Old topic New Question

I spent a lot of time reading most of the old posts that talk about SD variations and its effect on accuracy.
Since I got a Garmin Xero, I check new loads and old ones. I don't have a Ransom, but I do have a really good
rest that Ransom makes, so I can check aiming dot settings, etc.
I recently loaded some 45acp with Zero 185 JHP with VV N32, 5.1 gr.  I tested several other loads, 5.6, 5.4, and 5.3.  The 5.1 gives a fps of 775 give or take, and has good grouping.
However, I'm getting SD's of 38 to 50, and wide swings in fps, some as low as 685, some 815. This does not seem to affect accuracy, but it bothers the engineer behind the pistol.  I use a Dillon 550, extra small powder bar
and check weights frequently, averaging 10 drops.  No big swings.  OAL is 1.205, crimp about 0.470.
WTH is going on?  Will more crimp improve things, or just forget it and keep shooting?

The target is all that matters.

As mentioned in a very recent thread, N320 is not favourite for 45ACP:-

https://www.bullseyeforum.net/t23683-vv-n320-loads-45-acp

Of the VV powders, N310 is favourite. Some 50yds test data from fc60 also in a recent thread:-

Zero 185 JHP reloads with 4.2 grains of N310 (crimp 0.470) = 0.813" (730FPS)

ASYM 185 JHP factory (loaded with ~4.5 grains N310) = 0.718"  (803 FPS)

And, as stated already, never mind the SD values, does it shoot a good group?

As an engineer, figure the Standard Deviation and the mean of 20-30 powder drops.

If it bothers you, then it bothers you. SD that big indicate trouble…poor combustion efficiency, malfunctions. I also got unburned kernels of 320 that stuck to my glasses so there’s that. Better choices out there. I would be satisfied with velocity SD around 20

Years ago when I shot a lot of rifle, if the shooter downloaded a slow powder very often velocity variance became large.   I don’t load a lot of N320, but I do know that this powder is better suited for heavier bullets and/or higher velocities.  Perhaps this explains the larger SD.  It’s excellent in 9mm, and actually excellent in 38 Special, but it isn’t the best in low velocity 45 loads.

Yep, guess I will go back to N310.  I had a jug of N320, thought that might be a good way to use it up.  Wobbley, I did not know 320 was good for 38spl.  I load a lot of that in HBWC. Might try the 320 with some 200gr bullets. Thanks for the replies.

Greetings,

I tested some Zero 185 JHP bullets loaded with 5.22 grains of N320.

I chose 5.2 grains as my Reloading Software predicted a velocity of 775 fps.

The chronograph revealed my ten shot average as 778 fps, 64 ES, and 20.1 SD. I came close to the computer model.

The computer model also pointed out that 5.2 grains was not 100% burned powder, which Mr. Martindale points out from practical use.

I use the chronograph to verify the velocities. I have been paying less attention to the ES and SD values.

Why? Quite often my smallest group on paper has the worst ES and SD values. Still trying to understand why.

Here is my test target at 50 yards with an IMI NM7791414 barrel in a fixture. Not bad; but, N310 groups better.

Bear in mind these are only one ten shot groups.

Thanks fc60: I will bump up my load a tenth and see what happens.  I was
getting good groups with the 5.1 gr. Shooting a Les Baer modified (a lot)
5 inch barrel, which has been a good pistol.  Keep in mind my max range 
at the indoor range is just shy of 25 yds, so I am not competing, especially
given my old age creaky state.

According to my Ballistics Buddy App the difference between 775 fps and 800 fps is about 1/4" at 50 yards with a 185JHP, so a SD of 25 is something, but not the biggest contributor to group size.