Sub-sonic Bullet Design

[pillardrill]

Upon doing some research I discovered that the 45 degree cone at the back of my bullets would have a detrimental effect on the performance of these bullets instead of what I had hoped for.

Looking around I read that the best shape for the base was a truncated cone of sides inclined max 12 degrees. Base drag greatly affects the performance of a bullet at sub sonic speed.

I had to have this cone on my bullets however it was not as simple as just boring a conical hole in the punch forming the base. The formed bullet would stick to the punch. I had to make a small tool which formed the base and had an ejector to eject the bullet.

It works great with lead bullets, maybe later on I will make a punch complete with base shaper and ejector.

[deltaenterprizes]

Lube on the base would stop sticking.

[BT Sniper]

Great work. I see riffle bullets in your near future using this same design.

Keep it up thanks for sharing.

BT

[pillardrill]

Delta,

even if lubed they still stick, I like to look for the simpler solution before going through more trouble.

[Caveape]

Pillardrill,

I have made an interesting boat tail bullet for my 357 mag by turning my finished projectile around and feeding it backwards into my point form die. It gave a nice tapered boat tail, but it might not be the 12 degree taper you're looking for.
I had to unscrew the die just a little for this last step as the initial adjustment for the point forming was too much. I only wanted the base to go into the ogive area of the die about a 1/4 or 1/3 of the way to just get that initial taper.

I was pleased with the way they turned out and I did not have to purchase any special boat tail pieces to go with my set of dies. It just adds an extra step, but that's no big deal for a specialty round.

Hope this helps.....

Caveape

[pillardrill]

Hi Caveape,

thanks for the tip however I made proper punch which ejects the bullets with ease.

Beware the included angle should not be more than 22 deg, (angle of my new punch) otherwise the book of knowledge says the turbulence would act on anything that is behind the maximum diameter of the bullet and destabilize it. At the proper angles the the airflow sort of keeps the shape of the missing part of the cone (at the bullet base). Also any turbulence has less area to work on.

A rebated tail is best since the bullet does not fly through its muzzle blast apart from other benefits.

From what I have read

[Caveape]

Yes, I know of 2 benefits of the rebated boat tail:

1. deflection of muzzle blast away from flight path
2. reduced drag in flight for flatter trajectory

But, are there other benefits of which I am not aware? Please tell me more!

I don't know why there aren't more rebated boat tailed offerings out there. Is it a patented design by Dave Corbin or what's the deal? (Yeah, you're welcome, Dave!)

I think it's agreed that point #1 above makes them superior over other standard BT's.

What's your thoughts?

[pillardrill]

Another 2 major advantages the rebated boattail has over the boattail design:

- it is easier to accurately form the base of the bullet concentric with the bullet. If the taper on a regular boattail is slightly off, when the bullet base is about to exit the muzzle gas would escape at that place where bullet no longer seals. This escape of gas upsets the bullet.

- rebated bullets seal the bore better than boattails.

There are several patents on rebated boattails. I haven't yet found out who started manufacturing them first, and why they are not widely used. Most probably an extra step is necessary to manufacture the base.

Further research is needed here

[Caveape]

Thanks for the info, Pillardrill.
I now see there are lots of advantages over the standard boat tail design.
To get such a superior finished product as this, I would glady do the extra step to make them rebated.

Thanks!