Cast Bullet Ogive Shapes - Why ?

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Slug Gun posted this 3 weeks ago

I’m new to shooting cast bullets in rifles and came from the long range jacketed bullet shooting game (600 to 1,000 yards). Looking at some of the equipment lists in “The Fouling Shot” and searching mold maker’s websites; I’m surprised that there aren’t more spitzer or high ballistic coefficient ogive style bullets being used. Looking at the .30 cal. equipment list , most are shooting very blunt ogive shaped bullets at velocities approaching and exceeding 2,000 FPS. Why the blunt shape more then a more pointed ogive bullet. Is it because it is difficult to manufacture molds with a spitzer shape ?  Is it more difficult to cast a spitzer shaped bullet ? Are the blunt nose bullets more accurate at cast bullet velocities then spitzer or round nose bullets ?  Do the long nose blunt bullets allow more bearing surface then a pointed bullet ?

What am I missing here ?

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45 2.1 posted this 3 weeks ago

Quite a few things............ A lot of machinists are not able to calculate nose diameters on an ogive.... just because you spec something as a 5 diameter nose radius doesn't mean they know what to do with it. Another is bearing length. Long ogives usually produce short bearing lengths unless one knows how to get more land engraving down the nose. Most people try a normal two diameter bullet bore riding bullet such as the Lyman 314299 which is a good bullet, as long as it fits what you are shooting (and it doesn't most of the time). We can go on further, but other people can say some about it also.

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beltfed posted this 3 weeks ago

Interestingly, more and more "spitzer" ogive bullets are being used in Schuetzen where we all shoot at

200yds, velocities generally in the +- 1400 fps range.  People looking to get least wind deflection...

OTOH, in CBA Vin MIl, we are (often?) shooting the seemingly less aerodynamic ogive  311299 /311334 and other two dia bullets

in the 1600 + velocity range.

Go figure.....

beltfed/arnie

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RicinYakima posted this 3 weeks ago

In my opinion, wink, bullet material is not strong enough to maintain consistent shape and form during acceleration. Bullets don't all deform equally, so groups are bigger. The most successful designs appear to mimic a falling raindrop nose shape and Kamm form rear of the bullet to reduce drag at 1400 to 1700 f/s.

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45 2.1 posted this 3 weeks ago

^^^^^^ Veral Smith wrote a book about jacketed velocities with cast. In it he gave a pressure distribution from the base up to the nose, units in PSI. His pressure figures are plenty accurate. Everyone should have a copy. I shoot an alloy that air cools at 8 BHN and water drops to 19 BHN. Both AC & WD survive in a 308 at a velocity of about 2,400 fps with a approx. 180 gr. bullet. The only difference in them shot at long range and recovered out of a clay trap is the 8 BHN has full land engraving to the nose ogive and the 19 BHN one is halfway up the nose. Only damage is land engraving and dirt scuffing.... one could load them again. This isn't a one off test either as I've done it a couple of dozen times over the years.

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shootcast posted this 3 weeks ago

The books say that it hard to get those pointed  bullets to shoot because there is less bearing surface for the rifling to grip. The boys from South Carolina are doing fine with there’s. Many a match to show it can work. 

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Ross Smith posted this 3 weeks ago

Imho: My rifle that shoots a short squat bullet great has a hard time with the same weight bullet with a long pointy nose. It has a lot to do with bullet length rather than weight. 

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BudHyett posted this 3 weeks ago

The thermodynamics of the bullet entering the rifling and travelling the barrel are too hard to measure with our limited resources. Cast bullets are a momentary semi-liquid glob as they travel in the barrel. The heat and pressure work together to shape the bullet in the barrel while it travels.

The mechanical forces of the rifling keep the shape of bullet in place. The barrel dimensions are uniform and squeeze the bullet to hold the shape the bullet has as it enters the barrel. This shape can slightly vary from shot to shot even with breech-seating.

The barrel time is tenths of a millisecond which means the bullet shape is not affected. The rifling grooves impress on the bullet and seek to drive the lubricant out of the grooves coating the bore. 

The CBA shooters need to keep experimenting and find common successful traits to give answers. 

Country boy from Illinois, living in the Magical Pacific Northwest

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John Alexander posted this 3 weeks ago

When I started shooting in CBA matches in the late 1970s I was amazed at how blunt virtually all the bullets were.  Many with a big flat spots on the front - good for punching a hole in a deer not so good for punching a hole in paper.

Of course CB shooters are stuck a with the molds available and many custom mold makers either can't or won't make pointed bullets and that has been part of the problem. My NOE 22780SP has a point that could draw blood, so it can be done.

It wasn't exactly a new idea since the US had paid Germany for patent rights to pointy bullets nearly a hundred years earlier.

A CB shaped like the very low drag jacketed bullets now popular wouldn't have enough length of bearing surface for accuracy.  One shaped like a beer can has too much wind drift. Like all design problems there are tradeoffs.

However, I think the main reason the blunt bullets have stuck around in CBA competition is that most CB shooters are too conservative in adapting new ideas and have too much deference to the way they did it in the past -- Hudson's group over a hundred years ago yady yady.  We are smartening up that pointy bullets might make sense now after thirty years or so.

Ironic that the the Schuetzen shooters who worship the past have adopted pointed bullets faster than the modern CBA type shooters.

John

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RicinYakima posted this 3 weeks ago

John, for me it is not the point, but the noses are always small for my barrels, i.e. .298 or .299"  and the first driving band is 2/3 the way back from the tip. Of course 75 year old barrels aren't as smooth as modern ones. Ric

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Larry Gibson posted this 3 weeks ago

Are the blunt nose bullets more accurate at cast bullet velocities then spitzer or round nose bullets ?  

At midrange 1000 - 1600 fps a spitzer cast bullet can be as accurate as most any other type.

Do the long nose blunt bullets allow more bearing surface then a pointed bullet ?

Most of them do, especially if shooting the cast bullet at HV.  Then a bearing surface of 60+% of the bullets length, if not more, is desired for best accuracy at HV.  That doesn't leave a lot of length left for a real streamlined spitzer bullet nose. There are numerous real spitzer shaped cast bullets that have been available for many years.  None of them have been proven accurate at HV.

As already mention, the cast bullet goes through quite a deformation process when fired. Mostly it is some setback from acceleration and the swaging down during the internal ballistic phase that causes the problems.  In 30 cal for example the naked lubricated cast bullet will be swaged down to .003 - .005 less than groove diameter.  Unless this swaging down is symmetrically equal the bullet will be less balanced on launch and will be more adversely affected during the external ballistic phase (flight) of the bullet.  That's where some degree of inaccuracy will occur.  Thus the more bearing surface and support the bullet has in the barrel the less symmetrical imbalance will occur.

LMG 

Concealment is not cover.........

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John Alexander posted this 3 weeks ago

Larry,

I am interested in your statement that CBs are .003 - .005" smaller than groove diameter when they leave the muzzle. Seems like I have read this before.  That may be true, but if it is it isn't because of swaging as I understand the word.  Swaging is forcing a deformable solid into a containing die to make it assume the shape and size of the dies interior dimensions. I would think swaging would result in the bullet being groove diameter.

In fact 45 2.1 says in his post above that is exactly what happens and he has observed it many times on recovered bullets --  "full depth grooves on bullet" -- exactly what you should expect if the pressure and alloy hardness are in the right range. I don't remember Mann saying anything about the hundreds of bullets he caught in oiled sawdust getting smaller, maybe I should look again.

Under what condition of pressure/velocity/alloy have you observed bullets getting smaller? What mechanism would do such a thing?  I ain't swaging. This phenomena should excite the imagination of all CB shooters.

John

 

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45 2.1 posted this 3 weeks ago

Since it's been brought up, most 30 caliber barrels are hard put to have 0.004" ( that's 4 thousandths) deep rifling grooves. Larry's 0.003" to 0.005" less than groove should show up when you've measured recovered bullets. After measuring a whole bunch of recovered bullets (I'm into well over 4 figures on that) I haven't seen any diameter reduction or evidence on the recovered bullet that shows that. Maybe Larry can show pictures of a recovered bullet with a micrometer attached showing that. I'd be interested to see it.

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max503 posted this 3 weeks ago

Can you imagine trying to find a top punch to fit those pointy bullet noses?

 

 

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R. Dupraz posted this 3 weeks ago

"As already mention, the cast bullet goes through quite a deformation process when fired. Mostly it is some setback from acceleration and the swaging down during the internal ballistic phase that causes the problems.  In 30 cal for example the naked lubricated cast bullet will be swaged down to .003 - .005 less than groove diameter."

Setback on acceleration !!

I know that I'm no rocket scientist.  All that I basically know how to do mostly is light the fuse but this feeble brain does need an explanation not only on how that is possible but also how you can tell that it does happen.

 

R. 

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John Alexander posted this 3 weeks ago

max503 asks: "Can you imagine trying to find a top punch to fit those pointy bullet noses?"

The folks that make pointy bullet molds make top punches to fit.  Why not?

John

 

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R. Dupraz posted this 3 weeks ago

No problem. That's what J-B Weld is for.

 

R.

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Maven posted this 3 weeks ago

45 2.1, Didn't you design a spire point group buy CB on the Boolits site (Jay Downs/Aladdin honcho'ed it) years ago?  Wasn't it a copy of a Speer jacketed target bullet?  I purchased that group buy mold (don't remember what I used for a top punch though), but didn't get stellar accuracy from it at "normal" CB velocity, i.e., ~1,750 fps in my case.  However, on the suggestion of a Boolits member, I tried a healthy, but by no means  excessive charge of IMR 4350 and things improved immediately.  As I had more accurate CB designs molds available, I sold that mold to a CBA member.

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TRKakaCatWhisperer posted this 3 weeks ago

Maven - that was Jay Downs/Aladdin and myself.  I did the cad work and had many discussions with some folks that were in the business of ballistic design/shape/form.  Yes, it started with the Speer bullet.  I contracted with a local machine shop to make the nose-punches as well.  Still have my mold and have picked up 2 or 3 rare long-spire-boattail molds made years ago.

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TRKakaCatWhisperer posted this 3 weeks ago

The whole idea for that one was low drag and LONG rage accuracy.  I met with Jay once at  his home (on my way from Virginia to MNPLS).  I must say he made a respectable wine.

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max503 posted this 3 weeks ago

No problem. That's what J-B Weld is for.

 

R.

I just bought a Lee 102 grain mold for my 380 and I'm needing a top punch. I'll have to try the JB.

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