.50-70 Rainbow

[Noisydad]

First day back for the Seymour Black Powder Club today.
I had some time after shooting the 200 yard Big Bull event with my 1871 (iron sighted) Rolling Block in which I scored 2nd with a score of 73 so I had a crack at the 600 yard Big Buffalo gong.
With the help of a spotter calling the fall of shot I was able to walk the shots in till I hit the gong on the 6th shot with point of aim being the top of the hill behind the gong

Down range with the big buff gong way off in the distance.

IMG_0605.JPG (947.59 KiB) Viewed 6943 times

Using a GPS app in the phone after the range was closed, the holdover was measured at a whopping 25 - yes twenty five meters!
As I'd mentioned in previous thread I don't think the bullet hit the gong so much as landed on it! Never get tired of smacking gongs with open, iron sighted rifles!

[Bent Arrow]

Very cool. That's something I haven't had a chance to play with, can only imagine how much fun that would be

[in2anity]

Very cool ND, very cool indeed - I've been trying to reach out with my 30/30 lead loads myself. ND do you feel it would be possible to map that trajectory in a calculator? Translating actual back to theoretical is something I've been struggling with...

[Noisydad]

I was wondering about that trajectory thingy too and was hoping someone with a suitable program could do it because I have no idea.

[Gamerancher]

The Hornady website has a ballistics calculator you can use.

[Noisydad]

I'll have another play with calculator later. So far it's not matching known numbers but there's a few inputs I have to estimate.

[in2anity]

For me, those calculators don't seem to gel too well when my 165gr rounds go transonic; pretty sure it has to do with bullet instability wiping speed off faster than predicted. Not sure whether this is so much of an issue with fat 500gr projectiles though... (apparently not according to those in the know), hence my question.

[<<Genesis93>>]

We could work it backward for you.... with the 25m of holdover (bullet drop), assuming a velocity of....what?? 1200fps.(guessing).. more?

What type of bullet, estimate of BC? Woodleight have a 440gr BP 510dia example with a BC of 0.255.... however;

A drop of 25m (984inch) translates to a BC of 0.317 based on 1200fps....

This trajectory is indeed rainbow-ish, near parabolic (though a bullet trajectory is asymmetrical really) and would be close to that of a rimfire 22...

[in2anity]

We could work it backward for you.... with the 25m of holdover (bullet drop), assuming a velocity of....what?? 1200fps.(guessing).. more?

What type of bullet, estimate of BC? Woodleight have a 440gr BP 510dia example with a BC of 0.255.... however;

A drop of 25m (984inch) translates to a BC of 0.317 based on 1200fps....

This trajectory is indeed rainbow-ish, near parabolic (though a bullet trajectory is asymmetrical really) and would be close to that of a rimfire 22...

Could be wrong, but 0.317 doesn't seem right to me - that's SP bullet territory isn't it?

With a g1 bc of 0.1 (not too dissimilar to match 22lr), here's what I came up with:

440.jpg (190.3 KiB) Viewed 6853 times

[Gamerancher]

I don't reckon you'd be getting 1200f/s with only 55gr of 2f black-powder behind that bullet. Have you crony'd that ?

[<<Genesis93>>]

.317 was the iterative result from 25m drop and 1200fps(<thats a guess)
BC of 0.1 sounds a bit low... closer to a brick... made of foam..

[in2anity]

BC of 0.1 sounds a bit low... closer to a brick... made of foam..

Not really, think, 22 subs are 0.12 Besides isn't BC relative to MV anyway? (Lower the mv the lower the BC)

[Noisydad]

Nope still cant get it to play nice but thats no surprise to me - its a computer thingy.
Here's some input info (all in Inches) for those interested enough to have a go:
55 grains 2F Black Powder (compressed)
Cast pure lead bullet, 450 grain,
Dimensions (as it leaves the barrel) Length 1.047
Land diameter .473
Groove diameter .507
Bore riding length .700
Ogive .347
Flat nose diameter .180
Barrel Length 36"
R.o.T. 1;36

[<<Genesis93>>]

BC of 0.1 sounds a bit low... closer to a brick... made of foam..

Not really, think, 22 subs are 0.12 Besides isn't BC relative to MV anyway? (Lower the mv the lower the BC)

BC has nothing at all to do with MV.... it is a function of the 'slipperyness' or inverse of aero drag, relative to a 'standard projectile'...

[<<Genesis93>>]

Nope still cant get it to play nice but thats no surprise to me - its a computer thingy.
Here's some input info (all in Inches) for those interested enough to have a go:
55 grains 2F Black Powder (compressed)
Cast pure lead bullet, 450 grain,
Dimensions (as it leaves the barrel) Length 1.047
Land diameter .473
Groove diameter .507
Bore riding length .700
Ogive .347
Flat nose diameter .180
Barrel Length 36"
R.o.T. 1;36

I'm sure there is a computation to translate shape to BC, but all thats needed is the velocity.....we have the drop...

[Noisydad]

Ok this is now bugging me....did some trawling around and the velocity would be 1100 - 1200 FPS and probably nearer the 1100 mark and I wouldn't be surprised if it was as low as 1050ish.
I think Santa will bring me a chrony this year.

[in2anity]

BC of 0.1 sounds a bit low... closer to a brick... made of foam..

Not really, think, 22 subs are 0.12 Besides isn't BC relative to MV anyway? (Lower the mv the lower the BC)

BC has nothing at all to do with MV.... it is a function of the 'slipperyness' or inverse of aero drag, relative to a 'standard projectile'...

Then how do you explain this:

https://www.sierrabullets.com/store/pro ... -170-gr-FN

(just as a example) scroll down to where it stipulates the BCs based on MV ranges. Not that I'm mathematical enough to really argue, I don't think it's quite as simple as you make it out to be. I might be wrong...

[in2anity]

Here you go: "BC changes with the shape of the bullet and the speed at which the bullet is traveling, while sectional density does not." source http://www.chuckhawks.com/bc.htm I take it they are referring to muzzle velocity here. I was under the impression the coefficient calculation itself indeed factors in bullet slowdown, but the actual starting BC value that you feed in should ideally change based on MV. Not so much of a concern for unchanging target loads (or surplus ammo); the BC is pretty constant up that end of the spectrum, but becomes more of a factor down the low end. Again I might be wrong though... if so, flame on

Anyways getting back to OP, how about this ND:

440_3.jpg (189.35 KiB) Viewed 6784 times

Slightly higher BC with the lowered velocity. Do you have any more data ND? Any recorded drop for other distances? Also, how about sight height?

[<<Genesis93>>]

BC of 0.1 sounds a bit low... closer to a brick... made of foam..

Not really, think, 22 subs are 0.12 Besides isn't BC relative to MV anyway? (Lower the mv the lower the BC)

BC has nothing at all to do with MV.... it is a function of the 'slipperyness' or inverse of aero drag, relative to a 'standard projectile'...

Then how do you explain this:

https://www.sierrabullets.com/store/pro ... -170-gr-FN

(just as a example) scroll down to where it stipulates the BCs based on MV ranges. Not that I'm mathematical enough to really argue, I don't think it's quite as simple as you make it out to be. I might be wrong...

Yes... for a given bullet the BC will vary to a degree.... I was referring to your comment;

Not really, think, 22 subs are 0.12 Besides isn't BC relative to MV anyway? (Lower the mv the lower the BC)

lower mv = lower BC is absolutely not the case...as a generalisation...
If referring to specific projectiles and the slight variation over velocity - even your example has an increasing BC with reducing velocity....

[in2anity]

lower mv = lower BC is absolutely not the case...as a generalisation...
If referring to specific projectiles and the slight variation over velocity - even your example has an increasing BC with reducing velocity....

Yes agreed, my comment "(Lower the mv the lower the BC)" is not strictly true, sometimes they weirdly go up with lower MVs. I stand corrected here.

But my point is BCs are not constant for a given projectile (rather they change depending on MV), and I always found slow stubby RN/FN projectiles will have a markedly low BC (just like 22lr subs). Hence my (latest) estimation of 0.12 for OP. One thing is for almost certain, the BC for OP's particular projectile is definitely going to be closer to .2, nowhere near .3 territory

[<<Genesis93>>]

As I said the 317 was iterated with the 1200fps... and the woodleigh 50cal RN was in the .2xx range (^ I said up there somewhere) ...

If the velocity is lowered to 1050 with the same drop, then the BC would be a lot higher than the 0.317 value...

[in2anity]

If the velocity is lowered to 1050 with the same drop, then the BC would be a lot higher than the 0.317 value...

Fair enough, but given the MV, we'll have to agree to disagree on that one

[Gamerancher]

Okay, after doing some research, the Lyman 425gr .50 cal cast lead bullet has a B.C of .250, so I'd give Noiseys' 450gr a similar value. The only load data (actual, not assumed) I could find with measured velocities in .50-70 with blackpowder were with 70grains, not the 55gr load he describes. Those 70gr loads were measured at 1170fps with a 450gr Lyman bullet. So I go back to my original comment that I don't believe he's getting them out at 1200fps. I believe that a more conservative estimate of about 1050 fps would be a bit closer to what Noiseys' load is doing.
B.C's for big fat bullets at blackpowder velocities don't follow the trend that you would expect from long pointy supersonic jacketed small calibre bullets. Having a centre of gravity pretty close to the middle of the bullet that is about 3 x diameter in length gives about the best results for BC and hence stability.
Gravity acting on the bullet over time of flight is what gives you your bullet drop, lower velocity = longer time of flight = more drop.
I just ran it through the Hornady calculator online using 1000fps MV and got about a 21 yard bullet drop @ 600yards. Is that what we were after?

[Noisydad]

Sight height is .471" above the barrel.
I hold dead on at 200 yards.

[Gamerancher]

What brand of powder are you using Noisey?

[in2anity]

I just ran it through the Hornady calculator online using 1000fps MV and got about a 21 yard bullet drop @ 600yards. Is that what we were after?

I too was fiddling with the Hornady calculator- which is what makes me think the BC might actually l be under .2 A lot of .50 cast projs online have a BC less that .2

[Noisydad]

Using Wano. Cant afford Swiss lol.

[Gamerancher]

Fair enough. In my experience, I get 10% more velocity out of Swiss Vs Wano for the same loading.

[Noisydad]

Yeah I've heard that. Does it really burn cleaner? I figure that given its nearly twice the price I can put up with some cleaning.

[Gamerancher]

Definitely cleaner, especially your cases. I've also found that I can leave fired cases for up to a couple of weeks before cleaning, ( forgot about them after a large multi-gun shoot ). I've also been able to get that bit better accuracy out of the Swiss. Velocity S.D's down to single digits with Swiss compared to mid-teens to low 20's with Wano. That translates to less vertical dispersion which is what I need for silhouette and the long range. ( out to 1000yds )