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PF margin of error


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If the measuring equipment is not accurate shot-to-shot, then a range is mandated. The chronograph that is typically used at Nationals is not consistent shot to shot, this is provable. A range of values is the most equitable way of performing a PF check, if someone wants to hang around at the low end then they will eventually get burned. When it becomes necessary to load at 175 to ensure a 165 at Nationals there is a clear indication that something is wrong with the system.

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171.5PF consistently at home, before and after Area 6. While at Area 6 I went 164.1, minor. I just want to add that I feel that being 7PF higher is just not enough of a cushion in my opinion. I am now convinced, after all my planning, spending, and driving that I will never go to another match and not have a cushion of 10PF. The variables are too many to list between different chronographs, better safe than sorry, as I was with my 6.5PF cushion.

Well 4% of 171.5 is unfortunately 6.86. :-/

Anyway, I wanted to ask what your standard deviation was for your load?

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If the measuring equipment is not accurate shot-to-shot, then a range is mandated. The chronograph that is typically used at Nationals is not consistent shot to shot, this is provable.

How? Since our ammo varies from shot to shot it's pretty hard to prove it one way or the other. If someone comes up with something that delivers an absolutely consistent velocity to use as a check (like a check weight) we'd be set, but I'm not sure what that could be. R,

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How? Since our ammo varies from shot to shot it's pretty hard to prove it one way or the other. If someone comes up with something that delivers an absolutely consistent velocity to use as a check (like a check weight) we'd be set, but I'm not sure what that could be. R,

I thought that the conclusion in the chrono calibration thread was that shooting an Olympic class air rifle/pistol would give consistent muzzle velocities within around 2 FPS due to the demands for consistency needed for ISU events.

Ah, the irony of using this $4000 rifle to test a $200 chronograph:

http://www.pyramydai...num_Silver/1032

FWB_700_Silver_1032_zm-0.jpg

Edited by Skydiver
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If the measuring equipment is not accurate shot-to-shot, then a range is mandated. The chronograph that is typically used at Nationals is not consistent shot to shot, this is provable.

How? Since our ammo varies from shot to shot it's pretty hard to prove it one way or the other. If someone comes up with something that delivers an absolutely consistent velocity to use as a check (like a check weight) we'd be set, but I'm not sure what that could be. R,

How ? They use two chrono's; I watched the results on both screens (left and right) over the three shots.

First shot, left chrono showed a higher reading than the one on the right.

Second shot, left chrono showed a lower reading than the one on the right.

Third shot, both chrono's showed the same FPS.

If the chrono's were accurate (shot-to-shot) then this result would be impossible.

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If someone comes up with something that delivers an absolutely consistent velocity to use as a check (like a check weight) we'd be set, but I'm not sure what that could be. R,

A linear motor is the only reliable way that I can think of. An object zipping down this rail would be powered the whole way and could be used to determine the offset of any chrono. The object would need to pass over at various speeds to determine the range of offset and then this could be applied to each FPS reading of a competitors ammo.

Theoretically, its feasible.

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I thought that the conclusion in the chrono calibration thread was that shooting an Olympic class air rifle/pistol would give consistent muzzle velocities within around 2 FPS due to the demands for consistency needed for ISU events.

Ah, the irony of using this $4000 rifle to test a $200 chronograph:

Well, that was just an idea I threw out there...certainly seems reasonable. Now stop posting pictures of fancy air rifles...I want one and don't want momma to kick my butt for spending a couple grand on a "toy" gun...lol.

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If the measuring equipment is not accurate shot-to-shot, then a range is mandated. The chronograph that is typically used at Nationals is not consistent shot to shot, this is provable.

How? Since our ammo varies from shot to shot it's pretty hard to prove it one way or the other. If someone comes up with something that delivers an absolutely consistent velocity to use as a check (like a check weight) we'd be set, but I'm not sure what that could be. R,

How ? They use two chrono's; I watched the results on both screens (left and right) over the three shots.

First shot, left chrono showed a higher reading than the one on the right.

Second shot, left chrono showed a lower reading than the one on the right.

Third shot, both chrono's showed the same FPS.

If the chrono's were accurate (shot-to-shot) then this result would be impossible.

I've seen that happen as well, but I should have been more clear. How do we prove which one is right, and what is the range of error that's acceptable? We're giving the shooter the benefit of the doubt with the higher number as it stands now, so there's the chance that a system with no error would actually "hurt" as many shooters as it helps. I don't care either way, but it's something to consider.

Do you remember the typical spread from chrono A to B? I always forget to jot down the numbers. I'm going to try and get both sets of #s this year. R,

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Fourtrax,

What were the environmental factors?

What chrono do you use at home v. match?

Do you have a blast shield in front of the chrono at home?

What powder do you use?

There are so many variables that have an effect on measuring velocity that each needs to be examined to eliminate the true cause for such a wide variance in the readings.

I use the same chrono as in A2 and Nationals. I have control ammo to validate my readings. I have a powder that temp effects only when it is really cold (posted in another thread). The only real physical difference is sunlight v. light bulb.

Unless you are doing your reloading like they do for bench rest shooting then accept the possiblity for such a variance.

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  • 2 weeks later...

Fourtrax,

What were the environmental factors?

What chrono do you use at home v. match?

Do you have a blast shield in front of the chrono at home?

What powder do you use?

There are so many variables that have an effect on measuring velocity that each needs to be examined to eliminate the true cause for such a wide variance in the readings.

I use the same chrono as in A2 and Nationals. I have control ammo to validate my readings. I have a powder that temp effects only when it is really cold (posted in another thread). The only real physical difference is sunlight v. light bulb.

Unless you are doing your reloading like they do for bench rest shooting then accept the possiblity for such a variance.

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  • 2 months later...

ok what i didnt get was i was at area 1 and did the chrono, im standing there and i watch him fire 3 of my rounds and i see 1080..1080..1100 then he stops and it calculates out to 132pf? wtf with 124g bullets ? what kind of math did they use for that?

if 1086 was the average of those 3 shots my bullets would have had to weigh 121-122g instead of 124g? that seems a bit off...(rainier ballistics leadsafe 124g round nose fmj's)

Edited by Field
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you know what? i think not screwing up is the most powerful tool in the shooterz arsenal. its starting to become more apparent that when you are relaxed and smooth and simply concentrating on what you need to do, things never go too bad at all.

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Ah, the irony of using this $4000 rifle to test a $200 chronograph:

well yeah but they are selling like a hundred thousand of those $200 chronos.

(200x100,000)>>>>>4000

simple math.

Edited by Field
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ok what i didnt get was i was at area 1 and did the chrono, im standing there and i watch him fire 3 of my rounds and i see 1080..1080..1100 then he stops and it calculates out to 132pf? wtf with 124g bullets ? what kind of math did they use for that?

if 1086 was the average of those 3 shots my bullets would have had to weigh 121-122g instead of 124g? that seems a bit off...(rainier ballistics leadsafe 124g round nose fmj's)

ive seen bullets 3-4 gr off from what they supposedly weigh, both high and low. My precision molys are 200 gr, ut weigh in anywhere from 199.1 to 199.7. Some 200gr BBIs i shot weighed in around 203ish. gotta know the exact weight of them. some matches will go on what you say. the good ones, will weigh one to see what it really is.

As for verifying the chrono. the only way to truly measure is a highspeed camera and the black/white board like whats seen on mythbusters and the like. You can find the exact speed via the highspeed and then see if the chrono is accurate. Otherwise, we just gotta trust the technology... :sight:

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ok what i didnt get was i was at area 1 and did the chrono, im standing there and i watch him fire 3 of my rounds and i see 1080..1080..1100 then he stops and it calculates out to 132pf? wtf with 124g bullets ? what kind of math did they use for that?

if 1086 was the average of those 3 shots my bullets would have had to weigh 121-122g instead of 124g? that seems a bit off...(rainier ballistics leadsafe 124g round nose fmj's)

Did you see what weight he wrote down? How many of those Rainier bullets have you weighed to get a good idea of what they really weigh? It would have been 122gr and change, and there are a lot of bullets out there that are off that much from listed weight. R,

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I give myself a margin of error in three different ways.

1) I weigh 20 - 30 bullets. I check for consistency, and then take 2gr off the lowest weight for figuring PF.

2) I chrono the loads, recording every velocity, and figure avg PF and PF from the slowest round.

3) My chrono guns are a G17 and a G22, however, I shoot a G34 or a G24 in competition.

I go in knowing that at the very least, I am running a 135PF in Minor, and a 175PF in Major. In reality, I am well above that. My guns are sprung appropriately, there are no signs of overpressure, and they group well.

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huh yeah so i changed from rainier ballstics to some Remmington fmj's and then increased my powder charge from 4.4g to 4.5g (1.13-1.14 oal) and then i chrono 142pf at this NW Challenge match. Go figure. guess the remmingtons are a tad heavy and the rainier bullets are a tad light

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LOL! You probably won the chrono stage for Production. :-)

All kidding aside, congratulations on winning 2nd B in Production. (Sorry you had to leave early and missed the awards ceremony. Contact the MD to see if the plaque will be at the range, or if somebody picked it up for you.)

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  • 2 weeks later...

As ammo nazi at a major State match - weather in the mid 90's, very high humidity, the PF's were lower than normal, 2 of the 4 people DQ'd 1 shooting minor and the other shooting major.

The minor shooter was 120 (needed 125) out of the match gun and their own gun (9mm 1911) and the other shooter was 163 out of their gun (S&W revolver in 38 Super). Both shooters play close to minimun PF and the heavy, dense air puked them.

One shooter had told me earlier that he added an extra couple of points of powder to his load just to make sure he would make PF. His load just made PF on the third shot. This person is a longtime shooter and I know doesn't play silly buggers but he almost got bite.

FWIW I tested the chrono twice a day with ammo from the same box and it varied from 135 - 137, depending on how the humidity was at that time.

My 9mm is 137.72 and my .40 cal 172 or 177 depending on the powder loaded.

My minimum recommendations are

9mm/38Sp = 131

.40 S&W = 142 for minor or 175 for major (IPSC) or 170 (USPSA)

In the end you will go with what yoou want but the numbers I have recommended are provided to help you not get bitten in the a$$.

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As ammo nazi at a major State match - weather in the mid 90's, very high humidity, the PF's were lower than normal, 2 of the 4 people DQ'd 1 shooting minor and the other shooting major.

The minor shooter was 120 (needed 125) out of the match gun and their own gun (9mm 1911) and the other shooter was 163 out of their gun (S&W revolver in 38 Super). Both shooters play close to minimun PF and the heavy, dense air puked them.

DQ'd? I don't think you are allowed to disqualify somebody for not making their declared power factor.

I hope you mean that the minor shooter at 120 ended up shooting the match for no score, and the that the shooter at 163 ended up shooting with minor scoring.

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As ammo nazi at a major State match - weather in the mid 90's, very high humidity, the PF's were lower than normal, 2 of the 4 people DQ'd 1 shooting minor and the other shooting major.

The minor shooter was 120 (needed 125) out of the match gun and their own gun (9mm 1911) and the other shooter was 163 out of their gun (S&W revolver in 38 Super). Both shooters play close to minimun PF and the heavy, dense air puked them.

DQ'd? I don't think you are allowed to disqualify somebody for not making their declared power factor.

I hope you mean that the minor shooter at 120 ended up shooting the match for no score, and the that the shooter at 163 ended up shooting with minor scoring.

IDPA = a DQ.

USPSA/IPSC = for fun.

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As ammo nazi at a major State match - weather in the mid 90's, very high humidity, the PF's were lower than normal, 2 of the 4 people DQ'd 1 shooting minor and the other shooting major.

The minor shooter was 120 (needed 125) out of the match gun and their own gun (9mm 1911) and the other shooter was 163 out of their gun (S&W revolver in 38 Super). Both shooters play close to minimun PF and the heavy, dense air puked them.

DQ'd? I don't think you are allowed to disqualify somebody for not making their declared power factor.

I hope you mean that the minor shooter at 120 ended up shooting the match for no score, and the that the shooter at 163 ended up shooting with minor scoring.

IDPA = a DQ.

USPSA/IPSC = for fun.

Thanks! I didn't know failing to make Power Floor in IDPA was a DQ. I learned something new today.

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