Chrono: what’s an acceptable extreme spread?

[KevinA.]

[bruce381]

with mixed brass I get 20 or so range with 45 acp 9mm I do not know.

[slayer61]

My load development involves finding the load with the least deviation/extreme spread. I tinker from there.

Recently while trying Power Pistol & new (to me) 200 grain Hornady XTPs and brand new Starline brass, I found that MY gun (10mm Kimber) likes it at 7.8 grains. (average of 1137) I had an extreme spread of only 8 FPS over the 5 shot string. Yup. 8 FPS! That load is a keeper.

[SoCal326]

What sort of distances are you trying to shoot?

ES matters a lot when shooting a rifle at distances beyond 600 yards or so but I can't imagin it matters at all with pistols.

I'm not a handgun guy so someone correct me if I'm wrong but are you having percision issues with your loads?

[KevinA.]

What sort of distances are you trying to shoot?

I mainly keep it within 10-15 yards but will sometimes take it out to 50. Trying to build a load that mimics my carry stuff for 9mm. Not sure exactly what I want to do with 45, just chronoing different charges right now to see where I’m at.

Just trying to nail down consistency.

[JackEllis]

ES matters a lot when shooting a rifle at distances beyond 600 yards or so but I can't imagin it matters at all with pistols.

I load only for rifles so perhaps pistol shooters have other thoughts.

Consistency is important, but after running some experiments with a ballistic calculator, I don't get too fussed about extreme spreads so long as they're under about 100 FPS (3% of MV). There are too many variables at work, from the precise volume of the case to the precise seating depth to precise bullet weight to the precise powder charge. I also don't shoot past about 300 yards so relatively small changes in MV translate into relatively small changes in POI.

If you want to get really fussy, you need to sort your cases by weight, use match grade bullets, and use a very precise scale. My guess is, for pistol rounds all of that is a huge waste of time based on what little I think I know about pistol accuracy. I know that for hunting and any matches I shoot, it's not worth the effort, especially if there's even just a breath of wind.

[sigstroker]

I've never even checked it with my pistol loads.

[dmy]

When I was using older brass with the same headstamp, but different lot numbers, I was getting ES from 25 to125 fps with .45 and .38. My brass had been reloaded dozens of times. However, for reasons I can't explain, I had better groups with higher spreads.
Then I bought a few hundred new Starline cases. My ES dropped significantly and my groups tightened up also. I get the lowest ES with Tightgroup running very warm, not max, loads. My best ES was 8 fps with .45s and sub 1 inch six to seven shot groups at 10 yds. My opinion is that consistent case length leads to consistent crimps which leads to lower ES and smaller groups, but my opinions are not necessarily scientific.

[Dooder]

Mixed brass will offer sporadic ballistics as well as precision. If you want to chase consistency then use SD as by nature its better data than ES. An anomaly can give you a wide ES but SD represents overall performace. For example my 40 major load from my mixed brass buckets has an SD that hovers around 15. Factory ammo is typically 20ish. My last batch of 40 major with matching headstamps was 8.6 with an ES of 32, n=35. For ammo that matters I aim for single digit SD. The larger the sample the better representation as well. But all things - the components, the reloading gear, your technique all contribute to the numbers that your chrono reports.



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[KevinA.]

How many shots would you say is sufficient for a good sample size? So far I’ve been loading batches of 10 rounds each at varying charges. Is 10 enough or would more be better?

[Dooder]

30 is a general minimum in the world of stats. Some tests call for a larger sample. I was reading some stuff on a precision rifle forum and it seemed like 30-50 was common. I like 30 or so. Thats to get solid data to validate a good load. And in that case the more the better. But when developing if SD is too high in 10rnds then shooting more won't help. Just ditch that load and tweak the load and try again.

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[pacrat]

OP said:

Trying to build a load that mimics my carry stuff for 9mm.

Just for S&G, next time out chrono your SD carry ammo.

Generally speaking, for DEFENSE LOAD you choose max velocity/energy for quickest stopping capability. And ES be damned.

Back in the good ole days when dinos still roamed. [1970] I chrono'd some 125 gr SuperVel HP 357 mag loads. Out of a 4" S&W. Got a 10 round spread of IIRC about 100 fps. I haven't bothered checking for ES in pistols since. I figure if I happen to miss, the muzzle blast and fireball will take em down with one shot.

EXCEPTION..............for XP-100 and Contender.

[kcheung2]

Just recently got a competition electronics pro chrono dlx and took it out for the first time yesterday to test out some loads. I ran 9mm and .45 through it without a single missed shot. I’m just wondering what an acceptable velocity spread would be. I’ve had spreads range from 40-70fps, sometimes more, which seems quite excessive to me. I load with a Dillon 550C and use bullseye for 45 and titegroup for 9mm. My 9mm stuff has shown a smaller spread. I’m using mixed brass, which I’ve heard can contribute to this. Other than that, what could I be doing wrong? How can I get more consistent loads with the current press I’ve got?

There can be no consistency if the brass has no consistency.

Also, yeah it doesn't matter for pistol at 15 yds anyway.

[NeilMo]

The best way to tighten up ES is to use a "more correct" sized bullet. Using factory .355" & .400" JHP SD bullets in .40 and 9mm, along with new Starline brass I'm lucky to see an ES less than 40 or so, but when I cast and size for a specific barrel size, I have no problem dropping the ES to less than 15-20. However, like others have already said, I find it really makes no accuracy difference with pistols under 25 yards.

[Whiterabbit]

Pistol? Mine are ES 50+, including my 100 yard pistols.

My suggestion is to shoot for groups and leave the chrono at home.

Save it for rifle