How do you use a chronograph to work up a load?

[LeviSS]

I had another thread that spawned a couple more questions.

When developing a load, unpublished or otherwise, how do you use a chronograph to stay safe? I know about starting low and working up.

I understand you are looking for a certain velocity range that is considered safe. I've read where people are talking about standard deviation, and the lower the SD the better, but when does it become unsafe and what does it mean when there is a big SD?

I guess I don't understand how external velocity readings are indicative of internal pressure. It seems faster powders would have faster pressure spikes and slower powders would have less spike, but could give similar velocities.

If you could fill me in on the theory behind this, give examples of how you use a chronograph and tell me what you're looking for, I'd appreciate it.

Ive always stayed within published load data using the exact bullet and powder listed and never tried to push the envelope. Now im starting to see the need for a chronograph. Please don't beat me up too bad...just trying to learn the finer points of reloading.

Edited September 12, 2015 by LeviSS

[captain037]

Wow, that's a lot to answer. Firstly, a cronograph will not keep you safe. It will give you load velocity and sd. SD is the deviation in velocity between each round of the same load. In other words, if you shoot three rounds of 9mm 125 grn jhp with 8 grains of hs6 and they crono 1500, 1505 and 1510 sd is the difference in the three. The smaller the sd the more consistant the load and the more accurate it should be.

One way to avoid dangerous loads is to closely watch the condition of your fired brass. Look for excessive primer flattening and split or overly stretched brass.

Start with 10% below published loads and work up slowly. Use the crono to monitor velocity and sd. Check brass condition. Remember different powders react differently to heat or cold. Some spike pressure in the heat and some in the cold.

When in doubt, don't load it. It's not velocity that indicates internal pressure. Companies use strain guages to develop safe loads and data for publication.

. If you're not a very experienced reloaded, go slow pushing the envelope. If you don't have a good reason like shooting major loads for uspsa open, published loads are fine.

I hope this helps some and guys, correct anything I got wrong.

[rancher5]

Use a chrono to get your desired power factor, velocity×wieght, and check accuracy as you go up or down, Find lots of load data with coated bullets which i meet power factor 1/2 grain below minimum, where I load to book loads I'm shooting upto 40 PF+- over needed PF, important more so in Competition where lighter recoil faster follow ups.

[rishii]

i always start low, and work my loads up in 2 tenths grains increments until I hit the velocity I want

To check pressure, I mark my brass differently for every load, my starting load I'll mark the brass with 1 black line, 2 tenths grain up, 2 black line, etc. that way if my brass show pressure signs I don't have to guess which load it was

And lastly get a tablet and record every load you try, I list caliber, bullet weight and type, which powder and charge, brass and primers

High, low, and average velocities, and my power factor based off the average velocity

[wyoshooter]

My only helpful hint is this: don't shoot your chronograph!

[Hi-Power Jack]

If a friend of yours suggest you use 7.4 grains of WAC under a 124 gr MG JHP at 1.16" OAL,

and you load that up and fire it from your gun - what velocity have you attained?

Have you adequately made Major? (or are you under PF 165)?

Are you into excessive velocity territory? (PF 185+)?

From reading all the postings on reloading your caliber, you know that a certain charge

of powder (a range) under a certain bullet, at a cetain OAL will yield the PF you're

looking for.

BUT, each gun is different - Your gun may need only 6.6 grains to attain a "safe" major

PF, and someone else's gun may need 7.3 gr of the same powder.

The chrono tells you when YOU have "safely" attained your velocity goal, without

going over the top, or fail to meet Major PF.

One more piece of info in searching for a suitable source of ammo.

[IDescribe]

First, don't try to use brass and primers to read for pressure warnings with pistol rounds. It's more involved in rifle than what people will lead you to believe, and in pistol, it's slightly less reliable than reading chicken bones. If you see pressure signs with pistol rounds, you're not starting to go over pressure -- you are already well over-pressure, and you can actually go straight from brass and primers looking fine at one charge weight, and kaboom at the next increment. Don't get me wrong -- you should definitely pay attention, and if you see pressure signs with pistol, you should obviously stop, but you shouldn't rely on it to tell you when you're going to high or to prevent a catastrophic failure. It's a false sense of security.

As to using your chrono, it's helpful in a number of ways. When you load test strings to shoot over a chrono, I'd recommend 10 round strings. In terms of sample size, 10 round strings produce significantly more reliable/repeatable data than 5 round strings, but 20 round strings aren't significantly more reliable than 10. 10 seems to be the sweet spot.

First, make sure you are using the most appropriate published data for reference:

• Powders obviously must match.
• If you don't have data for your specific bullet, match the bullet weight first, and surface material second. By surface material, I mean lead/coated, plated, jacketed. There's a reason lead bullets typically use less powder in published data, and that's because the bullets are typically larger in diameter than jacketed, and they are softer and obturate better, which results in higher pressure for a given powder and charge weight. If you are loading a 124gr coated lead RN, and you have data for a 124gr FMJ and data for a 124/125gr LRN, go with the LRN. Match lead to lead. Don't go lead to jacketed unless that's your only option, and understand that at the same weight, lead is going to take a little less powder, 5-10% maybe, than jacketed.
• Third, try to estimate how deeply the bullet in the data is seated vs your bullet. As a general rule hollow points and flat points are going to seat deeper into the case than round nose, and deeper seating (I'm talking about how far the bullet base extends into the case, different from OAL) increases pressure, so if the closest data is round nose, and you are seating hollowpoint, the hollowpoint will take a little less powder because the hollowpoint's base is seated deeper into the case. The smaller the initial combustion chamber, the higher the pressure, so try to account for seating depth IF you can, and trust starting load if you can't. Starting load usually covers you, but it doesn't hurt to be aware of the issue and drop the starting load if it's sketchy.

#1 Now that you've gotten as close as you can with published data, you can use the chrono to monitor progress. If your starting load produces a velocity lower than the starting load in the published data, you can assume you're in a perfectly safe place and adjust your expectations accordingly. If your starting load velocity is midway up the load window from the publish data, you are higher on pressure than the published data, and you need to reduce the max load to compensate. If your starting load velocity is at the top of the published load window. You're done. It's about estimating from the published data you're using where you should be with velocity at particular charge weights, then using the chrono to check it.

#2 Standard deviations. This is not super reliable, but might warn you of problems. You also have to know what to expect with your powder. Some powders simply produce better standard devs than others. Okay, so you've got five strings with incremental charge weights of .1gr, running from the bottom to top of the load window. If your standard deviations are 6, 8, 6, 7, 9 for the five strings, that's not telling you anything bad. Or 6, 16, 7, 8, 12 isn't warning you either. It's less consistent than I like, but it's not warning me. If it's 6, 7, 6, 14, 22, THAT might be a warning me as it looks like something is going whacky as the charge weight is getting toward the top of the load window, suggesting pressure might be causing problems.

#3 This is probably the most useful one. Every string you shoot is going to have an incremental charge weight increase from the last. And you should have a corresponding velocity increase tied to the charge weight increase. The velocity bumps should be pretty consistent, and the velocity increases should increase toward the middle of the charge weight window, then start to decrease as you get to the top of the window. This is normal. If the increase you get for the next charge weight falls off too much, though, that's a sign of rapidly increasing pressure. You can't just keep increasing powder and getting more velocity. We're dealing with the law of diminishing returns. As pressures get too high, metals start to flex, and weird things start to happen. Imagine you have chosen to create a six-string load ladder from 4.0 - 4.5 grains, and you get this

4.0 -- 930 feet/sec

4.1 -- 950 feet/sec -- +20 feet/sec

4.2 -- 980 feet/sec -- + 30

4.3 -- 1010 feet/sec -- +30

4.4 -- 1040 feet/sec -- +30

4.5 -- 1060 feet/sec -- +20

Obviously, your increases in velocity aren't going to be perfect multiples of ten, but you get the idea. This ladder looks great. Very mild curve. Starts off at +20, then goes to +30, then falls back to +20. If this were my ladder, I would feel perfectly comfortable going higher and loading a couple more strings at 4.6 and 4.7. Those results indicate there's still headroom.

Or if you get

4.0 -- 930

4.1 -- 950 -- +20

4.2 -- 980 -- +30

4.3 -- 1000 -- +20

4.4 -- 1020 -- +20

4.5 -- 1015 -- +15

In the above case, it still looks pretty good, but I can see that at the top of the ladder, that +15 feet/sec might be the first sign that my incremental increases in velocity are starting to taper off in relation to increases in powder. This is a clue that I'm nearing the top end of usefulness for this bullet and powder combo. I'd still feel comfortable going another +0.1gr for another string. And if I get another 15 feet/sec, I might go another string higher, but if it falls off from +15 to +10 or +5, I'm done. If I want faster velocities, I can go to a slower burning powder.

If I get this

4.0 -- 930

4.1 -- 950 -- +20

4.2 -- 970 -- +20

4.3 -- 985 -- +15

4.4 -- 995 -- +10

4.5 -- 1000 -- +5

If I get that, I'm done. There is no point when it comes to that of adding more powder for more velocity. People do it. People get away with it. And some people blow up guns. You can actually go far enough that it reverses, where you get a velocity decrease with a powder increase. If that happens, you're stretching metals in a way you shouldn't be, and you're lucky the pistol didn't violently disassemble in your hands.

And if I get this

4.0 -- 930

4.1 -- 950 -- +20

4.2 -- 960 -- +10

4.3 -- 963 -- +3

4.4 -- abort

4.5 -- abort

If I get that, I'm not going to shoot the final two strings. I could. But even if I don't blow up the gun (probably won't), what's the point in trying? I'm clearly too high. I'm not going to feed my pistol a steady diet of that bullet with even 4.3 grains of powder, so why bother seeing what will happen if I shoot the 4.4 and 4.5? Take those cartridges home and break them down with a kinetic bullet puller.

This is how to use a chrono to safely develop a load. When the velocity increases tied to incremental increases in powder start tapering off, you are approaching the top end. If you want to go faster, move to a slower burning powder.

Note, the above ladders aren't real, but they are similar enough to what I've seen with a couple of very consistent powders and 124gr JHP to describe what's going on. They are hypothetical and meant to show patterns. Actual numbers can differ dramatically. 147gr bullets are going to show smaller increases in velocity from one string to the next than 124gr bullets, and 115gr will show bigger increases. Different powders will show different increases. Slower powders like AA#7 and N350 will have much larger load windows, maybe a full grain or more, than faster powders like AA#2 or N320, which might only be a half a grain. With small load windows, you might want your charge increases to be 0.1gr per string, whereas with slower powders you might want to do increases of 0.3 at the bottom and 0.2 at the top. It's about tailoring the ladder to your bullet and powder, using the chrono to observe what the strings are doing in terms of increases in velocity per charge weight, then stopping when those increases start tapering off.

Hope this helps.

--ID


Edited for clarity because someone accused me of being articulate and lucid, and I wanted to live up to it.

Edited September 14, 2015 by IDescribe

[TCBDoubleTap]

This is the best explanation of using chronograph results in developing a load that I've seen yet - thanks ID!

Tom

[LeviSS]

ID - Wow. I couldn't have asked for a more thorough explanation. You did a great job of filling in the gaps for me. I can't thank you enough for taking the time to type you're reply.

[9x45]

First off use the powder makers load data, start at minimum charge and maximum OAL, vary your charge by .3 grains and OAL by .020" until you figure out what is the most accurate. Dillon SD's throw +/-.1 grains, so changing by .1 grains doesn't tell you anything. Then if you shoot competition, it needs to make the floor. Always use the same head stamp when you run the chrono. Any velocity deviation you get will be due to the +/-. 1grain charge weight and the +/-.003" in OAL (depends on the press and operator) and small variations in bullet weight. After you confirm you are above the power floor, put the chrono away and get to shooting part. Reloading is just a necessary part of shooting, like cleaning guns, I hate both of those activities, but I like shooting.

Very few shooters have access to a pressure test barrel, but I can tell you that a double charged .45acp (TiteGroup) does not go KaBoom. But a set back of .100" will blow it to pieces.

My 9mm load is a 125 TC Bayou on top of 4 grains of TiteGroup at 1.100" OAL. Goes about 1,180 fps out a Glock 17 with a BarSto barrel. My .357SIG load is a 125 Montana Gold JHP on top of 8.0 grains of BE-86 at 1.140" that goes about 1,400 fps out of a Glock 31 OEM barrel. So it easily makes the floor for USPSA Major, just in time for the provisional Limited 9mm Major!

Edited September 13, 2015 by 9x45

[amokscience]

Once you figure out a good powder charge you may want to play around with COAL and bullet shape, usually in the pursuit of better accuracy. Be cautious as you shrink your COAL as this can dramatically increase pressure.

[mpssrh]

@IDescribe:

Thank you for this explanation, which is both articulate and lucid.

[BAWunder]

Excellent job explaining things ID!

One thing I'd like to throw out there is in regards to SD. When I started working up loads one if my focus points was getting the lowest, most consistent SDs possible. One day I was checking out 3.2gr of TG under 147gr Xtreme RN. The SD was absolutely horrible. Thought to myself I likely won't be using THOSE loads. However, after I chrono a load then I test for accuracy. MUCH to my surprise my accuracy tests showed it was one of, if not the most accurate load (in my 1911 Loaded) I'd ever put together. Needless to say, I've been using that load ever since in my IDPA matches.

Moral of the story, SD may help shed light on the promise of a load, but it isn't the whole story. Always test for accuracy. You might be surprised. Certainly don't use it as the holy grail.

[IDescribe]

Moral of the story, SD may help shed light on the promise of a load, but it isn't the whole story. Always test for accuracy. Certainly don't use it as the holy grail.

Absolutely, I was thinking about coming back and commenting on a couple of things with SD.

One of the things is exactly what you said. Smaller SD does not equal greater accuracy. It's an indicator of consistent reloading practice and equipment. And it's an indicator how consistent your chrono is, and how savvy you are at setting it up and running it. And it's a indicator of the impact the surface of the bullet has on chrono consistency. Tip: the duller the more consistent, the shinier the less consistent. I always get more consistent results from coated lead than I do plated or jacketed. But as you said, SD doesn't tell you the story about accuracy. You have to shoot to see that story unfold.

The other thing is about SD and pressure. While I listed it as something to look out for, simply including it might overstate its value. I look at it. But if the SDs start going haywire toward the top of a ladder, all it does it get my attention. If that happens and the incremental velocity bumps from string to string are still telling me I'm good, then I'm good.

[Doc10mm]

ID, that was an awesome summary.

[BigPapa]

Thanks IDescribe!

I'm new to reloading and this is EXACTLY what I needed. Now I'm off to look for the best progressive press!

Edited September 15, 2015 by BigPapa

[AzShooter]

Best progressive press is a Dillon. Buy it through Brian Enos's store.

If you load a lot get a 650. If you want to load rifle cartridges as well get a 550. I've had a number of 550s over the years. Just bought another one this year for a Christmas Present.

I gave my 650 to my son. Now I'm thinking of getting a new 650 to replace the 550. All I'm reloading these days are pistol calibers.

[ES13Raven]

Great info here.

If it wasn't already mentioned - have your chrono about 10 feet away from your muzzle. This will give you accurate readings and is also the distance that IDPA & USPSA use.

[dogtired]

I don't know if this will be lucid or informative but here goes...

In loading over book loads you have to consider some inherent variables. Volume and pressure are closely related. As an example "bullet setback" can reduce your volume in the case, there by increasing the pressure generated. So if you are loading above published loads and are not consistent on your bullet seating or COAL (cartridge over all length) you will have inconsistent pressure swings from batch to batch. If you use random brass, you will see some minor differences in case volume. Chamber dimensions also figure in here, as well as countless other variables, so a major load in one gun does not mean a safe load in its exact duplicate. If you see wide SD differences in your loadings, then mix that with some of the other variables mentioned, then you may be creating overpressure loads. In the same lot of homebrew ammo, most may be perfectly fine but that one that has "tolerance stacking" will do you in. All of this can be heady science but disaster can be averted by using a good scientific method. Hence the chronograph, log books, patience, etc.

I would not discourage you from buying a progressive press but would caution you to use it like a single stage until you have run a few hundred or thousand rounds thru it to really understand the process (assuming you are new to reloading). When I use loads I find in the "books" I do find that the powder weight used rarely correlates to what speed I am actually getting. I live at 7750 elevation so I am sure that factors in. My chrono has metered to the Match Chrono every time I have been tested, so I have confidence there.

[BigPapa]

I don't know if this will be lucid or informative but here goes...

In loading over book loads you have to consider some inherent variables. Volume and pressure are closely related. As an example "bullet setback" can reduce your volume in the case, there by increasing the pressure generated. So if you are loading above published loads and are not consistent on your bullet seating or COAL (cartridge over all length) you will have inconsistent pressure swings from batch to batch. If you use random brass, you will see some minor differences in case volume. Chamber dimensions also figure in here, as well as countless other variables, so a major load in one gun does not mean a safe load in its exact duplicate. If you see wide SD differences in your loadings, then mix that with some of the other variables mentioned, then you may be creating overpressure loads. In the same lot of homebrew ammo, most may be perfectly fine but that one that has "tolerance stacking" will do you in. All of this can be heady science but disaster can be averted by using a good scientific method. Hence the chronograph, log books, patience, etc.

I would not discourage you from buying a progressive press but would caution you to use it like a single stage until you have run a few hundred or thousand rounds thru it to really understand the process (assuming you are new to reloading). When I use loads I find in the "books" I do find that the powder weight used rarely correlates to what speed I am actually getting. I live at 7750 elevation so I am sure that factors in. My chrono has metered to the Match Chrono every time I have been tested, so I have confidence there.

Well at the moment I'm between 115 and 124gr bullets. I have at least 6-700 115gr JHP, and I understand that as the bullet weight increases so does the overall bullet length thus case volume decreases leading to increased pressures. I suppose what I'm trying to understand is there a rule of thumb that determines bullet setback as well as over all length, especially when changing between different bullet weights?

[IDescribe]

To clarify, setback is when in the process of chambering the bullet is pushed back in deeper than where you loaded it. I think you are talking about seating depth. Proper neck tension and doing a push test to make sure you don't chamber into the lands will make sure you don't suffer setback.

There is no rule of thumb to estimate how deeply a bullet is seated into the case based off OAL. Two bullets of the same weight at the same OAL could be seated to significantly different depths into the case. I have a 125gr bullet whose max OAL results in a seating depth of .310, and my favorite 147gr I seat shorter than max, and it is only at a depth of .260. So no, you can't look at a published OAL use a rule of thumb to compare it to your bullet. I track seating depth as well OAL for all my loads, and if working up a load with a bullet that I believe is seated significantly deeper than the published load, I will probably lower starting load 5-10%. Using starting load in general should protect you from a catastrophic failure, but I have used a starting load before that produced a velocity that matched the top end of the published load window, and that left me with 40 bullets to pull apart. When in doubt, load up 5 rounds at starting load, shoot them over the chrono, and see where you are. If it is way under the published load, you're good to build a load ladder that starts a couple tenths over published starting load, and if it is well over, you would do well to build a ladder that starts a few tenths under published starting load.

Edited October 6, 2015 by IDescribe

[dogtired]

Well said. Really time and patience will get you to build a good and safe load. No reason to rush it. You do need to be able to recognize patterns like the diminishing returns as mentioned earlier. You can not just plug in someone elses data when approaching this and the chronograph will help you find your groove.

[dogtired]

"Well at the moment I'm between 115 and 124gr bullets. I have at least 6-700 115gr JHP, and I understand that as the bullet weight increases so does the overall bullet length thus case volume decreases leading to increased pressures. I suppose what I'm trying to understand is there a rule of thumb that determines bullet setback as well as over all length, especially when changing between different bullet weights?"

I would say to start loading with the longest ammo your gun can accomodate, giving you the most case volume. Bullet setback would occur if your loading/crimping/feedramp combo cause the bullet to be seated deeper in the case when the gun feeds it into the chamber. That causes less case volume and there by more pressure. Max COAL may provide some built in tolerance with loaded pressure if some minor setback occurs, but don't count on it.

Bullet seating depth has been said to be similar to the diameter of the bullet, so 0.355, but I doubt you will get that much seated with a 115 and max COAL.

[Willz]

Great thread.

[BigPapa]

To clarify, setback is when in the process of chambering the bullet is pushed back in deeper than where you loaded it. I think you are talking about seating depth. Proper neck tension and doing a push test to make sure you don't chamber into the lands will make sure you don't suffer setback.

There is no rule of thumb to estimate how deeply a bullet is seated into the case based off OAL. Two bullets of the same weight at the same OAL could be seated to significantly different depths into the case. I have a 125gr bullet whose max OAL results in a seating depth of .310, and my favorite 147gr I seat shorter than max, and it is only at a depth of .260. So no, you can't look at a published OAL use a rule of thumb to compare it to your bullet. I track seating depth as well OAL for all my loads, and if working up a load with a bullet that I believe is seated significantly deeper than the published load, I will probably lower starting load 5-10%. Using starting load in general should protect you from a catastrophic failure, but I have used a starting load before that produced a velocity that matched the top end of the published load window, and that left me with 40 bullets to pull apart. When in doubt, load up 5 rounds at starting load, shoot them over the chrono, and see where you are. If it is way under the published load, you're good to build a load ladder that starts a couple tenths over published starting load, and if it is well over, you would do well to build a ladder that starts a few tenths under published starting load.

Thanks for the clarification. You were correct in your assumption in me meaning seating depth.

As for my seating depth, I don't currently have a crimper. Would it be recommended since I'm more likely to see bullet setback due to 115gr bullets? I just purchased a dillon xl650, and am using Hornady dies if that matters to seat the bullet, and deprime.

Edited October 7, 2015 by BigPapa