Issue with inconsistence with FPS

[Blank Zero]

Hello all,

Currently I am facing an issue that I don't know if it's me or it's the chrono. I am loading .45 ACP precision delta FMJ, with N320. My C.O.L variate from 1.262 to 1.266, with a consistant load of 4.85 grain of N320. However, when I chrono my load, it go from low is 650s to high which is 690s. I know this is a bit low, I need to increase on the powder a bit, however, the inconsistency of the FPS making me a bit nervous.

Can someone help me with this issue?

Thank you so much in advance,

Blank

[ben b.]

The spread is 40 fps. That is OK. Increase the powder charge to 5.0, make some test rounds and increase again to 5.2. Then re-test.

[Blank Zero]

So that is normal then? Because when I was reloading 9mm for production minor, I was able to keep the different with 10-15 fps

[GSWEAR]

You may try tipping the gun up before each shot if your not already doing it to move the powder to the back of the case, you will probably see and increase in the fps average and a decrease in extreme spread.

It will also get better as you increase the powder charge, N320 doesn't seem crazy about real light loads.

Greg

Edited May 13, 2011 by GSWEAR

[Blank Zero]

Thank you Greg

[g56]

Sometimes adding a bit more crimp can improve consistency on velocity, but an extreme spread of 40 fps isn't really bad.

9/28/2006

70 degrees Fed primer

5.0 gr WW231

230 gr Lead Round Nose

2 sets of data

1 750.2- 760.8

2 764.4- 799.5

3 802.1- 779.7

4 744.2- 787.4

5 806.9- 753.3

6 772.2- 763.2

7 780.9- 769.8

8 756.1- 765.5

9 802.0- 754.9

10 758.1- 756.7

Average 773.0- 769.1

High 806.9- 799.5

Low 744.2- 753.3

ES 62.7- 46.2

SD 23.2- 15.3

AD 19.4- 12.0

10/5/2006 75 degrees Fed primer

5.0 gr WW231 200 gr Lead SWC

1 766.4

2 748.8

3 787.3

4 775.7

5 787.5

6 785.2

7 767.3

8 775.9

9 780.3

10 790.1

Average 781.5

High 798.8

Low 766.4

ES 31.4

SD 10.2

AD 8.3

[Ryan N]

Sometimes adding a bit more crimp can improve consistency on velocity,

+1. I have found that not enough crimp can cause the bullet to be set back in the case when it hits the feed ramp before going into the chamber. This can cause higher pressure and therefor higher velocity.

Take a few of your rounds, gun and calipers to a safe place. Measure the OAL of your bullet. Cycle it through your gun and then remeasure the OAL. Beware, I have also heard that excessive crimp can cause accuracy issues.