Rounded bases

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  • Last Post 09 December 2015
John Alexander posted this 24 October 2015

I sometimes get rounding of the bases and other sharp edged of my 22 caliber bullets when the temperature probably should have been a little higher or my cadence a little faster or the sprue puddle a little bigger.  My testing has indicated that as long as the gas check won't fall off, fifty yard squirrel head accuracy is still there.

Has anybody done testing on larger caliber bullets to see if rounded bases degrade accuracy and if so how much? What about rounded bases that are not quite uniform all the away around? 

What about plain based bullets. It SEEMS like it should make a difference -- but does it? Could a rounded base on a plain base bullet perhaps be even  better because it reduces the fins on the back caused by the rifling.  Sort of like bevel based bullet are sometimes assumed to do? Opinions are welcome, but opinions based on testing are even more welcome.

John

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fa38 posted this 25 October 2015

I don't know if they shoot bad or good. When I get a plain base mould that gives a rounded base I either fix the mold or sell it if my fix does not work. On iron molds I use a sharpening stone to make a vent line at the top of the mold. For alum molds I use a very fine cut file to do the same. Only ever had one mold that continued to give rounded bases.

Since I shoot offhand it probably would not make any difference since my ability to hold has gone downhill.

If it's a gascheck bullet for one of my military rifles I don't think it makes any difference. I have shot good and bad scores with both but still try to fix the mold and the fix usually works.

This is on .25, 7mm, .30, and .32 caliber molds.

I have a couple of NOE .22 cal. molds and neither needed fixing.

Rereading the above it does not answer your question but I would think if you can fix the mold why bother with rounded bases.

Also it is a very small vent line probably smaller than the interior vent lines

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PETE posted this 25 October 2015

John,

The age old answer is..... It depends.

After cutting the sprue off I look at the base. If it's noticeably rounded it goes back in the pot. Goes for both PB & gc's.

When breech seating bullets I've often wondered if a slightly base is preferred due to the absence of fins sticking out the back. An old .32 cal. Win. Mold I have was made with a bevel base and is probably the most consistently accurate bullets I have in both fixed and breech seated. I've given up being super critical of my bullets a long time ago. I've shot literally hundreds of PB bullets in ASSRA 100 & 200 yd. competition and have never noticed a difference in accuracy.

I haven't done any testing with gc bullets but gave up being super critical of them also a long time ago.

To me the most critical thing is learning to shoot in all conditions. If a bullet is out of the group I misread something, or wasn't consistent getting into the rifle. People are always eager to blame the bullet or the rifle instead of the fact they really don't know how to shoot a rifle thats' capable of fine accuracy,

Pete

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R. Dupraz posted this 25 October 2015

Yup!   The one great variable that “trumps all the others and is often excluded is marksmanship. And the second is the ability to read conditions and correctly apply the correction.   Gee, I hope that wasn't political.

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PETE posted this 25 October 2015

The other point I'd like to make about PBB is something I've wondered about.

We shoot bullets that are .001” to .0015” over groove diam.in PBB bullet shooting. So lets say you have a slightly rounded base. Once the bullet is seated by breech seating or firing in a cartridge what happens to those “fins” that are created by the metal being extruded by that oversize bullet. That would seem to me to eliminate the round bases or extend them out the back of the bullet. Do these effect accuracy?

Also if the bases are slightly round wouldn't this extruded metal tend to square the base up and eliminate the fins?

When I seat gc's the base edge is rounded even if I use Lymans gc seater and put on a lot of pressure doing so trying to square the base up.

So... As long as the edge is even all the way around there's nothing to impede accuracy. Deforming the base at one point, as Mann proved, will effect accuracy.

Pete

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Brodie posted this 26 October 2015

I think that if the bases of your bullets are rounded (not bevel based) you have other problems as well. It seems to me that if there is insufficient fill out at the base you may also have rounded or incompletely filled out driving bands or the edges of grease grooves. Brodie

B.E.Brickey

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John Alexander posted this 26 October 2015

Brodie, You are right when a rounded base appears the other sharp edges may also be rounded -- and sometimes not.

I probably didn't state my original post clearly enough but I'm not looking for a cure I don't think I have a problem.  The bases on most bullets are sharp but if I slow down too much or pour only a small sprue puddle some are rounded.  No problem I am talking about a small percentage and faster or bigger puddle cures it. But how would those rounded base devils shoot? I agree that the practical solution is to remelt since there are only a few.  But I am curious.

Do they hurt accuracy?  My sorting isn't perfect and sometime almost non-existant. What if one slipped through and made it to the match?  I have done limited testing and can't see a difference but maybe I didn't have a big enough sample and they might cause a dreaded flier -- or maybe they shoot better. Is a little rounding is a good thing as Pete's experience with his bevel base mold suggests. Maybe I would be a terror at the next match if I used all bounded base bullets.

 I was also wondering if larger caliber bullets act differently.  I thought maybe someone else had checked it out. John

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frnkeore posted this 29 October 2015

I pressure pour from the bottom of a Lee 20 lb pot. I've always done it that way (until 3 years ago I used a 10 lb pot).

For the last two years, I've been trying ladle pouring and shooting our big May, 200 yard, Spokane match with both. First year I shot 400 bottom and 200 ladle. This year I shot 400 ladle and 200 bottom.

When casting pressure/bottom, I get completely filled out, sharp PB bands. When I use a lyman ladle, I get slightly rounded bases, even though I keep the ladle in contact with the sprue plate. Maybe just a .005 or slightly larger radius on the base.

I was 4th out of 30, 2 years ago, this year, 6th. My best 50 shot match for 2 years ago was 1230 out of 1250, bottom poured, this year 1224 ladle. Not a huge difference but, in a highly compitive match, it seems to have made a difference. I plan to give it another try but, not at the Spokane match again.

That's my experiance with slightly rounded bases but, it could be just random luck.

I would think in GC bullets, that it wouldn't be as much of a problem as there is slight radius in the GC corner.

Frank

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onondaga posted this 29 October 2015

I only get rounded bases on round balls and they are very important.

Gary

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JSH posted this 29 October 2015

IMHO it can make for a head game. If you know that a specific batch has some with what we think have an issue, one will tend to think some rounds out side of the group.

I weighed and sorted by weight for a while. I found little if any difference in the out come from my “eye” sorted bullets. I cull by eye now. Any that I don't like for what ever reason are culls and get thrown out of the batch. I threw the most of a casting session out because of some issues I think the had. My buddies always tell me “oh they will shoot". If one were to go and purchases store bought jacketed or cast, they would be labeled blems. My results on target tend to be over and above what their out come is a majority of the time. I put quality over quantity.

In short I feel if you accept so so bullets, you will accept so so results, or you should be prepared too. Jeff

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John Alexander posted this 29 October 2015

frnkeore wrote That's my experiance with slightly rounded bases but, it could be just random luck.

Frank Frank, I think you have hit the nail on the head with that statement.

The difference in the two top scores you quote is less than one half of one precent (0.48%.) And the two were shot in different years.  

I suspect there were other differences between the two years in terms of weather, your skill level and fatigue, and perhaps other variables that affect scores.

It would be nothing short of amazing if the two years were so closely matched  that all such differences were much less than 0.48 percent.

It seems to me that to think you have found a valid difference or even a small hint of a difference in the two casting method is wildly optimistic.   The fact that six points are helpful even in a 1250 point match is totally irrelevant.

You say you plan to give it another try.  Instead of trying to compare match result on different days, why not test them under the same conditions at your practice bench. Load fifty with each bullet.  Let someone else label the lots A and B without telling you which is which.  Shoot the 100 rounds under decent conditions by alternating groups of A and B while keeping everything else as nearly as possible the same.  See what the average group size with each bullet tells.

John

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PETE posted this 29 October 2015

John,

I was thinking along the same lines as you are.

But doing a test as you suggest still brings into play quite a few variables that can easilyy skew the results.

I'm far from being an expert on statistics, but shooting 10 ten shot, or 20 five shot groups brings into play fatigue more than anything, not to mention the temp., humidity, & position of the sun, even if you consider that there was no wind blowing. As the day progresses and the humidity dries off the grass and the ground temp. rises, mirage increases like you woukdn't believe, as I'm sure you know.

Frnkeore sounds like one H--- of a shooter, so maybe he could pull off a test that might be statistically valid.

As mentioned I'm no statistician, so what would you say would have to be the difference in the different groups to eveb be considered valid?

My point in my other message was I don't think a short test, or even a lifetimes worth of groups would show a big enuf difference to be able to say.... “This is the way to go". Not with all the variables you would have to deal with.

I feel that as long as the roundness of the bases is very close for ALL the bullets in the group, they will shoot as well as humanly possible against perfect bullets.

Pete

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Brodie posted this 29 October 2015

I don't think that we are really going to get an accurate hand on the minor variations in cast bullets and how each particular variable effects accuracy until someone develops a shooting machine.  One where a rifle can be bolted into the device, aimed and fired without further human interaction.  This of course would have to take place in an indoor range or at least fired down some sort of pipe or conduit.  The device would also have to return to battery in a accurate enough manner so that aiming variations could be eliminated.  It would give us a reliable way to judge the effect of minor cast bullet differences without the human component being involved with all of its variables.  Such a device would take all the fun out of what we do and completely ruin a really fun sport.  Brodie

B.E.Brickey

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PETE posted this 30 October 2015

Brodie,

They have such a device for piistols called a Ransom rest. Have used one many tmes for determining the best loads for handguns. Might be something for rfles I'm not aware of. Maybe something like    the universal receiver lthat Lyman uses for the work on their loading manuals.  You have to take the human error out of the equation. 

But, as you say it would take all the fun out of it.

Pete

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Brodie posted this 30 October 2015

Pete; I was aware of the Ransom Rest, but have never heard of anything similar for rifles.

B.E.Brickey

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Glenn R. Latham posted this 30 October 2015

John, I separate out partially-rounded bases for my plain base 45 ACP bullets.  One day I loaded some up and took them to the indoor range for practice.  Shot a 98 on the 50 foot slowfire target, and I rarely break 90!  They might make a difference at 50 yards, but not at 50 feet. Glenn :fire

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John Alexander posted this 30 October 2015

Old Coot wrote:I don't think that we are really going to get an accurate hand on the minor variations in cast bullets and how each particular variable effects accuracy until someone develops a shooting machine.  One where a rifle can be bolted into the device, aimed and fired without further human interaction.  This of course would have to take place in an indoor range or at least fired down some sort of pipe or conduit.  The device would also have to return to battery in a accurate enough manner so that aiming variations could be eliminated.  It would give us a reliable way to judge the effect of minor cast bullet differences without the human component being involved with all of its variables.  Such a device would take all the fun out of what we do and completely ruin a really fun sport.  Brodie 

Brodie,
 
The device you are describing is usually called a “rail gun” and there are a few of them floating around in jacketed bench rest.  We also have had at least three full fledged rail guns in CBA competition in competition in the last few years.  They are legal to shoot in CBA’s unrestricted class. Some of our unrestricted “pistols” are also rail guns or come very close and minimize the human element. I personally like to shoot factory rifles in competition but the folks shooting these contraptions don’t think they take the fun out of the sport. There are still plenty of variables to master such as wind, mirage, and load development. The conventional unrestricted rifles (15-30 pound monsters) beat the rail guns as often as not.
 
I agree that a rifle/load combination capable of high precision shooting in a tunnel is better than ordinary rifles at determining whether a change in the load really makes a difference.  However, perfectly valid tests can be run with more normal rifle/load combination outside in the weather with humans driving them to see if a “defect” matters, or which powder charge, lube, etc. is best if:
 
1. Other variables are controlled so they are just as likely to affect one condition as the other. Alternating 5 shot groups of the two conditions takes care of a lot of this.
 

2. You shoot enough shots with each condition to make reasonably sure that the difference in accuracy you think you see is real and not just a result of the natural variation of one group to another This variation happens with rail guns in tunnels just as with ordinary guns.


John

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John Alexander posted this 30 October 2015

PETE wrote: John,

I'm far from being an expert on statistics, but shooting 10 ten shot, or 20 five shot groups brings into play fatigue more than anything, not to mention the temp., humidity, & position of the sun, even if you consider that there was no wind blowing. As the day progresses and the humidity dries off the grass and the ground temp. rises, mirage increases like you woukdn't believe, as I'm sure you know.

Pete Pete, I agree 10 or 20 shot groups are a poor choice because of fatigue.  When comparing two loads, or seeing if a “defect” matters It's not the number of shots in the group but the total number of shots with each load. Five shot groups minimizes the fatigue during the group and are more efficient (tell you more for the number of total shots fired.)

All the other variables you mention can pretty well be rendered irrelevant by alternating five shot groups.  Sure the groups after the wind picks up will be bigger but they will be bigger for both loads and comparing the average group size at the end of the test for each load will be valid. For example if you fire the two loads alternatively and shoot ten 5- shot groups with each load it would be hard for a reasonable person to argue effective that the fatigue, wind, sun, humidity, mirage, etc. affected the accuracy of one load more than the other.

It is not a problem that the group sizes may have gotten bigger during the course of the testing. All we care about is the DIFFERENCE, if any, of the average group size of each load.

John

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PETE posted this 30 October 2015

John,

You make some good points.... the rail gun I'd forgotten about, and your reasoning on trying to allow for any variations during a test are valid. I just think that something missed while doing anyone articular test could throw out... unknowingly, a test that would have been “good".

It;s why I've never tried to do a test like you suggest. I know my limitations and know at the end of the day I'd be saying to myself “What did I prove". Basically I had the fun of shooting a lot of ammo with to many conditions making it useless to prove anything. Seems like a waste of time.

I think the old saying goes that you can give a poor shot the best gun and ammo in the world and they will do no better than their average. Give an excellent shot the poor shooters gun and ammo and they will outperform the poor shooters results. The thing I hate is when someone takes my gun and out shoots me with it. :) Happened more than once too. I don't let people shoot my guns anymore!

But don't let me discourage you from doing the test because I'll be the first in line to see the results.

Pete

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onondaga posted this 30 October 2015

http://www.castbulletassoc.org/view_user.php?id=59>PETE http://www.castbulletassoc.org/view_user.php?id=59> Being out-shot by someone with your own rifle hurts BAD. It can hurt bad the other way around too.....I did it to my grandson and out-shot him with his own rifle.  “well, that's the difference between the way we shoot.” was the only thing I could say. Then I told him his rifle shoots better than mine! and mine is the same model with a better trigger.....and that is true! I felt bad about the whole thing and wish I hadn't shot his rifle.

Gary

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Loren Barber posted this 08 November 2015

John,I can consistently make bullets with slightly radiused bases or squarely flat bases by simply pouring the lead from about 1/2 inch above the sprue cutter opening for slightly radiused bases or contacting the ladle to the sprue cutter and pouring with some liquid pressure as the alloy flows into the mold.  I don't think that there is any difference in accuracy provided that one uses the same approach for each batch of bullets.  I sometimes like to very lightly bevel my bases manually so that it is easier to get the gas checks squarely seated before going through the sizing operation.Loren

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John Alexander posted this 08 November 2015

Excellent point Loren.  A little rounding helps a bit on gas check shanks that are a little too big.

Being able to cast sharp or rounded bases at will make you the perfect guy to run a test to settle this question.  I suspect you would find that your opinion would be confirmed that it doesn't affect accuracy, even for your highly accurate bench gun -- my opinion only. You have probably casually (or not casually) observed that no difference was obvious but is there a little difference -- and if so which is better?

I know this probably isn't most CB shooters most pressing concern but it is something we don't know. (Although some think they know.) Why not find out?

I know the majority are probably tut tutting that any good caster should be able to last bullets with sharp bases.  But what if slightly rounded bases are better -- at least for plain base shooting because of the theory about fins. And if it doesn't make any difference under gas checks then why are we throwing away one type without really knowing whether rounded or sharp are better?

As I stated in the first post.  I have proven (at least to myself), by firing a lot of alternating groups that even quite a bit of base rounding does not affect accuracy (at the 1 moa level.) But that was only with the 22 bullets with gas checks.  But I have never seen a report of a test that replicated that for larger calibers or for plain based bullets.

Maybe it isn't worth doing and I have no quarrel with those that want to keep on just going with their opinion one way or another -- after all this is a hobby and we can do what we want.  Maybe I just have an overactive curiosity gene but I can't help thinking that understanding more about CB shooting would make it even more enjoyable.

John 

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mtngun posted this 09 December 2015

I throw poorly filled bases back in the pot so I don't know how they shoot.  :D

One of our members, Mustafa Curtess (spelling?) told me long ago that he believed bevel base bullets were more accurate than plain base because the bevel eliminates the “fin” problem.

Just this year I began playing with bevel bases in rifles and so far they at least as accurate as a flat plain base.   Perhaps they have a slight advantage, but it's too early to say for sure.

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