need help designing hb plug

[jason f]

85906

This is a 900 grain mold I am having cut for a hollow base.
Need some suggestions on designing HB. Thanks jason

[longbow]

I would go with something like the design here:

http://castboolits.gunloads.com/showthread.php?214680-10ga-foster-slug-mold-thoughts

post #13.

My suggestion is to not go less than 0.100" skirt thickness and 3 to 5 degree taper with flat or maybe hemispherical end on the pin to keep weight to the nose. When looking at skirt thickness don't forget the depth of the lube groove ~ you do not want the skirt to crush there.

Is this for rifled gun or smoothbore? If for rifled gun then HB depth and diameter don't matter except to achieve the weight you want but if for smoothbore you will want it at least half the slug length in depth or even deeper is better and a skirt thickness of 0.100" or more.

My thoughts anyway.

I will be interested to see the results along with range results when you are done.

Longbow

[turbo1889]

I try to make all my hollow base slugs have a skirt wall thickness that is no thinner then 0.08" at any point (for max bottom diameter of hollow base at bottom of slug that means subtracting 0.16" from the slugs diameter) and in the larger gauge sizes like to have 0.10" or slightly thicker wall thickness.

For a 0.73" outside diameter slug that means 0.57" absolute maximum diameter of the hollow base at the very bottom before you even start getting any taper and preferably more like 0.50" to 0.53" or so. You need at least three degrees of slope on the sides of that HB pin to get it to release reasonably easily but often the depth of your bottom relief/lube groove will often dictate a little more slope then that to ensure the skirt wall thickness does not thin out too much where that bottom relief/lube groove is.

As to depth of the hollow base, if you want the slug to be aerodynamically drag stabilized for firing from a smooth bore gun - just a little less then half the slugs length is the minimum depth (about 0.40" minimum depth on your 0.84" length) and the maximum depth is somewhat dependent upon the slugs nose shape (flatter noses can take more maximum depth and pointier noses can take less) but is generally around 2/3 of the slugs length or so. You've got a pretty flat nose there so you could probably go as deep as 0.60" with your hollow base but I wouldn't go any deeper.

As to the exact profile of the hollow base I personally like to keep it as square as possible while still ensuring good release and castability and don't usually like to round out the nose of my pins which puts unnecessary weight where it is not needed and does no good in my opinion and the only rounding of the tip I feel is necessary is just enough to make for reasonable castability. Just a little rounding of the edges of a fairly flat nosed plug tip.

Here is something along the lines of what I would do:

http://farm4.staticflickr.com/3745/10585691424_344a52fe0b.jpg

[turbo1889]

Well, while I was writing my post longbow beat me to most of it. The one thing I would note that he didn't mention as far as differences between the slug design you are using and the one for the 10ga. in the post he linked too is that the bottom relief/lube groove on that 10ga. design is deliberately shallower so as not to intrude into the skirt thickness and not have to make more then one angle on the plug side. With a deeper groove on the bottom like your design the best solution is to use a double angle on the pin sides to give kind of a bell shape to keep the skirt thickness where the bottom relief/lube groove comes in and still keep the skirt weight down to the minimum and keep as much weight up front as possible and only put as much weight in the rear as is structurally necessary.

[jason f]

Thanks for the info.

[TonyfromItaly]

8607686075

To make hollow base slug i used an adjustable pin inserted on the bottom of the mold (lyman style). This allows you to make the slug longer and heavier, or shorter and lighter.
I made the walls about 2 mm thick and it seems to work well. You could easily make the mold with 3 or 4 reducing rings, (i made it with 2) and make the overall diameter to fit the bore of your gun.