Factory loads and bullets?

[flyrobb]

After my curiosity got the better of me I pulled apart an American Eagle FMJ 124RN and 115RN. Both measured 1.150 +/- COL.

The powder charge was 4.0 for both. Looked a awful lot like B.E. when I compared to several powders I have.

The 124 was a flat base FMJ and the 115 was HB and the bullets length (tip to base) was .601 & .598 respectively, almost identical. This would seem to explain the same COL.

A two part question.
1)What I the purpose/advantage to the hollow base bullet? I have some Xtreme Concave Base but they are no where close to the "scoop" of the HB. Looking online I see that Winchester offers a HB that looks much like the Federal I pulled.

2)I was surprised the powder charge was identical for both bullets. I always understood the a heavier bullet would take less powder. Why would they use the same charge for both bullets?

[jwalts27]

All I can add to this is I use a lot of 'pulled' bullets I get pretty cheap in 40SW. they usually come as a mixed lot of both flat base and concaved base. After working several testings i see no difference when I chrony them or accuracy issues. I load them all the same now. This holds true for both 165g and 180g. Maybe somebody has a different opinion but that's what I see.

[fredj338]

It's not likely BE, but a non canister powder. Having the same charge tells me they are just saving $$ & down loading the 115gr a bit.
A concave or HB bullet will allow a bit longer bearing surface for the bullet & potentially reduce pressures just a bit, more case volume.

[Nevada Ed]

Scooping out the bottom of a bullet is a good way to reduce weight and also be able to have a longer OAL due to a longer bullet.

Having the same OAL and the same amount of powder ............
means less die adjustments and a saving of time and money making two different loads. Smart move.

They do it in lead bullets also.

[Twoboxer]

Don't know the right answer . . . won't let that stop me from guessing lol.

As mentioned above, the same OAL and the same powder charge with bullets having the same nose profile means the only equipment changeover is to swap bullets. A real time-saver, just like Sierra pulled foff when they suspended production of many lower-volume SKUs to produce more high-volume bullets during the "crisis".

The hollow base allows a longer bearing surface than a bullet of the same composition and weight with a flat bottom. Many believe this can improve accuracy.

[flyrobb]

That all makes perfect sense! It's all about economics when cranking out factory.

Also noticed the box specs are almost identical as well.
115g fps 1180/1110/1050. 124g 1150/1110/1050 (muzz/25yds/50yds)