Lead and By Iowegan

Most people find lead bullets can be more accurate than jacketed bullets, providing some procedures are followed to prevent bore fouling. Fouling and accuracy go hand-in-hand; as fouling builds up, accuracy diminishes. There are dozens of methods used by reloaders, some good, some not so good. The true test of how well lead bullets perform is when 50 or more rounds are fired in a single session. With a dozen or so rounds, most any will provide adequate performance because fouling hasn’t yet built up enough to alter accuracy. The key to sustained accuracy is having the optimized for lead bullets and to select the proper bullet hardness and diameter.

With jacketed bullets, reloading is pretty straightforward. Choose a load from a reputable reloading manual, follow the recipe, and you’re good to go. With lead bullets, there’s a lot more involved in bullet selection and the gun itself. When you have the right combination, accuracy can be superior to jacketed bullets.

The first major issue is the gun itself. Most US made revolvers are shipped optimized for jacketed bullets, which is what the average shooter will use. In most cases, the cylinder throats are too tight and the forcing cone is at the wrong angle for lead bullets. Most factory forcing cones are cut to 5 or 8 degrees. A wider 11 degree forcing cone has proven to work better with lead bullets because it helps guide bullets into the bore without damage or distortion. This improves accuracy and minimizes bore fouling.

The Small Arms and Ammunition Manufacturers Institute (SAAMI) sets standards for bore, chamber, and dimensions but do not have specifications for throat diameters, lead bullet diameters or forcing cones. SAAMI has managed to confuse the general public with their nomenclature. According to SAAMI specs, bore diameter is the largest sized rod that can be inserted into a bore. Of course that will be about .012” smaller than advertised bore diameter because of the , also known as “lands”. Example: in a typical 357 revolver (38 Special or 357 Magnum) SAAMI would rate the bore at .345”. Gun manufactures follow this specification but do not advertise their guns this way to avoid confusion. There are actually two bore specifications … the distance between lands, which would be .345” in the above example and the distance between grooves, which is .357” and is the traditional measurement. Another confusion factor, in a bore, the lands extend from the true bore but in a bullet, the lands engrave into the bullet so the high spot in bore is the low spot on bullets. Land diameter is very difficult to measure. Despite the confusion, SAAMII does maintain a very tight specification that all US gun manufacturers subscribe to. With any revolver made in the US after 1950, the bore will be within .0005” of advertised diameter. Of course there are exceptions for worn guns or manufacturing defects. Foreign gun manufacturers do not have to follow SAAMI specs so their bore diameters could be quite different. This is especially true with “clone” models made in Europe or Asia. For the purpose of this document, the bore diameter is defined as the distance between grooves. This is the conventional method of measurement and is much easier to measure.

1 Slugging a Bore: For the most part, this is a fruitless effort that will often yield false information. Unless you have considerable bore wear, a defective barrel, or are dealing with foreign made revolvers, there is really no need to slug a bore because SAAMI specs are tighter than most people can accurately measure. Slugging a bore involves using a “slug” made out of soft lead that is slightly larger in diameter than the actual bore. The slug is driven through the bore with a dowel rod then the outside diameter is measured. Several issues contribute to false measurements. First off, you need a caliper or micrometer accurate to .0001”. Next, you need a set of precise shims that are placed over the slug so the caliper/micrometer doesn’t bite into the soft lead and give a false reading. Of course this means you have to subtract the thickness of the shims to get actual bore diameter. If you use the wrong lead alloy, the slug will be resilient and expand after it is released from the bore. Any constriction in the bore where the barrel threads into the frame will squeeze the bullet smaller and give false readings. So basically, slugging a bore is usually a waste of time and will likely result in a false reading so it’s best to trust the factory’s SAAMI spec dimensions.

The above graphic shows the optimum measurements for shooting lead bullets in a revolver. As an example, a revolver with a .357” bore should have a throat diameter of . 358~3585”, a bullet diameter of .358”, with an 11 degree forcing cone. The concept is simple; the bullet needs to be delivered to the forcing cone about .001” larger than bore diameter. If a bullet larger than throat diameter is used, the throat will size it down, which is counterproductive. Depending on the bullet shape, a cartridge with a bullet larger than throat diameter won’t fully chamber. Additionally, if bullets larger than throat diameter are used, chamber pressure will elevate, possibly to damaging levels. Using a bullet smaller than optimum diameter or a having a throat that is too tight will result in the bullet being delivered to the forcing too small, which will cause excess fouling.

2 Assuming the bullet is delivered to the forcing cone slightly oversized, the forcing cone will act like a sizing die and reshape the bullet to fit tightly in the bore. Pressure applied from the powder charge (several tons per square inch) will reshape the lead bullet without shaving and will force the bullet to obturate or “bump up” slightly in diameter. If the bullet hardness matches the chamber pressure, a good seal between the circumference of the bullet and the bore will be maintained until the bullet exits the muzzle. As long as a good seal is maintained, lead fouling will not accumulate in the bore and accuracy will be optimum for at least 100 rounds without cleaning.

Bullet Hardness: Bullet hardness is rated in an industry standard called “Brinell Hardness Number” (BHN). Pure lead is BHN 5. As alloys such as tin, arsenic and antimony are added in small percentages, hardness can be increased to BHN 28. There are two common ways to produce lead bullets …. casting and .

Swaging: The swaging process is much more expensive due to equipment costs but does produce more consistent weights, diameters and hardness. The process uses a “lead alloy wire” that is slightly under the finished product diameter. The “wire” is cut into precise lengths to get the exact weight, then fed into a punch press die where it is pressure formed into a finished bullet. Because swaged bullets are not melted, they do not develop internal bubbles and maintain the same hardness. The swaging process works very well with soft alloys in the BHN 10~14 range but is not well suited for harder alloys. Both Speer and Hornady produce high quality swaged lead bullets, however the cost is typically more than double of cast bullets. Most swaged bullets have dry power lubrication applied so you must handle them properly or the lube will come off.

Casting: The casting process starts with creating the desired hardness by melting lead and adding tin and antimony to get the proper alloy. Pure lead doesn’t cast well so tin may be added to make the molten metal flow better in the molds. Antimony increases bullet hardness. When lead is alloyed, it takes on some strange characteristics. After a lead and tin alloy is cast in molds, it will soften with age. It takes about a month for the molecular structure to reach final hardness. Bullets cast with antimony are just the opposite and tend to harden after casting. Again, it takes about a month for the molecular structure to stabilize. Cast bullets are typically not as precise as swaged bullets. They can develop internal bubbles and because of the way the mold works, they have a spru that can increase weight if it is not cut off properly. Cast bullets are typically molded slightly oversized then run through a sizing and lube die. This sets the diameter to the desired measurement and forces a wax type material in the lube grooves. When cast bullets are within +or- 1% of an average weight, they will produce excellent accuracy. As an example, a bullet sold as a 158 gr could be as light as 156.4 grains or as heavy as 159.6 and still produce consistent accuracy. Of course, the more uniform the weight, the tighter it will chronograph and the more consistent accuracy will be. To determine average weight, weigh a random sample of 20 bullets and jot down the results. Add the weight of all 20 bullets then divide by 20. The average weight is seldom the same as advertised but it should be within a few grains. Cull out any bullets that are significantly light. Light bullets indicate there is an internal bubble or the molten lead did not flow well in the mold and caused a void. A void or bubble will cause the bullet to “whiffle” down range.

3 Most brand name bullets such as “Meister” and “Laser Cast” are typically too hard for lower pressure cartridges or reduced power loads. They are typically BHN 20 or more. “Hard cast” bullets work well in magnum level loads but are too hard to obturate at lower pressure levels. A few companies such as Missouri Bullets cast bullets in softer BHNs that are well suited for lower pressure loads.

Matching bullet hardness to chamber pressure is the key to accurate and foul free loads. The concept is simple …. it takes a given pressure to force a bullet to obturate. (bump up in diameter) The higher the chamber pressure, the harder the bullet must be. The process is a bit complicated and requires some math.

To compute bullet hardness, divide the chamber pressure by 1400 if rated in psi or 1440 if rated in CUP. Example: a 38 Special with a 158 gr lead bullet has a max chamber pressure of 17,000 psi; 17,000/1400=12.1 so a BHN 12 bullet would be optimum. A 38 target load with a 148 gr bullet generates about 14,000 psi; 14,000/1400=10 so a BHN 10 bullet would be optimum. A 38 Special +P load with a 158 gr bullet generates a max chamber pressure of 20,000 psi. 20,000/1400=14.2 so a BHN 14 bullet would be best. As long as the BHN number is reasonably close to the computed value, the bullet will obturate properly and shoot quite well. In the above example with the +P load, any bullet from BHN 13 to BHN 15 will suffice. When there is a significant mismatch between chamber pressure and bullet hardness, the bullets will leave a nasty lead deposit in the barrel, which builds up more with each shot and destroys accuracy.

Obturation: When a round is fired, chamber pressure builds up very quickly and starts pushing the bullet out of the case. Soon after the bullet starts moving, the nose will contact the internal forcing cone inside the cylinder. The internal forcing cone guides the bullet into the throat. As pressure begins to peak, the base of the bullet will have several tons of pressure applied. This will cause the bullet to expand, much like setting a bullet nose down on an anvil and smacking the base with a hammer. The throat will restrict the size of the bullet so it doesn’t over expand. The bullet passes through the barrel/cylinder gap (B/C gap) until the nose contacts the forcing cone. The forcing cone does two things … it causes the cylinder to move slightly to force the cylinder throat to align with the bore (thus the name) and it acts like a sizing die to reshape the bullet. At this point, the bullet still has several tons of pressure driving it into the bore. The pressure will cause the bullet to be engraved by the rifling and will keep the bullet expanded so it provides a good seal with the bore. Once the bullet is engraved, it will move down the bore quite easily as pressure starts to drop off. Pressure keeps pushing the bullet and keeps it expanded so it will seal well until the bullet exits the muzzle.

If a bullet is too hard, it won’t bump up in diameter and will lose the seal in the bore. When this happens, very hot, high-pressure gasses will blow past the bullet and erode the circumference by vaporizing the lead. Most of the lead vapor exits the muzzle but some is left behind in the bore to solidify, which corrupts the bore with lead fouling. As more rounds are fired, lead fouling will continue to accumulate until it starts deforming bullets and accuracy drops off.

4 If a bullet is too soft, the same thing happens as with bullets that are too hard. Pressure will breach the seal and cause very hot gasses to blow by the bullet. Again, it causes the bullet to erode and leave lead deposits in the bore.

If a bullet is too small in diameter, no matter how hard or soft it is, the same blow by happens and lead vapor fouls the bore. Contrary to popular belief, the base of a lead bullet will not melt, even though the temperature of the expanding gasses are well above 5000 deg F and lead melts at temperatures under 700 deg F. This is because it takes lead more time to heat up and melt than the short time the bullet is exposed to heat. The lead vapor strictly comes from the circumference of the bullet due to the erosive effect of high pressure gasses at 5000 degrees escaping through a narrow gap between the bullet and bore. A modest load in a 38 Special will generate at least 14,000 psi pressure … that’s 7 tons pushing a little bullet that weighs a third of an ounce.

Gas Checks: A copper can be crimped on the base of the bullet that will virtually eliminate gas blow by and lead fouling. The copper cap is sized just a tad larger than the bore so when high pressure is applied, the gas check will form to the bore and make an excellent seal. Gas checks can be used on high velocity handgun bullets or bullets and are typically used with hard cast bullets.

Bullets without gas checks can be driven to velocities from 600 fps to well over 1700 fps, providing the bullet hardness matches chamber pressure. For rifle velocities over 1700 fps, it’s best to use gas checks. Here’s an excellent reference that details , bullet hardness, facts, and myths: http://www.lasc.us/FryxellCommentsCBAlloys.htm

Now that the theory of obturation has been established, there are several questions left unanswered. How do you measure bullet hardness and determine chamber pressure?

Bullet hardness can be measured with a Lee Bullet Hardness Tester or a more refined Saeco Bullet Hardness Tester. The Lee unit uses a “calibrated dent” in the lead based on the spring tensioned ball bearing being pushed into the lead. The included microscope has an “optical ruler” that will measure the width of the dent. The width measurement is then converted to a BHN. The wider the dent, the softer the lead. Saeco testers have a direct reading scale and measure bullet hardness by turning a knob until the lead yields. The scale reads from 0 to 10, where 0 is pure lead (BHN 5) and 10 is BHN 25. An included chart will convert Saeco hardness numbers to BHN.

Most bullet casting companies do not supply BHNs with their products. They usually state “hard cast”, which means BHN 20~24. Missouri Bullets is an exception. They clearly label their products with bullet weight, diameter, style/shape, and BHN. If you buy commercial cast bullets, make sure you do your homework and identify the best hardness for your intended load. Likewise if you cast your own bullets, use the proper alloy formula to get the desired hardness then check it with one of the above testers.

5 Unless you own very expensive pressure testing equipment, the best way to determine chamber pressure is with a software program called “QuickLOAD”. QuickLoad has a large library of bullets, powders, and cartridges so you can plug in your exact bullet, cartridge type, and powder then determine what powder charge will give you the desired chamber pressure (using a reloading manual for a reference). If you already have bullets and know their hardness, it’s just a matter of multiplying BHN by 1400 to get the desired chamber pressure. If you are trying to determine what hardness bullet to buy, plug your reloading manual’s powder charge in QuickLOAD and divide the peak pressure by 1400. Note: If you have a bullet that is not listed in the QuickLOAD bullet library, you can create one by weighing a bullet, taking a few measurements, then entering the information. The charts come out remarkably close to data listed in reputable reloading manuals.

As you can see from the above QuickLOAD chart, a 38 Special cartridge was plotted with a 148 gr Speer LHBWC using 2.8 gr of Bullseye powder. The peak chamber pressure is about 14,000 psi. 14,000/1400=10 so a BHN 10 bullet would be a perfect match for this load.

If you look in the Speer reloading manual, you will see 2.8 gr is the starting load for this bullet and powder. The max load in the manual (3.0 gr) runs right at the SAAMI max pressure limit of 17,000 psi. 17,000/1400=12.1; so for a max charge, a BHN 12 bullet would be the best match. If you can’t find a bullet with the exact BHN, it’s better to use a softer bullet than a harder one.

QuickLOAD reference: http://www.neconos.com/details3.htm

6 Some other notable things in the above chart: Chamber pressure peaks (red line) when the bullet has traveled about .5” then drops off very quickly. Velocity increases very quickly in the first 2” of travel (blue line) then continues to increase but at a continuously slower rate. This is very typical of fast burning powders. After 6” of bullet travel, the velocity indicates 824 fps, however this does not consider pressure loss from the B/C gap. Each . 001” of B/C gap will reduce velocity by about 1.5%. so an average revolver with a .006” B/C gap would reduce velocity by 9%. .09x824=74 fps loss so the expected velocity should be about 824-74=750 fps. The Speer manual indicates 741 fps, which is very close. The pressure is just right to get the bullet to obturate as is passes through the throat and into the forcing cone.

If you don’t have QuickLOAD, you can estimate chamber pressure by using reputable reloading manuals. Usually the fastest loads listed for each powder will be just under SAAMI max pressure. Here are the SAAMI max pressures for the most common revolver cartridges and their optimum bullet hardness: The highest BHNs are for max loads. If you load lighter target loads, use the lower BHNs. It is very common to load 357 or 44 Mag cartridges to 38 or 44 Special velocities. Use the BHN for the Special cartridges.

32 S&W Long 15,000 psi BHN 10~11 32 H&R Mag 23,500 psi BHN 15~17 327 Fed Mag 45,000 psi BHN 28~32 38 Special 17,000 psi BHN 10~12 38 Special +P 20,000 psi BHN 12~14 357 Magnum 35,000 psi BHN 22~25 41 Magnum 36,000 psi BHN 24~26 44 Special 15,500 psi BHN 10~11 44 Magnum 36,000 psi BHN 24~26 45 Colt 14,000 psi BHN 9~10 45 Colt “Ruger Only” 25,000 psi BHN 16~18

Scenario: Let’s say you cast some 158 gr LSWC bullets in .358 diameter that tested at BHN 16. These are a bit too hard for a 38 Special or a 38 +P and a bit too soft for a 357 Magnum. The optimum chamber pressure would be about 22,400, which is well above 38 Special +P max pressure limits so a 357 Mag case will be used and “downloaded” to match chamber pressure. Using QuickLOAD, you can experiment with different powders and charge weights until you find a load that matches. In this case, a mid-burn rate powder would be best. Unique powder was used and the charge weight was changed in .1 grain increments until the optimum pressure of 22,486 was achieved with 6.2 grains. This would be a very good match for the BHN 16 bullets and should chronograph at 1000 fps from a 6” barrel. This would make an excellent mid-range load, faster than a normal 38 Special and slower than a Magnum.

As you can see, using this more scientific approach to loading lead bullets can be very rewarding. You can develop loads that are pretty much guaranteed to shoot accurately in any lead bullet optimized revolver and you can make loads that are not available in factory ammunition.

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