Number of rounds through a Chronograph?

[cfullgraf]

For a Chrony, wood dowels make good replacements for the diffuser rods, 1/8" diameter if I remember correctly.

 

[Rule3]

Replacing the metal rods is an excellent idea.

If you shoot a metal rod it will probably tear up the whole unit. Shooting a wood dowel will just snap it off and not mess up the unit.

 

[GaryL]

Having different shooters shoot the same round? That has nothing to due with statistical validity of velocity?
The human factor does not change the load. Accuracy yes. A true test would lock the firearm in a ransom rest of test chamber and as mentioned extreme temp changes if you live in an area that has them.

Actually, you can get a different velocity with different shooters. It all depends on how much of the initial recoil energy they absorb. I proved it to myself by changing my grip when I was recording some pistol rounds and noticed a definite change in velocities recorded. Maybe not large, but it was repeatable.

 

[Rule3]

Actually, you can get a different velocity with different shooters. It all depends on how much of the initial recoil energy they absorb. I proved it to myself by changing my grip when I was recording some pistol rounds and noticed a definite change in velocities recorded. Maybe not large, but it was repeatable.

Well OK if you say so.

So then you have Multiple Personality's ?

To clarify, you certainly can change the velocity reading by changing the position of the powder in the case. To get an accurate reading point the gun straight up and slowly lower it before pulling the trigger, The powder is then all clustered at the bottom near the primer.

 

[1SOW]

If I'm loading pistol up in .2 gr increments, I may only shoot 4-5 to note the rough speeds. When those in the range I'm looking for, get loaded --maybe 3 loads, I shoot 10to get accurate readings and pick my load for final testing on targets and freehand shots.

If I like how they shot, I'll load up 100 and chrono 10 more and play with the rest at varying ranges and targets.

Slow, but works for me.
When I first started reloading, I loaded up 300 for comp. before I had a chrono. When I got the chrono, I became a Master class hammer blaster, breaking those down those 300 to add a skosh more powder. :-(

 

[Walkalong]

To get an accurate reading point the gun straight up and slowly lower it before pulling the trigger, The powder is then all clustered at the bottom near the primer.

I do this to get powder back readings, and just the opposite to get powder forward readings, then sometimes I shake the gun while level to get powder level readings. There is a definite pattern that most powders follow here.

While working up loads, a small sample is fine. You can always run a larger string if you think you have something. I test at different temperatures as well.

It is easy to get caught up in numbers though. They are not the end all. Results on target are.

 

[1SOW]

To clarify, you certainly can change the velocity reading by changing the position of the powder in the case. To get an accurate reading point the gun straight up and slowly lower it before pulling the trigger, The powder is then all clustered at the bottom near the primer.

Only on the first shot, and only significant with some powders and some loads. Once a pistol is held level shooting over a chrono. the recoil and feed repositions the powder approx. the same every shot. A 3/4 case-full of powder isn't positional unless you shoot straight down.

 

[tcj]

I shoot 5 minimum when working up loads. When I'm fine tuning I'll go to 10 rounds.

 

[Walkalong]

A 3/4 case-full of powder isn't positional unless you shoot straight down.

I would have thought so myself, until I tested several like that. For pistols, bringing the gun up from barrel down to level and firing still affects velocity, even with many 75%, and more, load density loads. Very few powders are unaffected by position when less than 100% load density. When I first started testing this, I was really surprised with the results. As I posted, I get different results with powder back, powder forward, and powder level shooting. And the results are generally consistent from load to load. Naturally some are better and some are worse, but PB will give the highest velocity, PF will give the slowest, and PL will be in between the other two. I have only had one powder give more velocity PF than PB, and it has been discontinued. Some are horrible PB, and some don't lose much, but most lose enough to get your attention, and matter when shooting with the barrel in a downward position and shooting longer ranges.

PF can easily lose 100 to 400 (Or more) FPS from PB. The biggest losers are generally low pressure loads with lots of extra case. I had one load that ran 900+ FPS PB and would stick bullets PF.

 

[1SOW]

PF can easily lose 100 to 400 (Or more) FPS from PB. The biggest losers are generally low pressure loads with lots of extra case. I had one load that ran 900+ FPS PB and would stick bullets PF.

Interesting. So to game/maximize comp. chrono checks, tilt the bbl up before the shot?

Question. When the recoil spring on a semi-auto slams the cartridge home, wouldn't the sudden stop when it seats throw the powder forward? Assume the pistol is level, aimed at a target.
When drawn out of a holster, the powder is also forward. ????

 

[LiveLife]

When the recoil spring on a semi-auto slams the cartridge home, wouldn't the sudden stop when it seats throw the powder forward? Assume the pistol is level, aimed at a target.

Essentially for semi-autos, we are always testing "powder forward" as chambering force will slam the powder charge towards the bullet base.

Unless you are using compressed loads, I don't think we can change that but I don't mind as that's how my typical rounds will be shot anyways.

 

[TimSr]

For a Chrony, wood dowels make good replacements for the diffuser rods, 1/8" diameter if I remember correctly.

I'm using plastic zip ties with some red tape at the right height.

 

[Bart B.]

If statistical significance is important, here's the credibility different round counts have for any measure; pressure, velocity, accuracy, .....

3 shot test data can vary as much as 60% less to 250% more of the first one if you shoot 20 of them. Don't count on the first one to have either the biggest or smallest number; they're all random.

For 5 shot tests will have 33% less to 150% more spread than the first one if 20 tests are made.

10 shot test, 20% less to 25% more.

20 shot test, 11% less to 12% more.

30 shot test, 8% less to 9% more.

50 shot test, 5% less to 6% more.

How much confidence do you want that some round's numbers are meaningful?

5-shot benchrest records at 100 yards are under .010" Their average for several of those groups for aggregate records is about .200" which means the largest one is around .300".

Every time you measure ammo, you're rolling several pairs of dice representing the spread of every thing in the system; ammo, rifle and shooter.. All rolls of each pair doesn't read dead center (all is perfect, no error) or 7 every time; they have a spread from 2 to 12.

 

[CZ9shooter]

I shoot10 round groups for accuracy and velocity testing.

Ditto.

 

[Reloadron]

Typically when working up a load I will load groups of ten rounds each. I typically shoot those in five round groups, sometimes a ten shot group.

 

[dartor]

Quote:

"http://www.midwayusa.com/product/531...f1-chronograph"

I own the beta model of this chronograph, had it over 20 years. It has the display attached via a phone 20' phone cable so I can view the stats from the shooting bench. I also have the optional printer for a hard copy of the stats which I staple to the target for the load I am shooting. Everything goes into a 3 ring binder and the data is also recorded in an Exel spreadsheet.

I load 8 rounds of each weight for powder and shoot 1 string of 4 on two different days for an average.

 

[atblis]

From what I've been able to gather, the mean is actually pretty easy to predict accurately not requiring so many shots. Where it gets tricky is predicting the SD, or more specifically comparing the SD between different loads. That requires many more shots than most people are willing to do.

Something like this maybe?
http://www.stat.wmich.edu/s216/book/node80.html



A quick google search indicates that 20 fps for the SD is a reasonable guess. If you can tolerate an estimate that 95% of the time will be with in 20 fps of the actual mean, than 4 shots should do that. If you want estimates that are better than ± 20 fps, you need more shots.

 

[spitballer]

Published load data appears to be based on the first shot out of a cold barrel, therefore I pay particular attention to my first shot of the day and adjustments are made based on that first shot. I also note the rate of climb to the first peak velocity. This for a bolt rifle fired at a rate of one round per minute.