Angled Grease Grooves?

[Cast_Kid]

Has this type of design been tested before?
I might do a custom made mold for std 300blk 16", kicking around some ideas.

Was thinking maybe the angle would allow lube to flow off easier as bullet accelerates forward, etc.

Your thoughts?

[reddog81]

It looks like your cutting the amount of lube in half and I'm not sure the lube needs any help flowing.

[Hickory]

The "angled grooves" are usually ment for crimping the boolit in place to adjust boolit seating depth.
I suppose they can be used to supply extra lube when needed.

[Cast_Kid]

It looks like your cutting the amount of lube in half and I'm not sure the lube needs any help flowing.

The sizing of the angled groove would be changed to accommodate the needed amount. The pic was just for illustration purposes only. I am pretty sure that if angles would help in either lube or stable flight it would have already been done, I just don't see any data about it. I certainly do not want to recreate a new wheel, etc.

[country gent]

A lot of Minnie balls had grooves similar to those. some have the grease grooves cut at a slight angle front and back to aid in release from the mould. then there are the u shaped or rounded grooves.
It may help but I suspect the compression of the bullet and grooves aids flow more. along with the centrifugal force of rotation from the rifling. If you allow the lube to flow to fast it may not get all the way to the muzzle also.

[JSnover]

Kieth liked big square grooves for maximum capacity. Dick Dastardly at BigLube markets HUGE grooves. I like mine a little on the shallow side but wide and angled top and bottom, or rounded.

[Cast_Kid]

Kieth liked big square grooves for maximum capacity. Dick Dastardly at BigLube markets HUGE grooves. I like mine a little on the shallow side but wide and angled top and bottom, or rounded.

Angled all the way to the back, or just a edge chamfer? Is there any flight data for the various styles (one more stable than another)?

[JSnover]

Sort of like what you drew there but angled all the way to the bottom of the groove. Aerodynamically I doubt it makes a difference. I like the angled or rounded grooves because I believe they release lube more easily after leaving the barrel (I have no proof of this). I'd like for all of it to be shed quickly so as not to change the weight or balance midway to the target. That's my theory anyway.

[reddog81]

Typically the angled portion or he U shape is at the bottom of the groove to allow easier release from the mold. Cut too far into the bullet and you'll start to creat a bullet than can be snapped in half.

Like others have mentioned people can use larger grooves to allow for more lube. Angled grooves with the intent to help push lube forward just isn't needed. When spinning at 180,000 RPM the centrifugal forces will get the lube moving.

[beagle]

I think we often times get hung up on the amount of lube needed by a cast bullet. We know that Keith's square grooves made release more difficult but at the time was probably necessary due to the lubes available. With the improved lubes we have today, a huge amount of lube is not necessary providing the bullet fits. If not a good fit, it is just blown past the bullet before the bullet bumps up. The angled grooves may improve casting ease but I believe that's all you'll get. The heaviest lube capacity commercially produced mould I have ever used is the Lyman 429303. Hard to cast with too. I have picked lube "boogers" off the face of a 100 yard target when testing some in my Marlin M1894. Think you might be beating a dead horse here./beagle

[country gent]

On the moulds I made I didn't cut the grooves truly "Square" but gave them a 5* draft angle. on the short section of the groove it didn't show but did aid release and kept mould from breaking driving bands when bullet released. While not visible to the naked eye it could be seen with the optical comparator or the cmm with a special probe.

Most moulds have some draft angles incorporated to aid release of the part. Its not always arbitrary but may be determined by form of casting, material cast, and the actual parts requirements.

[Cast_Kid]

Typically the angled portion or he U shape is at the bottom of the groove to allow easier release from the mold. Cut too far into the bullet and you'll start to creat a bullet than can be snapped in half.

Like others have mentioned people can use larger grooves to allow for more lube. Angled grooves with the intent to help push lube forward just isn't needed. When spinning at 180,000 RPM the centrifugal forces will get the lube moving.

It's always zero to max speed, and under acceleration, so the rpm varies quite a bit depending on powder profile. I always wondered if two lube recipes could be stacked, a harder lube in 1st then topped with a softer lube. Or one in one groove and another in the other (or alternating lube recipes).

[JSnover]

That sounds like way too much work for a guy like me .

[Ballistics in Scotland]

Grooves with one side angled, as found in most Minié bullets, were from Tamisier's patent which preceded the hollow base. But the flat side was at the rear of the groove, and the logic was that the extra air resistance at the rear would keep the bullet nose forward. This was based on Tamisier's generally false belief that the spin-stabilised bullet remains in its bore orientation and thus at an angle to its curved trajectory. It may wobble, and those grooves might help control that wobble, but a bullet does follow its trajectory.

https://en.wikipedia.org/wiki/Tamisier

I also think part of the logic (and I have a vague memory that someone else made the grooves much larger) was that the conical section would act like a wedge and increase the tendency of the cylindrical bands to expand and grip the rifling. I doubt this myself. I think the expansion of a malleable metal when pushed can fairly compared with its stretching when pulled. The tendency will be for the bits with a small cross-sectional area to expand more than the larger parts. The expansion will take place in the grooves, where it doesn't do anyone any good.

As for improving the transfer of lube to the bore, if that mattered, I think spraying it ahead of the bullet would be even better. But I don't think that is significant. Centrifugal force at bullet rates of spin is quite enormous, and the heat is considerable. I think the lube will be trying to get from groove to bore for all it is worth, regardless of the groove shape.