How Important are Sharp Crisp Trailing Edges?

[dbarnhart]

I am a very new caster, having cast about 2000 rounds of .45acp over the past couple of months and shot maybe 500 of them. I have one of Tom's (Accurate Molds) molds (45-230M) and it produces very nice sharp trailing edges. Because of that, I'v been under the impression that sharp crisp trailing edges were important. Once in a while I'll cast a boolit that the trailing edge is a tiny bit rounded and I'll toss it back in the pot.

Today I was surfing around and happened upon a commercial caster who has this photo of his .45acp boolits on his website:

http://www.shootandreload.com/wp-content/uploads/2012/03/45-230GRAIN.jpg

The trailing edge is bevelled. So the answer is one of three things?:

1. Trailing edges are important.
2. Trailing edges are not important.
3. "You're shooting .45acp, kid you can get away with a lot."

[stubshaft]

Even though the base is bevelled the trailing edge on those are still sharp. Think boattail.

[runfiverun]

if you look at some lyman molds the base is a bit rounded like that also.
i usually work on the mold to reduce the size of that little bevel as much as possible.
the little bevel is actually helpful to get the boolits in the case better/straighter easier.
and you don't have to use as much case mouth flair.

[geargnasher]

Your accuracy in any gun comes from the base. If it's a BB design, the edges must be sharp and even. If plain based, the corners must be sharp. You can get away with a lot of other defects at pistol velocities, but the bases matter most.

Gear

[Cherokee]

What gear said +1

[BulletFactory]

If one side of the base, (or any other part) isnt sharp, its because the mold didnt fill out properly. In other words, there is less material in that location which will change the weight, and the bullets balance while spinning. A pistol bullet is turning at about 40,000RPM when it is fired, so even a little bit is going to affect the bullets flight.

[geargnasher]

More than balance, any irregularities on the base affect how the boolit exits the muzzle crown. If there's a dip in the edge of the base, the muzzle pressure will tip the boolit and make it go off on a tangent.

Gear

[williamwaco]

Bases matter!

They can be beveled but they MUST be uniform.

A perfectly square flat base bullet with a dent in the edge at the base is a reject.
A bevel based bullet with a dent in the bevel is a reject.

I can find no measurable difference in accuracy between a bevel base bullet and the exact same bullet with the bevel removed. ( but that test is not finished )

.

[44man]

More than balance, any irregularities on the base affect how the boolit exits the muzzle crown. If there's a dip in the edge of the base, the muzzle pressure will tip the boolit and make it go off on a tangent.

Gear
This is the correct answer.
Now to a bevel base even if perfect. It does not shoot as well as a flat base. This is a test after I removed the BB from a .357 mold. BB left. I had a low shot that I called on the right target.
Some with a BB will perform OK, it just depends.

[canyon-ghost]

I've seen bevel base get you 50 yards (with a pretty wide group) and plain base go to 100 yards (with a very tight group).

Wolfe's "The Art of Bullet Casting" contains some of the old experiments that prove the best base is the single most important factor in accuracy.

[mdi]

It is my understanding that the bevel base on a bullet has 2 benefits/reasons. One is for commercial casting; the bullets fall from the mold easier than a plain base bullet. The other reason is ease in seating for the reloader. Easier to start the bullet straight in the case. Much has been said about bevel base vs plain base in the accuracy dept, but I tend to believe 44man has the right answer.

As far as irregularities on the bullet base, visualize a bullet leaving the muzzle. A flat base gets pushed along by gasses on the base and as it exits the barrel, the gasses exert even pressure on the base, sending the bullet out straight. With dings or voids in the base, trailing edge, the gasses exert uneven pressure as the bullet leaves the barrel (some gas may leak past the bad edge as it leaves the muzzle) and the bullet may be "blown off course". The difference at the muzzle may be infantsimal, but on the target, 25 yards away, the effect is noticable. Best I can explain it...:veryconfu

[W.R.Buchanan]

I saw a test once in Handloader Mag where they deformed bullets intentionally to see what the effects would be .

They bent the noses, they ground the noses off at an angle, they beat flats on to the nose, they even loaded the bullet in the case backwards.

There was some small amount of accuracy lost.

Then they ground a small angle onto one side of the base.

The bullets were not found as the didn't hit the target or even come close.

The base matters, the rest is just cosmetics.

With a .45 you can get away with alot more cosmetic imperfections, as it is not going to be that far to your target.

However what you need to look at is YOUR products overall qualtiy. If everything is running right then most all of your boolits will be perfect or nearly so. If not you need to fiigure out what's going on and fix it. You will find all answers to all questions "Boolit" posted here someplace. Use the resource!

There is a thing which is called "pride of workmanship." How much you have is your business, but you really should be trying to do a better job everytime you make boolits.

Doing the best job you can everytime and trying to improve is what it's all about. At least for me. :cbpour: I suspect that others have the same standards.

Randy

[gwpercle]

I have never had much success with bevel base boolits at higher velocities. For the BB design I keep velocity at 800 fps or less, target loads. When I'm loading for velocities over 800 up to 1100 I find flat base work best and when I get to loads 1200 fps and up I start looking for a gas check design.

Bevel base boolits will work OK just dont push them real hard.

[DLCTEX]

We know how important a good muzzle crown is, and a good square base is just as important for the same reasons, as Geargnasher stated it.

[dbarnhart]

However what you need to look at is YOUR products overall qualtiy. If everything is running right then most all of your boolits will be perfect or nearly so.

I have to admit, I am pleasantly surprised at my increased accuracy since switching from FMJ to my own cast boolits.

[geargnasher]

.....There is a thing which is called "pride of workmanship." How much you have is your business, but you really should be trying to do a better job everytime you make boolits.

Doing the best job you can everytime and trying to improve is what it's all about. At least for me. :cbpour: I suspect that others have the same standards.

Randy

Boolits are easy to cast and easy to re-cast. It isn't like they go bad if you remelt them. I cull every one for visual defects, and my rifle boolits for weight if they're going to be shot past 50 yards. The way I see it, if it's worth the labor of reloading and the cost of a primer, it's worth learning how and doing it right rather than figuring the least I can get by with for acceptable accuracy.

Gear

[geargnasher]

BTW, here's a pic of an ad from Handloader magazine for equipment from a very popular vendor. I wouldn't shoot them if they were mine, and this one was presented for a full-page advertisement for heaven's sake. I don't get it.

http://castboolits.gunloads.com/attachment.php?attachmentid=28018&d=1293586260

Gear

[ammohead]

If you have a flat base mould and the bases are coming out rounded and not filling out, most likely you have venting issues. I will take a mill file and slightly chamfer the top edges of each mould half. Your rounding issues will vanish. This works with one and two cavity moulds. For three or more cavities you will have to make a line from the joining line to the outside of the mould between the cavities. This can be done with a 3 sided file if the edge is sharp.

Rounded bases can also mean that your sprue is way too small. Pour a bigger one. When the alloy hardens it will shrink some. If you don't have a nice puddle of liquid in your sprue your mould cannot stay filled out when the alloy shrinks.

[Echo]

If one side of the base, (or any other part) isnt sharp, its because the mold didnt fill out properly. In other words, there is less material in that location which will change the weight, and the bullets balance while spinning. A pistol bullet is turning at about 40,000RPM when it is fired, so even a little bit is going to affect the bullets flight.

Not only that, but as the boolit leaves the bbl, the defect will allow a jet of hot gas to leave early, causing a moment to act on the boolit, throwing it off.

My bad. Should have read further. Gear said the same thing.

[303Guy]

Ok, so what about a rebated boolit? A small rebate is what I'm asking about, added to the mold to eliminate base edge feathering from the rifling.

[Bret4207]

My biggest problem with BB designs is illustrated nicely in Gears big picture- look at the base. It's not even all the way around, not filled out correctly. Very hard to see in many cases.

[LUBEDUDE]

BTW, here's a pic of an ad from Handloader magazine for equipment from a very popular vendor. I wouldn't shoot them if they were mine, and this one was presented for a full-page advertisement for heaven's sake. I don't get it.

http://castboolits.gunloads.com/attachment.php?attachmentid=28018&d=1293586260

Gear



Unbelieveable

[Iron Mike Golf]

Ok, so what about a rebated boolit? A small rebate is what I'm asking about, added to the mold to eliminate base edge feathering from the rifling.

By "rebate" do you mean similar to a gas check shank without the check installed?

My thought is that the actual base shape doesn't matter. What matters, as has been stated before, is that the "vent" between the bore and boolit base just after the boolit exits the muzzle is uniform all around.

For me, a PB is easier and faster to inspect than a BB.

[1Shirt]

I go with gear on this one!
1Shirt!

[gnoahhh]

May I recommend reading the part in "The Bullet's Flight from Powder to Target" by Dr. Franklin Mann (available as a free download in Google Books) where he did extensive testing of this subject that overshadows a lot of what came along after the book was written 100 years ago. He proved conclusively that the condition of the base is key to accuracy.

That book should be required reading by anyone seeking to learn the whys-and-wherefores of cast bullet accuracy/ballistics. No point in re-inventing the wheel if one doesn't have to!

[Rockchucker]

My Daddy always said,"son, if it looks good, it will probably work good". I've always gone by this quote for about everything I do.

[.22-10-45]

Interesting topic & posts! Back when off-hand (schuetzen) matches were the rage,
H.M. Pope, and others always advocated the bullets base was it's "steering end". To obtain perfect bullet bases, they made nose-pour moulds, the glass smooth base had no sprue cut deformities. To preserve these perfect bases..the practice of muzzle-breech loading was used. A false muzzle was fitted & thru this the bullet was started true to bore & pushed down to a set stop..a primed & charged case was then inserted & breech closed, ready to fire. This system worked best with straight or duplex.. light smokeless priming charge under main B.P. charge. The theory was..any burrs from rifling displacement would be thrown forward & base would remain undistorted.
We don't here much of muzzle -breech loading now days...but what happened to those rifling-displaced burrs on bullets base? Of course with G.C., they are diminished..but still there..heck even on jacketed bullets they are present.
But a small bevel, or radius on the bullets base edge would tend to reduce the amount of metal protruding from rear. nearly all the early Ideal moulds had this small bevel.. It is an extra step in the cherry grinding procedure to put this on., and cutter set-up is more critical to position tool to mould top surface. I wonder if they were thinking of this metal displacement to go to all the extra work?

[303Guy]

So this topic set me thinking - again. Perfect base edges and all that. Nose pour versus base pour. Well, I just found a nose pour boolit lying around next to my keyboard and I was quite astounded. It has a perfect sprue cut off. If this could be achieved on a base pour we should be on our way.

http://i388.photobucket.com/albums/oo327/303Guy/PerfectSprueCut-Off004.jpg

But actually, I had been thinking about why a nose pour might or might not be better than a base pour and I got to wondering if it was to do with the sprue plate not producing a perfectly square and uniformly sharp base edge. A rebated or chamfered base might produce that but only with the correct design. A nose pour chamfered or rebated boolit might yet trump all.

Now to figure out how in heck I got that sprue cut-off so good ..... :roll:
Actually, apart from a sharp and acute sprue design, alloy probably plays a big part.

[popper]

I tried sizing 401175TC base first to 'crispen up' the FB and found I got several, not all, were 1/16 shorter. Those were probably way oversize as the rear band grew ~ .02". The bases were really nice though. Alloy is 50/50 Pb/#2 AC.