step in bullet base

[jim8115]

Just got some 9MM Zero 147 gr JHP's. The have a step at the base. i have never seen this on any other bullet, though I havent loaded a lot of 9mm yet.
What is the purpose of this? Can I seat these without expanding the case?

JIM

 

[blarby]

Pics please ?

I have a lot of zero bullets, and none of them have a step ?

A lot of the 147g 9mm bullets have a boat tail like design, but thats to accomodate powder spacing if I'm not mistaken.

 

[noylj]

You mean like this:

 

[gamestalker]

Do you think he is referring to a rebated BT maybe? Other than that, I've loaded with a good number 147's that had BT's, XTP's for sure. Nothing special about how you load with them, same seating procedure, use your barrel for the plunk test, start low, so on, so forth.

BTW, I don't bell any of my mouths when seating any jacketed bullets, I just chamfer the inside of the mouths, no crimp necessary either.

GS

 

[Blue68f100]

Looks like the bullet mold was design for a Gas Check.

 

[jim8115]

Yes, exactly like the image noy posted

 

[243winxb]

Bullet Base Designs

Remington Bullets 9mm (355 Diameter) 147 Grain Jacketed Hollow Point available now (2010) at Midwayusa. I had to see it to believe it. Who said only flat base bullets are accurate? I ask Remington ".Can you give some history on said bullet." There reply "Why it has the bubble shape is due to the manufacturing process." After some googling, if feel this is the real reason > This bullet base design will keep the hot gas from getting in front of the bullets nose as it leaves the muzzle, resulting in a more accurate cartridge.

 

[Jesse Heywood]

This bullet base design will keep the hot gas from getting in front of the bullets nose as it leaves the muzzle, resulting in a more accurate cartridge.

The convex base increases the surface area, which increases the force applied to the bullet without increasing the pressure. This would cause the base to expand faster, giving a better seal in the bore, thus increasing the accuracy.

Why it has the bubble shape is due to the manufacturing process.

I smell smoke! But without knowing how the striking die is configured, I can't prove it.

 

[243winxb]

Can I seat these without expanding the case?

I would guess, expand & bell case mouth, as normally done.

 

[Hondo 60]

Hmmm very odd looking.
That bullet looks like it's designed to use a gas check.

But I've never seen a plated or jacketed bullet that uses said gas check.
There's just no reason to use a gas check on anything other than a solid lead bullet

 

[LiveLife]

Aren't jacketed bullets, whether FMJ/JHP/CMJ already lead bullets with "full length" gas checks?


As to OP, my guess would be with 147 gr bullet with longer base, especially with JHP with cavity in the nose that would further increase the bullet base length, the step would be for preventing case bulge from case wall that thickens towards the case base and may not allow full chambering of finished rounds.

Or we could just call Zero/Roze and ask them.

 

[LiveLife]

Update. OK, I called Zero customer service and they confirmed the step in the 147 gr JHP bullet is to prevent case bulge so the finished rounds would fully chamber. Also, a regular amount of case neck flare was recommended for seating the bullet.

BTW, Powder Valley also stocks Zero bullets if you can't find them in stock on Roze website.

 

[Jim Watson]

Hornady's 147 gr bullets have an actual boattail for bulge free seating in the short thick 9mm case.

I suspect the bubble bottom Remington bullet is made that way for the same reason as the Hornady or Zero. If the "increases surface area" worked, there would be a lot more of them.

 

[Potatohead]

Wow, good work BDS.