slower bullet hitting lower - will not match actual pistol results.

[rwsmith]

Originally Posted by Joe4d

if you are getting 50 fps swings you are using the wrong components, or wrong loading techniques. I expect single digit SD from my loads and I dont really sort my brass beyond,, humm looks good, and humm looks bad.
But as stated, nowadays I cant even see a 50 yard target, if only miss by .75 I'm pretty happy.

,,,that are on the outside of what any throw-together ammo should do, Usually my powder load, bullet and, primer are all the same. (I try to keep power +/- .1 grain) But the brass is ALL OVER THE PLACE. (The only ones I discard are the ones with the knurls part way down the case.

Usually mine clocks about +/- 20 fps. And again, this satisfies my curiosity about the effect of velocity variation to where I'm sure I shouldn't sort brass by manufacturer, turn the cartridge on a lathe, trim to the same length and all that noise.

My eyes are horrible, too. Though with my cataract surgery I can focus on the front (and the rear) sights well, I'm shooting into a cloud of mush that may be the target. The bottom line is that all of my guns shoot far, far, far better than I do, with the possible exception being the Kel tec P11 past 7 yards.

The most shootable and inherently accurate gun is my 686 6". i can hit targets that are out there with that.

[Forrest r]

Sure is a lot of you should do this but I can't do that because of xxx in this thread.

At the end of the day anyone here can use a scope and a rest. Just saying

You'll find that the bullseye shooters developed/tested/use the same loads for a reason. Powders have come a long way.

AA#2 in the 9mm
titegroup for faster loads (make power factor)
clays for bullseye loads
wst is always worth a look

I'm sure there's more/better powders out there. Myself when I start looking for a "target" load. I start with test loads, a chronograph and run 10 to 12 rounds of a test load over the chronograph alternating between:
muzzle up, bring the firearm down & take a shot
muzzlle down, bring the firearm up & take a shot

When you find low es & sd when doing this, you will find you have something to work with.

[m657]

But standard deviation is really where the rubber meets the road.

In the realm of 'scientific ballistics' such independent co-variables are debatable and perhaps somewhat actually measurable.

The conflict arises when 'the Art' of the human interface performing repeatable results starting with those 'given controlled equals' attempting to achieve the desirable POI.

Argument can be made supporting any number of the co-variables to explain. I'm not one of those who has 1"/50yd groups in any case, so the approximation of theories is adequate. My own best SD was 6 in a 44 special load in a Colt SAA producing the smallest group I've ever made at 40'. Seeing that result on paper target a buddy produced a considerable stack of green poultice to soothe my anguish at not being able to reproduce such at will despite controlling all recipe components. His intent was to study that particular SAA performance at his own pace.
While I haven't seen any targets, his continued smile and refusal to let me reestablish ownership of that fine Colt does suggest at least satisfaction whatever the POI may be.

On the other hand, I've had great results (and poor as well) at SD of 11, 29, even 75!

While the rational part of me would like to believe there is a 'magic formula' that accounts for and controls the POI, I suspect there are other factors as well.

[Rogeronimo]

I will attempt to answer a question you didn't ask. Recoil impulse and barrel dwell time may be the two factors worth considering when discussing POI. I can't imagine that external ballistics and extreme spreads is that critical at 50 yards. Individual shooting disciplines and firearms may well be why we all have our own favorite powder/bullet combinations for a given cartridge. Powders "speak" to me, and sometimes they piss and moan about what I'm asking them to do for me.

[rwsmith]

Originally Posted by Joe4d

if you are getting 50 fps swings you are using the wrong components, or wrong loading techniques. I expect single digit SD from my loads and I dont really sort my brass beyond,, humm looks good, and humm looks bad.
But as stated, nowadays I cant even see a 50 yard target, if only miss by .75 I'm pretty happy.

...that this was 'slop' ammo, all different brass and I didn't weigh every charge as I would for a test or max load.

[njl]

Getting back to the original question, once a bullet leaves the barrel, it’s falling and accelerating toward the ground at about 9.8m/s/s. So, the faster the bullet, the smaller the bullet drop will be at any given distance. A ballistics calculator will give you that data.

Less tangible, the slower bullet takes longer to leave the barrel which is probably rising from recoil, and so your POA at the instant it leaves the barrel may be higher than when you pulled the trigger. How much likely varies according to several variables and will defy calculation.

I very rarely shoot pistols at >25yds and can’t say I’ve noticed any POI differences in my 9s and .45s with varying velocity ammo.

[Kiwi cop]

As the OP for the other ". 2 gn" thread can I add the following.

There are more variables in reloading and shooting that I care to count. My old Lee Auto Disc powder measure used to vary +/- .2 - .3 of a grain of powder from drop to drop due to spillage as the disc moved horizontally. My current Auto Drum measured a single .1 gn difference over 10 weighed charges when I got my first one (I now have three). A Dillon reloader tells me that a .1 - .2 gr difference in powder drops is nothing to worry about from his powder measure. My thread was based on average powder drops over 10 charges (4.2 - 4.4 gn) and as of today it seems the 4.4 gn charge is more accurate in my hands.

How you hold your pistol has an effect on point of impact. When I was shooting club level ISSF (back when it was still called UIT) I discovered that a one handed 6 o'clock hold had the same impact at 25 meters as a two handed centre hold due to the effects of recoil. How much pressure you place on the grip with each hand also comes into play.

In our Service Match we fire 6 rounds each prone, sitting/kneeling and each side of a barricade at 50 meters. My tightest groups, as expected, are shot prone while POI at the barricades goes up and down depending on if I use the barricade as a rest or shoot free from contact. And I don't want to think about single action/double action shooting differences.

Then there is the difference in where your sights are centered and how far away your target is. If using a 50 yard zero the bullet should be dropping onto the centre of the target as it hits, in which case it should be rising through the target centre at 25 yards, but a silhouette shooter zeroing out to 100 yards will want the bullet still rising at 50 or have to use holdover.

At the end of the day a .75" rise or fall giving a 1.5" group is probably possible off a rest but a bit beyond most shooters abilities to achieve. And I think that overall it is the shooter that is going to make the biggest difference.

Back when my duty gun was a .38 Special 5 " Model 10, I saw a shooter take 10 of my roughest .38 special 158 gn LRN loads along with my duty pistol and put all shots into the 9 ring of a UIT target, single action, single handed at 25 meters. I couldn't get them all into the 8 ring out of my 6" barrelled revolver.