Flat vs. hallow base bullets...

[Shinken]

As a beginner reloader, after buying everything (except the bullets) I need to make my first batch, I was stomped again to notice that bullets come with a hallow base vs flat base ! What is the difference between the two?

If it matters, I am reloading for a Sig P226, 9mm 115 grain, to be used primarily at the range.

CC

 

[BattleChimp Potemkin]

Theoretically, hollow base bullets:
1. The skirt on the bottom (formed from the hollow base) will expand under the pressure and give a "sealing" effect, giving more consistency (only going on what was told, someone correct me!!!)
2. Reduces chamber pressure by giving more case volume maybe?
3. More bearing surface by giving a higher/more? ogive.

All I know is that I do notice a difference in general accuracy (ransomed pistol at closer ranges) over solid base bullets with the same loading formula (but VERY slight, mircometer time!). However, at longer ranges, I tend to get worse accuracy (falls off around 25 meters or so).

Ive seen this question kicked around the internet for some time. Lets get a science dude in here and get a definitive answer!