Tell me I'm crazy...

[sdcitizen]

Ok, I just can't get this thought out of my head. We all know that the less residual pressure there is behind a boolit when it exits the muzzle, the easier it is to control any yaw from a less than perfect boolit base. So, with that in mind, would it stand to reason that a massive amount of porting in a barrel to relieve as much pressure as possible would make a barrel easier to shoot cast boolits accurately? I'm thinking along the lines of 6 or 8, maybe 12 holes around a barrel with about 2 or 3 inches of rifled barrel left between the last ports and the muzzle.

[nanuk]

try it, and let us know.....

[swheeler]

You're crazy!

[robroy]

OK you're crazy. What's that got to do with it? I can't think of a safety reason not to do what you're talking about. If you have a test mule to try it on that would be the way to go. I'd want chrono and accuracy data on a minimum of 5 5 shot groups before and after if I were doing it.

[Bullshop Junior]

Might be worth a try. But get double hearing protection.

[sdcitizen]

I like the adjustable bleed valve idea, hmmm. This state passed the firearms freedom act in 2010, so i'm not too worried about a shroud or crude supressor over the ports to cut some of the noise. I have been thinking of ruining a 308 handi barrel just to see if there is any validity to the hypothesis.

[Bent Ramrod]

You mean sort of like this?

Attachment 98272

Mr. Kent did quite a good business around the turn of the last century venting barrels for customers. Apparently he could drill from the muzzle into the rifling slantwise without leaving a burr in the barrel. (Hope the photo is readable; my scanner doesn't work any more for some reason.)

[leftiye]

I've read threads here where members were touting the value of using faster powders to reduce muzzle pressure. I told them to get a longer barrel. And use the slower powders that don't beat up the boolit so much. I think your idea is sound. I might do it myself to a high performance cast boolit rifle (say .35 whelen, or a magnum). Keep the pressure behind the boolit uniform on all sides ( don't drill just one or two hholes), maybe four holes radially two or more inches behind the muzzle. Venting like this into a shroud would be a fine facilitator for a suppressor.

[sdcitizen]

Ha ha! Of course someone was doing this a hundred years ago, it would seem that the old adage is true,"Anything related to guns and shooting has already been tried." My main thought is, doing this would be the same as fixing a damaged crown on a rifle. If either the crown or the boolit base are damaged the moment they separate with 8000psi of pressure or so, it is going to throw the boolit off. If we severely reduce the pressure at that moment, can one of them be less than perfect and not matter?

A gas check is used for a drive key to keep the soft lead boolit from stripping out on the rifling, but perhaps a more important role is to provide blast protection to the base when the boolit pops out of the muzzle. Leftiye, that is exactly what I was getting at, the ability to use much slower pressure curve powders to keep from damaging the base so much on acceleration. What would happen if we took all the drive bands out of a mold so it doesn't need the drive key effect, and powdercoated the plain base boolit, so it essentially looks like a J-word, and then reduced muzzle pressure to a point where the base damage wouldn't cause any off kilter jet effects when it exits? I have a .309 230 Lee mold on order, and plan to see if I can get it going fast enough to stabilize out of the 308 handi, and then I am thinking about trying this, progressing through slower and slower powders.

[leftiye]

You would still be better off with a good crown. They're easily had.

Considering .300 Blackout data, and if you have enough twist, that shouldn't be a problem to use the 230 gr. boolit. It may actually help accuracy. You can drill no lube groove straight sided boolit molds easily (make your own?).

[johnson1942]

their was a machinest up in the black hills of south dakota who made and testesd a lot of what your talking about. he came up with a design that increased accracy a great deal and reduced recoil. your right on with your way of thinking, go for it.

[sdcitizen]

Leftiye, you are on the same track of thinking that I am, of course a good crown is easily had, but getting boolits that are 'perfect' at exit is the other half of the crown theory. I like the idea of making a simple single cavity smooth sided boolit mold, that would probably be the way to go for testing. Johnson, I may be able to find out who that is, I am meeting with another fella in the industry this weekend to try some PC in his select fire toys, if I don't know the machinist, I bet he will (both were involved in the 408 development if I'm not mistaken). If nothing else, I'll do the hammer a lead slug in the barrel and drill away!

[MT Chambers]

I don't think that with the lead fouling, no good could come of cast bullets and porting barrels.

[Whiterabbit]

I'm not confident it would make a big difference.

First, barrel time for the base of the bullet to travel, say, 1 inch (from ports to crown) is VERY short when the bullet is very near or at its maximum velocity. At 1500 fps, that's .00005 seconds per inch. or .0555555 milliseconds. Combine that with the simple mass transport issue. You are trying to bleed the pressure off from X psi to 0 psi (in a perfect world of course). At 0 psi, the driving force for simple matter transport is very low, and movement speeds will be low to nil. So we can only get a reduction, X - y psi. Where the bigger y is, the better the ports work.

y is going to be based on two factors. the first is X, the initial pressure. That's the driving force of bleedoff. Second, the size of the ports. Now, the size of the ports is not unlimited, and the frankly the goal is already to get X very low because it does not help you to get a low muzzle pressure by starting with an even higher pre-port pressure before bleedoff!

Finally, the barrel time really fixes the amount of time for bleedoff to occur. How much mass (airmass) do you think you can jam through those ports in .05 milliseconds, even with 10ksi or more of driving force behind it?


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IMO your best bet is to choose a powder and tailor the load to burn as much powder as possible by the time the bullet gets almost to the muzzle, such that the expansion chamber itself will be of sufficient growth rate to inherently bleed off the pressure by the time the base of the bullet is uncorking from the barrel.

Just my opinion.

[Doc Highwall]

The base of the bullet is most likely to get damaged upon firing where the pressure is greatest in the throat and the first couple of inches of barrel travel. The crown of the muzzle has to be square along with the base of the bullet allowing the gasses to break evenly at the muzzle, so I do not think it matters as long as the powder has been consumed in the barrel. When I see a large muzzle flash makes me believe that too slow of a powder is being used and unburnt powder particles could influence the base of the bullet.

Bench rest shooters are running high muzzle pressures with flat base bullets and getting extreme accuracy so as long as you use powders that are fast enough for your cartridge and barrel length I would just make sure that the bases if your bullets are flat and your muzzle crown is not damaged.

[Whiterabbit]

for pistol, the faster powder I use, the more muzzle flash I get.

[sdcitizen]

I suspect that most muzzle flash is from igniting hot CO that is produced during the combustion of 'cooler' burning powders. That is to say that there wasn't enough oxygen present in the powder to convert combustion by-products to mostly CO2. Whiterabbit, there is definitely a limit to what one can do with ports when it comes to pressure reduction, however, I was envisioning about a 2" section of porting, with a 1" blank left at the end of the barrel, so that would give the first row of ports approx 3" of barrel travel. Seems that there is some consensus that keeping muzzle pressure below 7000 psi makes a meaningful difference, so it may only need to bleed a few thousand psi off to be effective.

[Dan Cash]

Mann tried what you are suggesting and it did not work. A bullet with a base damaged or out of square is out of balance and will yaw regardless what you do to the muzzle.

[leftiye]

Who said you have damaged bases? Don't.