9mm 125 HAP COL Effect on Velocity Data

Okay, time to bore you (pun intended).  Measured velocity of 3 COL's on the same handloads.  CCI Blazer range brass, 4.7 gr. CFE Pistol, 125 HAP (.356), LFCD light crimp.  Pro Chrono @ 5 feet.  78F, calm, humid, sunny.  Hyskore benchrest 10 rounds each, 5 rounds each 50 yd. target then repeat.  All rounds in Chambers 1-5 of an S&W 986 5".  

COL            AVG          HI         LO         SD        7/10 Group Size      Deviation From POA

1.150          981         1001      938        19.6      2"                          1" high  12:00
1.120         1023        1059      991        20.0      2"                          1/2" high  1" right
1.090         1052        1072     1026       11.8      3 1/2"                     2" high   1 1/2" right

I'm guessing the poor 1.090 group was due to distance from the forcing cone despite the good chrono data.  As usual I get 1 to 3 flyers despite my good efforts.  Noticeably more wobble at 4X than usual after 2 cups of coffee.  I have gotten the 1.120 COL at 2X, same recipe, to group all 10 rounds once at 1 7/8" on a good day.

What size are the 10/10 shots?

S148 wrote:What size are the 10/10 shots?

3 to 4", clearly flyers.

Were they called flyers?  Or are you calling them flyers simply because they were outside of the "cluster"?

1.090 is a typical oal, try working the load using that oal

At least with rifles and I don't see how this is different with pistols, "flyers" usually is caused by the load close but not on the accuracy node.

S148 wrote:Were they called flyers?  Or are you calling them flyers simply because they were outside of the "cluster"?

Well outside the cluster randomly distributed.  I swear my crosshairs are at least touching the 1" bull (my focus) when the pistol fires on every round.  It's hard for me to accept my loads vary enough to cause such a variance.   All my loading is on a single stage press.  My powder never varies more than half the beam zero line on the 5-0-5 scale when taking random samples.   I use a Redding Competition micrometer seating die.  My light or no crimps appear very consistent.  There  doesn't seem to be any difference when I load virgin Starline brass.  I accept that I'll never consistently break the 3" group barrier at 50 yards on a manual benchrest.   I get 1 to 3 flyers in 10 rounds nearly every time which are undoubtedly out of the "cluster" by 1 1/2 or more inches.   One day I had a friend shoot 5 rounds then I shot 5 in the same target at 50 yards.  We overlayed a 2 1/4 inch group with no flyers using Blazer range brass.  I've gotten groups of 10 with no flyers twice but the occasion is very rare.   The upside is I still have fun handloading and trying.  My performance has really improved since I've started loading subsonic rounds.

I don't think your problem is your reloading technique which looks decent to me.  What you need to understand is although consistency will remove problems associated with inconsistency, a rifle/pistol can still shoot badly when the load is not on an accuracy node - those are two separate independent things.  There is a misunderstanding out there that if you get everything consistent, it will shoot well - this is NOT TRUE.

Barrels are like a bell, when it is struck, it will ring/vibrate.  That vibration will travel from the chamber to the crown and be reflected back and forth many times.  If a bullet exits the crown when the vibration is there, that is bad because it can impart a sideway push on the bullet.  There is also a possibility that the crown can open up slightly to allow gas to escape unequally which is also bad.  The trick is to load the round so that it's MV allows the bullet to exit the barrel when the vibration is as far away from the muzzel as possible i.e. at the chamber.  We call this "barrel time".

So for a pistol, you can adjust this exit time by a number of ways - powder charge surely, seating depth which affects pressure, and crimp which also affects release time.

This is why a precision reloader can have a charge which shoots lights out but other charges handled in exactly the same way not have as good a group.  If your charge is close to but not on an accuracy node, you can imagine some of your rounds which is not exactly the same will fall outside the accuracy node and result in flyers.

The issue (and it’s minor) with the described reloading info is the “light or no crimp seems consistent”.  Not crimping can lead to flyers.  SAAMI lists the max case mouth as .3800.  I’d taper crimp so that the case mouth is not more than .378 nor less than .375.  Even with jacketed.

Bigtrout,  it sounds like that's simply how your gun shoots that ammo. 

Don't ignore the data: include the flyers in your group measurement.