BPCR Guide: Bullet & Primer

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Written by: Dick Trenk

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Any weight of 45 caliber rifle bullet may be used but accuracy is related to the barrel twist rate and bullet length. For example, a 45 caliber barrel with a twist rate of 18:1 will properly stabilize bullets longer than 1.1 inch. Bullets of shorter length may be fired but may have a excessive spin rate and be inaccurate at long range. Bullets cast in a lead alloy between 20:1 and 30:1 lead:tin ratio work best and will weigh between 475 and 550 grains.

Other twist rates are found in original and replica 45 cal. rifles and other calibers. As a general rule, fast twist rates are required for long heavy bullets and slower twist rates for short lighter weight bullets.

Commercially made smokeless powder ammunition is available from many firms and usually is loaded to a low pressure and velocity in consideration of some original rifles which are considered to be on the weak side.

Almost all of this ammo uses 300, 350, or 405 grain bullets which will generally be accurate enough for hunting out to perhaps 200 yards.

Reloaders can easily surpass the performance of such commercial ammo using black powder or smokeless powder.

45 caliber hunting bullets are usually cast of pure lead or a soft alloy.

On large size game it is important that the bullet expand properly and not exit out the far side of the animal. Hard alloy bullets would not tend to expand in a satisfactory way.

In order to cast bullets of a particular lead/tin ratio you must start with pure tin and pure lead. Automobile wheel weights are made of unknown alloys and may include zinc, arsenic, antimony and other metals which we do not want to use in bullets.

Therefore, although wheel weights provide a cheap and hard alloy and work quite well in many rifles, you are advised not to add wheel weight metal to a pot which has pure lead and tin in it.

Once you add the wheel weight metal you will be dealing with an unknown alloy which cannot accurately be duplicated in the future. It is better to just use the wheel weights alone and once you have developed an accurate loading, you can then duplicate the load using the pure metals.

It is important that the bullet carry sufficient lubricant to help powder fouling to remain soft and thereby maintain accuracy between shots. Bullets with 4 or 5 grease grooves are best. Fewer grease grooves will also provide enough lubricant capacity if the grooves are deeper or wider than normal.

The final diameter of your cast bullet should be the same as the groove diameter of your gun barrel or up to .002″ larger than the groove diameter.

Still, we know that cast lead bullets “obturate” a great amount and fine accuracy is sometimes obtained with bullets which were up to .005″ smaller than your groove diameter.

Obviously you need to “slug” your barrel just in front of the chamber and also near the muzzle and get an accurate measurement of your groove diameter.

You should find the same dimensions at both locations (as well as near the center) If the diameter is slightly large near the chamber end, this indicates a tapered rifling and is a good condition which promotes accuracy.

All modern replica rifle makers are using the following groove and bore diameters:

40 caliber groove .408″ with a bore of .400″. For 45 caliber the groove is .458″ with the bore at .450″. However…you are advised to slug your gun to make certain of these vital dimensions. Be advised that old time original barrels are found with wildly different sizes so measurement is really important.

Also be advised that it is extremely hard to obtain a really accurate fully expanded slug from a rifle barrel. Many owners report that their barrel is far too large or way undersize on the groove and bore diameters.

The fact is though…modern machining methods produce barrels with very tight tolerances and it is the owner or inexperienced machinist who is making the error by improper slugging of the barrel or measuring incorrectly.

Due to the ability of a lead bullet to expand (or squeeze down) to fit the barrel, we find that so called “out of specs. ” barrels which are found to have dimensions not in agreement with the standard sizes listed above really do produce fine accuracy and do not require any rebarreling or internal corrections as long as they have consistent dimensions throughout the barrel length.

45 caliber bullets should be cast with a diameter of between .458″ and .460″. Most moulds will produce bullets of .459″ diameter and this is considered normal size. In most rifles, .457″ bullets will also produce normal accuracy because of the obturation affect which is a word meaning the bullet is puffed up or expanded to fit the barrel tightly even if it started out slightly smaller than the groove diameter. This is another of the many areas where the reloader can experiment to see what his particular rifle likes best.

Cast bullets are assumed to be nearly perfectly round as cast. In reality, this is rarely achieved and such perfection is hard to find in all but the most costly custom moulds. As a basic rule, if your bullet measures within .002″ of roundness it is about average. If your mould makes bullets with a smaller amount of out-of-roundness you have a unusual mould which you should plan on keeping forever.

On the other hand, if your new mould happened to produce bullets more than .002″ out-of -round, I suggest you send it back for an exchange or perhaps a refund.

Such nearly round bullets (if close to your rifles groove diameter) should not be sized through a lubrisizer sizing die which is smaller than the cast bullet because the original near perfect roundness may be lost once the die touches one side of the bullet.

Many shooters use a lubrisizer die .001″ larger than their cast bullet and thereby are able to lubricate bullets in a lubrisizer press without altering the cast diameter.

Some reloaders avoid the lubrisizer entirely and lubricate bullets in a shallow pan by pouring the heated lubricant into the pan and then cooling it, or apply the lubricant by other means.

Cull your cast bullets to remove those having external or internal flaws. The internal voids are evidenced by bullets being too light. Separate bullets into groups according to their weights, as follows.

For plinking or informal shooting use bullets weighing within 2.0 grains (high low spread.) For serious target shooting and for developing and testing loads use bullets weighing within 1.0 grains (high low spread.) Some champions cull bullets to plus/minus 0.2 grains weight but working to such extreme accuracy may not actually be necessary. Given the many other variables in BPCR shooting, you can set up your own weight tolerances and if you obtain good accuracy then stick with that tolerance.

NOTE: The base of the bullet is where accuracy lies. Any bullet not having a sharp crisp base edge will usually not be accurate for target purposes. Bullet moulds in which the molten lead is poured through the nose are called “Nose Pour Moulds” and such moulds produce near perfect bullet bases.

These types of moulds are more expensive than “Base Pour Moulds” which always show a cut off scar where the metal entered the bullet.

Tests indicate that a well made base pour mould bullet can produce the same accuracy as one made from a nose pour mould. However a good nose pour mould will produce more perfect base bullets and result in fewer being culled out, which save lots of casting time.

Also, for obvious reasons, a nose pour mould must have a flat point (meplat) while a base pour can have a curved, rounded or pointed tip.

Casting good bullets takes a certain amount of skill, learned only by lots of practice. I poor caster may get poor bullets from the very finest mould.

When culling bullets, throw out any bullets which have driving bands not fully filled and crisp in appearance. Turn each bullet and examine it all around to see if some portion has poorly filled bands. Such a poorly filled out bullet will not fly accurately and may cause a “flier” or erratic strike on the target.

After inspecting and culling out the rejects, store the “keepers” base UP in a suitable box or rack.

At most pistol shooting ranges you can pick up empty 45 acp boxes and the plastic racks used in such ammo boxes will hold 50 of your rifle bullets safely.

Some commercially made rifle bullets have a large 45 degree angle on their base. These bullets load into the case mouth very easily and are ok for Cowboy Action type matches fired at short ranges. These bullets will NOT produce acceptable accuracy at longer ranges and should not be used when you are expecting long range precision accuracy. The flat base and perfect base edge is absolutely required if you want accuracy far out.

As a general rule…serious match shooters do not purchase commercially made lead alloy bullets but cast or swage their own, for the simple reason that well made bullets with perfect bases are not available at affordable prices.

Originally, most BP cartridges used what is called a “paper patched bullet.”

Such bullets have no grease grooves and require the use of a “grease cookie” installed below the bullet and over the powder. Most modern shooters do not use the PP bullets today but great accuracy can be obtained by reloaders willing to do the careful work required to make a PP bullet.

Today, when using PP bullets many shooters wipe out the barrel between each shot and therefore do not have to use any grease cookie at all (although some do.)

Due to the time restrictions in Silhouette match competition it is not practical to wipe the barrel between shots so PP bullets are not used without the grease cookie.

If you want to try PP bullets you can learn about making them by reading one of the many good books on this subject.


The large capacity BP case holds so much powder that strong primer action usually works best. Any large rifle size “standard” or “magnum” primer will get the job done but it must be noted that Large Pistol primers will also fit the primer pocket in the case but these pistol primers are made from thinner metal, produce a much weaker flash intensity and also are not high enough. For these reasons DO NOT use Large Pistol primers with cases holding more than 75 grains of BP.

Also, because the pistol primer is shorter than a rifle primer, the pistol primer is slammed back against the breech block when powder ignition takes place. In some guns where the breech block front surface may be of a softer steel, this continuous primer “set back” can result in permanent indenting of the area around the firing pin hole. As is usual, this subject is also one where different opinions and results have been noted. Some reloaders like the mild Large Pistol Primers and get good accuracy with them.

All the rifle manufacturers are well aware of reports of indentation of the breech face caused by the Large Pistol Primers slamming back against the breech face.

The cure would be to make the breech block face much harder and brittle and because this can cause fracturing around the firing pin hole it is not a safe or suitable change. The only other cure would be to install a special hard bushing around the firing pin hole and allow the breech block to remain somewhat softer. This bushing is not installed by the gun manufacturers but can be done by a competent gunsmith.

I recommend not using the Large Pistol Primers as any measured advantage they may produce can also be duplicated by simply placing one or two wads of newsprint over the flash hole before dumping in the powder charge. The .003″ newsprint wad has the effect of smothering or reducing the primer flash slightly and tests have indicated the results are close to those obtained with the Pistol Primers.

However, this is but another of the countless things which need lots of experimentation and testing.

What is required would be a Large Rifle primer having pistol primer material inside. I suspect it will be made available in the near future since there seems to be a reasonable demand for such a special primer.