Q about the importance of the chronograph

[Cy Soto]

Every time someones asks about a new load, many folks here will immediately tell them that they need a chrono in order to properly develop their load.

When I begin working on a new load I start by checking with a reloading manual. I typically start at the bottom of the recommended load and work from there. I am more concerned with finding one or more loads that are very accurate and; only after I have found what these are, do I chrono to make sure that they make the required PF.

If I were to put a load together for the simple sake of making PF but that wouldn't group worth anything, I would feel like I was wasting my time and components. So why do some folks recommend starting with the use of a chrono? Should I be able to predict accuracy based on the SD and ES?

[ParaGunner]

If it's not making the required power factor you can't even use it.

[MarkCO]

Got to make PF first. SD and ES will have a "little" to do with accuracy at USPSA target distances. When you start to get out to the 80 yard standards, then it will have more of an effect. If your SD is <20, you won't be able to tell much about the specific accuracy with a typical handgun. Bullet to bore diameter, sufficient pressure to obturate (if your bullet even will), crimp, etc. will have a larger impact on on accuracy than average velocity changes. Some of the tough jackets on 9mm bullets need a lot of pressure to obturate if the bullet is a tad undersized or the bore is a tad over. This creates some problems for 9mm minor loads w.r.t. accuracy. Also, the chrono tells you the "theortical" accuracy potential of a particualr load and also helps you to see where the load is the most efficient. Efficiency, for a given bullet weight, in most cases means less felt recoil than maybe a load just below.

[Cy Soto]

Also, the chrono tells you the "theortical" accuracy potential of a particualr load and also helps you to see where the load is the most efficient. Efficiency, for a given bullet weight, in most cases means less felt recoil than maybe a load just below.

That right there exactly the information I was hoping to find! Would you please elaborate?

[dansy]

If it's not making the required power factor you can't even use it.

+1 the only time I care more about accuracy is for steel load...were you don't care about the PF just the accuracy and the feel & function of the gun

[Jman]

Cy, a simple analogy would be this. A chronograph is to ammo what a dynamometer is to a engine. Without one we are only

guessing it's power. As mentioned bores, OAL and crimp among other variables effect the power of our reloads right along

with charge weight. It simply takes the guess work out.

Don't let the USPSA be first to run your ammo over one.

Jim

[MarkCO]

Sure...

Here is a data set for .40 S&W using a 181 plated slug all with the same OAL:

Ave V Hi V Low V ES PF

987 998 969 29 179

984 1031 945 86 178

966 993 934 59 175

954 969 940 29 173

942 963 891 72 171

928 937 911 26 168

915 958 899 59 166

911 961 890 71 165

So the load with the theortical best accuracy was the 928 @ 168 PF. I then took that powder charge and .1 grain less and changed the OAL by 0.003" up and down and changed the crimp an 1/8th turn left and right. When I got 2 or 3 I liked based on the chrono, I shot for group off of bags AND freestyle. I picked one of the loads based on the data which ended up being .1 grain less, seated 0.003" deeper and a PF of 166.

[Cy Soto]

Oh, no doubt; I totally agree that we have to be able to meet PF with our load before we use it. My question is more along the lines of: is there more use to the data provided by the chrono than just the PF?

We all mention our SD and ES when we write out our chrono results so there has to be something that this data is providing us that we can use in our load development process. Kinda like what MarkCO mentioned about "theoretical" accuracy. Though I collect this data, I am not using it to interpret my results because I don't know how to.

[Cy Soto]

Sure...

Here is a data set for .40 S&W using a 181 plated slug all with the same OAL:

Ave V Hi V Low V ES PF

987 998 969 29 179

984 1031 945 86 178

966 993 934 59 175

954 969 940 29 173

942 963 891 72 171

928 937 911 26 168

915 958 899 59 166

911 961 890 71 165

So the load with the theortical best accuracy was the 928 @ 168 PF. I then took that powder charge and .1 grain less and changed the OAL by 0.003" up and down and changed the crimp an 1/8th turn left and right. When I got 2 or 3 I liked based on the chrono, I shot for group off of bags AND freestyle. I picked one of the loads based on the data which ended up being .1 grain less, seated 0.003" deeper and a PF of 166.

I made my previous post prior to seeing this one. That makes sense now. Thank you for explaining it!

[TerryO]

Sure...

Here is a data set for .40 S&W using a 181 plated slug all with the same OAL:

Ave V Hi V Low V ES PF

987 998 969 29 179

984 1031 945 86 178

966 993 934 59 175

954 969 940 29 173

942 963 891 72 171

928 937 911 26 168

915 958 899 59 166

911 961 890 71 165

So the load with the theortical best accuracy was the 928 @ 168 PF. I then took that powder charge and .1 grain less and changed the OAL by 0.003" up and down and changed the crimp an 1/8th turn left and right. When I got 2 or 3 I liked based on the chrono, I shot for group off of bags AND freestyle. I picked one of the loads based on the data which ended up being .1 grain less, seated 0.003" deeper and a PF of 166.

PF of 166? IMHO I think that's to close for comfort if you're going to shoot major matches where you will be chrono'd. Differences in chrono's, elevation, temperatures etc. will bite you if you're that close. For major PF my minimum comfort level is 170 and I prefer 172. YMMV

[Seth]

The other thing is chrono mapping.

Extrapolating the data to understand the pressure spikes.

Great info:

http://www.brianenos.com/forums/index.php?showtopic=88258&st=0&p=1015247&hl=mapping&fromsearch=1entry1015247

and

from HSMITH:

"When the velocity increase per charge weight increase flattens out you are approaching the point where strange things will begin to happen like the ES opening up quickly. If you keep going you will see the velocity flatten out completely and possibly drop, at that point you are knocking on the door for pressure spikes that could be serious. Keep going from there and you will see wild velocity swings, pressure signs Ray Charles could find, etc. "

[MarkCO]

PF of 166? IMHO I think that's to close for comfort if you're going to shoot major matches where you will be chrono'd. Differences in chrono's, elevation, temperatures etc. will bite you if you're that close. For major PF my minimum comfort level is 170 and I prefer 172. YMMV

Okay...Please add this warning to my 166 PF load: "Warning, shooter is a trained anal-retentive engineer with lots of graphs and charts and tests and data. Do not try this at home or the range."

I've been chrono'd numerous times with this load, never went minor. I've been 165 a few times.

[dansy]

I'm just don't see what is the gain to chrono that close to the PF....I can shoot my gun's as fast with 170 that I can at 165? unless you go to like 135PF there is IMHO no real difference and a timer would tell you that....in other way to put in all in the mind....lower PF I'm faster but in reality all smoke and mirror....

And I do own a CED M2 and used it all the time to recheck my load.....

Edited November 11, 2010 by dansy

[MarkCO]

I'm just don't see what is the gain to chrono that close to the PF....I can shoot my gun's as fast with 170 that I can at 165? unless you go to like 135PF there is IMHO no real difference and a timer would tell you that....in other way to put in all in the mind....lower PF I'm faster but in reality all smoke and mirror....

And I do own a CED M2 and used it all the time to recheck my load.....

Hey, I am slow, fat and getting older. So I'll have to impress with getting as close to the edge as possible. Probably comes from my NHRA and NASCAR racing roots.

[Cy Soto]

Hey, I am slow, fat and getting older. So I'll have to impress with getting as close to the edge as possible.

That's funny!!

[G-ManBart]

I've been chrono'd numerous times with this load, never went minor. I've been 165 a few times.

Shoot enough big matches, and you will....

[MarkCO]

I've been chrono'd numerous times with this load, never went minor. I've been 165 a few times.

Shoot enough big matches, and you will....

I'll take that bet.

[Jman]

When do you know someone is an engineer?

They'll mention it on the odd numbered sentences.

[TerryO]

I've been chrono'd numerous times with this load, never went minor. I've been 165 a few times.

Shoot enough big matches, and you will....

I'll take that bet.

OK, that's easy money. You're from Denver. Shoot 166 there and then go to Houston. The elevation difference alone will get you not to mention temperature, humidity and the biggest one is variances in chrono's. Ever notice when two chrono's are used at a match the difference in them. It's easy to have a 2% variance from one chrono to another. Shoot 166 and have a chrono that reads just 1% lower than yours at home and you're now shooting minor. If you are shooting Production, you're now shooting for no score. I can not tell the difference between 166 and 172 pf, but I can tell the difference between minor scoring and major.

Edited November 21, 2010 by tohlmann

[dansy]

He probably doesn't travel much ....I really don't care for him if he doesn't....

[G-ManBart]

Sure...

Here is a data set for .40 S&W using a 181 plated slug all with the same OAL:

Ave V Hi V Low V ES PF

987 998 969 29 179

984 1031 945 86 178

966 993 934 59 175

954 969 940 29 173

942 963 891 72 171

928 937 911 26 168

915 958 899 59 166

911 961 890 71 165

So the load with the theortical best accuracy was the 928 @ 168 PF. I then took that powder charge and .1 grain less and changed the OAL by 0.003" up and down and changed the crimp an 1/8th turn left and right. When I got 2 or 3 I liked based on the chrono, I shot for group off of bags AND freestyle. I picked one of the loads based on the data which ended up being .1 grain less, seated 0.003" deeper and a PF of 166.

I made my previous post prior to seeing this one. That makes sense now. Thank you for explaining it!

Keep in mind that the areas I highlighted both have quite a bit of variation in them from round to round. In most cases, you'll get at least that much variation for both, so if you set it at 1.125" and 4.0gr (for example), you're going to see plenty that are 1.222" and 1.228" with a range of 3.9gr to 4.1gr (or more), so I'm not buying that you'll see any increase in accuracy with that little bit of change, and if you do, it's going to be slight. In fact, I'd find any gun (barrel) suspect that showed a significant difference in accuracy with that little change. R,

[BlackBuzzard]

Maybe I'm inexperienced, but I have never had any reasonable load fail to group well enough for almost any uspsa match distances.

Perhaps the cmore needed a slight tweak going from 115 to 124 bullets, but that's all.

If the load is on PF, the group size is always more that good enough in my experience.

BB

[Cy Soto]

Maybe I'm inexperienced, but I have never had any reasonable load fail to group well enough for almost any uspsa match distances.

Perhaps the cmore needed a slight tweak going from 115 to 124 bullets, but that's all.

If the load is on PF, the group size is always more that good enough in my experience.

BB

I think that the slower powders used by Open shooters added to the faster speed at which the bullet leaves the barrel, makes for an inherently more accurate load than those used by, for example, Production shooters. When I load for Production I am using the fastest powder I can (these days is Solo 1000 though in the past I have used Clays & Titegroup).

The burn rate of these powders give me a light recoil impulse when shot around 130PF but my load doesn't seem to be as accurate as what I have seen Open shooters achieving at similar distances.

[G-ManBart]

Maybe I'm inexperienced, but I have never had any reasonable load fail to group well enough for almost any uspsa match distances.

Perhaps the cmore needed a slight tweak going from 115 to 124 bullets, but that's all.

If the load is on PF, the group size is always more that good enough in my experience.

BB

I think that the slower powders used by Open shooters added to the faster speed at which the bullet leaves the barrel, makes for an inherently more accurate load than those used by, for example, Production shooters. When I load for Production I am using the fastest powder I can (these days is Solo 1000 though in the past I have used Clays & Titegroup).

The burn rate of these powders give me a light recoil impulse when shot around 130PF but my load doesn't seem to be as accurate as what I have seen Open shooters achieving at similar distances.

The slower powders and faster bullet being more accurate theory doesn't work at all. Look at what bullseye shooters use...very fast powders (like Clays) and slow velocities.

I chrono'd a batch of my .38SC ammo recently, then shot groups with it (after setting up my 1050) just to make sure all was well. The ES was 45fps, the SD was 12fps, and the load shot multiple 1" 10-shot groups at 25yds off a bag rest. Those ES and SD numbers aren't that great, but the accuracy was better than I could hold it...a smaller dot, and better rest might have helped, but when you can keep every round inside a standard target paster, who cares?

Most duty style (M&P, Glock, XD, etc) guns are actually harder to shoot good groups with. It took me quite a while to figure out that my M&P needed a vise-like grip off the bench to group well, and the triggers aren't likely to be quite as good as a 1911/2011, then throw in Open shooters with dots, and it all pretty much adds up to Production guns simply being harder to shoot accurately for precision groups. R,