Boat tail angle and punch material

[MFG_BOP]

Hi guys, two questions here for the expert.
What is the best boat tail angle and length for the .204" similar to this ONE (http://www.midwayusa.com/product/1076339016/berger-varmint-bullets-20-caliber-204-diameter-40-grain-hollow-point-boat-tail?cm_vc=ProductFinding)?
Also, what other steels, beyond the 1144, can I use as punches? Do they
need to be heat treated when I use with carbide dies (insert)? Sorry, I looked up
here but didnt find info. My bad!
Regards
Cheers.

[MFG_BOP]

Nobody?
What I found out is the length of the BT which is 0.1". Now, I need the angle.
Also are the punches made out of 1144?
Cheers

[boltaction308]

Boat tail angles should be about 9 degrees and not more than 11

This is the general rule for all rifle bullets.
Anything more than 11 degrees causes turbulence

This is from books by McCoy and by Carlucci

[MFG_BOP]

boltaction, cool!!! thanks for the info... I think I will go for the 9 degrees and for the carbide insert. Cheers

[aaronraad]

I prefer H13 at the moment with hardness in the range of 56-58 HRC at the most. Softer the better for boat-tails to ensure maximum toughness of the material.

Boat-tail lengths and angles are a function of a projectile's overall design. Boat-tails are designed to cause a certain amount of drag by pulling the centre of pressure back and push the centre of gravity forward. Long ogive projectiles will always have a centre of pressure ahead of the centre of gravity and therefore require more spin to keep them point forward. The preference of course would be to have the centre of pressure behind the centre of gravity, but that is why we can stabilise arrows and rockets with fins at the rear with zero spin required and all the accuracy required. Problem is though they don't launch well out of a barrel at supersonic velocities without some sort of very, very, very (I did I say very) well controlled/timed/repeatable discarding sabot.

Take the extreme for example. Flat base projectiles are just a 90 deg boat-tail and are adequately stable, are they not, when done in correct proportions to the shank, ogive and meplat to produce accurate and stable short range projectiles out of a rifled barrel?

So to answer your question on boat-tail angle and length, you need some idea of bullet weight, shank length, ogive length, ogive radius including offset (i.e. 0 offset = tangent; offset > 0 = secant). Sorry I don't have that detail for the example you hyper-linked to. Corbin's DC-1001 Spitzer Bullet Design Program starts to become a very useful comparison tool, especially when you can calibrate it off a well detailed, accurately measured existing projectile with a corresponding real world form factor ( or BC's if you like but you'll need to know Mach values as well).

No one says the 168gr Sierra MK isn't accurate and stable, but it's boat-tail limits it's range potential for it's weight, compared to other designs.

[MFG_BOP]

aaronrad, tks for that! I have some Ulrich dies and the punches look to be not hardened. I am guessing, but I read here somewhere that 1144 is being used for punches. Just correct if I am wrong.
I just ordered the carbide inserts for the .204 I will make. For now, they will be FB and as soon as I realize the boat tail details, I will order it. I will lap them also.
Interesting details on your web site. I am located in NZ, BTW. Do you make your own jackets?
Cheers

[aaronraad]

aaronrad, tks for that! I have some Ulrich dies and the punches look to be not hardened. I am guessing, but I read here somewhere that 1144 is being used for punches. Just correct if I am wrong.
I just ordered the carbide inserts for the .204 I will make. For now, they will be FB and as soon as I realize the boat tail details, I will order it. I will lap them also.
Interesting details on your web site. I am located in NZ, BTW. Do you make your own jackets?
Cheers

Hi MFG BOP

I fear you may have used up all your luck!

1) You have a set of Ulrich dies;
2) You live in NZ;
3) I'm guessing you also hunt in NZ; and
4) You don't need specialised permission from the Attorney General to fit a silencer/sound suppressor to your bolt-action rifle. :)

There would be an absolute plethora of material grades used for punches over the years and currently, especially given the ingenuity of members on this forum. Predominately it comes down to what is available for the dollars at the time of order, what works with your forming/heat treatment equipment and what works with your jackets and dies.

You can always run a file over the head of a punch to get some idea if it's under or over 60 HRC roughly speaking. I would also suggest speaking to George Ulrich before attempting to make a boat-tail punch yourself for his point form die. I know he has some fairly specific preferences in relation to his core seating die and point form die when it comes to boat-tail bases. George can make boat-tail punches to specification, but if you can't give him the details he would really need the die set to make a boat-tail punch guaranteed to work. It's a conversation worth having even if you decide to go ahead and machine the punches yourself. Conical boat-tail punches (as opposed to rebated boat-tail punches) crack if you look at them wrong way and can get relatively expensive and time consuming to replace frequently.

I see you are ordering carbide inserts for the .204, I assume this is for a boat-tail core seating die as opposed to a point form die? If so, I believe carbide is overkill for core seating unless you are looking at wear rate for high volume/temperature, surface finish for ejection/minimal lubrication, or another specialised requirement.

I've been avoiding making my own jackets because I want to move on from basic cup & core designs, but it looks like it could be unavoidable if I want to keep producing traditional, long range, match grade projectiles.

Cheers
Aaron