Trying to Blow Up a Bullet

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Trying to Blow Up a Bullet

Postby pitted bore » Sat May 15, 2010 11:44 pm

One year ago today I made my first post on the calguns thread, Wildcatter's response two days later started my search for 3000 fps. There was some followup on that thread about selecting bullets to avoid blow ups cause by too-fast spin. I used Hornady totally encapsulated 185-grainers to try to avoid that problem. I didn't have any disintegrations.

In the attempts to reach 3000 fps, at one point I looked for 185-grain 45 bullets that had a cannelure to aid with crimping. The only one I could find was a Prvi Partizan hollow point listed by Grafs. (I showed their illustration on another thread: LINK.) Grafs was out of stock until a few weeks ago, but the bullets that I received had no cannelure.

The bullets were only 0.4495 inches in dia, with enough variation in length to indicate that quality control was taking a back seat to price. I decided to find whether these would blow up as predicted, so I made up a series of increasingly stiff loads with Lil'Gun, with a side-crimp. The C.O.A.L. was about 2.000 inches.

Here's a photo of a bullet and a round. For comparison a 250-grain FTX and a factory 205-grain round are shown. (Truth in advertising: In the image, the Prvi bullet is in an empty fired case, and is not crimped.)

Image


At the range, the velocities over a chronograph 8 feet from the muzzle went from 2700 to 2900 fps; all the bullets made it to the target.

So, what's next in an attempt to get a blow-up?

I want to see little puffs of gray dust. I could maybe coax another 100 fps out of these bullets, but they are already doing about 3X their designed speed and rotation. I know that thin-plated bullets don't fare very well, but the predictions were for the hollow-pointed jacketed type. I'm open to suggestions.

Thanks.
--Bob
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Re: Trying to Blow Up a Bullet

Postby gunnut » Sun May 16, 2010 1:50 am

I had problems with the 230grn. TMJ bullets. The jacket would separate and make 2 holes in the target at 25yrds. If they made it that far! Some hit the ground before the target! Others? Don't know where they went!! :o
OOPPPss! That should have been TMC. Total Metal Clad. They are thin skinned. more of a foil then a jacket
Last edited by gunnut on Sun May 16, 2010 1:54 pm, edited 1 time in total.
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Re: Trying to Blow Up a Bullet

Postby BD1 » Sun May 16, 2010 10:37 am

The only time I ever experienced the "gray dust" involved 40 grainers in a friends 22/06 at about 4,000 fps out of a 7 twist barrel. They were spinning at something over 400,000 rpm. There's all kinds of rifles that will spit them out at velocities yielding the 200,000 rpm range, and most bullets will stay together at those rpm. To get even 300,000 rpm out of your 16 twist barrel you'd need to push the projectile to over 6,500 fps. Seems unlikely. You might get the odd jacket separation, but not the "gray dust".
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Re: Trying to Blow Up a Bullet

Postby thebrassnuckles » Sun May 16, 2010 5:55 pm

BD1, i believe he is using a 1:16" twist on a bolt gun correct?

thats why he is able lo load these sumbitches so fast.
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Re: Trying to Blow Up a Bullet

Postby pitted bore » Sun May 16, 2010 9:05 pm

thebrassnuckles wrote:BD1, i believe he is using a 1:16" twist on a bolt gun correct?
thats why he is able lo load these sumbitches so fast.

thebrassnuckles-

You're correct if you are referring to the rate of rotation as being fast. The 1:16" contributes to that. However, if you're thinking of the bullet's forward velocity, I don't think the rate of twist contributes much in this instance. Increasing twist rate often results in lower velocity, all else being about equal. Rather than pushing the bullet down the barrel, a bit of the energy of the powder goes toward overcoming the increased friction from that higher twist rate, and toward the spinning of the bullet.

The bullets from the 16-twist barrel at 3000 fps are spinning at about 135K rpm, which BD1 pointed out on the calguns thread a year ago. (OK, it was only 363 days ago.) Wildcatter responded with a information-packed post about twist rates that I still re-read occasionally. Apparently at some point he had hollow-point bullets fail to reach the target, which he attributed to over-spin.

With these 185-grain hollow-point Prvis, I think BD1 is correct. A destructive spin rate would require a really high velocity like his suggested 6500 fps. That velocity probably could not be achieved even with a 460 Weatherby case necked to .451. (I'll let somebody with a bench gun that weighs 50 pounds tackle that project.)

--Bob
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Re: Trying to Blow Up a Bullet

Postby thebrassnuckles » Mon May 17, 2010 9:38 am

i was talking about the velocity of the bullet.
i believe you stated in your thread about getting to 3k FPS that you wouldnt try those loads in a semi..

if not sweet, cause i would like to hit 3k FS in my 450 upper
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Re: Trying to Blow Up a Bullet

Postby pitted bore » Thu May 27, 2010 9:39 am

thebrassnuckles wrote:i was talking about the velocity of the bullet.
i believe you stated in your thread about getting to 3k FPS that you wouldnt try those loads in a semi..

if not sweet, cause i would like to hit 3k FS in my 450 upper

-thebrassnuckles-

My warning notes include a cautionary statement that my observations with a bolt gun may not apply to a semi-auto. I have no idea what the pressure curves of the loads might be, and whether they might cause extraction or ejection difficulties. Possibly they could damage a semi-auto or its operator. The loads are not showing traditional "pressure signs" in my gun, but they may be a problem in a semi-auto where port pressure is important.

--Bob
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Re: Trying to Blow Up a Bullet

Postby wildcatter » Fri May 28, 2010 9:43 pm

pitted bore wrote:
thebrassnuckles wrote:i was talking about the velocity of the bullet.
i believe you stated in your thread about getting to 3k FPS that you wouldnt try those loads in a semi..

if not sweet, cause i would like to hit 3k FS in my 450 upper

-thebrassnuckles-

My warning notes include a cautionary statement that my observations with a bolt gun may not apply to a semi-auto. I have no idea what the pressure curves of the loads might be, and whether they might cause extraction or ejection difficulties. Possibly they could damage a semi-auto or its operator. The loads are not showing traditional "pressure signs" in my gun, but they may be a problem in a semi-auto where port pressure is important.

--Bob

Bad Bob, what was the before and after case head diameters or total case head expansion?..t
Safety First..t
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Re: Trying to Blow Up a Bullet

Postby pitted bore » Sun May 30, 2010 5:09 pm

wildcatter wrote:Bad Bob, what was the before and after case head diameters or total case head expansion?..t

T-
Alas, I don't have those data. Usually I make such measurements, but I did not in this series. I usually can backtrack to an approximate measurement, but in this instance I can't because the cases had been used for a series of tests with 300-grain bullets, which did a bit of enlargement over the factory dimensions.

I'm likely to duplicate this test, and I'll try to get some measurements then.

Sorry.
--Bob
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