MP Moulds - WOW!

[Matt_G]

My guess is balance, not aerodynamics, is involved.

I doubt the airflow in front of that blind hole is significant, but I believe small differences in wall thickness could be important to a projectile spinning at high RPM's during flight. Again, just guessing.
Sort of the same way a small void in a bullet can have influence on trajectory.

After thinking on it some more, I'm inclined to buy into your theory over mine.
It sure wouldn't take much to throw it out of balance, that's for sure.

 

[Tomme boy]

I'll bet if you look real close the hp is not even. Happens when you drop the bullet too soon out of the mold. It happens more with the penta than the round hp pins.

 

[358156 hp]

My guess is balance, not aerodynamics, is involved.

I doubt the airflow in front of that blind hole is significant, but I believe small differences in wall thickness could be important to a projectile spinning at high RPM's during flight. Again, just guessing.
Sort of the same way a small void in a bullet can have influence on trajectory.

But if you're going to have any variances, the nose is the best place for them. When I cast pentas, I make certain that I'm holding the mould upside down when I open it. This gives me a better chance of having the bullets drop straight down. This minimizes the potential of off-center HPs caused by releasing the bullets at an angle while the bullets still soft enough to be deformed.

 

[Rally]

I have noticed a difference in accuracy between a DP and Hp pins in my Noe Rg moulds. The DP pins are more accurate in my guns than either the Fp or deep Hp. I cast them from the same alloys at the same time to help eliminate some weight.variation, and have incorporated a short pause in my casting cadence when I first open the mould to allow the noses to cool a tad more. I noticed elongated holes in the deep Hp’s and the slight pause in cadence eliminated that. What really made the most noticeable difference in casting with Hp moulds, was polishing the pins with an electric drill with synthetic two cycle oil.and real fine steel wool. An extra tap to the side of the mould once it has been closed also seems to make the pins in multiple cavity mould settle in place before pouring. I also built guys/ platform on the base of my Lee 20 lb pots so the pin bases never touch anything.

 

[Petrol & Powder]

Shot up the remainder of the penta point, HP bullets today. With a stout loading of Bullseye putting me in the +P territory, things were a little better but still not great.
I'm hoping the round HP pins produce better accuracy.

I switched back to some old SWC and WC loads that are known to be good and the hits came easily. The bullet weights are all close, so I'm thinking the penta points are the problem.

 

[RBHarter]

CPO obvious......... A&B shoot great but C that weighs the same A&B but with a gapping hole in it doesn't. Must be the shape of the hole .......

In a direct comparison a 325 gr TAC-X Barnes would weigh 395 gr in lead only it would have more metal in the HP cavity or be solid and even heavier in matching shape . Upwards of 415 gr actually.

How much does the uncooperative HP weigh solid? How much longer is it than A&B ? It might not matter at all .......it might matter a lot.

I ordered a MM custom 453-350 RF because a 458-340 worked well enough at 351 gr I figured I could get away with it .......it's .1 longer and even cheating like all get out it will do about 8" at 50 in it's intended roll while the 340@351 ran about 4" right out of the gates . A 25-50 gr HP won't change the fact that I have an OAL restriction and it's too long to stabilize.

 

[Petrol & Powder]

The bullets with the round hollow point cavities shot better. I think I'll stick with those.

 

[burbank.jung]

The bullets with the round hollow point cavities shot better. I think I'll stick with those.

Did you drop you cast penta points upside down so the hole would not be distorted?

 

[Petrol & Powder]

Dropped them on an old towel, folded a few times for thickness. I think one or two pins are slightly different from the others, resulting in variations in the bullets.

 

[burbank.jung]

I own a 2 cavity mold and alternated the pins so I drop one round and one penta hp. My round nose casts are more accurate.

 

[Petrol & Powder]

I own a 2 cavity mold and alternated the pins so I drop one round and one penta hp. My round nose casts are more accurate.

I suspect it is easier to make the round (cone) pins consistent.

 

[Petrol & Powder]

UPDATE
Been some time since I could work on this.
With the larger, round, HP pins in place, resulting in a larger HP cavity, the average weight was about 156grs.

A stout load of Unique gave OK results but not great. Clearly in the +P territory but the accuracy dropped off.

I loaded up some HP-38 (AKA WW-231), one of my old stand-by powders for 38 Special, and got promising results.

With 5.0 grains of HP-38, NRA 50/50 lube, sized to .357", seated to the crimp groove - The hits were very consistent. No leading

The load is likely right below +P levels. Shooting them in a 2 1/2" Model 66, so plenty of strength to spare there. No worries.

I don't think this bullet will replace my standard SAECO #382 (SWC) and Bullseye powder but I like having this option.
Still some testing to do but I think it will be HP-38 with this bullet.

 

[nanuk]

Did you drop you cast penta points upside down so the hole would not be distorted?

Dropped them on an old towel, folded a few times for thickness. I think one or two pins are slightly different from the others, resulting in variations in the bullets.

I think burbank.jung is asking if you dropped them while you opened the mould perfectly upside down, so they would fall off the pins without any torque on the nose edges, which could bend them out

I have always thought it was common to drop them from upside down, simply to remove any chance the bullet sticking in the upper half and dropping onto the bottom half, or with a hollowpoint, sticking on the pin, then hitting the lower mould half on the way down once released