Mold design, lube groove depth.

[Changeling]

Is there a limitation to depth of a lube groove or width? What is considered a realistic depth/width for a 45 caliber bullet groove both 1 and 2 groove. Actually is there any realistic/engineering reason for given measurements?;-)
No, I didn't state the weight/length.

[felix]

Boolit balance is the name of the game. Generally, the shorter the boolit, or the smaller the diameter, the depth of the lube grooves must be shallower to maintain an optimum flying boolit. ... felix

[HollowPoint]

That's an excellent question Changeling:

There is no real limitation so long as your lube-grooves aren't so deep that the core of your bullet's strength isn't compromised. If they are too deep, when your gun is fired it may squish the bullet like an accordion rather than allowing it to obturate and seal the bore.

I'm presently working on a new bullet for a .45 caliber air rifle that initially presented problems along those same lines. I guess they weren't really problems; I just had to decide if I was going to follow the crowd -with respect to lube-groove dimensions- or size my bullets so that the body was of "bore-riding" dimensions and the driving-bands sized about three-thousands larger.

Strangely enough, I've done a little bit of research into the "lube-Groove/driving-band" depths and numbers, thicknesses and general dimensions. In fact just recently someone I consider to be a knowledgeable and pretty sharp cookie on this forum posed a question similar to what you've just asked.

The only documented info I was able to find regard "lube-grooves" or "driving-band" dimensions had to do with the shallow rifling present in pneumatic guns. It stated that the optimum width of the "driving-band" should be around .060. It mentioned nothing about the width or depth of the lube-groove.

This was in order to minimize friction while still creating enough contact with the rifling to initiate spin and seal the bore. I imagine to some degree the same would apply to powder burning firearms.

It seems like one would decide on the "lube-groove" numbers and dimensions based on how far the bullet has to travel to reach the end of the barrel and how much lube would be needed till it gets there.

It may not sound like it after stating what I have up to now but, I'm in complete agreement with Felix. There is a "Bullet Balance" that has to be determined but, if a thousand different guys are designing bullets, there are potentially a thousand different balances that may come out of it.

I also tend to agree with Felix's other statement. "Generally, the shorter the boolit, or the smaller the diameter, the depth of the lube grooves must be shallower to maintain an optimum flying boolit."

But, in the tiny bit of research I've done, I've found various examples of bullets shaped like Dumb-Bells and Wasp-Waists and Caterpillars that have been proven to shoot like gang busters out of various types of Air Guns and Powder Burners.

As far as any real "Engineering reasons; " I haven't turned up any documented evidence that even remotely attributes any ballistic benefits to the depth or number of lube-grooves or driving bands.

I guess if it's "bullet balance" we're looking for we have to be prepared to do some bullet design experimenting.

HollowPoint

[melloairman]

I cast and swag for air rifles . I like to try different bullets in different rifles . Some like groves and some do not . That goes for rifles as well as bullet makers .IMO . LOL Marvin
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_5909AAA-1.jpg
http://i301.photobucket.com/albums/nn55/melloroadman/IMG_6615A.jpg

[Changeling]

Well guys I really appreciate your input and it has even given me some new ideas . Felix managed to put the whole basic idea in 2 sentences that actually can't be argued with, maybe. I do have some radical ideas but I would consider them "soft" radicals to attain things "I" consider important. On the bright side I could be right, on the bad side I could be very wrong. Nothing ventured , nothing gained!

[Bass Ackward]

I would actually prefer that grease grooves be shaped like large crimp grooves. Better aerodynamics for flight, for rearward balance, and for getting lube to the bore surface on an accelerating object.

The real mistake, and the very real bias that you see in many designs, is why they all have to be the same size or the same shape even on the same slug when it has long been known that pressure is accumulative on the base of an accelerating slug.

[excess650]

That maxi-ball has wide, deep grooves for a very real reason. They're intended to be thumb started in the bores of MLers with the grooves filled with lube. When the BP is ignited, the base accelerates before the nose, and causes the bullet to shorten, and expand into the grooves to create the seal. This does work with very soft lead in the low pressures encountered in MLers.

I shot in the snow as a teenager, and recoverd the bullets after the snow melted. In the case of the 370gr 50cal maxi, they shortened noticeably, probably between 1/16" and 1/8", and the rifling was well engraved on all of the bands.

[HORNET]

IIRC, Paul Matthews did some experimenting back quite a while ago on shallow groove cast bullets that was in The Art of Bullet Casting. He used grooves that were spec.'ed out to be just under the bore diameter of the barrel on a .375 H&H. As I recall, he found the need for a REALLY GOOD lube due to the minimal lube volume carried. I don't think he played with it enough to really work out the concept but some of his results showed some promise. The better the lube, the less you need. Many on here only fill a few of the grooves on Loverin designs with good results. Sharpe's Guide to Handloading had some lube groove recommendations, but those were for the lubes in use 60 years ago, lots of better lubes available now.

[Changeling]

Hornet thanks for the reply. I know what you are saying and the concept/idea has a lot of validity. However I believe the extremely shallow concept could run one into a low lube situation. While it is true that best accuracy has been found to be for bullets with only the amount of lube necessary in a given barrel, that is taking things out to the raged edge so to speak, better to have a little to much than not enough.
I really appreciated your bring that up though, thank you.

[geargnasher]

BABore posted some interesting results for us to ponder, he was comparing single to double lube grooves between two otherwise similar boolits. His results for that one test showed repeatedly that the accuracy with two grooves was better.

Too much lube can be as bad for accuracy as too little. Once you graduate beyond the basics of getting a good boolit fit, alloy, and power shooting with decent accuracy and without leading, then you can tinker with lube and groove design. Just for the sake of preventing leading and not considering much else, you'd be amazed how little lube it really takes to prevent leading. If you have leading, it's reasonable to think that if you just had a bigger groove that held more lube it would fix it, but that's not necessarily so.

Gear

[madsenshooter]

I don't know anything about this subject, but I have one John Ardito designed 30 caliber bullet, the Eagan MX3-30-AR, that I use in my Krag. The bottom of the groove is .265 in diameter, and it is .090 wide, shaped radially. It holds quite a bit of lube. The long throat of my Krag has it seated just above the mouth of the case, and I'm thinking most of this lube is blown out ahead of the bullet, which seems to work pretty good, for it's quite accurate. It may not be what John Ardito intended, but I like the idea, blow it forward and pick it back up as the bullet passes.

[Southron Sanders]

The modified Wilkinson bullet as adopted for the muzzleloading M1854 Austrian Rifle had very deep lube grooves and opon firing, was supposed to collaspe, (accordian style) thereby isncreasing its diameter to seal the bore and allow it to take the rifling.

Conversely, the British adopted the paper patched, smooth sided (i.e. NO lube grooves)Metford-Pritchett bullet (a modified Minie Ball) for their Model 1853 Enfield Rifle. This combination proved to be very accurate.

[HORNET]

Also remember that the lube grooves provide someplace for the alloy to go to as it's displaced by the rifling lands. They probably also should be deeper than absolutely necessary to allow for a wider range of sizing diameters. This is not so vital in some calibers as in others. Most .22 barrels need around .224/.226 for a diameter whereas something like the .30's can vary all over the place with bores down to .295 and grooves up to .318 (it's a wonder anything fits some of them). Alloy and intended velocity can greatly affect lube requirements. However you do it, try for a little taper on the sides of the grooves to help with release. Some of those straight-sided grooves are a bugger to get out.