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

[FTDMFR]

This thread is great!

One thing I'll add is that when I'm working up a load, I'll usually test at least 6 groups of 10 in .3 gr increments, take the means of those groups and fit a line to them, and then use that line to determine the right charge for whichever velocity/PF I'm looking for. That helps even out any measurement errors when weighing out charges for the ladder.

The fitted line will usually give me an oddball charge, like 3.17 gr. Since my scale only reads in tenths of a grain, I'll throw 10 charges and go by the average.

To be sure that I have enough PF margin, I'll pick a charge where the mean velocity for that charge is about three standard deviations higher than the minimum velocity for that PF.

I'll also start WELL below the minimum charge when working up. Components are cheap.

Edited October 7, 2015 by FTDMFR

[IDescribe]

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.

Taper-crimping with straight-walled automatic pistol cartridges isn't really crimping. You're not supposed to crimp the casemouth into the bullet. You just remove the bell you created with your expander/belling die. Case tension is what holds the bullet in place, not the crimp, and proper case tension is going to come from your sizing die.

Anyway, if you are belling the casemouth before seating, you do want to get a taper-crimp die to remove that bell. However, with jacketed bullets, if you're very careful to keep them straight up and down going into the seating die, you can actually get away without belling, and if you didn't bell, you don't need to crimp anyway. Plated, lead, and coated lead with definitely need a bell and then a crimp.

Edited October 8, 2015 by IDescribe

[dogtired]

You can figure out how deep your are seating them by getting an unseated bullet and estimating how deep you are. Of course another arguement ensues when discussing which crimper you should use. I have been using the Lee Factory Crimp Die with great success but others hate it.

[IDescribe]

Any normal crimp die -- Redding, RCBS, Lee, or Hornady -- will work fine so long as the rest of your process is good.

The Lee Factory Crimp Die can fix problems or it can cause problems, but when it fixes problems, they're problems that shouldn't exist to begin with if the rest of your process is good. I'd recommend going with a standard taper crimp die and making sure the rest of your process is right. Plenty of people use the Lee Factory Crimp Die with success, but I'd be hesitant to recommend one to a new reloader who isn't having problems otherwise.

[usmc90]

Following

[PiratePast40]

When you're working up your loads, be sure to load enough that you can also test each load for accuracy. Velocity and power factor are important, but you also care about accuracy, and a higher power factor may be significantly more accurate. I try to have at least 10 more of each load to look at accuracy at 10-15 yard targets off the bench, plus another 10 to test how the gun feels with the load. Just because the load has almost zero recoil, doesn't mean that the combination is the most accurate for the gun, or that it will generate enough force to operate the gun consistently.

I set up a standard target a few feet behind the chrono so that I have a consistent aim point. Each load gets 10 rounds through the sticks and into it's own 3 x 5 card. That also shows me how accurate they are at short (12-15') distance. Keep in mind that the chrono is brutally honest about your trigger press. You'll find out what that means soon enough!

[Oskino]

ID, thanks for the great info and sharing your knowledge.

[dogtired]

In thinking about this subject, I decided to perform an experiment. I took 10 of my minor 9mm loads and intentionally set them back to 1.04. I then took 10 normal rounds, measured them all for similar length, normally loaded to 1.155 +/-.

I went to the range with the chrono to see what effect such a set back would have. My abbreviated results:

Normal load:

10 shot average- 1046 fps, SD 12.56, PF 129

Set back load:

10 shot average- 1078 fps , SD 22.36, PF 133

While not an incredible variance, at higher charges I am sure it would prove to be more significant. I am screwing together my 9Major gun currently but when I am done I will crunch more numbers.

[IDescribe]

Bro, dropping .115 off a known load is not safe, even at minor. Power factor is a measurement of projectile momentum, which does not in any way correspond to chamber pressure. Very low power factor loads often have very high chamber pressures, which is what setback further increases. I wouldn't want new reloaders to think doing such a thing is no big deal -- it can blow up a gun -- and I'm shocked you got only an extra 32 feet/sec.

I recently did something similar with N320. In my case, however, I took some safety precautions. First, I did it as a progression, shooting ten round strings over a chrono, reducing each string in OAL by .02, starting at the longest OAL and checking velocities as I went. I started with a load well under minor, in fact under the starting load of a ladder I had recently done with the same bullet and powder. And I did it with a bullet I normally load quite short for my CZ, so the shortest OAL tested wasn't that much shorter than what I was accustomed to loading the bullet at anyway. To give me room at the top end to lengthen the OAL, I used my deep-throated VP9, which oddly chronos loads within a few feet per second of my CZ.

It's off-topic for this thread, so I'm not going to post and discuss the whole thing, but whereas you got 32 feet/sec bump for a .115 decrease in OAL, I got an extra 70 feet/sec for a .08 reduction with N320 and a Montana Gold 124gr JHP, from 1.12 to 1.04.

As a general rule, when you have a known load, if you want to reduce OAL, start back at starting load, and work the load back up.

Edited October 22, 2015 by IDescribe

[dogtired]

Thanks for your concern brother. I was quite confident of my safety.

I only calculated PF for this board, it really only figures in when coming up with a gamer load. It is pertinent when at 170 PF though and you get such a variance that I tried to illustrate with my bunny fart load.

I would hope the readers were able to discern my intent and not blow something up.

[LeviSS]

I finally broke down and bought a chrono, so now I can put this info to good use.

Edited December 4, 2015 by LeviSS

[ChemistShooter]

Really good job, ID, and I speak as someone who writes technical documentation. You've probably kept a lot of new reloaders from blowing their ass up. Mine included.