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Brian Enos's Forums... Maku mozo!

OAL and PF


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As noted, you'll have to test your ammo.


That said, my notes show with a 115 gr bullet in a 9mm using 5.0 Silhouette in a 5" barrel going from 1.160 to 1.120 (0.040" reduction OAL) power factor went up 6. 

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You definitely need a chrono.  There isn't a linear relationship.

That being said, the same load with a shorter COL will typically have more PSI than the same load with a longer COL.


My experience going from 40S&W MajorPF loads for 2011 use at 1.185" COL to the same load for a G35 at 1.140" makes a +2-5% difference.  Shot in the same 5" 2011 barrel.

Minor PF changes in COL seem to vary much more widely. 

Edited by Yeti
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I did a small test with a 10mm. Same load just changed length. 
1.270-1202 fps

1.250-1209 fps

1.240-1193 fps

You have to take into consideration that your not only changing the internal volume of the case but also the chamber, ie the jump to the lands. It was also interesting that the shortest had the lowest ES. 

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  • 3 weeks later...

I think it has to do with the jump to the lands causes a psi jump at the peak burn, in other words, timing. If you look at my numbers the middle of the road is the fastest and by measuring the brass it also had higher psi. I’ve noticed this for a long time on rifle rounds. 

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Uh so..... this was a faulty test. I switched guns between OAL changes. The tanfo is in fact about the same PF. The A01 however has a bit faster barrel. Thus is why I have had higher PF. 


So in the end going from 1.119 to 1.130 made negligible difference in PF. It has however seemed to fix my feeding issue in the tanfo. 

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