bullet design software

[scion19801]

does any one know if the is any free or reasonably price software for trying to come up with a slug that works well in our airguns. I have a few ideas in mind and want to try to come up with something that can be cast and be effective in the 34 gr range and have the biggest hollow point possible. Also hoping to get it to work with 1:18-1:21 twist rates.

[rkr]

Kolbe calculators will get you started, the drag calculator shows bullet shape, BC and twist: http://www.geoffrey-kolbe.com/external_ballistics.htm

[rsterne]

Any drafting software will allow you to DRAW a slug.... but I don't know of anything that will assist you in making the decisions on the dimensions.... at least not that is designed for subsonic work....

Bob

[scion19801]

never gave the subsonic side of things a thought. wonder if the NOE .223 could be resized to work for .25 cal yet come in at the 34gr range with a massive hollow point.

[rsterne]

I have no idea which NOE .223 you are talking about.... but if you extrapolate the diameters our to .25 cal, without changing the length, the weight will increase by about 26%.... If you scale the bullet up in length as well (so that it is the same proportions in a larger caliber).... then the weight would increase by about 41%....

Bob

[scion19801]

so if scaling up wouldn't be to good to do, as it would drastically increase weight.
would taking a flat based slug like the .249-rf hollow point and then expand it to .251" for the drop diameter. then possibly put a narrow body section so that it would ride the bore at the nose, maximum meplat and hollow point?
my thought it one to reduce the weight to the 34 gr area, and try to limit the barrel drag so am to increase the velocity some. so it would have basically a bore band diameter at the front, and also a bearing contact at the rear to keep it stable in the barrel.

[rsterne]

You could cut away a portion of the parallel midbody, from the back of the nose, to within about 0.050" of the base, to leave a drive band there, while eliminating some of the bore contact area between that and the nose.... There isn't a lot of length there, just over 0.10" that you could reduce to about 0.240" diameter to clear the lands.... It would not remove much weight.... Of course you could also make that portion smaller in diameter until you got rid of 5 grains, but it might be pretty tiny, more like a pellet than a slug.... I doubt you could get down to 34 gr. without shortening the slug overall, and you don't want to reduce the bearing length to less than about 2/3 of the caliber, which doesn't give you much to play with.... Mind you, NSA doesn't worry about the length of parallel bore contact....

Check out the NSA website for the .25 cal slugs.... Here is one pretty close to what you want....

https://nielsenspecialtyammo.com/collections/25-cal/products/33-5-grain-275-count-250-slug-nsa?variant=28618256285789

I wouldn't worry too much about the extra length of bore contact causing drag.... Just size the bullet down a thou or so.... That is what all the slug swagers do if the drag is too high.... The shortest NSA slugs (like the one I linked and shorter) don't really have a parallel section, the nose Ogive goes all the way to the base.... which is why there is a note on that page that the diameter is less than 0.250"....

Bob

[ballisticboy]

The Kolbe calculator cannot work for hollow point bullets and will give inaccurate  stability predictions. It is also not good at speeds between 1000 and 1200 ft/sec and does not agree with other software or measured results.

You would need a program to calculate the true centre of gravity position and then an aerodynamic prediction program for the stability calculations.