New Page 2



!!

You are a Guest at TalkHunting

As a guest here, you are able to view some of the topics to get a feel for how this site works. However, you will not be able to post replies until you become a member. We hope that you will register (free) and become a member. This will open up all of the website for you to see. We are a very friendly group and we do not allow any bashing, fighting, or vulgarity. If you are looking for a family friendly site to talk about hunting, you have found it here at TalkHunting. You will find this a very comfortable and friendly place to visit and hang out. We hope to see you soon!

If you are having problems getting registered or you didn't receive your activation email, click the "Contact Us" link at the top left of this page.

New Page 3

Google Ad

Author Topic: Handloading Accu-Loading Part 3: Bullet prep  (Read 552 times)

Offline TalkHunting Mag

  • Button Buck
  • Join Date: Mar 2013
  • Posts: 44
Handloading Accu-Loading Part 3: Bullet prep
« on: April 03, 2013, 06:44:00 AM »
In our pursuit of consistency obviously our bullets have to all be identical if they are going to launch and fly the same, shot to shot. So according to our cartridge and advice given we have picked a bullet or two to try in our absolute accuracy endeavor. So let’s get out our box of 100 bullets, or even better our 500+ bulk box. Our bullets need to be as microscopically identical to each other as possible. So we are going to discuss the various measurements and inspections to ensure this, as well as how we can tune up our bullets a little bit.

The first two steps are generally unnecessary with high quality match grade bullets. So believe it or not I do them anyway. I leave little to no room for assumption.

1.   Let’s measure the diameter of ten percent randomly picked bullets. Some people will surely ask; why measure the diameters? I’m not suggesting that the bullets will be so far out of spec as to be dangerous. But we want to rule out anything and everything that may cause inconsistency. A true diameter measurement is done several places along the length, along its axis as well as several places around it measure it, rotate it a little measure again. Measuring radially will let you know if the bearing surface is really round or not. For the record I doubt if a bullet being egg shaped by .0001” or .0002” (two ten-thousandths of 1 inch) will affect accuracy as the bullet will engrave to the barrel and is in a plastic state while it’s in the tube, so the barrel will reform the bullet to a more round state. However the very act of reshaping will cause addition resistance thus increasing pressure and this means variance of velocity.
Tip: If you want to do an easy “egg” test; on a level bench that has a smooth top as you handle the bullets lay them on the bench and give them a gentle push. Now watch carefully! They should roll until they lose momentum and stop rolling. If they stop and roll back slightly I’d be willing to bet you found an “egg”. Have you ever tried to stand an egg on its ends? It is possible but not highly probable.
 
2.   Now we move to a critical test. We’re going to measure the length of the bearing surface of the bullet. Evidently this spec is far harder for the manufacturers to hold than weight or diameter. The bearing surface is the only part of the bullet that touches the bore. Let say we have an average standard bearing surface length of (.500”) a half inch for the sake of round numbers. But if a bullet shows up with .490” bearing surface, which is .010” (10 thousandths) short of standard, we know it will not have as much surface rubbing the bore, which will not cause as much pressure buildup, so that bullet will achieve a lower muzzle velocity and it will impact low. Ah ha! Now we are learning. Conversely if a bullet shows up with a .510 bearing surface or +.010” longer than standard. We know it has a little more surface area contacting our bore, which equates to more resistance, which extrapolates to higher pressure and more velocity, resulting in a higher impact.

How do we measure bearing surface lengths? There are different ways, but since we already have established we have a good set of dial or digital calipers, let’s just go that route. It’s a little cheaper too. The other tools needed are a pair of bullet comparators for your caliber. To measure the length of the bearing surface, we insert the caliber specific bullet comparator inserts into the bodies and just slightly snug the set screw. Now place a body onto each jaw of the calipers and snug the thumbscrew. (If you wish to measure base to ogive just use one comparator and caliber insert.) Continuing on; make sure the comparator inserts are lined up with each other as closely as you possibly can. Do this by feel, dragging a finger across from the end of one to the start of the other where they meet. Now with the comparators installed and aligned gently slide them together and zero your calipers. I get several containers and place a yellow sticky note on them or position them on a paper and record the bunch dimension. We’ll need several containers, hopefully not more than ten. It’s okay that not all the bullets are exactly the same as far as the sorted batch goes. You can see by the right picture below I found a variance of .007 when I sorted this batch. We just want to have a specific bearing length per trip down the tube in the field or at the range so they all have as near identical muzzle velocity as possible. The left image below shows the calipers and comparators installed and measuring the bearing surface of a bullet.
 

There are other tools and methods a little more advanced, but we can get into “fine tuning” your tools and techniques later, perhaps in another article.

3.   About those meplats. The meplat is essentially the point of the bullet. So why are we concerned with them? WE ARE FOREVER CHASING CONSISTENCY. Not all Meplats are created equal. And considering the bullets come out of my 300 Win mag with a 10 twist barrel @ just over 2900 fps- they are spinning in the neighborhood of 211,000 rpms if my math is correct. (No guarantees there!)

So if you go through your box of match bullets, you’ll quickly see many bullets have OBVIOUSLY inconsistent meplats. A meplat trimmer is a simple tool that uses an endmill to trim back the meplat to the point that it’s cleaned up and consistent. And when we run all our bullets through the trimmer, their all have exactly the same meplat diameter and are square to the bullet base. True, a meplat trimmer blunts the bullet a teeny bit, and that does make it a bit dirtier. “Dirty” is a slang aeronautical term that means NOT aerodynamic. Yes “dirty” reduces BC (Ballistic Coefficient= Flight Potential), but the BC was not consistent with dirty bullet points anyway. So pick your poison. Have an inconsistent and untrue but published high BC, or have a bit lower BC that is dead on consistent bullet to bullet, shot to shot at the range.

4.   Bullet “Pointing” by using a die system that presses a keener point on hollow point match bullets. This increases BC which allows the bullet to retain velocity, energy and wind bucking ability better. Most long range shooters are shooting 6.5mm and bigger bullets, because the “carry” better. Bullet “pointing” has great gains in .224” bullets as well as good gains in 6mm, but the larger diameter the bullet the more negligible the return. Here again it is up to you to decide.

5.   Our final test is to weigh the bullets. You may be asking with all the measuring and testing we’ve already done they should be close enough in weight. No, you can’t measure jacket thickness or core density. To have this step worthwhile you must have a very fine set of mechanical balance type scale or a digital scale capable of weighing to .01 of a grain (hundredths) and .001 (thousandths) is even better. Let’s weight 25% or so and make sure the weights are consistent. So as long as a small test batch looks good, you could assume the lot is fine unless you deem your time, and rifle’s potential worth splitting hairs. If so, weigh EVERY bullet and sub sort them in .02 grain (or finer) lots.

Well now that wasn’t that difficult was it. We are now confident that our bullets are as uniform as possible. And we are now ready to move onto Step4: Powder Selection and Building our Ladder Test Load Table.

Dutch-Hunter

Full document is attached with picture.

PJ

 

New Page 3

Google Ad