Post by Bullshop on Apr 7, 2018 13:07:26 GMT -7
I am going to ramble on here a bit about this question, " how much lube is enough ". I have often wondered just why some of my cast bullet loads some days shoot good and some days not as good. I have also wondered just why when some loads that I conjured up that I thought should shoot well but were a disappointment. Why will a certain style of bullet of a certain weight shoot so good but another style of the same weight not so good ? In short there is no shortage of why's to disappointing performance but maybe just maybe I will here touch on one possibility that can apparently be controlled.
In the past year or so I have acquired not one but two very nice (for me) old Husqvarna made rolling block rifles both chambered for the 8x58 RD cartridge of which I have written a little bit about here in the recent past. I will also mention here that I have now gained much experience with these rollers and am planning another more detailed review of them.
Anyway in developing loads for the rifles I felt I was seeing a trend toward vertical stringing of groups using bullet designs that carried a lot of lube. I should mention here that the 8x58RD is a robust cartridge but that these old sporting rolling block rifles have long slender barrels that make then quite sensitive to load changes and tend to vertical stringing with less than very consistent loads.
The load that I have standardized for these rifles to shoot to their original sights had to be very close to the ballistics of the original loads or the POI would be low or high depending on the weight deviation from standard which was a 196gn bullet at between 2100 and 2200 fps. Once I got my cast bullet loads within those standards the rifles shoot right to the sights at 100 yards. The bullet I standardized for these rifles is a 200 gn so within 4gn of original and just over 2100 fps so right in the slot for original velocity.
The custom bullet design I have standardized for this cartridge has four lube grooves but because of the long throats in these rifles requiring bullets to be seated very long and the slightly short brass I am making from 45-70 there are two lube grooves outside the case neck. For this reason I was not lubing the two exposed lube grooves and lubing only the two grooves inside the case neck. Though I was not sure this alone seemed to help reduce group size by reducing vertical stringing in my groups. What I thought I was seeing made me wonder enough to set up a short test that I did today.
I had bigger plans but the rain changed them and since The Bullshop only gives me one day off a week on Saturday I had to get the shooting done that I prepared for yesterday evening. I had planned to chronograph these test loads to see if changing the amount of lube had an effect on velocity or consistency but the rain foiled that plan. I have had my Ohler 35P for 25 years or more and is like an old friend and I do not want to mis-treat it so the Ohler stayed in the house today.
My plan was to use a bullet design that has multiple lube grooved and with the same load fire groups with this bullet that go from having all the grooves filled down to having only one groove filled. This didn't go quite as expected because right in the middle between having two grooves filled and three grooves filled I got an unexpected vertical string that seemed to violate the trend. None the less though overall this very short test showed two things #1 was that more lube than necessary seemed to cause vertical stringing the more lube the greater the dispersion, and #2 that as lube quantity got nearer to optimum the POI seemed to climb.
As you will see if I can get Tina to put up some pictures I took the tightest group and also the highest on target is the one that had only one lube groove filled. A visual inspection of the bore may or may not show a slight color change from dark to slightly gray going from all five lube grooves filled to only one but the difference is so slight that it may not even be but the important thing is that there is no perceivable leading. These bullets were basically quenched WW alloy so should run abought BHN-20. The lube is our Lotak smokeless powder lube. And the bullet diameter is .328" even though the books say the 8x58RD uses a .323" diameter bullet and my bore slugged out at .326" in the grooves. This I hope to shed some light on in my Lord willing upcoming report on the 8x58 RD rollers.
In the picture of the target backer you can see a composite of all the shots fired with the tight little cluster at the top the shots that had only one lube groove filled. The targets are numbered for the number of grooves that were lubed for the corresponding target. I set up the target backer so that the same aiming point could be used for all the shooting but for each individual group a fresh paper could be slipped behind the aiming point.
On #5 the one with all five lube grooves even though I had the target recording paper in the taller upright position the vertical stringing was so great that I could not catch all the shots on the record paper even though I shot 5 at that target to do so. On another target that puzzled me greatly there are four holes the reason being that one shot was unexplainably low so I fired another at that target expecting it to go higher into the group but it too went low. That target was the puzzler in the test as it didn't stay with the trend and I have no idea why.
In short though I will now rethink some of my pet loads and maybe see if they can be refined by adjusting the lube volume. The load I had standardized for these rollers in 8x58 RD is using our 200gn custom that has four lube grooves but only two filled I will now have to re-evaluate and try just one groove filled.
I suspect that pressure and velocity are going to figure into the equation. I suspect that using a specific bullet design at lower velocity/pressure will require less lube and higher velocity/pressure loads will require more lube. An educated guess as to the pressure of the loads used today I would put in the high 20's to low 30's Just how much lube is another area of testing that I have now been enlightened to that may be just as important to accuracy as are the right components as well as powder type, burn rate, and amount. This just keeps getting more interesting all the time!
You can click on the images to make them larger.
In the past year or so I have acquired not one but two very nice (for me) old Husqvarna made rolling block rifles both chambered for the 8x58 RD cartridge of which I have written a little bit about here in the recent past. I will also mention here that I have now gained much experience with these rollers and am planning another more detailed review of them.
Anyway in developing loads for the rifles I felt I was seeing a trend toward vertical stringing of groups using bullet designs that carried a lot of lube. I should mention here that the 8x58RD is a robust cartridge but that these old sporting rolling block rifles have long slender barrels that make then quite sensitive to load changes and tend to vertical stringing with less than very consistent loads.
The load that I have standardized for these rifles to shoot to their original sights had to be very close to the ballistics of the original loads or the POI would be low or high depending on the weight deviation from standard which was a 196gn bullet at between 2100 and 2200 fps. Once I got my cast bullet loads within those standards the rifles shoot right to the sights at 100 yards. The bullet I standardized for these rifles is a 200 gn so within 4gn of original and just over 2100 fps so right in the slot for original velocity.
The custom bullet design I have standardized for this cartridge has four lube grooves but because of the long throats in these rifles requiring bullets to be seated very long and the slightly short brass I am making from 45-70 there are two lube grooves outside the case neck. For this reason I was not lubing the two exposed lube grooves and lubing only the two grooves inside the case neck. Though I was not sure this alone seemed to help reduce group size by reducing vertical stringing in my groups. What I thought I was seeing made me wonder enough to set up a short test that I did today.
I had bigger plans but the rain changed them and since The Bullshop only gives me one day off a week on Saturday I had to get the shooting done that I prepared for yesterday evening. I had planned to chronograph these test loads to see if changing the amount of lube had an effect on velocity or consistency but the rain foiled that plan. I have had my Ohler 35P for 25 years or more and is like an old friend and I do not want to mis-treat it so the Ohler stayed in the house today.
My plan was to use a bullet design that has multiple lube grooved and with the same load fire groups with this bullet that go from having all the grooves filled down to having only one groove filled. This didn't go quite as expected because right in the middle between having two grooves filled and three grooves filled I got an unexpected vertical string that seemed to violate the trend. None the less though overall this very short test showed two things #1 was that more lube than necessary seemed to cause vertical stringing the more lube the greater the dispersion, and #2 that as lube quantity got nearer to optimum the POI seemed to climb.
As you will see if I can get Tina to put up some pictures I took the tightest group and also the highest on target is the one that had only one lube groove filled. A visual inspection of the bore may or may not show a slight color change from dark to slightly gray going from all five lube grooves filled to only one but the difference is so slight that it may not even be but the important thing is that there is no perceivable leading. These bullets were basically quenched WW alloy so should run abought BHN-20. The lube is our Lotak smokeless powder lube. And the bullet diameter is .328" even though the books say the 8x58RD uses a .323" diameter bullet and my bore slugged out at .326" in the grooves. This I hope to shed some light on in my Lord willing upcoming report on the 8x58 RD rollers.
In the picture of the target backer you can see a composite of all the shots fired with the tight little cluster at the top the shots that had only one lube groove filled. The targets are numbered for the number of grooves that were lubed for the corresponding target. I set up the target backer so that the same aiming point could be used for all the shooting but for each individual group a fresh paper could be slipped behind the aiming point.
On #5 the one with all five lube grooves even though I had the target recording paper in the taller upright position the vertical stringing was so great that I could not catch all the shots on the record paper even though I shot 5 at that target to do so. On another target that puzzled me greatly there are four holes the reason being that one shot was unexplainably low so I fired another at that target expecting it to go higher into the group but it too went low. That target was the puzzler in the test as it didn't stay with the trend and I have no idea why.
In short though I will now rethink some of my pet loads and maybe see if they can be refined by adjusting the lube volume. The load I had standardized for these rollers in 8x58 RD is using our 200gn custom that has four lube grooves but only two filled I will now have to re-evaluate and try just one groove filled.
I suspect that pressure and velocity are going to figure into the equation. I suspect that using a specific bullet design at lower velocity/pressure will require less lube and higher velocity/pressure loads will require more lube. An educated guess as to the pressure of the loads used today I would put in the high 20's to low 30's Just how much lube is another area of testing that I have now been enlightened to that may be just as important to accuracy as are the right components as well as powder type, burn rate, and amount. This just keeps getting more interesting all the time!
You can click on the images to make them larger.