bullet tip

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Kurt
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Re: bullet tip

Post by Kurt »

If the bullet is wobbling you would see the oval penetration through the paper in different directions.
I have pulled targets at Lodi and seen this going on.
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gunlaker
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Re: bullet tip

Post by gunlaker »

Distant Thunder wrote: Fri Jun 03, 2022 1:08 pm ...

I think some of the tipping was the bullets running with their points into the wind gusts.
...
Yeah, I'm sure that's what's going on. I've shot the same rifle on paper at 300 in string gusts and have seen all of the holes showing tipping slightly to the left. I thought the splatters on the ram were interesting. It's not too often I get to shoot at a clean ram and then take a picture before anyone else gets to shoot it.

I wonder in this rifle, since it's not overstabilized, if the bullet carries the nose above the trajectory. I imagine my 16 twist .45's probably do, but have no real evidence.

In the pits, I haven't seen tipping bullet imprints too often. I think that mostly, if you use common bullet lengths and don't get too crazy with mold selection, these 1:16 and 1:18 twists will stabilize the most popular bullets. The ones in the pits that really get your attention are the dirt diggers and ones that are tumbling and whizzing. I wonder how many of those are from bullets that are too long, or simply from crappy casting technique or gas cutting. With bore diameter PP bullets I'd always suspect gas cutting. Interestingly, my first dedicated PP rifle is a .45-70 with a chamber cut using Dan Theodore's bore diameter PP reamer. Not knowing any better I started off with the BACO 446545 money bullet which is 1.515" long! I think it's about as long a bullet as you can get out of a Saeco mold :-). It shot quite well at 500m in that 1:18 twist gun, but I imagine it'd fall apart at long range. I haven't used that mold in maybe 10 years I'll bet.

Chris.
semtav
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Re: bullet tip

Post by semtav »

gunlaker wrote: Fri Jun 03, 2022 4:24 pm Not knowing any better I started off with the BACO 446545 money bullet which is 1.515" long!

Chris.

Has anyone come up with a simple chart for rule of thumb maximum lengths?
i.e.
40 cal
13 twist.....
14 twist.....
16 twist.....
18 twist.....

ETC
gunlaker
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Re: bullet tip

Post by gunlaker »

There are a few calculators out there based on different rules but I'm not sure how well they really work. The rifles I own that are "least stable" are my various .32-40's. I think the twist rates are tuned to make them marginally stable at 200 yards or 40 rods. With black powder they'll tip badly in dense winter air but be pretty good in thin summer air. Longer pointier bullets are generally more stable in my .32-40's than shorter stubby bullets of similar weight. Dan T. did a lot of thinking about this. At one point in time he wrote that he'd come to the conclusion ( for our type of bullets ) that weight was a better predictor of stability than length.

I know that there is the Miller rule and the modified Miller rule and Greenhill's. I have never tried testing any of them. My BPCR/BPTR shooting started to get way better by simply copying people who I saw winning matches and I stopped worrying about it :-).

Chris.
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Distant Thunder
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Re: bullet tip

Post by Distant Thunder »

Brian,

​You can use various calculators that will give you a maximum bullet length for the different twist rates for ​whatever caliber at a specific velocity, but it's only a number. There are more things that come into play, some are known and some are probably unknown. In the end the only way to know where the fine line of stability is is by shooting a specific bullet at various distances and under a variety of conditions.

Even bullets that are long for the caliber can shoot very under mild, stable conditions. It's when the flight gets bumpy that the same bullet can have trouble and fail.

Distance plays a part as well. At 500 yards a longer bullet may shoot very well, but may not do so well at 1000 yards. Such a bullet may only be marginally stable and that can become a problem at greater distances, or when the wind is really pushing.

I think that bullet length is the best gauge to use in judging the potential for stability in a given twist, but Dan had a point saying that weight was important. The heavier of two bullets that are the same length is most likely going to be more stable. That is because to be heavier the shape has to be less streamlined, assuming the same alloy.

The bullet with the shorter, blunter ogive would be the heavier of the two. With more weight in the nose the center of gravity is moved forward, shortening the distance between the center of gravity and the center of pressure. The result is a bullet that is not as easy for the wind to destabilize.

For what I call "optimum stability", meaning greater stability over various condition, it's better to stay a bit shorter than the calculators will say, keep the ogive length around 40 to 45% of the OAL, make it with an elliptical nose and have a tip radius that is 30 to 33% of the caliber. That all helps keep the center of gravity well forward while still having a ballistic form that is beneficial through the transonic zone.

Some people don't believe any of this matters, but I find it fascinating and I have put the above to good use in the bullets I designed for my rifles.

I haven't zeroed in on exactly how much shorter to stay below the maximum, but here are a few examples that I have worked with:

.40 caliber 18 ROT - 1.250" This 1 is a round nose & might be too long in a more pointed design like a money.
.44 caliber 17 ROT - 1.400 - 1.420" Elliptical
.45 caliber 18 ROT - 1.420 - 1.440" Elliptical

As always, YMMV!
Jim Kluskens
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Distant Thunder
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Re: bullet tip

Post by Distant Thunder »

In my examples those lengths are based on 1300 fps. If you increase the velocity you increase the spin and the length can be increased too. In a .45 caliber with an 18 ROT at 1400+ fps a bullet that is 1.460" long is good.
Jim Kluskens
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Distant Thunder
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Re: bullet tip

Post by Distant Thunder »

Of course I'm running paper patch, I forget that there are some people out there that are still using grease groove! :lol: :lol: :lol:
Jim Kluskens
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Woody
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Re: bullet tip

Post by Woody »

Hey, I'm one of them. They work just fine. You have seen me shoot.

Woody
Richard A. Wood
If you are surrounded. You are in a target rich environment.
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Distant Thunder
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Re: bullet tip

Post by Distant Thunder »

I meant no offense, Woody. So many of the people up this way shoot PP that I forget that it's not that way everywhere. I thought I should mention that I do shoot PP just in case someone reading this didn't know.

I have seen you shoot and though it was many years ago I remember it well and grease groove bullets did very well for you as you knocked over 9 chickens! I've seen some pretty good chicken shootin' over the years, but that was the best.
Jim Kluskens
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Woody
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Re: bullet tip

Post by Woody »

That was one of those "Magic" days.

I got to see another "Magic" day last weekend in Kentucky. Justin Abrams ran his first 5 in a row chickens. Now that's "Magic".

Woody
Richard A. Wood
If you are surrounded. You are in a target rich environment.
mike herth
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Re: bullet tip

Post by mike herth »

For me a magic day is putting all ten shots into an eight-inch bull at 200 yards off the bench. Hitting a chicken offhand at that distance, hah! Hitting the bucket at 350 yards at Quigley, another dream. But it is all fun.
Woody
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Re: bullet tip

Post by Woody »

Yes it is.

Woody

I get my first chance at the Q this year.
Richard A. Wood
If you are surrounded. You are in a target rich environment.
ian45662
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Re: bullet tip

Post by ian45662 »

A friend sent me a 38 cal grease groove money bullet for my wife to try. 2 reduced bands but it’s 1.48” long. She is going to try it this weekend for the long range match. We will get our pit crew to snap some pictures of them also. I will load 53 grains or so of Swiss 2F. Should be interesting or maybe frustrating :lol:
gunlaker
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Re: bullet tip

Post by gunlaker »

Ian it will probably work at short range :-). I have Paul Jones elliptical that is even longer and it's good at 200m out of a gain twist .38-50 ( ending in 1:14 twist), but it's more of a schuetzen rifle so I've never shot it past 200.

I mostly shoot a much shorter 1.3" Brooks elliptical paper patch bullet ( breech seated ) in that one. One of these days I'll have to see how far it shoots.

Chris.
ian45662
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Re: bullet tip

Post by ian45662 »

We shot our 38s over the weekend. I never found paper at 800. My wife did though with her 1.48” money bullet. We got a picture of that and it is perfectly round. After that relay though things were much better. I found paper at 900 and 1000. He forgot to take pictures and I forgot to remind him but he said both of our holes were round. I shot an 80 and 900 and a 86 at 1000. If they were not stable then I don’t think it would be possible to shoot an 86. Winds were mild. Sometimes they would be coming from 90 degrees and other times they would be blowing at us. Had to wait out a few changes on the 1000 yard relay and make some adjustments but it didn’t feel much different than my 45….. once I found paper that is. We will shoot another long range match in September and a 1200 yard match in October and I will keep plugging away with this 38
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