Boolit nose dimension variance within the same boolit. Any significance?

When I started experimenting with powder coating, I started paying more attention to nose diameters of my boolits.
I was surprised to find that my RCBS 25-100 casting boolits from 1:10 (lino-ww) varied on the nose from .251 to .254 on the same boolit. This is right before the first driving band, and before any powder coating. Not all boolits show that much OOR condition, but many vary from .252 to .253. Now this boolit is not what I would call a bore rider, but is .001 to .003 OOR condition on this fairly short nose cause for concern in trying to shoot good groups and scores in CBA competition?

Not sure what you mean. Are they out of round or does the diameter decrease as you go from the driving band to the nose?

Some bullet designs are tapered in the area in front of the drive bands. You may have one of those.

Differences in bullet dia between bullets is usually due to differences in alloy or mold temperature.

If it supposed to be a bore rider (even with that short nose) the forward portion should be a constant dia. The longer bullets I use do not end up that way. I suspect it is due to temperature differences in the mold over the length of the bullet. I 'solve' the problem by body and nose sizing, both before and after PC.

Most every boolit is slightly OOR right in front of the first driving band. Most are .251 to .252 , but some are .251 to .254 OOR. Should this make a difference in accuracy?

Out of round is not necessarily the same as out of balance. The lands encircle the nose of the bullet so it is still lightly engaging the lands to center itself in the bore. You can not say if the OOR actually affects the way the bullet shoots or not. What does the target tell you?

Dusty--I formally used Cramer 55A , which is a nominal 100g boolit.
I decided to try the RCBS 25-100 and I initially got a few groups that were around an inch at 100 yards. Lately the groups have not been so good. I'm trying to find the cause. Could the occasional flyer be one of those boolits that is .003 OOR just ahead of the first driving band?

Perhaps you should mic those bullets to see exactly what you are dealing with. Set the mold seam at 12-6 and mic and record the readings at 11-5, 7-1 and 9-3. That will tell you exactly if the mold is out of round or the pins have slipped and the blocks are not aligned. Then consider if you need to fix any out of round condition.

Since you are powder coating, you have altered the cast bullet form and fit so you might be chasing a red herring anyway. If it shot well before PC, then........

There are two scenarios I have experienced that have caused an out of round bullet some of the time. A third was an out of round mold, but every bullet would be that way. #1 is poor fill out. It is very possible to have a bullet out of round because it did not fill out completely. It is also very common to see fill problems right at the mold parting lines. #2 Is a mold block not closing all the way or misaligned. This can be caused by alignment pins not being mated correctly, lead between the mold halves, or simply not closing and holding the mold closed firmly.

An out of round bullet can shoot ok, but I've always had problems with them. The biggest problem was if the bullet wasn't being sized fully all the way around, and causing a poor seal when firing. If you take careful measurements, every bullet is going to be slightly out of round. Ideally they would be measured in tenths with a micrometer. I'd definitely be concerned of any measurement over .001" if accuracy was the goal. This would be doubly true for a small bore rifle such as this.

Shuz, I recently discovered that after casting for over 50 years I wasn't getting the mold blocks fully closed each and every time. My discovery came with trying to figure out why I was getting a few 10-thousandths variance in diameters of boolits for paper patching which was causing problems. It all straightened out when I started giving my mold handles a couple good "taps" as I squeezed them closed. Since I introduced this little "tap-tap" into my casting procedure all my boolits have got more dimensionally consistent.

I don't know if that would help your problem but it couldn't hurt to give it a try if you aren't already doing a "tap-tap" thing. When I talked about my "discovery" amongst some of my BPCR shootin' buddies I discovered that a couple of them had been doing the "tap-tap" thing for years and didn't realize the rest of us didn't know about it. 50 years I've been messing up!

Just to try and clarify, the driving band area is concentric at .259".
Just forward of the first driving band is wher the OOR condition exists. I suspect it is incomplete fill out, but of course not sure.
I'm curious as to how you tap the handles to insure the blocks are completely closed.

I had a Lee mold that was about that much out of round, but, it was because I had lapped it to a slightly larger dia. Sizing nose and body removed the inconsistency and they shot well enough. Not good enough for match shooting, a bit over 1.5MOA most of the time.

If it is not OOR on the nose, only right around the band, probably not the problem. It is 'close' to a bore-rider' design, PC will add some dia. but the nose should go into the throat. Did you change from lube to PC or is this first trys with a different bullet?

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Originally Posted by popper

If it is not OOR on the nose, only right around the band, probably not the problem. It is 'close' to a bore-rider' design, PC will add some dia. but the nose should go into the throat. Did you change from lube to PC or is this first trys with a different bullet?

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Popper--I changed from lube to pc and now back to lube. Powder coating "seemed" to give me more 1 shot flyers than lubed, but I am not really sure. It seems to me that if the OOR condition right before the first driving band is there, it may be amplified by powder coating.

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Originally Posted by Shuz

Just to try and clarify, the driving band area is concentric at .259".
I'm curious as to how you tap the handles to insure the blocks are completely closed.

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I have a little hardwood stick I use to tap on the joint of the mold handles when I need to encourage boolits to drop out of the mold when casting. I use the same stick and the same "tap" to tap on the joint when closing the mold -- I'm assuming it is the vibration helping seat the blocks. On the molds that have that third handle you use in sprue cutting such as the 6-cavity Lee, I'm finding it easier to tap the end of the handles as though I was seating a handle that had come loose.

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Originally Posted by earlmck

I have a little hardwood stick I use to tap on the joint of the mold handles when I need to encourage boolits to drop out of the mold when casting. I use the same stick and the same "tap" to tap on the joint when closing the mold -- I'm assuming it is the vibration helping seat the blocks. On the molds that have that third handle you use in sprue cutting such as the 6-cavity Lee, I'm finding it easier to tap the end of the handles as though I was seating a handle that had come loose.

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OK thanks! Now I unnerstand!

This may or may not work for you.

One of the bullets I cast is a long one, Acc 31-210E, for my .308. It has a long bore riding section. I had to play with lead and mold temps for quite a while before I got the nose section filled out properly. There was something like an OOR condition that I could not figure out. I tried colder lead, hotter lead, casting faster (hotter mold), casting slower (colder mold), hot plate pre-heat higher and lower. Nothing seemed to work. Whenever I got the mold hot enough to fill out the driving bands well it seemed the nose portion didn't 'like' it.

My guess was that the nose portion of the mold was holding more heat. So I adapted a technique I learned a long time ago, kind of a modification of Richard Lee's wet towel method of cooling the mold. I would pre-heat the mold and start casting. My method was to pour, wait for sprue to cool (about 5 sec), then place the bottom of the filled mold on a soaking wet paper towel for approx 3 sec, then dump mold. The time can be changed to suit your casting speed and mold.

This has kept the mold at a more even temperature and the bullets are coming out much more consistent.

Caution: Never place an open mold on the wet towel. It could introduced water into the mold and lead to an issue when pouring the next bullet.

Charlieb-- sounds like something I should try!
Thanks
Shuz

OOR shouldn't cause a problem as the barrel sizes it anyway. HV (fast spin) can cause flyers if the bullet is out of balance.

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Originally Posted by popper

OOR shouldn't cause a problem as the barrel sizes it anyway. HV (fast spin) can cause flyers if the bullet is out of balance.

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But the bbl doesn't size the boolit portion right in front of the first driving band that is OOR!