Looking for the collective wisdom to help understand a ballistics issue

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Post by straybrit on 9/16/2019, 11:14 am

I was playing with new loads over the weekend to see just how light I could go for a 45 indoor load. Looking through load information here and elsewhere I was struck by something that I've never really understood.

Why does a heavier bullet (e.g. 200g SWC) get quoted as (typically) 3.5g BE for an indoor load where a lighter bullet (say 160g) gets quoted with a hotter load - typically 4.0g BE? My simple mind thinks that a lighter bullet would need a lighter load to achieve the same velocity. What am I missing here?

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Post by james r chapman on 9/16/2019, 11:20 am

Not about velocity, it’s about enough pressure to cycle the action I believe.
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Post by straybrit on 9/16/2019, 11:41 am

Ah - yeah - that would make sense. Thanks Jim.

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Post by Wobbley on 9/16/2019, 11:42 am

Not so much pressure as it is momentum. The 1911 operates on a delayed short recoil. The slide has to have all the momentum needed to cycle the gun by the time the bullet leaves the barrel. By calculations, the slide gets all of its oomph in the first .050 to .090 of its travel. When you lighten the bullet you have to raise the velocity to get the momentum. That takes a hotter load. Often people who shoot 160 grains claim the recoil is less but it’s “snappier”.
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Post by Olde Pilot on 9/16/2019, 11:44 am

At ignition, lighter bullet begins to move before a heavier bullet. So, there's less time for pressure to build in the cartridge case. Even with increased powder charge versus that used with a heavier bullet, felt recoil MAY be less.

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Post by S148 on 9/16/2019, 1:08 pm

Even with the same powder charge, light bullets tend to go slower than heavier bullets.

See figure 2 at this link:  https://www.shootingtimes.com/editorial/power-factor-recoil-bullet-weight-gives-edge/99399

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Post by Olde Pilot on 9/16/2019, 1:54 pm

Correct. Because the pressure build-up in the case is less.

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Post by Allgoodhits on 9/16/2019, 3:07 pm

If it is accurate at 50 yds, it is accurate at 50 ft. The reverse is not true. Load accordingly.
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