standard variance in velocity from 45 acp making 170 PF

[planenut]

Hello,

I'm new to reloading and new to shooting IPSC.

With a friends help and assistance, I loaded up some 230 grain LRN (Home cast) bullets and WST powder. I've started with two different loads (4.0 and 4.2 grains).

I was suprised at the differnce in velocity. What is the normal amount of change in velocity between rounds of the same load?

I will have to start over once my gun gets back from Colt as I have been trying them with my short barrel Kimber 2.75 but am enjoying the experience and learning curve.

The 4.0 loads are getting anywhere from 605 to 658. Kimber 2.75 barrel

The 4.0 loads are getting anywhere from 685 to 725. Colt 5" barrel

The 4.2 laods are getting anywhere from 673 to 696. Kimber 2.75 barrel

The 4.2 loads are getting anywhere from 767 to 787. Colt 5" barrel

Thanks.

Edited October 18, 2010 by planenut

[Flexmoney]

A good thing to do along the lines of "load development" is to graph the loads (velocities), charting changes at every 0.1 grain of powder.

Then you know the data for YOUR gun and YOUR loads...at a particular point in time/space. You may later see smaller variances due to barrel wear, temp., humidity, altitude, gyroscopic precession, magnetic declination... (oh wait...maybe not those last two:) ).

[planenut]

I can see where graphing would be very helpful.

It was a starting place for me.

It also seems that the 4.2 loads are more consistant. ie a spread of only around 20 fps from slowest to fastest whereas the weaker 4.0 loads had a spread of around 50 fps. 700 to 750 seems like a lot of variance while 730 to 750 not so much..

That was my original question that I did not word very clearly. What would the normal spread in velocity be for a given load of 45 acp?

[Lee King]

Hey Billy,

I'm by no means an expert loader and others may have a lot more insight.

There are a lot of things that can affect consistency in velocity. I had a wild variance when I first started loading .45 and eventually it settled down to where I was cron'ing with just 7-8fps between rounds. I couldn't tell you back then what I changed to make it settle down. But over time I noticed a few things that may make a difference.

1st, powder burn rate can be a factor. WST, IIRC, is a slower powder than others. You may not get a complete powder burn in the shorter barrel.

2nd, how much does the powder fill the case? I can't speak to wst in .45 but with tightgroup (in .40) I found that if I was sub-major I was getting 30-40 fps variation. Then as I approached major the velocity settled down. For giggles I tried the old hold the gun up and tap the powder to the bottom of the case between each shots trick and my velocity variation dropped down to the 10-15 range with the same loads (sub-major). Titegroup is a very low volume powder (i.e. 4.9 grains barely fills 1/3 of the case). I think the closer I got to major the more the powder filled the case the more consistent the burn.

Lastly, if you're new to loading, technique can come into play. It always seems like it takes 500-1000 rounds to get accustom to making sure to go full range of motion with the lever, make sure you push good to seat etc. If you short the stroke by the tiniest bit it can affect OAL which affects velocity etc.

Lee

Edited October 18, 2010 by Lee King

[planenut]

Thanks Lee,

I hope to see you at the next event!

Billy

[BallisticianX]

Alot of things can affect velocity variation. Powder position in the case, that will change the characteristics of the burn and pressure at time of bullet release. There are some powders (i.e. titegroup) is not very sensative to this. Variation in case length will cause incosistant crimp force. More crimp on the "longer cases" have more hold back of the bullet allowing pressure to build higher before release thus a higher velocity. Consistancy of cases, are they all the same brand? The same amount of firings? If not the different brands vary in the material hardness and as you fire brass it work hardens. This will change the case's springback and the tension it holds on the bullet.

All these factors and the 40 fps variation is not a concern at short range consistant with USPSA and Steel. At 50 yds though it will destroy any hope of a good group.