Concave 115 FMJ

[halfmoonclip]

I've been going with Everglades for my jacketed bullet needs (and they are great to deal with, prompt, and very cost competitive...and all prices includeshipping, tho' of course the prices get better with a larger buy).

Generally, I've been buying the concave base 115 FMJ 9mms; they shoot fine, but I've always wondered what the concave base was about.

Their flat base 9s are getting to the point of being cost competitive with the concave version.

Any ideas, or even good guesses, what the concave bases were for?

Thanks in advance,
Moon

[Uni-Vibe]

I think those are Armscor, made in Phillipines.

I just received 4000 of the flat base 115s, Made in USA.

[halfmoonclip]

That would explain the better price. I may get the flat base next time.
Any idea of the 'why' with the concave ones?
Moon

[gaijin]

Best guess; the concave base helps to obturate, “slug up” and provides a better seal for the bore, which prevents gas “blow by”, helping accuracy.
A .22 has a skirted base for this reason.

[5shank]

I thought I read that the 115 concave bullets were a little under size? Need to order soon and have always used RMR but may try Everglades if the accuracy reviews are good with the 115 gr concave.

[gaijin]

That would make sense; undersize bullet allows blow by, the concave base would act as a “skirt” and help seal the bore.
Have no clue what their reasoning is, if bullets are, in fact, undersize.
Sounds screwy to me.

I use Everglades JHPs in 9mm. They are properly sized and very accurate.
The 124’s I use look like Zero bullets.

[Bimmer]

Best guess; the concave base helps to obturate, “slug up” and provides a better seal for the bore, which prevents gas “blow by”, helping accuracy.
A .22 has a skirted base for this reason.

Hmmm... I wonder how much a modern jacketed bullet does this. Minie bullet were designed that way, but they were soft lead, and they were muzzle-loaded.

Another thought: Making the base concave increases the bearing surface relative to weight.

And the .22lr's bullet is just a relic of how revolver cartridges used to be made, right? The bullet is is as big as the case, and so the back of the bullet must be skirted to fit in the case?

Lapua made some skirted bullets for aero reasons (like a squared-off boattail), but that never caught on...

[gaijin]

Hmmm... I wonder how much a modern jacketed bullet does this....

A jacketed bullet will slug up, but it takes considerably more chamber pressure to do so than a soft, lead bullet.

Reading that the mic'd bullet was .355"- my guess the concave base was to help seal bore with a sloppy bullet fit- doesn't appear to have any merit.

[Bret]

Another thought: Making the base concave increases the bearing surface relative to weight.

BINGO! Even if there are other reasons, my bet is that this is the primary reason for the concave bullet.

BTW, that's an excellent price on the concave bullets. Their price on American made 9mm bullets is kind of high. I think they're getting their 147gr JHP's from Zero Bullets. They're price is much better on the same.