Sillouette-style at higher speeds?

[sideironjohn]

So, I'm loking at these RCBS moulds, like the 289-494, 222-269, (and especially) 689-098, etc.
These are all long, with a really long nose (maybe 3/4 of the bullet length?), and I can't tell from the pic, but it seems the front band is a wee smaller than the body, and constitutes about 2/3 of the nose. And then about a 45% meplat at the end of maybe a 2r ogive. And there's only one, maybe two lube grooves.
These lok very much like some of the bullets I've "made up" on paper, but I've always wondered how they might shoot. Looks like the idea is already there; wonder do folks run these up to 2kfps+?

[Buckshot]

.............John, It's not an RCBS silhuette number but it IS an RCBS boolit and that is my fav-o-rite 7mm slug. The 7mm-168 it's a way long bore rider and I've shot it with sub 1.25" accuracy at 50 yards (5 rnds, iron sights) at 2450 fps. This from a Brazilian contract DWM M98/08. As issued.

From the mould, it weighs 172grs in the 14 BHN alloy I like. It performed as well in a 1897 Rem RB in 7x57 too.

I'd always kinda thought a long bore rider would have torsional issues with the deep engraving taking place so far back on such a long boolit. But hey! It was just a thought :D

I have heard good things about the 145gr silhuette slug from others but never had a chance to shoot any.

...............Buckshot

[trk]

Yo - Buckshot -

I have a couple of moulds in that (2 & 4).

I assume you're referring to a 7x57. Rate of twist?

I'm thinking of two irons - a Ruger #3 in 7-08 and a Rem 221 rebarreled in 7mm IMHSA.
(I'll have to check the twists).

Any issues with velocity vs. rate of twist?

[w30wcf]

sideironjohn,

Not the same bullet #'s you were asking about, but the same design .....

I have had very good success with the RCBS .30 Caliber 165 gr. bullet. In my Rem 788 .30-30, it shot one of the best 5 shot groups @ 100 yards (1/2")that I have ever fired from this rifle. :D

The bullet alloy was linotype, the velocity, 2,300 f.p.s. (36/748- not for lever action rifles!) and the lube ..... 50/50 beeswax/alox (NRA formula).

IMPORTANT: The long bore riding nose must be a tight fit in the bore to prevent the bullet from yawing in the barrel, which would lead to inaccurate shooting. My mold drops bullets that are .302" on the bore ride which is .001" larger than my rifle's .301" bore.

It chambers easily since the bore diameter just in front of the throat has eroded a bit. I size to .311" which matches the throat diameter pretty closely and is .002" over groove diameter.

w30wcf

[sideironjohn]

Well, great. Now as for "bore" riding, what is the functional part of it? You want it tight, yes? So would it be wise to go, say, .359" and .354" in a .358-50" bore? And why not just have it be caliber-thick the whole way? And how much of the bullet can be not touching? Seems on most of these it's less than two calibers radius in the front, but some of my designs are four.
My intuition is that it's more than just a percentage of the bullet length....

[Bass Ackward]

Well, great. Now as for "bore" riding, what is the functional part of it? You want it tight, yes? So would it be wise to go, say, .359" and .354" in a .358-50" bore? And why not just have it be caliber-thick the whole way? And how much of the bullet can be not touching? Seems on most of these it's less than two calibers radius in the front, but some of my designs are four.
My intuition is that it's more than just a percentage of the bullet length....


John,

Most bore riders designs are to fit bullets in either short or really long throats. If you can fit a one diameter, then do it. A one diameter will have more land area to handle RPMs for the same weight as a BR design.

I keep to a pretty narrow formula for bearing length on one diameters. Heavy for caliber bullets I design must have 75% supported and here I still aim for 80%. And lighter bullets are 80% of overall length is bearing. I never go over 70% on the meppy and I believe 60% performs more accurately in the larger bores.

The key is to maintain "enough" ballistic coefficient for the range you expect out of it. The less you get, the harder you will have to drive it to stabilize on out. Thus when that velocity drops, away she goes. HTH.

[sideironjohn]

OK, well, for instance, a 300g .358" with a .20" meplat (56%) and a .750" nose, .30" front band, 1.21 overall. That seems to give a .888" bearing length, or around 73.4%. A little under your parameters, but still 2.5 caliber's worth of bearing length. At .432" throat length, most chambers would need a bore rider vesion I guess, which would significantly reduce the bearing surface.
It looks mean, and if no one can tell me a reason it less-than-might or ought-not work, I'm going for it.

[Bass Ackward]

OK, well, for instance, a 300g .358" with a .20" meplat (56%) and a .750" nose, .30" front band, 1.21 overall. That seems to give a .888" bearing length, or around 73.4%. A little under your parameters, but still 2.5 caliber's worth of bearing length. At .432" throat length, most chambers would need a bore rider vesion I guess, which would significantly reduce the bearing surface.
It looks mean, and if no one can tell me a reason it less-than-might or ought-not work, I'm going for it.

John,

First, you will probably need a 12" twist to stabilize it. Based on my work in this caliber you should find success around 1800-1900 fps with it at 14 BHN because of the weight. If this is what you want, then you should be fine.

[sideironjohn]

Well, I'm looking form more like 2000-2100. I figured I'd need to go more like 18BHN, but didn't think it had anything to with the weight, just the speed. Why would a heavier bulelt need a particular hardness?
Thanks.

[Buckshot]

"Yo - Buckshot -

I have a couple of moulds in that (2 & 4).

I assume you're referring to a 7x57. Rate of twist?

I'm thinking of two irons - a Ruger #3 in 7-08 and a Rem 221 rebarreled in 7mm IMHSA.
(I'll have to check the twists).

Any issues with velocity vs. rate of twist?
__________________

..........Yes they're both 7x57 and have the standard twist of 8.6". No issues with velocity and twist. As I said, they were scooting along at better then 2400 fps. I have not fired them at that speed at 100 yards.

..............Buckshot

[Bass Ackward]

Well, I'm looking form more like 2000-2100. I figured I'd need to go more like 18BHN, but didn't think it had anything to with the weight, just the speed. Why would a heavier bulelt need a particular hardness?
Thanks.

John,

Because the effects of pressure are accumulative trying to over come inertia. You have to drop powder speed to compensate for it, and then you can't get enough powder in the case to get the velocity without barrel length to burn it. Examples from my loads: 210 gr - 2400 fps, 220 grain 2300 fps, 250 grain - 2100 fps, 265 grain - 2050 fps. Now these are examples of accuracy loads that I have developed for bullets that I designed at 14 BHN using RL15. That is how I made your prediction, but remember, this is based on my results. YMMV.

Going to a harder bullet has had a very small percentage increase in velocity unless you accept a new accuracy standard. The most dramatic effect on velocity increase occurs with the lightest bullet and the percentage drops from there. I have a 14 twist and appear to be limited at 265 grains for stabilization because when I slow this down to 1500 fps, I start to get oval holes at 100 yds. That is the predicted velocity of the 365 gr bullet at 200 yards when it starts out at 2050.

You might be able to improve on these figures, I have only been working with this for 2 years so not everything has been tried. If your rifle is new, you throat length will lengthen as the angle of the rifling changes. Leave yourself about .60 below the neck (width of the check) so as this angle changes you have the bullet length to seat out and maintain contact. I had to sell the 210 grain mold and probably should sell the 220 grain too because the throat length now makes these impractical for hunting. Just so you know.

[sideironjohn]

Thanks BA. I have a case from the 404 Jeffery, holds about 113g water to the top of the neck. Slow powders are not a problem in that one! ;-)
But I'm thinking about the 35 Whelen and 35 Remington, two chamberings I hope to acquire in the near future, in a Rem 650 and Marlin 336, resp.
If you meant .06", then for the 35 Whelen we have room about a 1.3" bullet (at 1.23" mine would fit well, and also in the 358 Winchester for the daring!) and for the Rem loaded to 2.55" we have a 1.02" bullet or so. I'll make a 250-60g for that one. Makes more sense anyway. Wonder how that would fair, 1850fps perhaps? That's the same SD as the 45/70's 405g, which does about that....

[w30wcf]

sideironjohn,

In answer to your question..."Why would a heavier bullet need a particular hardness?"

Because as the bullet weight increases in the same caliber, the sectional density increases and thus so does the resistance, calling for higher pressure to atain the same velocity which calls for a bullet of increased hardness.

w30wcf

[sideironjohn]

So, is it pressure or velocity that requires harder alloy? IOW, would all 40k psi bullet weights need the same hardness, or all 2k fps bullet weights, if you see what I'm asking.
I figured it was a speed thing, but if it's a pressure thing, then you should be able to get a 100g .308" bullet to go pretty quick from a 308 without leading, right?

[felix]

Stripping/leading is based upon speed and pressure together. If the pressure is too high and the speed too low, then the boolit will strip. If the pressure never exceeds a certain amount and the speed is commensurate, that is, the boolit does not "obturate" past a certain amount, then all is fine and dandy. However, I have seen boolits fly out of the muzzle at 3000 fps, leaving no leading behind. That's like going down a dirt road with small chuckholes. You don't feel the chuckholes after a certain speed. Likewise with boolits. Driving accuracy is typically lost on both accounts. ... felix

[sideironjohn]

Thanks Felix. I think I get it. It sounds like you're suggesting that a bigger case will do a better job at high velocity, running moderate pressures, than a standard case pushed to the hilt pressure-wise.
Can anything be said regarding burn rate? I.e., say two cases push a 250g 35 cal at 2200fps, at 40k psi. The Whelen does it with 3031, the Norma with 4350. Is there a general ruele, you might exect one to fair better? (All else equal.)
And W30WCF, is it the SD that increases pressure? Seems it would be the surface area. IOW, a longer, pointed, heavier bullet with the same bearing surface might give the same resistance as a lighter, shorter, round nose?

[Bass Ackward]

Thanks Felix. I think I get it. It sounds like you're suggesting that a bigger case will do a better job at high velocity, running moderate pressures, than a standard case pushed to the hilt pressure-wise.
Can anything be said regarding burn rate? I.e., say two cases push a 250g 35 cal at 2200fps, at 40k psi. The Whelen does it with 3031, the Norma with 4350.

John,

What causes most of the pressure is bullet weight. This adds to inertia. The old, "you can push a bank vault door closed with your finger, but if you kick it, you will break your leg." Or why a 270 has a velocity advantage over a Whelen.

Look at the powder choices made for a 150 grain bullet in 30 caliber and then look at the choices for a 200 grain. Same thing really because when you study resistance and it's effect on pressure, there almost is none comparred to copper. That is why you have a harder time with ignition with lead and have to do something like add the resistance of rifling engraving or choking so that it has to size down to get consistent pressure. Neither of which you would EVER think of doing with a jacketed bullet.

And you have figured out the secret to cast bullets. Ever wonder why you always saw longer barrels on lead guns? Anytime you can start a cast bullet off easier and still get good ignition, you have a better high velocity bullet at longer range. And I get 2100 fps with a Whelen and 46 1/2 gr of RL15 at about 32,000 psi. according to Quickload. I can get 32,000 from 3031 to, but the pressure peeks after one inch of bullet travel as opposed to almost 2" from the RL15. Lights go on? In 30 caliber the limit goes up to 34,000 before failure. (lighter bullets) This is where 14 BHN fails in a one diameter bullet design. Bore rides are lower. (less bearing area) Case capacity is your friend up until you get slightly over bore, then it narrows your working powder selections to try for accuracy.

Now please don't misunderstand what I am saying here. 2100 fps with a 250 grain at 14 BHN hold less than one inch at 100 yards. In fact, I have several 1 1/4" 200 yard groups. Harden the bullet to 20 BHN and speed it up to about 2250 and you now need 45,000 psi to do it, and your new accuracy standard better be 1 1/2". The difference for hunting though is dramatic at longer range. The 14 BHN is running over 1500 fps at 200 yards and expands nicely on smaller game like deer. The 20 BHN only expands well down to about 1800 fps which is reached about 120 yards. So even though velocity is higher, it isn't as effective for smaller (large) game. On something like ELK on up, yea. And you can learn tricks like nose annealing and such, but that is another discussion.

[Char-Gar]

Just a couple of thoughs on this thread.

1. I have great luck with RCBS 165 Sil (30 cal.) in several rifles at 2K fps

2. What Felix said about pressure and speed cannot be overemphaized and should not be overlooked. A bullet that is shoved out the barrel at 2K fps by a slow powder will be far more accurate than the same bullet spanked out the barrel at the same speed by a fast powder. The rate at which the pressure is applied to the base of the bullet is a very important factor in cast bullet shooting with accuracy.

When I discovered WC872 I started to get first rate accuracy in the 1.8 -2.2K fps range with boring regularity. This very slow powder shoves the bullet out without smashing the base into the nose.

[sideironjohn]

Wow. Major bells going off.
Thanks a ton guys. You are all a big help.
Big help. Actually makes for more questions, but I'll sit down for now....
Bass Ackward, I really appreciate the depth of your response.

[Newtire]

Hi Chargar!
First off, sending good thoughts down that way & hoping that storm goes easy on you folks in your town.
Next, Have the 165 RCBS Silhouette & only tried one load & that was with 28 gr. RX-7 in an '06. Was real accurate but only shot at 50 yds. Don't have any Surplus powders here but have some 4895 and 4064. Never tried anything much slower than that with cast bullets. Had real good luck with H-335 in a 30-30 @ about 35,000 psi (published pressure) with a 170 gr. bullet so thinking maybe look for one about that range in the '06 with H-335 maybe?