Shape shifting boat tail bullet

[pillardrill]

I made these bullets with a rebated boat tail in order to reduce base drag at subsonic velocities.
I would like to understand what is causing these bullets to change shape. The bullets (fired from a pistol) tend to shrink in diameter over all the length of the bullet by around .02" (0.5mm) and increase in length by about .04" (1mm). The bullets weigh 158gr. They are swaged from cast slugs, knurled and lubed. The knurling on the bullets shows no sign of rifling. The loads follow the recipes found in loading manuals, and I have tried fast and less fast powders. There is no leading in the bore.
At first I was using dead soft lead then I went to straight wheel weights, but the problem persisted. I haven't setup a proper hardness tester but I used an automatic center punch. The indentation in the soft lead bullets was .077"(1.96mm) in diameter whilst that in the bullets cast from wheel weights was .063"(1.6mm).

The bullet ( cast from ww) in the pic was fired into soft sand.

Has anybody encountered such a situation? The bullets change shape in the bore, accuracy is nonexistent and you can hear the bullets scream in flight as they tumble.

[44man]

I just have too many silly questions so I won't say anything.
Too much weight forward, too short for drive area, no rifling bite from knurling and a nice funnel for hot gases. But I am sure there is more I missed.

[pillardrill]

I have the same problem with flat based bullets which are also knurled. Bullets are .356" for use in a 9mm.

The drive area is the same length as that of a regular bullet, just the tail is added.

You may be right 44man, but how do you explain how the diameter shrinks and the length increases. The shrinkage is not even close to the bore diameter. The pic may not be good enough to see that the bullet was not stripped whilst traveling in the bore. The knurls are still fresh and not filled in.

[303Guy]

Hi there pillardrill

Can you post a pic of the lubed and ready to fire boolit?

I have encounted a knurled and surface lubed boolit retaining the knurling and showing no sign of having contacted the bore but rifling impressions are sharp and clear.

I would say the lube is acting as a jacket and the boolit is being compressed by hydraulic action. There is a possibility of the boolit 'free-floating' in the bore and not being spun up to speed.

[pillardrill]

Hi 303, long time no see

Yours would be a sensible answer. The lower bullet in the pic is unfired.
The trapped lube would prevent the knurls from being damaged. I will try an unlubed bullet.

Thanks 303.

[Doc Highwall]

Some of the 38/357's have only a 18-3/4" twist which would cause the boolit to be unstable. I shoot 200+ gr boolits out of my 1885 lowwall in 357 mag and I try to keep them going at least 1200 fps. to stabilize.

[pillardrill]

The reason the bullets were tumbling was some messed up powder I was using. I followed the recipe and it stripped the lead bullets making them ride the rifling. I had problems with hard cast regular shaped bullets too.

Using another powder solved the problem.

[DLCTEX]

The boolits are being stretched by tumbling at a high rpm rate (hence the scream). The design is too unstable. A huge, deep hollowpoint may help, but you have a lot of weight forward to overcome. A shorter tail would help. I have seen the same effect on 22 LR bullets fired underwater, which I believe was caused by the drag of cavitation, but may have been tumbling.

[Al_sway]

First, I don't think you even mentioned what cartridge, let alone type of firearm, you are using. That could make some difference in any advice offered.
Secondly, based on the photos, I would make the following observations:
- They are not large enough for the bore, as there is no evidence of rifling on the knurled portions on the fired bullet.
- You are getting severe gas cutting, as the 'changed shape' shown on the fired bullet appears to be severe melting of the bullet. This is another indication of the bore fit problem.

A bit more information please.

[Echo]

Among the desired info is the groove diameter of the pistol. My experience is that 9mm's like fat boolits, so I size mine .358. As long as they feed, size 'em big.

[qajaq59]

I see none of the rifling marks I would normally find on my retrieved cast bullets. And the bullet looks like it was badly battered on the way down the barrel. How big is that bullet compared to the groove diameter?

[Freischütz]

Do you have anything to shoot into besides sand? My best results come in water or snow. The ground (even if rock free) always damages the bullets.

[Harter66]

I read that heavy knerling will sometimes reduce effective dia.while that material must go somewhere . Constructively I might suggest reducing the depth of your knerling an leaving an unknerled band at the BT step as to keep a full bore seal. (Fit is king I hear). Also I agree with shortening the tail.

I have a 200gn 30cal boolit that I have have as of now achieved good groups and minimal leading plain based to 1500fps with 3 lube grooves of just about .005 deep and wide with a single cut file knerel on the bore ride section . I should add that this long pointy boolit also should not fly , yet it does quite well.

[pillardrill]

The bullets were a project to "improve" on subsonic 9mm ammo. I have also shortened the tail. The bullets are .356". I had even tried leaving a .356" unknurled band at the base but to no effect. As I said once I changed the powder the problem evaporated. Accuracy was satisfactory at 100 yrds, no more tumbling even with the remaining long tail ones.
However I stopped making these bullets as they are too much trouble to make when compared with regular cast bullets.

[MtGun44]

Most probably way too small diam. Slug your bore and make the boolits .001 or .002
larger. I think that knurling weakens the surface, may hold a trace of lube but a lube
groove would be better.

Fit is critical and too small is one of the most common problems. You see that jacketed
are .356 so why not cast? Believe that many/most 9mms need .357 to .358 diam to work
properly.

As to boat tail for drag reduction. I think it is likely to provide maybe a 1/4" flatter trajectory at
50 yds, which for a boolit that will likely group 2-4" at 50 yds does not seem to be very
significant. Boat tails at 400 yds, sure, maybe 4-5" less drop. At pistol ranges (unless we
are talking about sillywet rams) I think you may expect more gain than there is to be
had.

Bill

[mdi]

If a lead bullet is squished through a smaller dia bbl. it will elongate (extrude). I would try making the bullet dia the same as bore dia. before knurling. Knurling displaces metal and increases the diameter, but only on the points of the knurl. With the points at .356" there may not be enough material to grab the rifling and the bullet will just skid down the bbl.

I got no ideas about the boat tailed design but it does look like there is a sholder on the base to help seal the bullet/bbl.

BTW; Keep experimenting! Don't let anybody tell you "it'll never work" or "it's not worth the trouble". If we listened to all the nay-sayers would we have gas checks made out of beer cans? or bullets lubed with floor wax?

[303Guy]

Too much weight forward, ...

Not sure about that. I'd want as much weight as far forward as possible but more importantly, I'd wan't as much weight toward the perifery and forward as possible, like an air rifle pellet - they work just fine in a smooth bore!

I'm still curious as to how bad powder could do that to a boat tail (or any) boolit.

[pillardrill]

Hi 303,

as to how the shape shifts is a mystery to me. I didn't manage to fire many of these bullets but there was no lead residue in the barrel.

The powder (B&P 26A) must have been a super fast burning thingy. The loads were only marginally hotter, the powder must be very very low tolerance. I had serious problems with jacketed bullets with damage (thankfully repairable) to the gun. With jacketed bullets I had case bases being swaged into the ejector recess. Thankfully again the gun only suffered a broken firing pin. I am surprised the ejector was not blown off too.

I tried these bullets with a powder I use regularly with no problems. Recovered knurled lead bullets had the regular rifling marks we all know and love

Regards,

Pillardrill

[leftiye]

Maybe lose the knurl, or only partially scribe it in, and use rooster jacket, or something like that. Sounds like maybe the knurls aren't giving a gas seal (no rifling engraving marks), maybe the boolit's outside is being melted off by gas cutting. Usually though this causes leading. I'd still try it without the knurl. There's another thread going on in Lubes about using a paint as a lube (hint hint).

[Bret4207]

The best way to improve the 9mm sub-sonic IMO is to go to a FN boolit. That BT....well, that's different. It was tried decades back, more than a century back in fact in the early days of self contained metallic cartridges. Maybe you can make some new breakthrough, but it goes against everything I think of as a properly designed cast lead boolit.