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Comparing computed data to the real thing.

JasonMPDJasonMPD Senior MemberPosts: 6,557 Senior Member
I went to the range to do some data validation for my SPR. So, without further adieu...

Rifle
18", 1:8 twist barrel
Griffin Armament SPR brake adapter
Load
Sierra 77gr SMK (OTM)
23.5gr Varget
CCI 400 small rifle primer
Winchester brass, new
2.26" COL
Scope
Primary Arms 4-14x44 FFP, mil/mil
Chronograph
Magnetospeed V3, 3" from muzzle

I was satisfied with previous grouping with this load and took it further and loaded 50 of them. I shot four 5-shot groups and they were all MOA or better and I chronographed all 20 of them in one continuous string:

Avg = 2620 fps, SD = 12

I use three separate trajectory calculators: Strelok+ (phone app), Bullet Flight Pro (Knight's Armament app), JBM Ballistics (online). I like several sources. For drop at 200 yards provided a 100 yard zero with the 77gr SMK (0.362BC, 0.997" long), they were as follows:

Strelok = 2.8"
BulletFlight = 2.5"
JBM = 2.4"
Average = 2.57" drop

I zeroed at 100 yards and moved to 200 yards without any preliminary scope adjustments. Once done, I measured the centers of the average group sizes and found the drop to actually be 4.0". It's 55% more drop than predicted.

Strelok+ offers a validation feature which allows you to plug in the practical drop and compare it to the calculated drop to yield a "corrected" bullet velocity. According to Strelok, the bullet is actually moving 2353fps. This is 11% less than the chronograph reading of 2620fps. With the new velocity prediction, I substituted the chrono velocity for the new 2353fps prediction in Bullet Flight and JBM. The new velocity yielded a drop prediction of 4.0" in Bullet Flight and 4.1" in JBM--spot on with the observed drop.

One, always validate your data. Two, this sucks. It's a very accurate load, but I want to get closer to 2500fps actual velocity. Three, is my chronograph error really 11% or so? If it is, that sucks also.
“There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
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Replies

  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    According to Quickload, you should be getting that velocity at about inch #11 on the barrel-- remember that it is typically still gaining speed all the way until it exits the barrel. Getting a lower velocity closer back toward the breech as opposed to the muzzle velocity makes sense.
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    Jermanator wrote: »
    According to Quickload, you should be getting that velocity at about inch #11 on the barrel-- remember that it is typically still gaining speed all the way until it exits the barrel. Getting a lower velocity closer back toward the breech as opposed to the muzzle velocity makes sense.

    I just need to fiddle with the load again. 23.5 Varget is not max, 23.7 compressed is listed max, but CFE 223 does a tad better velocity-wise.

    So my actual muzzle velocity is 2353 instead of the chronograph measured 2620. For now.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • zorbazorba Senior Member Posts: 23,663 Senior Member
    "In theory, there's no difference between theory and practice. In practice, there is..."

    As someone who only barely understands this thread, I'd be interested in where your error ends up being in actuality. Any way to check the calibration of your chrono?
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    zorba wrote: »
    "In theory, there's no difference between theory and practice. In practice, there is..."

    As someone who only barely understands this thread, I'd be interested in where your error ends up being in actuality. Any way to check the calibration of your chrono?

    Without probably $10,000 in calibrated test equipment, not likely.

    My chronograph (Magnetospeed) uses magnetic fields to detect the bullet passing two points and calculate a velocity.

    Now, the kicker is that smaller bullets disturb the magnetic fields less than larger bullets and MAY disrupt the readings to some extent. What extent is that? I have no clue. 11% seems like a good place to start?
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • zorbazorba Senior Member Posts: 23,663 Senior Member
    JasonMPD wrote: »
    11% seems like a good place to start?
    Makes total sense to me since that's what you're seeing. I bet the error (wherever its coming from) is non-linear too, just to keep things interesting.
    -Zorba, "The Veiled Male"

    "If you get it and didn't work for it, someone else worked for it and didn't get it..."
  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    zorba wrote: »
    "In theory, there's no difference between theory and practice. In practice, there is..."

    As someone who only barely understands this thread, I'd be interested in where your error ends up being in actuality. Any way to check the calibration of your chrono?
    I wasn't following him at first, now I see what he is saying....

    How high is the scope from the centerline of the bore?
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    Jason, IME, MOST companies are QUITE generous in assigning BCs to bullets.

    Also in my experience, I have found if I leave the velocity at what my chronograph says it is, and play with the G1 BC until my projected drop matches my actual at, say 200 or 300 yards, THEN using that "corrected" BC, the projected ballistics out to 700 have been MUCH closer to my actual trajectory (usually within 1 MOA or so)

    Also, I have found that using Brian Litz's (sp?) G7 BC (Some programs let you specify if you're using a G1 or G7 BC) to yield much closer projections than ANY G1 projections past 3-400 yards

    edited to add:
    Since the chronograph you're using attaches to the barrel, find a friend that has a "normal" chronograph, set it up 10' or so from the muzzle, while using your barrel mounted chrono and compare the readings.

    That should give you a better idea if it's a chronograph error, or a "generous" BC on the part of the bullet maker
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    Here is what Quick Target gives me. I think the velocity is spot on at 2602, the drop predictions are wrong...
    20150530_000535_zpsbyv6anoe.jpg
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    Jerm, You have Quick Target that came with QL, I assume.

    Plug in his velocity/bullet with a G7 BC of 0.190 and see how it compares to his actual trajectory.

    I haven't found/re-installed my version of QL/QT since my recent harddrive crash, or I'd do it myself.
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    knitepoet wrote: »
    Jerm, You have Quick Target that came with QL, I assume.

    Plug in his velocity/bullet with a G7 BC of 0.190 and see how it compares to his actual trajectory.

    I haven't found/re-installed my version of QL/QT since my recent harddrive crash, or I'd do it myself.
    I need the height of the scope above the barrel. It significantly affects the "drop" between 100 and 200 yards. After that, I will plug yours in.
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    Jermanator wrote: »
    I need the height of the scope above the barrel. It significantly affects the "drop" between 100 and 200 yards. After that, I will plug yours in.
    It's an AR, 2.5" will be pretty darned close
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    knitepoet wrote: »
    It's an AR, 2.5" will be pretty darned close
    ... and when I do that and put the velocity at his measured 2620fps, I get about 3.75" of drop from 100 to 200 yards. His chronometer is spot on.
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    At 2.25" above the barrel, it gives me the 4" that he is getting for actual results.
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    Jermanator wrote: »
    I need the height of the scope above the barrel. It significantly affects the "drop" between 100 and 200 yards. After that, I will plug yours in.

    3.625"
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    JasonMPD wrote: »
    3.625"
    That gives me -2.6" @ 200.
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    JasonMPD wrote: »
    3.625"
    How are you getting the center of your scope that high above the bore, and how do you get a cheek weld with it that freakin' high???
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    knitepoet wrote: »
    Jerm, You have Quick Target that came with QL, I assume.

    Plug in his velocity/bullet with a G7 BC of 0.190 and see how it compares to his actual trajectory.

    I haven't found/re-installed my version of QL/QT since my recent harddrive crash, or I'd do it myself.
    I switched to G7 BC and got a drop of 3.9" with that scope height.
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    Jermanator wrote: »
    I switched to G7 BC and got a drop of 3.9" with that scope height.

    Hmm... All of mine say that a G7 of 0.18 or 0.19 and 2620fps (with my scope height) is about 2.5" drop at 200.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    knitepoet wrote: »
    How are you getting the center of your scope that high above the bore, and how do you get a cheek weld with it that freakin' high???

    It's an AR15.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    JasonMPD wrote: »
    It's an AR15.
    Okay??? I understood that from your first post, I have 5 rifle uppers, and ALL of them are right @ 2.5" scope height +/- 0.25"

    edited to add: 2 are a "hi-rise" & a EOP (elevated optics platform) upper and the other 3 have risers also I forgot one 5.56 upper
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    Jermanator wrote: »
    I switched to G7 BC and got a drop of 3.9" with that scope height.
    Imagine that :tooth:
    :beer:
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    Jermanator wrote: »
    That gives me -2.6" @ 200.

    That was my average, too. But my observed drop is 4".

    2620fps, -4"@200 yards = 0.163 G1 BC (is better than that)

    2353fps, -4"@200 yards = 0.342 G1 BC (the published BC)
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    knitepoet wrote: »
    Imagine that :tooth:
    :beer:

    I don't.

    Screenshot_2015-05-30-09-14-572.jpg
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    JasonMPD wrote: »
    I don't.
    So Jerm's lying?
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    What difference does how high the scope is mounted matter IF it is Zeroed @ 100 yards, that means it is zeroed yes and should follow estimated drop out further more or less, correct or not?

    A bullet is gonna follow a trajectory from the muzzle depending on what angle the muzzle is anyway and if his scope cross-hairs have it dead on @ 100 yards shouldn't it be kinda predictable where it should impact @ 200 yards?

    Or am I missing something here like his sighting picture being off because of the high scope mounting?

    I know scope adjustments can be a challenge with high mounts on some scopes (like running outta clicks or the like) to get the cross hairs aligned for the impact to be where you want the bullet to strike.
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • knitepoetknitepoet Senior Member Posts: 21,094 Senior Member
    Big Chief wrote: »
    What difference does how high the scope is mounted matter IF it is Zeroed @ 100 yards, that means it is zeroed yes and should follow estimated drop out further more or less, correct or not?
    Your line of sight is a straight line. The sight height determines how much angle you have to have for the LOS and and point of impact to intersect at at a certain point.
    Sure, at THAT point, wherever it may be, the two intersect, but the sight height determines the actual angle the bullet is moving in relation to that straight line. That's why you can see a bullet hitting above the line of sight further down range. The bullet isn't actually rising, it starts dropping the moment it leave the bore, BUT, since it it fired at an upward angle, in relation to the line of sight, it rises above the LOS and then drops back too it and crosses that straight line again.

    Look at the picture Jerm posted in post #9 and you can see how the bullet appears to rise, then fall
    Seven Habits of Highly Effective Pirates, Rule #37: There is no “overkill”. There is only “open fire” and “I need to reload”.


  • Big ChiefBig Chief Senior Member Posts: 32,995 Senior Member
    So say he fired and was dead on @ 100 yards and called it his 100 yard zero, and then using the same target moved it out to 200 yards without making any scope adjustments and aimed at the same bullseye, shouldn't it hit/drop somewhere in the calculated charts/programs of X number of inches?

    Isn't that reason they give us such data to predict the drop if you zero at a known rnage, where it will strike @ 200-300-400-500 whatever range?
    It's only true if it's on this forum where opinions are facts and facts are opinions
    Words of wisdom from Big Chief: Flush twice, it's a long way to the Mess Hall
    I'd rather have my sister work in a whorehouse than own another Taurus!
  • JermanatorJermanator Senior Member Posts: 16,128 Senior Member
    knitepoet wrote: »
    So Jerm's lying?
    I am not saying I am lying, but I am not sure how I got that 3.9". I have ran it through again and again and can't get that number again. Here is what I get with G7 and that scope height...
    20150530_121425_zps09qcxmng.jpg
    Reason obeys itself; and ignorance submits to whatever is dictated to it.
    -Thomas Paine
  • BigDanSBigDanS Senior Member Posts: 6,973 Senior Member
    How are you measuring your scope height? It should be bore centerline to scope centerline. Unless you have it mounted on the carry handle, your measurement seems high.

    D
    "A patriot is mocked, scorned and hated; yet when his cause succeeds, all men will join him, for then it costs nothing to be a patriot." Mark Twain
    Alcohol, Tobacco, Firearms and Explosives.... now who's bringing the hot wings? :jester:
  • JasonMPDJasonMPD Senior Member Posts: 6,557 Senior Member
    BigDanS wrote: »
    How are you measuring your scope height? It should be bore centerline to scope centerline. Unless you have it mounted on the carry handle, your measurement seems high.

    D

    I am measuring the scope height buy dropping a tape measure from where the to have of the scope rings come together to the center line of the barrel. I am using a section of rail on the side of the handguard as a reference for the center line of the barrel.
    “There are three kinds of men. The one that learns by reading. The few who learn by observation. The rest of them have to pee on the electric fence for themselves.” – Will Rogers
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