Shape of Bullet nose affet accuracy?

[fiscus]

I'm trying to design a mold (mountain) for an old french revolver I have, it has a .328" groove diameter and 4-1/4" barrel. I want to shoot a 130 grain bullet at around 800fps, it should be about 14000psi. I won't be shooting farther than 50 yards. It has a very fast twist rate of 9.5inch (not a typo).

Here are 4 I came up with on mountain molds program, which of these designs would work best? Any advice on changes to make?

http://img704.imageshack.us/img704/1420/59432750.jpg

Russel

[44man]

I'm trying to design a mold (mountain) for an old french revolver I have, it has a .328" groove diameter and 4-1/4" barrel. I want to shoot a 130 grain bullet at around 800fps, it should be about 14000psi. I won't be shooting farther than 50 yards. It has a very fast twist rate of 9.5inch (not a typo).

Here are 4 I came up with on mountain molds program, which of these designs would work best? Any advice on changes to make?

http://img704.imageshack.us/img704/1420/59432750.jpg

Russel
I believe the two on the left, RNFP's, would do best. Where and how the boolit engages the forcing cone and rifling is important.
If one of the truncated cone boolits on the right matches the forcing cone angle, it will also shoot pretty good.

[Bucks Owin]

FWIW, I was burnin' powder yesterday with 2 designs in my .45 BH. One was the Lee 252 gr SWC and the other the ol' standby 454191 Lyman. The Lyman was quite a bit more accurate and less "fussy" as to powder type and charge. That would seem to bear out your philosophy 44man. Fired some XTP's too but that's a different story with the usual not so great ending! (Accurate but unpredictable expansion due to velocity changes) FWIW, Dennis http://i15.photobucket.com/albums/a356/BucksOwin/recoveredXTP.jpg

[fiscus]

The forcing cone is large with a long taper, less steep than those truncated cone bullets. The rounded flat point ones would enter the cone more smoothly. Does the forward/rearward weight balance affect the accuracy for low velocity short range shooting? I notice most commercial bullets are not shaped like this.

[Bass Ackward]

I'm trying to design a mold (mountain) for an old french revolver I have, it has a .328" groove diameter and 4-1/4" barrel. I want to shoot a 130 grain bullet at around 800fps, it should be about 14000psi. I won't be shooting farther than 50 yards. It has a very fast twist rate of 9.5inch (not a typo).

Here are 4 I came up with on mountain molds program, which of these designs would work best? Any advice on changes to make?

http://img704.imageshack.us/img704/1420/59432750.jpg

Russel


Russel,

Which design? Question is what do you need with a fast twist?

If you are only interested in 50 yards max and those are the choices, then I vote the olgivals. My reason is that with a fast twist, you are losing bearing length with overly long unsupported nose weight of all those designs which simply isn't necessary. And the trune will need to be harder to begin rotation without stripping. And at 14k, who wants to shoot rocks? :grin:

Think about this: With the olgivals, you will engrave farther forward than where you size the leade drive band which will cut this unsupported weight. In essence, it will strengthen the front drive band. But it doesn't increase bearing length cause unnecessary weight is still on the nose for the ride.

So if you like the trune design and want to shoot softer, then you need to cut nose length slightly and use the weight to widen the front band a little more to achieve the same band strength as the olgival. Coarse, when you cut the nose length, you are strengthening the band anyway.

In the end, if bullet weight remains equal, the trune will ALWAYS have the greater bearing length for the same weight because the nose weight that was forming the rounded portion, is now somewhere forming the bearing length. (better for faster twist)

This is why light for caliber bullets tend to be semiwadcutters or trunes. Why Elmer whined when they cut the size of his front band. And also why olgivals perform better in the heavier weights. Because they need it to get the bearing length for launch.

[fiscus]

Thanks for the info, that's a lot to process. I have more questions, does the fast twist make it need more bearing length for the same weight bullet to be stable, even at 800fps? Do I need to add more bearing length to the above design? The wider I make that front band the sharper the angle on the front of the bullet becomes, so it seems like it would not pass through the forcing cone as smoothly.

http://img63.imageshack.us/img63/8236/82340201.jpg

[Bass Ackward]

1. I have more questions, does the fast twist make it need more bearing length for the same weight bullet to be stable, even at 800fps?

2. Do I need to add more bearing length to the above design?

http://img63.imageshack.us/img63/8236/82340201.jpg


1. You need the bearing length to hold the rifling with softer lead. If you launch it well, it should fly fairly well to 50 yards. I assume that you would want that flexibility. And don't forget that your band will widen as it sizes down to your groove diameter. The larger the diameter bullet you can use up to the size of the throats, the sooner that bullet will contact steel on the other side of that cone.

2. Need? You need enough bearing length to reach across that deep cone so that when the base clears under pressure, that you have enough of the front band in the bore to support the length of the bullet so that it doesn't flop around. That's why guns that develop deeper cones over the years tend to need heavier bullets to do as well. IF you can't get the length to do this, you need the velocity to get it across before gravity gets hold of it. That ain't going to happen with 14k. So I 'll answer your question with another one. How deep (long) IS your cone? Once you have that measurement and you compare it to your bullet, you can answer that better than I can.

If you CAN't reach across it to seal and prevent gas cutting with softer lead, then maybe a GC would be a consideration. All depends on what you measure. Making sence?

[fiscus]

I measured the depth of the forcing cone this morning by dropping a flat-base bullet base-first into the breech, it is .465" deep. The calculated length from base to top of front band for the above three designs are .34", .38" and .42", which doesn't look overly promising for sealing it off. The ogive is full diameter in front of the front band so that does add a tiny bit.

If I bump the weight up to 140 grain it is long enough to seal the forcing cone, but I believe the original load for this revolver was only 120 grains (jacketed), so there might be an issue with the point of aim changing.

[Bass Ackward]

Flat base bullet? Is that bore diameter or throat diameter? Can be a big difference in the measurement.

The two ways to shorten this measurement is to set the barrel back or enlarge the throats. Or go GC and hope for the best. The easiest is to enlarge the throats cause you can do that yourself. Cheap too if you can rent the reamer.

I think that you have a good picture of what you are facing now.

Be patient in this process. I generally take a week without going to MM sites to forget what I did the last week and then design again. When I get three weeks in a row with the same design, then I generally am happy with the outcome.

[TCLouis]

Is the revolver accurate enough at 50 yards to discern that boolit shape makes a difference.

I realize you are going for the most "accurate boolit" and then the rest of the dispersion on the target is you, powder and the revolver.

What does this gun use for base brass?

[Bass Ackward]

Here is an idea of what can be possible because you do have a fast twist.

This is 135 grains and has .495 bearing area. Diameter is .330. Bands are .110 which should be wide enough in this bore diameter. Call it an improved wadcutter. You can actually lengthen the bearing area by increasing the GtoB which will shorten the center band. This should increase case capacity. Current seating depth is @ .300. Nose length would be @ .360.

You fill the bottom lube groove and you crimp at the back of the front grease groove.

[fiscus]

From what I've heard these guns are supposed to be fairly accurate, probably better than me. It uses 32-20 brass cut down to 1.07" and the loaded round has a 1.425" oal. The throats are half a thou over the groove diameter at .3285". I have looked at 3 and they all have the long forcing cone, they were made like that.

I wonder if the purpose of the forcing cone being longer than the bullet bearing area was to allow the bullet to find its way if the cylinder is not aligned perfectly?

http://img692.imageshack.us/img692/8105/45174849.jpg

[Bass Ackward]

[QUOTE=fiscus;796346]I wonder if the purpose of the forcing cone being longer than the bullet bearing area was to allow the bullet to find its way if the cylinder is not aligned perfectly?


Good chance cause when things are line bored, there is no need for a cone.

[44man]

[QUOTE=fiscus;796346]I wonder if the purpose of the forcing cone being longer than the bullet bearing area was to allow the bullet to find its way if the cylinder is not aligned perfectly?


Good chance cause when things are line bored, there is no need for a cone.
If that were true, there is no need for a ball throat or any taper to the lands in a rifle.
Line boring does not solve a thing because it is done without a barrel in the frame. What happens if the bore is not dead center in the barrel? What if the barrel threads put the bore a little out of line? What if the frame is not perfect to start with? Then the chambers have to be cut from the other end too.
Now add a cylinder with zero play. [smilie=b:
Line boring is nothing but a selling point so more money can be charged for the gun. There is not a single shred of proof that it is more accurate then a Ruger, BFR or S&W along with a bunch of other brands. I would think twice about not having a forcing cone or zero cylinder play.
Nothing is perfect, no matter what machine because there is wear and tolerance in the machines that do the work. Hand fitting parts is even more accurate, so accurate that without oil, parts can seize.
Yes, we are getting close with CNC and computers and scanners to find a problem.
I have to wonder if some gun makers aren't putting oversize bores on their guns so the bullet can find the hole from line bored cylinders! :p

[Bass Ackward]

[QUOTE=Bass Ackward;796375]
If that were true, there is no need for a ball throat or any taper to the lands in a rifle.
Line boring does not solve a thing because it is done without a barrel in the frame. What happens if the bore is not dead center in the barrel? What if the barrel threads put the bore a little out of line? What if the frame is not perfect to start with? Then the chambers have to be cut from the other end too.
Now add a cylinder with zero play. [smilie=b:
Line boring is nothing but a selling point so more money can be charged for the gun. There is not a single shred of proof that it is more accurate then a Ruger, BFR or S&W along with a bunch of other brands. I would think twice about not having a forcing cone or zero cylinder play.
Nothing is perfect, no matter what machine because there is wear and tolerance in the machines that do the work. Hand fitting parts is even more accurate, so accurate that without oil, parts can seize.
Yes, we are getting close with CNC and computers and scanners to find a problem.
I have to wonder if some gun makers aren't putting oversize bores on their guns so the bullet can find the hole from line bored cylinders! :p


Yep. Saying line bored don't make it so. But if it is made right, then it IS just like a rifle. Even in a rifle you have to have a gentle taper on the lead to begin engraving. Well, you don't, but a smart man would.

Oh you are dead right in a way. Line boring isn't one bit more accurate than a plain ol Ruger with peak loads. The difference is that you don't have to spend 2k to 10 k breaking it in. It just shoots every load and bullet design like most people want their best loads to perform. Here is the key: IF IT"S MADE RIGHT.

That means you can shoot soft or hard, this design or that. Granny's home lube or LLA. Even Bullseye!!! Flexibility is all. Ever heard that before? :grin:

[S.R.Custom]

I'm going to diverge from the pack here and recommend a full-on wadcutter, with a crimp groove far enough down on the bullet to permit the front driving band of the bullet to fill the space in the chamber between the case mouth and where the throat tapers to its smallest diameter. Here's why:

(1) With a fast twist and all your shooting inside 50 yards, you don't need a pointed, non-bearing nose. A pointed nose wastes bullet mass that could be dedicated to increasing bearing surface.

(2) With no nose, bearing length is maximized. This minimizes the amount of propellant gas that blows around and past the bullet as it jumps down the long forcing cone. Make the bearing length long enough, and you may even be able have a bullet long enough to be sealed either in either the throat or the barrel the whole time it makes the transition.

(3) Maximum bearing surface permits a softer alloy. Useful if you have to rely upon obturation to mitigate dimensional anomalies in the gun itself.

(4) Maximum bearing surface is inherently more accurate. I could go on for days why, but suffice it to say that maximal bearing length is one of the reasons all the old time bullseye shooters shoot wadcutters in their K-14s.

(5) Wadcutters are inherently more accurate than other types of bullets in guns simply because they're wadcutters. (Let that sink in a minute.) And the reason is, in every revolver, the chambers are not perfectly aligned with the bore. Some are worse than others. In making the jump from the cylinder, the bullet gets knocked to one side or the other (or up/down) and this distorts the bullet. If the bullet has a long nose, the nose ends up off-center. The more a revolver's chambers are out of line with the bore, the more accurate wadcutters will be in comparison to nosed bullets.

I hope this helps and doesn't serve to just muddy the water. There's a lot to think about with these old guns. You've got a fun project on your hands.

[Edubya]

I'm going to diverge from the pack here and recommend a full-on wadcutter, with a crimp groove far enough down on the bullet to permit the front driving band of the bullet to fill the space in the chamber between the case mouth and where the throat tapers to its smallest diameter. Here's why:

(1) With a fast twist and all your shooting inside 50 yards, you don't need a pointed, non-bearing nose. A pointed nose wastes bullet mass that could be dedicated to increasing bearing surface.

(2) With no nose, bearing length is maximized. This minimizes the amount of propellant gas that blows around and past the bullet as it jumps down the long forcing cone. Make the bearing length long enough, and you may even be able have a bullet long enough to be sealed either in either the throat or the barrel the whole time it makes the transition.

(3) Maximum bearing surface permits a softer alloy. Useful if you have to rely upon obturation to mitigate dimensional anomalies in the gun itself.

(4) Maximum bearing surface is inherently more accurate. I could go on for days why, but suffice it to say that maximal bearing length is one of the reasons all the old time bullseye shooters shoot wadcutters in their K-14s.

(5) Wadcutters are inherently more accurate than other types of bullets in guns simply because they're wadcutters. (Let that sink in a minute.) And the reason is, in every revolver, the chambers are not perfectly aligned with the bore. Some are worse than others. In making the jump from the cylinder, the bullet gets knocked to one side or the other (or up/down) and this distorts the bullet. If the bullet has a long nose, the nose ends up off-center. The more a revolver's chambers are out of line with the bore, the more accurate wadcutters will be in comparison to nosed bullets.

I hope this helps and doesn't serve to just muddy the water. There's a lot to think about with these old guns. You've got a fun project on your hands.

SuperMag, that is a great post! I have tried to say the same thing. If it weren't for my inability to communicate, I'd a said it.

One more thought: If you have a hollow base, or at least a concave base, it would obturate to fill the case then again as it leaves the case which would result in the same as a sealed barrel before it leaves the case.
EW

[NHlever]

[QUOTE=Bass Ackward;796375]
If that were true, there is no need for a ball throat or any taper to the lands in a rifle.
Line boring does not solve a thing because it is done without a barrel in the frame. What happens if the bore is not dead center in the barrel? What if the barrel threads put the bore a little out of line? What if the frame is not perfect to start with? Then the chambers have to be cut from the other end too.
Now add a cylinder with zero play. [smilie=b:
Line boring is nothing but a selling point so more money can be charged for the gun. There is not a single shred of proof that it is more accurate then a Ruger, BFR or S&W along with a bunch of other brands. I would think twice about not having a forcing cone or zero cylinder play.
Nothing is perfect, no matter what machine because there is wear and tolerance in the machines that do the work. Hand fitting parts is even more accurate, so accurate that without oil, parts can seize.
Yes, we are getting close with CNC and computers and scanners to find a problem.
I have to wonder if some gun makers aren't putting oversize bores on their guns so the bullet can find the hole from line bored cylinders! :p

Truth again 44 Man. One of the big problems with revolver barrels is getting the front of the frame perfectly square with the barrel threads, and that raises cain with line boring too. If you were to check the "constriction" where the barrel enters the frame on revolvers that we often hear about you would find that it is actually a slight "kink" in the barrel because of that out of square condition between the frame face, and the barrel threads. It is no coincidence that guns that exhibit this "constriction" also often have front sights that are too low..... guess which way the frame is out of square? The CNC's help because the frame can be bored, threaded, and faced in the same operation which keeps things lined up much better if the frame doesn't move during the operation. I once made a lead screw threading fixture for a Bridgeport mill so I could do the same thing on a manual machine. ( I had three frames that needed to be timed the same for rib barrels too, 22LR Security Sixes that the world never saw) Some newer guns with ribbed barrels are machined with a "pressure washer", or concentric ring that compresses when the barrel is torqued on. That minimizes the effect of any out of square condition, and minimizes uneven stresses on the barrel.

[44man]

[QUOTE=44man;796932]

Truth again 44 Man. One of the big problems with revolver barrels is getting the front of the frame perfectly square with the barrel threads, and that raises cain with line boring too. If you were to check the "constriction" where the barrel enters the frame on revolvers that we often hear about you would find that it is actually a slight "kink" in the barrel because of that out of square condition between the frame face, and the barrel threads. It is no coincidence that guns that exhibit this "constriction" also often have front sights that are too low..... guess which way the frame is out of square? The CNC's help because the frame can be bored, threaded, and faced in the same operation which keeps things lined up much better if the frame doesn't move during the operation. I once made a lead screw threading fixture for a Bridgeport mill so I could do the same thing on a manual machine. ( I had three frames that needed to be timed the same for rib barrels too, 22LR Security Sixes that the world never saw) Some newer guns with ribbed barrels are machined with a "pressure washer", or concentric ring that compresses when the barrel is torqued on. That minimizes the effect of any out of square condition, and minimizes uneven stresses on the barrel.
Makes me remember all of the Dan Wesson revolvers that had the barrels pointing to the left. :holysheep Yeah, all to the left, never seen one go to the right. The hole threaded into the frame for the barrel was off as far as the front face of the frames. Then the front of the cylinders were not trued, would wobble and if you set the gap on the short side, the cylinder would lock against the barrel on the long side. It is funny to look across the top of a gun and see the barrel crooked! [smilie=b: I seen some so bad that the rear sight was all the way to the right and it would not hit at 50 meters, still shot way left.

[Bass Ackward]

Not all line boring results in perfect guns.

Here, read this. Apparently they do test and reject.

http://www.gunsandammomag.com/cs/Satellite/IMO_GA/Story_C/Inside+Freedom+Arms

[44man]

Not all line boring results in perfect guns.

Here, read this. Apparently they do test and reject.

http://www.gunsandammomag.com/cs/Satellite/IMO_GA/Story_C/Inside+Freedom+Arms
Rejects still make it out the door, sad to say. I don't find it justified to spend that much money and take the chance and then have them try to charge postage both ways and charge for a fix without an argument.
Most of them shoot darn good but it is "most" that turns me away. I would prefer "all" of them shoot. That is just too much money to fool with.

[Edubya]

"One correspondent writes that the shooting periodicals should devote primary attention to cheap guns. I have had occasion to confront this attitude for a long time, and while I do not condemn it as sinful, I do disagree with it. Cheap guns are OK, and we must make due with what we can afford, but I do not think that being broke is a circumstance to be sought. Here in the opening years of the 21st century, Americans can buy serviceable personal firearms over the counter, and for that we are immensely grateful. But it is a fact of life that nobody needs a rifle. He wants a rifle, and he is happier wanting a good example than a poor one."
http://tinyurl.com/Cooper-quote
EW

[44man]

"One correspondent writes that the shooting periodicals should devote primary attention to cheap guns. I have had occasion to confront this attitude for a long time, and while I do not condemn it as sinful, I do disagree with it. Cheap guns are OK, and we must make due with what we can afford, but I do not think that being broke is a circumstance to be sought. Here in the opening years of the 21st century, Americans can buy serviceable personal firearms over the counter, and for that we are immensely grateful. But it is a fact of life that nobody needs a rifle. He wants a rifle, and he is happier wanting a good example than a poor one."
http://tinyurl.com/Cooper-quote
EW
True, more balance is needed. We are not all rich. I hate gun books full of expensive guns. One page has 1911's at $2000, the next page is $5000 guns and the next page has $15,000 rifles. I only paid $15,000 for my first house! What about the normal person?
At times I think the gun sites are dominated by those that make $300,000 a year or more. You forget about us that had a hard time making $50,000. I started at less then $1.75 an hour yet had money left to buy a few guns. Now it takes $50 an hour to survive and buy toys.
Now in retirement, $40,000 is a LOT of money. $2000 for a gun???? You have to be out of your mind and if it doesn't shoot, it is a HUGE letdown, not something that can be sluffed off, just buy another!
Hardship is why I learned to make guns shoot and if anyone tells me I need a $3000 gun or it is junk, I have news for you. My first BH cost $96 and will still out shoot your $3000 gun.