BPCR Guide: Accuracy

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Written by: Dick Trenk

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GOING FOR ACCURACY

After you have understood and mastered the advice, rules and tips listed previously, you are ready to start work on developing the most accurate load for your rifle, your bullet and your other components.

Several things are known to affect the accuracy of BP cartridge reloading, and they are:

  1. Bullet shape and length
  2. Powder type and quality
  3. Primer type
  4. Powder volume and compression
  5. Overpowder wad type and material
  6. Bullet lubricant
  7. Case neck grip on the bullet (crimp or no crimp as well as fit in case neck)
  8. Bullet position in relation to where rifling starts
  9. Many more little things which are capable of affecting accuracy

While learning to reload for the BPCR, you have likely been shooting your reloads and have some idea of what the rifle can do in the way of accuracy.

To properly evaluate accuracy you must shoot at a paper target so you can measure the group size produced and thereby get a correct opinion as to whether or not a change in one reloading step was for the better or actually was worse.

You have to start somewhere so I suggest doing the following.

  1. Position your bullet in the case so it is in light contact with the rifling of the barrel.
  2. Use enough BP so that the bullet (and wad) will then compress the powder .050″ when the bullet and wad are seated to this length.
  3. Load and fire 5 rounds at a paper target and write down the group size.
  4. Add 1.0 grains (by volume) to the powder charge and make no other changes (if yours is smaller than 40 caliber, use 1/2 grain increments).
  5. The seating of the bullet and wad will compress this taller powder charge more than .050″ and this should also be recorded.
  6. Fire the 5 rounds and note the group size obtained.
  7. Repeat the process of adding 3. 0 grains of BP and firing 5 rounds etc.
  8. When you have reached the point where the powder is compressed about .300″ you should end this incremental loading process and sit down and study your group size results. Almost every rifle will display a shrinking of group size when the powder charge gets to where that rifle likes it. You will find a certain powder charge volume and powder compression which produced the smallest groups. You can then work around that data by adding or subtracting 1.0 grain of BP at a time in an effort to refine your load even further.
  9. Once you have determined the powder volume and compression which seems to produce your smallest group sizes you then turn your attention to the other items seen on the first list above, such as changing the location of the bullet back off the rifling.

When working up a load remember this simple rule. Change only one thing at a time and keep written notes of what you are doing!

PROBLEM SOLVING TIPS

We hear reports from time to time, of bullets hitting the target sideways (key-holing) or of guns producing bad accuracy. As you can imagine, many things can produce or contribute to such results and we offer a list of things which can usually be found to be the cause or involved in the cause.

  1. Bullets too small in diameter, or much too large.
  2. Lead alloy too hard or too soft. Being too soft is the more serious problem as it can allow the ogive of the bullet bump up erratically causing unexpected flight paths. When too hard an alloy is used it may not allow the bullet to properly obturate into the groove diameter.
  3. Bullets too short for 45 cal. 18:1 twist barrel or the 40 cal. 16:1 twist barrel. This would be 45 cal. bullets under 375 grains wt. or 40 cal. bullets under 300 grains wt.
  4. Bullets having beveled base design which usually are not too accurate
  5. Lack of lubricant or poor lubricant, allowing fouling build up.
  6. Fouling or lead in barrel or barrel or chamber
  7. Case necks too small in outside diameter for your chamber, and having inside diameter requiring too small a bullet diameter. Cases previously fired in your gun should be used when developing loads.
  8. Case length too long and metal has flowed forward jamming into chamber throat (ball seat), leade, or rifling. Measure case length first.
  9. Too weak powder charge may fail to fully obturate bullet into the groove diameter of the barrel.
  10. Too powerful a powder charge resulting in excessive muzzle velocity (smokeless powder only). Too soft an alloy combined with high muzzle velocity and shallow rifling can cause the bullet to “strip” and not engage the rifling properly.
  11. Inconsistency with powder charge volume, compression, seating depth, bullets weights, bullet crimp or other assembly variations.
  12. Black powder burning badly with variable pressures due to poor quality or deterioration of the powder caused by moisture or storage conditions.
  13. Primer inconsistency of intensity and flame. Improper firing pin action can also change the primer intensity between each shot.
  14. Front or rear gun sights loose or not properly mounted and some portion is loose and moving with each shot, preventing accuracy.
  15. Poor shooting skill or eyesight problems. If in doubt have another experienced shooter test fire your rifle. Use a sandbag support under the forearm of the rifle as a starting point for bench tests.
  16. Failure to pre-foul the bore. Almost all BP loads do their best only after 2-3 shots have been fired and the bore coated with some fouling residue. Some loads work best only with a clean wiped bore for each shot. Find out what works best for you.
  17. Bullets poorly cast and having internal voids causing severe wobble in flight.
  18. Use of a scale to weigh bullets will let you cull out bullets which are below proper weight (indicating an internal void). For practice use, bullets weighing within 2.0 grains of one another.

For load refinement and match use, use bullets weighing within 1.0 grains.

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