Is my thinking right on this?


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SC_Dave
December 20, 2012, 05:40 PM
115 gr 9mm RN FMJ

Difference in Hornady and Precision Delta is length of bullet;

Hornady .5400
PD .5650

This is the only difference I see in the two bullets.

With Hornady I was using 4.5gr of Win231 (this is mid range per Hornady 9th) with a COL of 1.100 (this is per Hornady 9th)

Can I use this same data with PD with a COL of 1.350? Am I thinking right or way off?
David

PS: I am using this for plinking and self-defense practice.

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rcmodel
December 20, 2012, 05:57 PM
Length of the bullet doesn't matter.

Ogive profile does.

The shorter Hornady bullet probably has a more blunt secant ogive, and may need to be seated deeper to prevent jamming into the rifling leade.

You need to determine your OAL using the new PD bullets by doing the "Plunk test" in your barrels chamber.

Whatever length just misses the rifling leade is the correct OAL for that bullet in that barrel.

Your load is light enough OAL will not matter.

rc

SC_Dave
December 20, 2012, 06:04 PM
Again RC you have helped me and I appreciate it!!!!
David

1858
December 20, 2012, 06:05 PM
How did you come up with COAL of 1.350"?

0.5650" - 0.5400" = 0.025" therefore I would have thought that your COAL would be 1.100" + 0.025" = 1.125". That way you would have the same internal case volume for both loads and the COAL is well within "standard" specs.

SC_Dave
December 20, 2012, 07:15 PM
You know when I typed an COL of 1.350 that seemed long but I didn't catch it. That would have been 1/4 of an inch longer. :banghead: My mistake.

Walkalong
December 20, 2012, 07:32 PM
Assuming the same OAL for each bullet, the PD would seat .025 deeper, which would be significant if you were close to max. At 4.5 Gr of W-231 you will be fine, but will see a velocity increase.

An increase in OAL to 1.125 with the PD would pretty well even things out.

I usually run 115 Gr RN bullets in 9MM at 1.130 to 1.135 OAL.

SC_Dave
December 20, 2012, 08:14 PM
Thanks Walkalong, good info!
David

Centaur 1
December 20, 2012, 10:46 PM
I smelt lead from an indoor range so I get to compare a lot of different bullets. 9mm's seems to have the largest variation in length for bullets that weigh the same. When you have a load that you like, calculate how much of the bullet is inside the case and duplicate that number with the new bullet. Then do the plunk test that RC mentioned, and just like he said the ogive will determine if you can chamber the round. I have a Ranch Dog mold that uses a tangent ogive, even though the bullet is very short it has to be seated deeper.

4895
December 20, 2012, 11:23 PM
I would seat them at 1.125" with a 4.5 gr charge of 231 and call it good.

Might want to bump the charge up to 4.6 or 4.7 if the lighter ones work well for ya.

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