Front Driving Band design

[azvaquero]

Hi Veral,

This question is on front driving band design.

As you state in your book, a heavy front driving band keeps things lined up and can take a lot of abuse not easily handled by shorter bands.  It not only takes the knocks better than a short band, but also rests up in the leade a bit and helps alignment upon ignition.  Shorter banded bullets tend to skip around a bit before they find their way into the throats.

In a .45 Colt cylinder, with .452" throats, a bullet sized .452" is not a slip fit but must be driven through with a mallet.  Therefore the front band cannot be too long or the round will not chamber (all of this you know, but I am leading up to the question).  

If the front driving band is .100" wide, yet the gun could conceivably take a .115" front band and still chamber the round, alignment could be a little better (i.e., the bullet will bounce off the leade before entering the throat).  The wider the discrepancy, the worse the accuracy.  As all chambers may not be cut exactly the same, and dirt and crud must be accounted for, however, front band width should be purposely made a little on the short side (i.e., .100" in a gun that could possibly handle .110" or .115").

A .451" bullet on the other hand is a nice slip fit through the throats.  A bullet sized .451" could utilize a band long enough to pass the lead and actually enter the throat upon chambering, giving superior alignment.  The front band could be .150" long, for example.  Not that you would want it that long, necessarily, but my point is that it would chamber.  The downside is that the seal may not be as good as the .452" bullet, perhaps.

Here is the question then: Have you ever tried a bullet with your recommended .100" long, full diameter (.452" in this example) front driving band, with another smaller section (maybe .050" long, at .451") just in front of the front band?

This would give the great seal and durability of a heavy full diameter front band as you so ably propound in your book, and vastly superior alignment at the same time in instances where the full diameter front band might normally bounce off the leade.  The front driving band would still be able to take all the abuse, yet the .050" long section up front would help decrease battering on the front band even more.  This  both by giving near perfect alignment upon ignition and maybe even helping line things up a little when going into the forcing cone, like a cone fitting into a cone.  Sort of a bore ride concept, without the downside traditional bore riders have of not having a wide, full diameter front band.  

Of course, an additional benefit will be realized when sizing the bullets in the first place (if sized nose first, as in a Star Sizer).  Instead of the bullet tipping and teetering a little when entering the sizing die, the slightly smaller front section would tend to help align it better, tending to slip into the die more easily.  All the advantages that a nice, smooth ogive enjoys verses the sharp shoulder of a SWC design, with the ogive "advantage" extending out a full .050" giving you even better alignment than the more abrupt ogive.

If the above will not work in your opinion, would you advocate going with the .452" idea and having none of the front band up in the throat (albeit some of it will be in the leade)?  

Or would you prefer the .451" approach, with a heavy wide front band, sitting past the leade up in the throats?

By the way, thanks for taking the time to answer questions on this site, and thanks for making a great product!

[Veral]

You've given a very through question, which I like because it is educational for my readers.  Which is the whole purpose of this forum.

   I made the original molds for the Federal Cartridge bullets which are my basic WFN, with the nose reduced in diameter several thousandths, and only a tiny full diameter driving band out front.  You have well described the reason in your question.
  Here are the problems.  If a reduced diameter bearing length of only .001 or .002 is used, eventually bullets will be cast with the mold slightly open, from trash on the block faces or whatever.  Presto, the tight tolerance reduced upfront band hangs you up on chambering.  

  Let's look at the true facts, or history, of why I make my bullets as I do and reccomend opening cylinder throats till all are the same, and slightly over groove diameter. -- When I started making molds about 25 years ago, it was nearly impossible to find a revolver with cylinder throats that were not at least .002 and up to .005+ over nominal bullet diameter, and barrels which also ran oversize, but less so.  Accuracy was abominable.  I learned what the problem was, wrote a few articals and preached the facts to my customers.  Then, in the early 90's I came out with push through slugs which made measuring the internal dimensions a snap for anyone with a good micrometer.  A thing never before possible for the layperson.  Bingo, customers complained to manufactures, they tightened tolerances dramaticall until almost all revolvers today come out with cylinder throats and barrels well under nominal bullet diameter.

  Had manufactures been holding tolerances tight as they should have, say no more than .001 over nominal bullet diameter, I would never have learned the critical aspects of accuracy as I did.  - In other words, better for you to size your 45 bullets at 451 than to mess with the reduced diameter nose.  You'll get great accuracy, because you are fretting about a tolerance of perhaps only a half thousandths inch.  That is quite close to 7 times smaller than a white mans hair,  or 12 times smaller than a black mans hair. (They seem to be built tougher all over.   :wink:)  A gun can hardly tell the difference in such a small loosness,  IF THE BARREL IS SMALLER THAN THE BULLET.  

  Therefore I reccomend, to get the optimum fit, for shooters to use sized bullets as a guage an open cylinder throats till bullets slip fit.  That will actually be a good half thousandths loose.  To get real basic.  The idea is to keep bullets from tipping.  They don't tip measurably in a cylinder throat hole even .001 over bullet diameter, and what little tip they do get is almost entirely corrected in the barrel if the forward driving band is heavy and as large or larger than the barrel.

[azvaquero]

OK, thanks Veral, for your reply.  So if using a .451" bullet in a .452" chamber (a "slip fit"), would there be any advantage in using a front driving band of, say, .150" that actually fit up into the throat past the leade, lining things up nicely, versus a .451" bullet with a smaller .100" wide front band that did NOT fit up into the throat, but had to funnel itself past the leade into the throats?  

There is an excellent article on this concept in October's Handloader, which talks about short front banded bullets lying in the bottom of a huge chamber which must bounce around on the leade a bit before entering the throats, which the author states shoot less accurately than bullets fitting further forward up next to the throats.

What is your take on this?

Thanks.

[Veral]

I don't believe there is much advantage gained in the cylinder throat area with a long driving band v.s. short so long as it's a close fit and does extend into the straight part of the throat.  

  Two factors not mentioned in my previous answer is that of the bullets bearing length and how close the loaded round fits to the chambers, both of which determine how much the bullet base can lean on takeoff.  As a general rule, longer bearing increases accuracy if the bullet doesn't have to be made too blunt for good form stability to gain the bearing length, and the closer the loaded round fits to the chamber the more accurate.

  Likewise, the shorter distince the bullet jumps until the forward band hits the  to the rifling, the less stripping problems are likely to cause problems,  and the higher accuracy potential will be, providing setting the bullet out doesn't make too much powder space, causing inconsistent ignition, which is degrading to accuracy.  This last issue is important only with lightweight/short bearing bullets.  When selecting bullets from the LBT catalog, normally the weights just down from the heaviest will be easiest to get top accuracy with.  The heaviest will often have to be pushed hard to get spin up to top accuracy levels.  The lightest can present too much jump, unconfined powder problems etc.
  I sincerely hope this second explanation gives understanding and not confusion, because we are delving far deeper into bullet design than is practical.  In other words, if my customers just tell me what gun they are fitting and what their needs are, my mental PC of 27 years experiance kicks in,  they will get what they want, and I can afford to make the mold.  If I have to go into this type of fine tuning with each mold, and many customers will go into it if their minds get running on the matter, moldmaking becomes impractical and unafordable, even with my high custom prices.  Having said all this against such debates, my company name is Lead Bullet Technology, and teaching that is my primary goal.