Bore riding boolit nose issue

[Shuz]

I discovered that the nose of one of my bore riding .30 cal boolits is not uniform from boolit to boolit. Some boolits measure .301-2 and others are .302-3 and a few were even .304-5. These boolits came from a run of about 200 boolits cast in a 4 cavity aluminum mould, from a respected manufacturer of quality moulds. I discovered this when boolits seated to my normal OAL would not chamber in my .308 due to the fatter boolits engaging the lands to the point where the bolt would not close. I wish I knew whether it was just one cavity or more that were the culprits, but that will try to be determined during the next casting session. My alloy is 10:1 (ww:lino) and the casting temp was measured between 700 and 750F. The boolits are cup point and I obtained excellent fillout, altho my weight dispersion ran from a low of 194g to a high of 200g, with most falling in the 196 to 197g range.
The concern I have is that I may be running at too high a mould and/or alloy temp, causing the mould to "grow" in size, at least in the nose, and perhaps elsewhere due to the great weight variation.
I invite and appreciate all comments--Shuz

[country gent]

It may be an expansion issue with the mould. Cast some with a larger pad area and drop where you know what is what. Start and drop several in an area justafter you get good bullets. and cst at a brisk pace for a short while then a couple drops in a second pile. cast at your pace for 10-15 mins and a couple drops again do this until you run out of room for "known" piles. Measure the noses in each pile and see where they start to grow. This mould may rquire a slightly lower lead temp or slower pace t maintain proper temp level. Also monitor lead temps as to nose size.

[JonB_in_Glencoe]

How are you sizing them?
If you are "base first" sizing (in a lyman or RCBS) you could be 'bumping' the nose larger.
If 'bumping' is happening, look for bent boolits, have you checked runout on your ammo?

[Shuz]

How are you sizing them?
If you are "base first" sizing (in a lyman or RCBS) you could be 'bumping' the nose larger.

The measurements were taken before any sizing on a pile that I still hadn't sized.
However I did measure the noses on some before sizing in my Lyman 45, and they were the same size after sizing. The alloy was quench cast.

[JonB_in_Glencoe]

OK, surely not bumping then.
That alloy should cast pretty good at a lower temp, (even as low as 650º) ...I guess that's where I'd start during the next casting session, cast as cool as possible.

[Shuz]

I turned down the heat to 700 deg F and cast a batch this afternoon. Based on measurements from four drops of 4 boolits each, it is evident that the nose diameter increases from cavity 1 to cavity 4 on all four sample drops. The amount of the increase is .001 to .002. The weight also increases from cavity 1 to cavity 4 on all four drops. The weight delta from low to high on all four drops is: 1.4g, 3.0g,1.8g, and 1.3g. The question is: am I splitting hairs here, or is this a normal size and weight variation on a nominal 200g 30 cal boolit?
The mould pins seem to be in alignment, but the fact that the boolits grow in size and thus in weight going from cav 1 to cav 4 would indicate something may be amiss. Again, comments are invited and appreciated.--Shuz

[popper]

Try reversing the order of pouring. See if it follows a cavity or heat. That is a long heavy boolit. 1.5gr seems OK, the 3 is an outlier. What is the diam. variance of the drive bands/body?

[country gent]

Does each cavity stay consistant to its other casts sizes and or dimensions? IE does cavity 1 stay the same thru the run with others from cavity 1 same with 2, 3, and 4. If so then there is a difference in the cavities. How are the driving bands for size as cast? Again cavities 1 2 3 and 4.

On this its hard to make smaller cavities where needed. Some on multi cavity moulds mark the nose so each cavity can be shot together as a group. You could have a nose sizer made that sizes noses on them to the same dia ( another step in the process)

MAke a run keeping the cavites separated as to 1234 and see what that tells you.

[earlmck]

My consistency in diameter and weight improved considerably on several of my multi-cavity moulds when I began incorporating an extra "tap tap" of the mold on the casting bench as I squeeze the handles closed. I wasn't getting any indications of incomplete closing other than some boolits being larger than others. So this has now become a habit whether the mould needs it or not. Might help with this mould of yours.

[Shuz]

Try reversing the order of pouring. See if it follows a cavity or heat. That is a long heavy boolit. 1.5gr seems OK, the 3 is an outlier. What is the diam. variance of the drive bands/body?

Popper--of the 4 drops mentioned above, 2 were cast front to back and two from back to front. No difference noted.

[Shuz]

On comparing the driving band dimensions, I find that cavity 1 was always .312, and cavity 4 was always .313+. The other two cavities were mostly .312 or .312+. So it appears that cavity #4 is dropping boolits larger in all dimensions that the others, but the others seem to increase somewhat in size as I move from cav 1 to cav 4.
Next session, I will try earlmck's suggestion of tapping the hinge pin a couple of times before I knock off the sprues.
Thanks for all the help!

[JonB_in_Glencoe]

I turned down the heat to 700 deg F and cast a batch this afternoon. Based on measurements from four drops of 4 boolits each, it is evident that the nose diameter increases from cavity 1 to cavity 4 on all four sample drops. The amount of the increase is .001 to .002. The weight also increases from cavity 1 to cavity 4 on all four drops. The weight delta from low to high on all four drops is: 1.4g, 3.0g,1.8g, and 1.3g. The question is: am I splitting hairs here, or is this a normal size and weight variation on a nominal 200g 30 cal boolit?
The mould pins seem to be in alignment, but the fact that the boolits grow in size and thus in weight going from cav 1 to cav 4 would indicate something may be amiss. Again, comments are invited and appreciated.--Shuz

from a respected manufacturer of quality moulds.

Since you did another casting session, and inspected the mold and kept close track of what boolits were dropping from each respective cavity and those are the results you got, then I will surely say, those size/weight variations are NOT within the range I would accept for a rifle boolit. I would be contacting the respected manufacturer.

[bullseye67]

Good morning,
Ahhh....the joy of multi hole aluminum molds....
I find especially on long rifle boolits, it is difficult to get consistent diameter. I have several 5 cavity molds that cast the centre 3 within .01grs the end 2 are heavier by ~1-1.5grs. The end boolits are also slightly larger, .310.09 as opposed to .31005. I sort accordingly. The outliers are TL and used for plinking practice out to 100 yards.
I have several old single cavity molds. If you want consistent boolits you don’t have to sort that is the way to go. I have cast 1000 boolits and had no differences in a large sample of 100.
The question I ask. Is it faster to sort, or to, cast from a single cavity?
Have an awesome weekend

[Dan Cash]

My consistency in diameter and weight improved considerably on several of my multi-cavity moulds when I began incorporating an extra "tap tap" of the mold on the casting bench as I squeeze the handles closed. I wasn't getting any indications of incomplete closing other than some boolits being larger than others. So this has now become a habit whether the mould needs it or not. Might help with this mould of yours.

I agree that your problem is mechanical, not arcane mystical phenomenon. Unless the cavities are bored to different sizes, a change in mould handles might solve the problem. I use a number of multi cavity moulds that have no measurable difference in their cast. One set of my handles does not fully close the blocks on both ends and is looking for a new home.

[country gent]

I give a couple very light taps on the mould handles finger after closing and before closing sprue. ( Brooks mould site recommends this) This insured the mould is closed and pins seated well. I use a small 8 ounce dead blow mallet to cut sprues and the light tapping. The couple (2) light taps on the side made a big difference for me. Another thing is setting the blocks on a flat rail when closing them as this pre alighns them some saving wear on the pins and sliding. I use the edge of the roller tray I use, but a length of 3/4" X3/4" X 1/8" angle iron set point up works well also.

Another spot to watch is closing the sprue may slightly open blocks if your not carefull

[Shuz]

Well, I think the nose issue has been solved. I cleaned the area around the mould pins and mould pin holes that had built up just a little residue from the M-P molds special sauce whatever it is. I also buffed the mould cup pins to make sure they were fitting in the slots properly and not holding the blocks open slightly.
I once again made 4 drops, keeping track of the cavity numbers. I'm happy to report that on all 4 drops all cavities dropped boolits that were either .301 or .301-.302 on the noses. The driving bands on all boolits were .312 to .3125. The weight deltas on the 4 groups were 1.9g, .3g, .7g, and 1.8g.
Bottom line.....there was nothing wrong with the mould,(it is not an M-P by the way), and it had just built up enuf "stuff" in the critical spots to prevent proper operation. Thanks for all the help!-Shuz