Ammuniton accuracy. free pistol, handgun, rifle
Posted: Thu Jan 10, 2013 2:29 pm
Some very interesting comments on ammunition selection for a variety of guns have appeared on some TT discussions. These were particularly interesting from the point of view of people who don't use these guns in competition, and for whom a 600 free pistol score is at the beginner level and will not pass go for actual work.
These comments may have absolutely no relevance for those in competition shooting, but they still might be of interest.
Reprinted with permission, but without reference to source.
The following may be total junk for target shooters, but they may be something to think about. They are a summary of views from people who design and make precision guns, or use them for non-competition purposes mostly.
Ammunition:
What is the most important, and worth doing to get similar performance ammo?'
Cartridge dimension consistency, bullet mass and concentricity, symmetric bullet mass distribution, chemical consistency of the powder, grain size, and moisture content of the powder are important, but hard to sort after the cartridge is assembled. Best to "equalize" these by starting with cartridges that basically are well made. Most of the W European mfrs are in that category, and also in the past, the Olymp Moscow ones (not so much the TEMP). Examples range from SK/WolfMatch, Lapua, Eley, RWS, Fiocchi, GECO except the CCI produced ones, but there are others.
Once the general category of ammunition is chosen, the first sort is density of powder packing. The main factor in muzzle velocity and barrel vibration pattern is the flame temperature and burn speed. This is most sensitive to the free space between the powder grains, and is proportional to the cube of 1/(free space). Easiest way to measure this is by indirectly measuring the consistency of seating depth of the bullet. This is done by sorting using the top to bottom length of the cartridge, and sort to within .1 mm or .02" in groups.
This is especially important with cartridges that are "filled" with powder, like some 9mmXanything, or the 7.62 Tokarev, but also with those that are not filled completely. The design of the .32SWL WC cartridge minimizes the packing variation most of the time, making sorting by length usually not worth while for that particular cartridge, if the manufacturer is good.
Sub-sorting within groups by overall weight can help further, but to be honest, in the above mfrs, the powder and moisture content is so well controlled, usually there is very little difference. Usually the powder is pretty consistent between cartridges. What can differ is moisture content, which this also measures.
The third option in sorting is rim thickness in .22RF, but this actually has little effect. Primer ignition is a piezoelectric effect, with little dependency on rim thickness. Primer burn rate and temperature vary a bit with rim thickness, but not enough to be worth measuring. In the past, rim thickness measurement did help a bit, but it should not have. I think the reason it did help is what with lower quality cartridges and poor manufacturing methods (pre 1970), the rim thickness disparity was identifying poorly made cartridges in general.
The above method applies to all cartridges. With the best RWS and sometimes, the best Lapua and Eley cartirdges, consistency is so good, that there is no difference notable.
For testing the cartridges IN the gun, the ammunition DOES need to be matched to the gun for best accuracy. The reason primarily is barrel vibration pattern, which really is very important for all free pistols. For selecting cartridges, the gun must NOT be clamped on the barrel, because that changes the vibration pattern. Some feel it must be done handheld to duplicate what occurs in actual firing, but a pistol rest can help reduce the effect of hand tremor, if that is a problem. Some groups, such as a few in Europe, further insist that the "rest" must duplicate the geometry and mass distribution and head position of the human and his grip on the gun, to take into account coupling effects or effects of the grip or stock on aim.
Some factories test the guns with the barrel clamped, because it suppresses barrel vibration when their 100 kg clamps are used, and gives a falsely high degree of accuracy.
This also is the reason that in some free pistols (rarely), the HV ammunition is more accurate than the SV ammunition: the different vibration pattern produced, even though the muzzle blast effect is adverse. Also, the vibration pattern affects not just the barrel, but the entire gun. The feedback or interaction between the barrel vibration and that of the rest of the gun is significant.
Once an optimal ammunition is found, if the pistol has auxilliary weights (for example, some free pistols, the GSP, 208-215 series Hammerli guns, etc) , these can be adjusted to tune the feedback dampening vibration to improve accuracy further. An example is the Steyr system. This does not work well with the "air weight" system, but does work with any weight that is firmly attached to the gun and mechanically linked to the barrel. The TOZ35 add-on front piece that couples the metal front end to the barrel also can be used in that way.
As to chamber fit, in general the tighter the chamber fit, the more consistent the firing due to less gas loss. However, the tight fit can create a problem in extraction. This is an area of compromise. The tighter the fit, the less gas loss and more consistent will be the gas loss until full seal occurs. Remember, in a rim fire cartridge, the seal occurs just forward of the rim area, rather than at mid cartridge as in the rimless cartridges. If the cartridges stick, the inner part of the chamber can be coated with MoS2, or one of the organic antitstick agents, as can the cartridge casing. Regarding the latter, lubrication will not affect the seal IF the coating is in the forward 3/4 of the cartridge. The seal is at the rear 1/5 of the cartridge just forward of the rim. MoS2 however can affect the seal IF it is in that most rearward part of the breech area.
Of course, when evaluating what is good and what is bad, desired accuracy is all a matter of what one desires. For some, all 50 or 100 shots in the 10 ring is fine. For others, the objective is all rounds contained within a 6 or 7mm circle at 50M.
Aim:
As to the aim, there are basically two methods, one the static, and one the dynamic method (firing while the gun is moving downward to the target point). In FP shooting, the dynamic may work better as muscle fatigue is less. The dynamic method shooting with the gun moving) takes a little practice to learn, but with the FP, the learning is easiest as the movement of the gun is disturbed so little by pulling the trigger. The same method can be used with other guns as well, but the heavier the trigger pull, the more difficult this method becomes.
The dynamic method also reduces the effects of hand and arm tremor. If using the static method, do NOT lock the arms, but leave them slightly flexed at the elbows to reduce tremor. Also it may be necessary to learn to "time" any tremor present.
The inverse dynamic approach, of raising the gun and shooting as the gun rises, also can be used. The advantage of that is clearer view of the target point, and better ability of the brain to time the movement of the gun. Also remember to focus NOT on the overall target, but on a specific 2x2mm spot of the target as your aimpoint.
The perception of drawing a line to the target by the dynamic method is a perception only. The actual mechanism is that the brain and optic system are extremely good in timing and advance targeting of moving objects, physiologically called "anticipation" targeting. This accuracy is so good, even in lowly humans compared to birds or cats, that the timing and targeting of the anticipation method can be better than the static method.
Muscle tremor primarily is a static phenomenon, that is suppressed partially or completely during movement. As a result, the moving gun method avoids or at least markedly reduces the error from tremor. The brain also is more adept (hard wired) for advance or anticipation targeting, than it is for timing tremor and adjusting the aim to compensate for that.
With a free pistol the trigger pull should be light enough that you do not actually pull the trigger consciously to fire the gun. It should fire as soon as you think about firing. This relates to the details of brain control of motor movement more than anything else, which are a 2 stage process with dual circuits that can override one another.
In the end, whether the static or dynamic method is better depends in part on the individual shooter, and how their brain works (or malfunctions).
To further confuse the situation, rarely one comes across an individual whose accuracy consistently is better than should be possible with the gun and ammunition used. Some of these individuals accomplish this by remembering variation the gun has with each shot in the sequence, and adjusting for it. However, that doesn't explain the whole picture, and other things must be talking place, which are pretty hard to understand.
These comments may have absolutely no relevance for those in competition shooting, but they still might be of interest.
Reprinted with permission, but without reference to source.
The following may be total junk for target shooters, but they may be something to think about. They are a summary of views from people who design and make precision guns, or use them for non-competition purposes mostly.
Ammunition:
What is the most important, and worth doing to get similar performance ammo?'
Cartridge dimension consistency, bullet mass and concentricity, symmetric bullet mass distribution, chemical consistency of the powder, grain size, and moisture content of the powder are important, but hard to sort after the cartridge is assembled. Best to "equalize" these by starting with cartridges that basically are well made. Most of the W European mfrs are in that category, and also in the past, the Olymp Moscow ones (not so much the TEMP). Examples range from SK/WolfMatch, Lapua, Eley, RWS, Fiocchi, GECO except the CCI produced ones, but there are others.
Once the general category of ammunition is chosen, the first sort is density of powder packing. The main factor in muzzle velocity and barrel vibration pattern is the flame temperature and burn speed. This is most sensitive to the free space between the powder grains, and is proportional to the cube of 1/(free space). Easiest way to measure this is by indirectly measuring the consistency of seating depth of the bullet. This is done by sorting using the top to bottom length of the cartridge, and sort to within .1 mm or .02" in groups.
This is especially important with cartridges that are "filled" with powder, like some 9mmXanything, or the 7.62 Tokarev, but also with those that are not filled completely. The design of the .32SWL WC cartridge minimizes the packing variation most of the time, making sorting by length usually not worth while for that particular cartridge, if the manufacturer is good.
Sub-sorting within groups by overall weight can help further, but to be honest, in the above mfrs, the powder and moisture content is so well controlled, usually there is very little difference. Usually the powder is pretty consistent between cartridges. What can differ is moisture content, which this also measures.
The third option in sorting is rim thickness in .22RF, but this actually has little effect. Primer ignition is a piezoelectric effect, with little dependency on rim thickness. Primer burn rate and temperature vary a bit with rim thickness, but not enough to be worth measuring. In the past, rim thickness measurement did help a bit, but it should not have. I think the reason it did help is what with lower quality cartridges and poor manufacturing methods (pre 1970), the rim thickness disparity was identifying poorly made cartridges in general.
The above method applies to all cartridges. With the best RWS and sometimes, the best Lapua and Eley cartirdges, consistency is so good, that there is no difference notable.
For testing the cartridges IN the gun, the ammunition DOES need to be matched to the gun for best accuracy. The reason primarily is barrel vibration pattern, which really is very important for all free pistols. For selecting cartridges, the gun must NOT be clamped on the barrel, because that changes the vibration pattern. Some feel it must be done handheld to duplicate what occurs in actual firing, but a pistol rest can help reduce the effect of hand tremor, if that is a problem. Some groups, such as a few in Europe, further insist that the "rest" must duplicate the geometry and mass distribution and head position of the human and his grip on the gun, to take into account coupling effects or effects of the grip or stock on aim.
Some factories test the guns with the barrel clamped, because it suppresses barrel vibration when their 100 kg clamps are used, and gives a falsely high degree of accuracy.
This also is the reason that in some free pistols (rarely), the HV ammunition is more accurate than the SV ammunition: the different vibration pattern produced, even though the muzzle blast effect is adverse. Also, the vibration pattern affects not just the barrel, but the entire gun. The feedback or interaction between the barrel vibration and that of the rest of the gun is significant.
Once an optimal ammunition is found, if the pistol has auxilliary weights (for example, some free pistols, the GSP, 208-215 series Hammerli guns, etc) , these can be adjusted to tune the feedback dampening vibration to improve accuracy further. An example is the Steyr system. This does not work well with the "air weight" system, but does work with any weight that is firmly attached to the gun and mechanically linked to the barrel. The TOZ35 add-on front piece that couples the metal front end to the barrel also can be used in that way.
As to chamber fit, in general the tighter the chamber fit, the more consistent the firing due to less gas loss. However, the tight fit can create a problem in extraction. This is an area of compromise. The tighter the fit, the less gas loss and more consistent will be the gas loss until full seal occurs. Remember, in a rim fire cartridge, the seal occurs just forward of the rim area, rather than at mid cartridge as in the rimless cartridges. If the cartridges stick, the inner part of the chamber can be coated with MoS2, or one of the organic antitstick agents, as can the cartridge casing. Regarding the latter, lubrication will not affect the seal IF the coating is in the forward 3/4 of the cartridge. The seal is at the rear 1/5 of the cartridge just forward of the rim. MoS2 however can affect the seal IF it is in that most rearward part of the breech area.
Of course, when evaluating what is good and what is bad, desired accuracy is all a matter of what one desires. For some, all 50 or 100 shots in the 10 ring is fine. For others, the objective is all rounds contained within a 6 or 7mm circle at 50M.
Aim:
As to the aim, there are basically two methods, one the static, and one the dynamic method (firing while the gun is moving downward to the target point). In FP shooting, the dynamic may work better as muscle fatigue is less. The dynamic method shooting with the gun moving) takes a little practice to learn, but with the FP, the learning is easiest as the movement of the gun is disturbed so little by pulling the trigger. The same method can be used with other guns as well, but the heavier the trigger pull, the more difficult this method becomes.
The dynamic method also reduces the effects of hand and arm tremor. If using the static method, do NOT lock the arms, but leave them slightly flexed at the elbows to reduce tremor. Also it may be necessary to learn to "time" any tremor present.
The inverse dynamic approach, of raising the gun and shooting as the gun rises, also can be used. The advantage of that is clearer view of the target point, and better ability of the brain to time the movement of the gun. Also remember to focus NOT on the overall target, but on a specific 2x2mm spot of the target as your aimpoint.
The perception of drawing a line to the target by the dynamic method is a perception only. The actual mechanism is that the brain and optic system are extremely good in timing and advance targeting of moving objects, physiologically called "anticipation" targeting. This accuracy is so good, even in lowly humans compared to birds or cats, that the timing and targeting of the anticipation method can be better than the static method.
Muscle tremor primarily is a static phenomenon, that is suppressed partially or completely during movement. As a result, the moving gun method avoids or at least markedly reduces the error from tremor. The brain also is more adept (hard wired) for advance or anticipation targeting, than it is for timing tremor and adjusting the aim to compensate for that.
With a free pistol the trigger pull should be light enough that you do not actually pull the trigger consciously to fire the gun. It should fire as soon as you think about firing. This relates to the details of brain control of motor movement more than anything else, which are a 2 stage process with dual circuits that can override one another.
In the end, whether the static or dynamic method is better depends in part on the individual shooter, and how their brain works (or malfunctions).
To further confuse the situation, rarely one comes across an individual whose accuracy consistently is better than should be possible with the gun and ammunition used. Some of these individuals accomplish this by remembering variation the gun has with each shot in the sequence, and adjusting for it. However, that doesn't explain the whole picture, and other things must be talking place, which are pretty hard to understand.