Acceptable spread while chronoing?

[buenhec]

I tried several loads today trying to find a light load for steel. I am using 200 grain 45ACP lead with VV N320 powder.

At 4.5 the load felt great but the FPS ranged from 720FPS to 800FPS with an average of 746.
At 4.6 grains it was about the same average.
At 4.75 it ranged from 780 to 820 with an average of 801 FPS.

I liked the feel of 4.5 but 4.75 was more consistant. What is an acceptable spread? I mainly shoot steel matches. At some matches they have small diamond plates which are pretty hard to hit. The smaller the spread the better the accuracy?

 

[Halo]

Look at your standard deviation for a better indicator of how consistent your rounds are. You might have only one oddball flyer that can give you a wide extreme spread, but that doesn't really give you an accurate picture of the rest of the ammo from that test batch.

Lower SD means greater consistency, basically it describes how tightly the individual measurements are clustered around the mean (avg). If I correctly remember back to statistics, in a normal distribution (bell curve) one standard deviation encompasses 68% of the test group.

 

[ReloaderFred]

A fellow High Roader and I just had this conversation. My belief is that any safe load that shoots consistantly well for you is a good one, in spite of what the chronograph readings are. Many reloaders are happy reloaders, until the day they buy their first chronograph and find that the load they've been shooting one hole groups with actually has a large spread in velocity. Then they start messing with their pet load and get everything screwed up.

I've got a PACT Professional Chronograph, which is my second chronograph, and I take it out every couple of years if I get curious about a load. I'll put a few rounds across it and get the average, and then it goes back in my shop for another couple of years. The last time I had it out was to see what some 9x25 Dillon loads were doing, velocity wise. I knew what they were doing on paper, but just wanted to see how fast they were actually going.

Test your loads on paper, and if they shoot the way you want them to, group wise and recoil wise, then call it good.

Hope this helps.

Fred

 

[The Bushmaster]

What ReloaderFred said. The chronograph is a nice tool when you are working up a load. BUT... The down range information on the paper is the best indicator of shooter, gun and bullet performance...

 

[DEDON45]

I agree with Halo, the SD number is probably more important... but ES can be an indicator of problems too... just as an example, my mass, progressive press reloaded .45ACP LRN rounds, all kinds of cases, will run around 35fps ES... that's close enough for me. My .300Wby Rifle, around 6fps if I trickle in the charge (and it's a particular charge--more or less seems to have a negative effect, I suspect that I found the sweet spot where all the powder is burned consistently every shot), and I'm using the same lot of brass, all fired the same number of times. I wouldn't dwell on the numbers so much... I always beat the factory, even with mixed cases!

 

[snuffy]

I have the same chrono that Fred has. BUT, mine goes with me every time I head for the range. If I'm just shooting for fun, no load work-ups, I don't set it up. But if I'm testing new loads, whether it's handgun, rifle, shotgun, or even muzzle loaders, it gets set up.

Not using it while working up a new load, is like flying blind. I want to know everything I can know about the load. How consistent is it? How fast is it in reality,(not what the book says it SHOULD be).

Extreme spread is a good indication about how consistent the load is. It also indicates whether the powder's burn rate is right for that load. Huge ES is an indication that the powders burn rate is wrong for that particular load combo. Or that you have ignition problems. Usually published loads in manuals use powders with suitable burn rates for that load.

A chrono can be an indicator that you are pushing pressures past the limits. When the velocity gain for each incremental load increase slows down you're at the maximum for that powder, bullet, rifle.

I have a load for 40 S&W that has an ES of 5! It also shoots nice tight groups. Not that it matters, it's my IDPA/IPSC load. A load like that for any gun is the holy grail. Consistent AND accurate.

For rifle, a low ES is an assurance of long range accuracy. Sure, some tight 100 yd. groups turn out to have high ES. Now shoot that tight 100 yd. load at say, 600 yds. You will see vertical stringing! It IS possible to have both low ES AND tight groups. It has to do with barrel harmonics, the bullet exiting at the same place in the vibration cycle.

 

[.38 Special]

Depends on what I am using the particular load for. For an accurate rifle, I prefer to keep it under 25 FPS. For a handgun, 50 FPS. But as others have pointed out, if you like what your targets are telling you, ES can go hang. Especially when speed shooting big targets at close range with a handgun, I don't think I would worry about it at all.

Now, I'd be interested to hear what scale you are using that allows you to measure hundredths of a grain, and -- more importantly -- what powder measure allows you to hold that level of accuracy!

 

[Slamfire]

Handgun cartridges generally give much higher SD's and ES's than rifle cartridges. When I have had extreme spreads in the range of 200 or 300 fps, then the powder/cartridge combination was not appropriate.


The attached data is from loads that I have found to be quite acceptable in my M1911. I consider a pistol cartridge SD under 20 to be quite good. I have found a couple of rifle loads where the ES is under 20.

But what really counts, is what does it do on target.....


230 gr LRN 4.5 grs Bullseye Mixed Brass WLP
OAL 1.250"taper crimp .469" 25-Feb-07 T = 68 °F
V. Accurate
Ave Vel = 792
Std Dev = 14.38
ES 74.67
High 829.3
Low 754.7
N = 27


230 FMJ GI 5.5 grs W231 Mixed Military WLP
9-Oct-05
1.265" OAL T = 64 °F

Ave Vel = 792.4
Std Dev = 15.87
ES 70.15
High 825.5
Low 754.9
N = 24

 

[Walkalong]

I have a .38 Spl load that will shoot bugholes & is super clean, but gives Extreme Spreads from 75 to 150+ depending on the gun. These are terrible to me, but like Fred said, I shot good groups with it for years, blissfully ignorant.

Now it bugs me.

I can no longer go back to blissfully ignorant, but maybe I'll get over the numbers and take it for what it is, a good load.

All that aside, much smaller numbers are attainable in most pistol calibers while still shooting great.