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Another home made BHN tester

Posted: Sat Feb 16, 2008 9:07 pm
by mtngun
from the old forum:

I had an itch to revise my BHN tester. The old one gave good numbers but it was awkward and time consuming to use, so it didn't get used much.

To hold the bullet, I made a shell holder thingy, except with a flat surface.

I wanted a 10 mm indenter because that is the "official" size, but didn't have any 10 mm balls laying around, so I turned a 10 mm round nose on a piece of 5/8" drill rod. The round nose was heat treated, tempered, and polished.

My universal die holder holds the indenter. This is the same die holder that holds my push-thru dies. A $5 stick of 5/8" W-1 drill rod will make a lifetime supply of push-thru sizing dies.

Force is supplied by a weight hung on the handle of the reloading press, with the die adjusted so that the handle is horizontal. My press has a 6.38:1 leverage at the horizontal position, so it needed a 15.7 kg weight to create the recommended 100 kg. force on the ram. I didn't have a 15.7 kg weight, but I cobbled together a 16.5 kg weight from some barbell weights. It's a hassle to assemble the barbell weights so I really need to make a dedicated BHN weight. It could be something as simple as a paint bucket filled with lead ingots, sealed and marked.

The load is applied for 30 seconds, then the indent diameter is measured with a magnifying glass and calipers. It's easy to measure the big indent on soft bullets, but great care is required to measure the small indent on hard bullets accurately.

A spreadsheet crunches the numbers. If I ever get around to making a proper weight, I'll print out a table to convert the indent diameter to BHN.

Here are some sample measurements:

30:1 -- 4 BHN

WW & 2% Sn air-cooled -- 11 BHN

Lyman #2 -- 16 - 18 BHN

my lino -- 23 BHN

a customer's lino -- 21 BHN

oven treated WW, 4 months old -- 33

2+ year old bucket-dropped, alloy unknown -- 20 BHN

By the way, that bucket dropped bullet measured 28 BHN when I tested it 2 years ago, so it has held up better than I would have predicted. Some one gave it to me, so the alloy is unknown, but looks to be mostly WW.

Problems? The die cannot be adjusted correctly for very long bullets. It works fine for bullets up to about 1" long, 35 caliber and up. The lathe-turned round nose came out pretty smooth, but a ball bearing would be smoother. A ball bearing could be epoxied into piece of 5/8" steel so it would fit in my die holder.

But mostly it works well, and if I ever get around to making a dedicated weight, it'll be perfect.