Designing pistol Boolit moulds without grooves for PC/Hi Tek

[Blanco]

What are the design features that should be considered when building moulds for coatings?
Most of the designs I see tend to be nose heavy bias. Some are split even between base and nose. Since there is more bearing area does the base need to be shorter? What are the effects of this on velocity and accuracy?
So many parameters it is hard to determine which are beneficial. I realize there are always tradeoffs. Just wondering if anyone has noticed any features that work well with coatings and the lack of lube grooves?
Seems a few of the long held ideas may need to be revisited and possibly revised

[longbow]

I guess my take is that whether PC'd or not, a good design should be a good design. Not sure why a standard lube groove design is bad for PC'ing to start with. No first hand experience here experience here but but I am wondering what is wrong with say the H&G #503 Keith style SWC PC'd as is? Or say the Lyman 311299? Both are proven designs for their purpose and PC'ing isn't going to change that.

If for some reason lube grooves bother you then the only way you can use the same basic design is to shorten it (so not really the same), add a hollow point which is going to change the CG some with less weight in the nose and more in the base for a same proportion boolit or add a large relief between two driving bands which shouldn't affect performance but really isn't any different than say two smaller lube grooves.

With a long heavy boolit like the Lyman 311299 removing the two small lube grooves would not likely change the weight by very much so a smooth design of something like that might be just a slightly small bore ride section to allow for PC thickness and slightly smaller diameter smooth bearing area to allow for PC thickness.

With most or at least many handgun boolits the lube grooves are substantially larger so removing them to make a smooth boolit would have to result in a shorter boolit that would likely affect BC some or maybe even a lot. Hmmmm, I have the H&G #503 modeled in 3D from when Dale53 ran that group buy and got me to make the drawing. I could remove lube grooves and see how much weight is added. Better than speculation.

Not trying to be argumentative here, I am trying to figure out why existing lube groove designs are not suitable for PC'ing as is and just what happens to the overall design if lube grooves are removed ~ how much CG moves, bearing surface length changes, etc.

Having said that, I have smooth designs I use in my push out moulds paper patched (not much anymore) or knurled and tumble lubed, and sometimes smooth as cast over a lube cookie and some are modeled on existing designs like the Lyman 311299. They shoot just fine for me but I have not done side by side shooting comparisons with the standard designs.

Longbow

[williamwaco]

I do not PC and have no experience there but I think groove free bullets would be great.

I might be mistaken but I believe they would be much easier to cast.

Next mold I buy will be groove free and I will use it for TL.

[Blanco]

I would say there is nothing wrong with PCing boolits that already have grooves. As far as PC goes it does change the dynamics of a given design.
Case in point: I have the Lee TL356-124-2R in a 6 cavity. As a lubed boolit it failed miserably in my 9mm pistols. I never had any luck with it at all. I had about 50 fresh ones lying around and need a test subject for some of my PC. I coated them as a test only and had not planned to actually load them. As is often the case I was loading some of my favorite 9mm and came to the end of the boolits and still had a dozen or so cases left in the loader. On a whim I grabbed some of the coated TL's and loaded them up.
My next range trip I passed off the TL's to my brother in law and told him they were just some junk leftovers.
I was floored when he showed me the target he shot. Literally one of the best groups ever out of my Beretta.
So I know the PC changes the dynamics enough, but I don't really know what i'm looking for.
My theory is that the boolits were a bit undersized and the PC helped fill them in a bit?
The great part here is you may want to go back and try PC on boolits that just didn't work for you.
I guess it's just going to be new territory to explore and experiment with.

[BRobertson]

I am just getting around to starting a similar experiment.
I just ordered an Accurate Molds # 43- 305Z that TOM placed in his catalog for me.
My new Freedom Arms M83 that I ordered last year ( 8 1/2" octagon barrel) will hopefully be ready next month, and
I plan to wring it out with this design , and a few others.
I will be using powder coat,( I am a long time powder coater for truck parts) and the new Hi-Tek powder version.
Also had Lathesmith make me a .430 die without any lube holes .
I plan to mount a 2-8 VXIII Leupold on the M83 for load testing, and then use open sights for hunting.
A good winter project!!

Bob

[Cap'n Morgan]

Long, slender boolits, like a 150 grains 6.5mm would probably benefit from not having lube grooves, simply by being more resistant to bending during launch. But I'm only guessing here...

[longbow]

williamwaco:

I think you will find that you will need to knurl the boolits for tumble lube. I have tried smooth boolits cast from moulds I make and in my .44 Marlin I got leading if I didn't use either a lube cookie or knurl the boolits to hold tumble lube.

For PC'ing this of course wouldn't be a problem and per Cap'n Morgan's comment, with PC'd boolits there is likely potential to push velocities so any form of deep lube grooves might indeed be an issue with regards to collapsing. I have had Lyman 429421's collapse at the lube groove when pushed hard in my Marlin. So it certainly can happen.

Longbow

[williamwaco]

williamwaco:

I think you will find that you will need to knurl the boolits for tumble lube. I have tried smooth boolits cast from moulds I make and in my .44 Marlin I got leading if I didn't use either a lube cookie or knurl the boolits to hold tumble lube.

For PC'ing this of course wouldn't be a problem and per Cap'n Morgan's comment, with PC'd boolits there is likely potential to push velocities so any form of deep lube grooves might indeed be an issue with regards to collapsing. I have had Lyman 429421's collapse at the lube groove when pushed hard in my Marlin. So it certainly can happen.

Longbow

Thanks for that. I just lost interest.
I am looking for less work, not more.

[Blanco]

The up side may just be that the PC actually works like a plating and holds the bullet together better?
I have seen with a hammer test that you can deform the boolit from many several directions, but the PC wont let go.
It may split and crack but is extremely tenacious.

[longbow]

williamwaco:

Knurling doesn't have to be a lot of work. Simply rolling the boolits under a coarse file can be enough to hold some lube. In my case, I made a knurling tool and works quite well. Kinda like the Corbin tool but on steroids... and not nearly as nice as theirs, but it works.

I am actually getting better accuracy from my .303's using smooth/knurled boolits than with factory GG moulds.

Anyway, this is a little off topic for a PC thread.

I would figure Lee tumble lube designs would be good for PC'ing as well as tumble lubing.

Longbow

[FISH4BUGS]

Politically Correct bullets? Sorry....i couldn't resist! It's a Tourette's thing you know.

[Blanco]

On most boolits if you divide it at the point where the nose radius starts. some designs are longer in the nose. I see a lot of 9mm like this. Or on the .40 they are mostly evenly divided or lean to being base heavy

Attachment 113531
I consider this a nose heavy bias as the nose is longer than the base




Attachment 113532
This one has the shorter nose and carries the majority of weight in the base

Not sure for the reason, but from what I have seen so far the the base heavy design seems to be a bit more accurate. This is just from my personal experience, YMMV

[TomAM]

For accuracy, long bearing surface is usually better. But it can effect feeding reliability if not suited to the auto in question, and it reduces powder capacity and therefore power potential.
There are lots of things to consider when designing for a small capacity auto cartridge.