Help Designing a Mold

[Andy_P]

I'd like a 7mm Mold from Mountain Molds producing a 0.287" gas-checked bullet weighing about 200 grs that must satisfy the following criteria:

- Tangential Ogive;
- Meplat: 70%;
- nose length (bullet outside of neck) cannot exceed 1.150" (mag length restriction)
- bullet cannot be more than 0.335" inside the neck (so it doesn't go below the neck); and
- the ogive on the bullet must measure 0.284", at the 0.400" mark of the nose (ahead of the neck). That's the throat length.

How do I begin?

[just.don]

http://www.mountainmolds.com/

start @ top left, drop down menu for cal.

[Andy_P]

http://www.mountainmolds.com/

start @ top left, drop down menu for cal.

Thanks, but that doesn't answer my question. I have used their application many times, and nowhere in it does it allow you to enter all my criteria. The important part is "the ogive on the bullet must measure 0.284", at the 0.400" mark of the nose (ahead of the neck)". I can fool around with other criteria once that's set.

[John Ross]

Start with these specs and tinker. I used .350" for the front band and .050" for the bore ride to get you close to your .400" length for .284" ogive point. Seat it out a hair. No idea if it will shoot.

Best would be to shorten the nose to .200" or so, the front band and bore ride to .050" each, and get more lube grooves and seat it out with lube grooves exposed.

http://i307.photobucket.com/albums/nn302/JohnRoss_07/7mm.jpg

[John Ross]

Thanks, but that doesn't answer my question. I have used their application many times, and nowhere in it does it allow you to enter all my criteria. The important part is "the ogive on the bullet must measure 0.284", at the 0.400" mark of the nose (ahead of the neck)". I can fool around with other criteria once that's set.

Ignore this. Find a shape that you think will shoot and plan on seating the bullet out so the .284" dimension is .400" in front of the end of the case.

Look at my drawing from the screenshot, and then envision more lube grooves on that .350" long front band.

You'll figure it out...

[John Ross]

Okay, here's a better starting point.

http://i307.photobucket.com/albums/nn302/JohnRoss_07/2nd7mm.jpg

The .284" diameter at .400" in front of the case neck will be the front of the front band. You will thus seat this bullet out so that the back of the front band is .350" in front of the case neck, and your shank in the case will be .350" LESS than the figure of .68" shown, or .330"

This gets you what you want, but weight is only 170 grains. If you want more weight with the other dimensions held to spec, you're going to have to lengthen the nose and put more weight in front of the front band. The resulting bullet may be inaccurate. I have no experience with cast rifle bullets under .458" diameter.

[Andy_P]

That's a nice bullet, almost a Loverin style, but still lighter than I'd like. What are the pitfalls of this design? It would be crimped at the first lube groove, about 0.240" in the case, with some lube grooves exposed, with about 1.000" of bullet out of the case.

http://www.pridham.ca/7mm_200gr_Mountain_Molds_Design_1.jpg

[Piedmont]

What is the twist of your rifle Andy? The standard rifling was set at something like 1 in 9" for a 172-175 grain bullet. What are you getting with a 200 grain? A properly made solid in 7mm of around 175 grains would shoot through an elephant's head. Why do you want more than that?

[Andy_P]

What is the twist of your rifle Andy? The standard rifling was set at something like 1 in 9" for a 172-175 grain bullet. What are you getting with a 200 grain? A properly made solid in 7mm of around 175 grains would shoot through an elephant's head. Why do you want more than that?

1 - 1: 1.866, and it nicely stabilizes a bullet 1.5 " long.

2 - Because I want it.

[nanuk]

2 - Because I want it.


sounds like a good enough reason to me

[singleshot]

The Mountainmolds program won't allow you to design a 7mm boolit that heavy. Trust me, I've tried. You'll have to look elsewhere.

[John Ross]

The Mountainmolds program won't allow you to design a 7mm boolit that heavy. Trust me, I've tried. You'll have to look elsewhere.

The last screenshot would seem to disprove this.

[John Ross]

That's a nice bullet, almost a Loverin style, but still lighter than I'd like. What are the pitfalls of this design? It would be crimped at the first lube groove, about 0.240" in the case, with some lube grooves exposed, with about 1.000" of bullet out of the case.

http://www.pridham.ca/7mm_200gr_Mountain_Molds_Design_1.jpg

Looks good. I was tired when I posted before. WHAT is your twist again? Did you mean one turn in 8.66 inches?

[Andy_P]

The Mountainmolds program won't allow you to design a 7mm boolit that heavy. Trust me, I've tried. You'll have to look elsewhere.


The last screenshot would seem to disprove this.

You're both right. The Mountain Molds program in this instance gave every appearance that the design could be produced and when you go to buy it, it tells you it's too long. The blocks are 1.5" high, so I suspect that he can't mill 1.25" at 0.284". Anyways, it's a no-go.

My twist rate is 1:8.66".