What is my FPS average?

[beanz2]

The following are chrono readings I obtained though during the last session:

2846
2758
2779
2969
2724
2813
2839
2778
2809
2725

Unfortunately, I was in a rush and only did 10 rounds. This was out of a 16 inch AR with 1:8 twist, IMI 69 grain, Sierra Match King bullets.

Would you guys take the anomalous high reading out and average the rest, or would you take the entire set of 10 and average all of them?

[200Apples]

The one round displaying the anomalous high velocity is just one reason why we handload: for consistency.

That said, what does it matter if you average the ten rounds or, tossing the one, nine? if these are not your handloads...


I'll give you the quintessential calguns! answer: Average BOTH!

[beanz2]

Haha, of course.
For this class, we are limited to factory loads. In higher classes, hand loads would be allowed. If you are faced with these numbers, would you shoot for the FPS of the nine closely spaced ones?

[200Apples]

Class?

This is beyond my pay grade.

If you are faced with these numbers, would you shoot for the FPS of the nine closely spaced ones?

You have lost me.

Forgive me for wasting your time. Someone else should be along soon.

[JackEllis]

I'm confused, in part because I have no idea what you're trying to do or where you're going with this.

The straightforward answer is, you take the average of all 10. Why would you not want to do that?

[beanz2]

Class?

This is beyond my pay grade.




You have lost me.

Forgive me for wasting your time. Someone else should be along soon.

No, I still appreciate your input

Have a mid-distance marksmanship class this weekend at Front Sight. From 50 to 350 yds. Standing unsupported from 50, any position with no support from 100, any support from 150 to 350. Skills test at the end to graduate to higher longer distance precision classes.

I'm confused, in part because I have no idea what you're trying to do or where you're going with this.

The straightforward answer is, you take the average of all 10. Why would you not want to do that?

Trying to pass the test with the ammo I got, that is all. Trying to work out the ballistics before class, so my own numbers don't trip me up. But maybe for only 350 yards, it matters only a little?

[200Apples]

Trying to work out the ballistics before class...

Ah HAH. I think I can pick up whatcher puttin' down...

Try this:

Average the ten and graph your arc.

Average the more-consistent nine and graph another arc.

Compare the two ballistic arcs (arcs, right?), then split the difference for your hold. Make sense?

If it doesn't, it's ok, because I've never done what you're doing before. I just ring steel and punch paper and go from there...

[Fjold]

With only ten rounds tested, you can't tell if the one high reading is an outlier or not. What if five of the next ten rounds also clock the higher velocity?

You can average nine but be prepared to throw a flyer at least ten percent of the time.

[trackcage]

Extreme overthinking.

Average of all 10 is 2804. Average of 9 after removing high value is 2786. So 18 fps different, or less than 1% difference.

Don't get in the habit of suppressing chrono values unless they are obviously out of wack (e.g. says 3,000 from a 9mm round). All 10 were fired from your gun. They all count. If it happened during your class, you would have had to deal with that shot, right? So deal with it here too.

[JackEllis]

Trying to pass the test with the ammo I got, that is all. Trying to work out the ballistics before class, so my own numbers don't trip me up. But maybe for only 350 yards, it matters only a little?

The first thing you need is a ballistics calculator. gundata.org has one. Ballistic for the iPhone is another. I play with these all the time to help me understand how things like MV affect bullet drop.

Since I'm too lazy to feed the numbers into a spreadsheet, let's assume the average without the high number is 2800 FPS and you have your rifle zeoed to be dead on at 100 yards based on 2800 FPS. At 100 yards the difference is going to be too small to notice. At 350 it's going to be somewhere between 3 and 4 inches.

Not knowing exactly how things are scored, I'm pretty sure you won't need a perfect score so don't sweat one in ten "outliers" but consider getting more consistent ammo, like ADI.

[oktavist]

What is my FPS average?

arithmetic mean average = sum of data set / number of items

Would you guys take the anomalous high reading out and average the rest, or would you take the entire set of 10 and average all of them?

If I wanted a mean average, I would include everything. If I wanted a median average, I would throw away all the values except the one in the middle. It depends on what you're trying to measure. If I was anti-gun I'd throw out everything until I got what I wanted.

Average of all 10 is 2804. Average of 9 after removing high value is 2786. So 18 fps different, or less than 1% difference.

Yes, but the standard deviation differs by about 38% when you remove that value. If I was handloading, I would be much more interested in SD...

[trackcage]

Yes, but the standard deviation differs by about 38% when you remove that value. If I was handloading, I would be much more interested in SD...

Sure, but OP isn't handloading.

I like tight, single digit SDs in my handloads too, but I don't throw out values to get me there.

[CCrawford]

From the website gundata.org

Picking your extremes:
Range__Fast__Slow___Fast__Slow
0 -1.4940 -1.4933 2968 2724
50 -0.1936 -0.0891 2811 2574
100 0.0055 0.0019 2659 2430
150 -1.0266 -1.3812 2512 2290
200 -3.4382 -4.4239 2369 2155
250 -7.4002 -9.3414 2231 2024
300 -13.1105 -16.3838 2098 1898
350 -20.7982 -25.8420 1969 1778
400 -30.7304 -38.0551 1846 1663
450 -43.2177 -53.4166 1728 1554
500 -58.6218 -72.3810 1615 1453

So at 350 Yds., the drop difference is a little over 5" between the fastest and slowest. Questions that come to mind are what type of target are you shooting at? Bullseye, B27, Steel plate of X diameter? What would shooting at 22 1/2" of drop get you? Since the majority of the rounds were on the slower side, you could go to 23 or 23 and a half of drop. Really need more info then you have provided so far to help you more.

If you are shooting at a larger target, then it will not matter as you will be on target either way. I have never been to front Sight so no idea what the targets look like for close up or distance.

You did not mention the group size the rounds produced. If it is single hole or close at 100 yds. great. If not, the drop may be the least of your concerns at distance. No insult intended there.

Good luck and have fun.

Criss

[sonofeugene]

I'm confused, in part because I have no idea what you're trying to do or where you're going with this.

The straightforward answer is, you take the average of all 10. Why would you not want to do that?

Sometimes outliers can be way out, in which case not factoring them in is sometimes done. However, one then has to ask, why are there outliers?

[beanz2]

From the website gundata.org

Picking your extremes:
Range__Fast__Slow___Fast__Slow
0 -1.4940 -1.4933 2968 2724
50 -0.1936 -0.0891 2811 2574
100 0.0055 0.0019 2659 2430
150 -1.0266 -1.3812 2512 2290
200 -3.4382 -4.4239 2369 2155
250 -7.4002 -9.3414 2231 2024
300 -13.1105 -16.3838 2098 1898
350 -20.7982 -25.8420 1969 1778
400 -30.7304 -38.0551 1846 1663
450 -43.2177 -53.4166 1728 1554
500 -58.6218 -72.3810 1615 1453

So at 350 Yds., the drop difference is a little over 5" between the fastest and slowest. Questions that come to mind are what type of target are you shooting at? Bullseye, B27, Steel plate of X diameter? What would shooting at 22 1/2" of drop get you? Since the majority of the rounds were on the slower side, you could go to 23 or 23 and a half of drop. Really need more info then you have provided so far to help you more.

If you are shooting at a larger target, then it will not matter as you will be on target either way. I have never been to front Sight so no idea what the targets look like for close up or distance.

You did not mention the group size the rounds produced. If it is single hole or close at 100 yds. great. If not, the drop may be the least of your concerns at distance. No insult intended there.

Good luck and have fun.

Criss

Thanks for your input. The targets vary from 3" circle to 7" circle depending on distance. The shots from 350yd are on the 7" target. All on paper.

I guess I should have picked an even higher quality ammo, but from the better quality ones I had on hand, the IMI 69gr seemed to group as well as SSA 77gr when I brought them all to the range for comparison. Being a cheapskate, I naturally picked the IMI for this class

At 100yd, my bullet holes were not touching, but within 2". Now mind you, I have never been a precision shooter before and had always shot an AK on rifle classes until this class Time to shoot better, which is why I need to take this class.

But I'm committed now, the ammo has been ordered and is sitting at the hotel and we can't bring them back