Lee 405 gr. 459" Hollow Base

[BudRow]

Is the purpose of the hollow base to shift the center of gravity or to take advantage of the Minie effect? Or both? The cavity doesn't seem large enough in diameter to be effective as a Minie. Will the initial boot from a smokeless load expand the skirt? Looking to use it in an original Springfield trapdoor. Thanks. Bud

[country gent]

Like a Minnie these are meant to be cast soft. They expand out to fill rifling. More like a 38 HBWC. Even the original thin skirt minnies originally had a mating tapered plug fitted to help the skirt expand as back in the day it wasn't thought pressures would expand them reliably. The thin skirt minnies will blow deform at much over 60 grns of black powder. In the 45-70 with 60-80 grns they should do well. In your Trapdoor ( possibly a larger bore) the 405 lee at carbine level loadings should perform well If the hollow base worries you lee has a solid based version also

[kootne]

Bud, all you will ever need to know about that mold and trapdoor Springfields is in this book.

https://www.shopspg.net/Loading-Cart...ridges4570.htm

My 1884 Infantry rifle will put 10 shots into 5"-6" groups at 200 yards with the 405 hollow base bullet cast 20:1, well it did when I could still see through those fine sights.
But you need to read the book, there is a lot of subtle differences between modern loading conventions and how these cartridges were originally made.

[BudRow]

Thanks guys! I am casting 20:1. Is there a smokeless load fill out the skirt without exceeding trapdoor pressures? I also have the solid base version. Grooves slug at .461-2" Thanks,Bud

[415m3]

I just shot my TD this week with that bullet over 25gr of 5744 and found it to be very accurate at 100yds. I must say that I greatly preferred a duplex load of 2F over 5744. Get the book mentioned above. These loads and others are in detail there.

[Carrier]

I use H4198 but my Trapdoor is most accurate when using black powder. I use the 405 HB as well.

[flintlocke]

I'm using the Lee 405 HB, wheelweights with a little tin added, with 28 gr 4198, Win brass, Win LR primer, 1 gr dacron or cotton powder positioner, 1354 fps, pretty consistent 2 1/4" 5 shot groups at 100 yds. Trapdoor cadet.

[Larry Gibson]

BudRow

"Is the purpose of the hollow base to shift the center of gravity or to take advantage of the Minie effect? Or both? "

Neither. The Lee 405 HB bullet was designed for Lee by Spence Wolf, a noted "Trapdoor" expert. He designed the bullet to, as closely as possible, replicate the M1873 arsenal bullet. The dimensions of the bullet, including the HB, are very close to the original bullet dimensions. The HB is actually called a "dish" in the descriptions of the bullet on the original platte drawings. It's stated purpose is to allow, by varying the size of the "dish", the external dimensions of the bullet and the weight of the bullet to remain constant regardless of the alloy used.


"The cavity doesn't seem large enough in diameter to be effective as a Minie."

That is correct. Additionally the thickness of the skirt precludes any meaningful "bumping up" or expansion at most TD pressures, especially BP load pressures. It's one of the reasons [lack of "bumping up"] that the arsenal went with a heavier 500 gr bullet in 1882 that had the mass to allow "bumping up" to better obturate in the bore. It's also why the M1882 load with the 500 gr bullet was more accurate than the M1873 load with the 405 gr bullet.

"Will the initial boot from a smokeless load expand the skirt? Looking to use it in an original Springfield trapdoor. "

Not at trapdoor pressures, even with softer alloys, if the bullets are sized .459 and you expect good obturation into TD grooves to any meaningful degree it just won't happen. There's just not enough mass to the bullet. However, if the Lee bullet is sized at groove or larger diameter (I size mine .4615 for my TD with a .460 groove diameter) it can be made to shoot as well and any other PB 400 +/- gr cast bullet in TDs.

[Chill Wills]

BudRow I would be interested in you explaining how you measured your Springfield bore and groove. I have had six Springfield trapdoor rifles and I use a somewhat goofy way to measure them. I think it only gets me close. I do pin gauge the breech and muzzle too. That measurement is less useful.

[flintlocke]

Looking forward to hearing about measuring groove dia on a trapdoor. I couldn't even begin to understand the explanations and formulae here on this forum from a few years ago. When I slugged mine, I dressed the slug perfectly flat on one end, attached a centered machine screw "handle" on the other end, prussian blued a Morse taper #1 sleeve, and gingerly inserted the slug squarely into the sleeve, rotated it carefully 60 deg or more, withdrew the slug and measured the diameter of the witness mark. I doubt it's dead nuts accurate, but I did get more consistent readings than the shimstock method.

[Larry Gibson]

Simply take a piece of thin shim stock 1/2" x 3-4" [beer or soda can will do] and wrap around the slug from the barrel. Pinch it tightly together on one side and then measure the diameter. Then subtract twice the thickness of the shim stock and you have the groove diameter. This works well for measuring the slugs from other odd numbered lands and grove barrels also. You can use calipers or a micrometer. Measuring to the nth degree is not necessary...with in .001" +/- .0005 is sufficient for measuring groove diameters of TDs.

Better is to do a chamber cast and measure the small throat diameter directly in front of the chamber mouth. Then size or use cast bullets sized to just fit that diameter.

[Chill Wills]

I have heard of this before, not tried it, but I guess I am not understanding how this works. 180 degrees across in any direction from a groove is a land. Wrapping still does not produce two grooves 180 degrees apart to measure. What and I missing? Are you trying to produce enough "edge" or "overhang" next to the major diameter to measure something?
I am still interested in hearing back from BudRow if he in interested in telling his method.

I have a different system that is likely very good, but it is not the correct 120 degree vee block.

Thanks.

[marlinman93]

Even with smokeless powders the hollow base will expand some if you're using a little softer mix. I'd go to 25:1 or even 30:1 to get it to expand, if you even need expansion. It may be that the bullet fits your groove diameter, and it wont need to expand at all.
I like hollow base bullets for the weight forward effect they have. In my guns where I use them they have been more accurate than plain base bullets of equal weight. I think the weight forward stays stable longer than plain base bullets.

[17nut]

I have heard of this before, not tried it, but I guess I am not understanding how this works. 180 degrees across in any direction from a groove and a land. Wrapping still does not produce two grooves 180 degrees apart to measure. What and I missing? Are you trying to produce enough "edge" or "overhang" next to the major diameter to measure something?
I am still interested in hearing back from BudRow if he in interested in telling his method.

I have a different system that is likely very good, but it is not the correct 120 degree vee block.

Thanks.

Instead of measuring a slug with odd groves you measure a "true" cylinder that is 2x foil thickness bigger.
That way you get very close to a proper diameter measurement.

If you want to jump alle the hoops then use this:

How to measure odd grove bullet diameter

The V-anvil micrometer is the best way but it is an expensive and specialized tool that most people won't want to pay for, especially to measure only a few slugs. A way to simulate one is to make a small V-block of the appropriate included angle (108° for five grooves), calibrate it with an accurate diameter pin, and then measure the bullet and V-block with an ordinary micrometer. Then do the math given below.

The math goes like this:
Let a = the included angle of the V-block,
t = the thickness of the V-block from the bottom of the V to the bottom,
h = the measured height of the bullet and V-block,
and d = the diameter of the bullet.

Then d = 2(h - t)/(1 + 1/sin (a/2) )

An example:
For a 5 groove bullet, the included angle (a) is 108°, assume the V-block "thickness" (t) is .250" and the measured total height (h) is .5854", then
d = 2(.5854 - .250)/ (1 + 1/sin (108/2))
d = 2(.5854 - .250)/ (1 + 1/sin 54)
d = 2(.5854 - .250)/ (1 + 1/.80901)
d = 2(.5854 - .250)/ (1 + 1.23607)
d = 2(.5854 - .250)/ (2.23607)
d = 2(.3354)/(2.23607)
d = .6708/2.23607
d = .300

The easiest way to determine the V-block thickness (t) is to measure a known cylinder and then calculate it from

t = h - (d/2) (1+1/sin(a/2) )

With typical groove depths, you should be able to measure both land and groove diameters if the slug isn't too long.

Note: this process will work with a 90° V-block (using 90° for the included angle) and a 5 groove slug for groove diameter if you are careful to position the slug with the large diameters on the slopes of the V. You won't be able to measure the small diameter though.

Or this:

[Chill Wills]

Instead of measuring a slug with odd groves you measure a "true" cylinder that is 2x foil thickness bigger.
That way you get very close to a proper diameter measurement.

If you want to jump alle the hoops then use this:

So if I understand correctly, measuring the true cylinder involves bridging over the land space and mic'ing over the foil above the air space created by the wrap. Did I get this right?
Respectfully, Michael Rix

[john.k]

What a lot of complex waffle......simple to pin gauge the bore ,then slug and measure any diameter.....this will be the pin diameter plus one groove depth......deduct pin from diameter gives groove depth,which can be assumed regular....Question is ,with a 3 groove rifling of equal land and groove width,why do you need a bullet any larger than bore +one groove?

[flintlocke]

Why didn't we think of that? Down under cousins would rule the world if they weren't dizzy from standing upside down all the time. Grin.
Thanks john.k

[bigted]

My way to measure three groove or 5 groove or 7 groove ect. Barrels is maybe overly simple ... but it has served me well thus far.

I drive a soft lead ball of 50 or 54 cal down a well greased bore.

I then clean it carefully and in several places, measure the rifling depth ... followed by averaging my findings.

Now measure from the groove on one side to the bore on the other side.

Now add groove depth to this for a groove depth. Subtract this groove depth for your bore diameter.

As Larry mentioned above, I find that the arrival of + or - .001 to .0015 being sufficient.

By far the easiest tho for almost sure accuracy is the following,

Take three fired cases from your rifle. Carefully remove any crimp left on the mouth of these cases. Measure the neck area on the three and average the finding. This will be your magical number to cast and size your boolits ... now all that is left is weight of boolit ... powder ... primer kind and power ... compression of BP ... ect ect ect.

Easy peasy. Works for me.

[BudRow]

Chill Wills, I have a 9" South Bend lathe with a 3 jaw chuck. I took a 1" piece of 1/2" O.D. soft rubber tube/hose and slid a drill bit in it so it wouldn't collapse easily. This I put deep into the jaws of the chuck to offer radial resistance as the jaws were closing. I took my slug and carefully closed the jaws of the chuck until the slug just barely slides in and out on the 3 lands of the slug. A while back I bought a set of pin gauges 1/4" thru 1/2" by one thousands and so pin gauged the jaw opening to arrived at .461". Of course pin gauged the bore easily. Bud

[oscarflytyer]

Trapdoor level smokeless load. Waters Pet Loads. I use the Lee 405 HB (cast of WW+2% tin for my Marlin, but could easily use 20/30/40:1 alloy) pushed by 38.5 grns of IMR 3031. Size it to .460 for the Marlin MG. Shoots great out to at least 100 yds with peeps and my old eyes. Very easy recoil and a real deer thumper to boot!