Cerosafe or lead

[WayneS]

Which is better for getting the throat Dementions ?? Cerosafe or lead ?? and what to use to get the lands Dem. for a bore riding .224 bullet ??

[Veral]

  Cerro is near worthless for getting precision measurements, because the diameter it give is unpredictable even with one person making the casting and doing the measuring on timely schedules to catch the shrink curve.

  However it is very good if a soft lead slug is also sent so the shrink or expansion of the cerro can be proven at any one point.  Say on at the rifling origin.  Once one has the shrink rate all dimensions can be taken from a cerro cast with high precision.  But cerro casts are hard to make.  Lead slugs, done the way I recommend, are easy, precise, and inexpensive.  Which is why I recommend lead throat slugs.  All dimensions required for making a mold will be on one.  I strongly recommend that you get a straight bearing bullet if you rifle will handle it.  They will outshoot any bore ride bullet ever made, if the throat is long enough to take one in the weight you want.  Bore ride nose bullets is a crutch to get more lead in a short throated gun.  Nothing more, nothing less, and like all crutches, one can get along with them, but they aren't as good as the real thing.

[goofyoldfart]

  Veral : can you clarify what you mean by a "straight bearing" boolit

[Veral]

  Bullet bearing, is the largest diameter part which contacts the rifling.  Many cast bullets have a bore riding nose which is a part of the bullets bearing surface, and a very poor part of it in my opinion, so I avoid making them unless it's mandatory to get a desired weight and the customer is content with that design.   I contend that best accuracy is possible only with optimum bullet bearing support which means all of the bullets bearing length be in contact with the full barrel surface, which dictates bullet has a straight bearing of at least groove diameter, or larger. So, bore riding nose bullets, with part of the bearing length small to ride the lands, are called two diameter bullets, never boolits.  That's a forum name.

[goofyoldfart]

OK. that's the term they use, so I did,too. But, your explanation clarifies the issue for me. thank you. I appreciate the answer.

[Veral]

  While cutting molds today I was pondering this post and the use of cerrosafe throat castings.

  Nothing is better for checking the concintricity of a chamber/throat to the rifling and bore.  Make the cast to include at least 1 1/2 inches of rifling and only a little throat is needed, but all the throat and part of the chamber is ok.  Chuck the rifled portion in a lathe and use a dial indicator to be sure that portion is running dead true, or mark it's exact high and low spot, and amount of wobble the chuck is throwing into it.  Then move your indicator to the throat/lead  just before the rifling, (if the throat has a gentle taper) or with chamberings like the 45-70, 30-30 and similarly chambered rifles which have very abrupt chambers, set your indicator on the chamber neck area.  If runout is more than .001, a bullet that is over groove diameter will be forced out of balance when fired, so make your bullets hard as possible and size them close as possible to groove diameter.  This arangement almost always gives excellent accuracy, but as speeds are raised to the accuracy limit, expect some fliers.  Not wild fliers, but group ruiners.

 If chamber/throat runout is under .001, best accuracy will normally be obtained if that portion of the bullet held inside the case neck, and as far as possible into the throat, are made as large as the chamber will tolerate.  The bullet body forward of that which extends out into the throat and to touch the rifling lead, should be cut close as possible to groove diameter, with as much as a half thousandth under groove being as good as an exact fit, or in most cases up to .oo1 or .002 over groove being just fine.  The object of fitting this way, and why it gives the best accuracy possible is that a full chamber neck area will not allow the bullet to tip as it's nose is entering the rifling.