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9mm


Drillbit
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I know this is a broad question. 

I'm loading 9mm with 148rn coated HI-Tec bullets using Sport Pistol.  The velocity are more then I want.  If I wanted to reduce velocity, would a tenth be meaningful, or go 2 tenths?

I realize that all powders are different /burn rate etc.. just looking for some accumulated  knowledge. 

 

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I am not loading the projectile weight you are but I reload 125gr hitek coated rounds.  In my experiences I fluctuate up and down a tenth just due to measurement error.  Is the press even capable of holding a tenth?  When I started loading I was using 4.2, 4.4, and 4.6 of Bullseye and the difference between each could be noticed when firing.

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This is what I got in a cz shadow 2 using 147 acme f/p coated bullets with chi 500 primers.

sport pistol 3.0 grs 1.110 oal  851 fps

sport pistol 3.1 grs 1.110 oal  877 fps

sport pistol 3.2 grs 1.110 oal  901 fps

This should give you and approximate of what one tenth of a grain will do.

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40 minutes ago, Dwbsig said:

This is what I got in a cz shadow 2 using 147 acme f/p coated bullets with chi 500 primers.

sport pistol 3.0 grs 1.110 oal  851 fps

sport pistol 3.1 grs 1.110 oal  877 fps

sport pistol 3.2 grs 1.110 oal  901 fps

This should give you and approximate of what one tenth of a grain will do.

Based on this, it looks like you can safely estimate powder charge based on the velocity you are looking for. 

 

We could safely assume that 2.9gr would be 821fps, 2.8 would be 792.4fps and etc.   

 

I have done a lot of estimation like this for Power Pistol and it works very well, just don't exceed maximum charge weight.    

Edited by chevrofreak
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3 hours ago, Drillbit said:

 The velocity is more then I want. 

 

What is the velocity ?   And what velocity are you looking for ?

 

p.s.  Dwbsig, I'm very surprised that 0.1 grain difference resulted in such a large drop in velocity.

        Thanks for sharing that.   And, even more surprising is that the drop is linear - a 6% drop in

         powder drops the velocity 6%.   Shocked.

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8 hours ago, Hi-Power Jack said:

p.s.  Dwbsig, I'm very surprised that 0.1 grain difference resulted in such a large drop in velocity.

        Thanks for sharing that.   And, even more surprising is that the drop is linear - a 6% drop in

         powder drops the velocity 6%.   Shocked.

If you take into account errors, it may not actually be that much or even linear. Many manufacturers, including Dillon, will tell you the expected error in their equipment and the shape of their powder-power curves. You have to take all that into account plus your own errors. Doing formal error analysis is very time consuming and not for the uninitiated. In other words, be careful abut drawing any conclusions based on a few points obtained with the equipment we use.

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do the math, 

current charge weight x desired velocity / current velocity = new charge weight 

 

so say your load is 4 grains of whatever and your load is going 1300fps but you want 1200 fps 

 

4 x 1200 / 1300 = 3.69 

 

This works really well within the normal charge range of most powder cartridge combinations, verifying that the new charge weight is still a safe load is always prudent.

 

you can also use power factor numbers if you prefer that seems to work as well

 

Current charge x desired PF / current PF = New charge

 

Edited by MikeBurgess
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51 minutes ago, MikeBurgess said:

This works really well within the normal charge range of most powder cartridge combinations, verifying that the new charge weight is still a safe load is always prudent.

Mike - That has been my experience working within the usual published low-to-mid charge ranges.  i.e. Works pretty well for eyeballing the lower velocities I reload for. But at higher charges, the relationship is non-linear and increasing charge does not increase velocity proportionately. That is getting into the danger zone where pressure increases but velocity does not. That might be in Lyman's or one of the other reloading manuals. So one needs to be careful, cognizant of these issues, and "check their work". I recall one of the powder manufacturers posted somewhere, can't remember where, that relationships are seldom linear even if they appear so at lower charges.

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My experience has been that increasing charges by 0.1 grains accomplished 

almost zero.   Even 0.2 grains showed slight changes.   So I'm floored to

see this kind of change with a small powder charge difference - guess it

depends on the individual powder and bullet type/weight. 

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2 hours ago, MikeBurgess said:

do the math, 

current charge weight x desired velocity / current velocity = new charge weight 

 

so say your load is 4 grains of whatever and your load is going 1300fps but you want 1200 fps 

 

4 x 1200 / 1300 = 3.69 

 

This works really well within the normal charge range of most powder cartridge combinations, verifying that the new charge weight is still a safe load is always prudent.

 

you can also use power factor numbers if you prefer that seems to work as well

 

Current charge x desired PF / current PF = New charge

 

 

This is very interesting Mike.  I tried it on some other known loads I've made and it's very accurate.  Because I will be adjusting down, I feel safe in giving this a try.

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