Re: Ladder test with BACO 409420M2
Posted: Sat Apr 03, 2021 4:38 pm
OK Guys,
It seems I need to educate some of you about ladder tests & the benefit thereof, including some of you “naysayers”. BTW, ladder testing is also known as the ladder technique or “The Incremental Load Development Method”. Although apparently not well-known is the BPCR community, ladder tests are an acceptable and excellent way to help zero in on a specific bullet & load that the rifle likes. It’s a technique used by many smokeless precision rifle shooters & the benefits also apply to BPCR.
So you have a new rifle or want to try a new bullet. So where do you start concerning load development? Many of you use start with a load based on recommendations or one that results with a certain amount of compression, etc. You load up a few rounds & head to the range. If you’re real lucky the results are excellent (tight groups) & you’re happy. But in many or most cases the grouping is not as good as you’d like. So what do you do next - typically change the amount of powder – right? Load up a bunch more and head to the range again. Or maybe you load up a bunch for a match & wonder why they did not perform as good as you’d like. After trying different loads & possibly attending several matches you eventually settle on a load combination that you can live with. That’s a lot of effort, time & expense.
The ladder test is a way to identify one or more velocity “sweet spots” for a given bullet during one shooting session. I believe most of you are familiar with the term sweet spot concerning barrel vibration & the benefits of resting the barrel on the cross sticks at a specified location. There are also sweet spots concerning velocity which affects barrel vibration & accuracy. If you can identify them you won’t waste the effort, time & expense trying many different load combination.
To run a BPCR ladder test I 1st determine the required powder for minimum compression for a specific bullet & cartridge overall length. Starting with the minimum compression, say 0.035” or so, I proceed to load rounds by increasing the powder in increments of 0.5grs until the maximum compression is reached (0.300” in this thread example). Each round is labeled with the powder weight and shot in order starting with the minimum charge.
Under perfect shooting conditions and with no human error affecting the shot placement one might expect each subsequent bullet to hit slightly higher than the last one on the target due to the increased velocity – move up the ladder so to speak. But barrel vibrations are a very significant factor influencing the shot placement. Therefore the shot pattern may move up then stop for 2 or 3 shots or more prior to moving up again, which identifies a possible sweet spot. It’s common to find a couple of potential sweet spots in a ladder test given sufficient number of loads. A true “sweet spot” is the point the rifle doesn’t care about the powder charge weight or resulting velocities, as long as it remains within a certain range. The result of the ladder test technique is simply to pick a charge in the middle of the sweet spot group charge weight range. The selected load should be tolerant to minor variation in powder charge weight & other load component variations.
Once the potential sweet spots are determined then load up 10 identical rounds or so with that powder amount for each potential sweet spot & head back to the range to see which one results in the best accuracy. So in a couple of trips to the range you’ve identified the best bullet/load combination for your rifle.
For a lot more details & better description of ladder testing, including the benefits, see the following link: https://www.6mmbr.com/laddertest.html
Wayne
It seems I need to educate some of you about ladder tests & the benefit thereof, including some of you “naysayers”. BTW, ladder testing is also known as the ladder technique or “The Incremental Load Development Method”. Although apparently not well-known is the BPCR community, ladder tests are an acceptable and excellent way to help zero in on a specific bullet & load that the rifle likes. It’s a technique used by many smokeless precision rifle shooters & the benefits also apply to BPCR.
So you have a new rifle or want to try a new bullet. So where do you start concerning load development? Many of you use start with a load based on recommendations or one that results with a certain amount of compression, etc. You load up a few rounds & head to the range. If you’re real lucky the results are excellent (tight groups) & you’re happy. But in many or most cases the grouping is not as good as you’d like. So what do you do next - typically change the amount of powder – right? Load up a bunch more and head to the range again. Or maybe you load up a bunch for a match & wonder why they did not perform as good as you’d like. After trying different loads & possibly attending several matches you eventually settle on a load combination that you can live with. That’s a lot of effort, time & expense.
The ladder test is a way to identify one or more velocity “sweet spots” for a given bullet during one shooting session. I believe most of you are familiar with the term sweet spot concerning barrel vibration & the benefits of resting the barrel on the cross sticks at a specified location. There are also sweet spots concerning velocity which affects barrel vibration & accuracy. If you can identify them you won’t waste the effort, time & expense trying many different load combination.
To run a BPCR ladder test I 1st determine the required powder for minimum compression for a specific bullet & cartridge overall length. Starting with the minimum compression, say 0.035” or so, I proceed to load rounds by increasing the powder in increments of 0.5grs until the maximum compression is reached (0.300” in this thread example). Each round is labeled with the powder weight and shot in order starting with the minimum charge.
Under perfect shooting conditions and with no human error affecting the shot placement one might expect each subsequent bullet to hit slightly higher than the last one on the target due to the increased velocity – move up the ladder so to speak. But barrel vibrations are a very significant factor influencing the shot placement. Therefore the shot pattern may move up then stop for 2 or 3 shots or more prior to moving up again, which identifies a possible sweet spot. It’s common to find a couple of potential sweet spots in a ladder test given sufficient number of loads. A true “sweet spot” is the point the rifle doesn’t care about the powder charge weight or resulting velocities, as long as it remains within a certain range. The result of the ladder test technique is simply to pick a charge in the middle of the sweet spot group charge weight range. The selected load should be tolerant to minor variation in powder charge weight & other load component variations.
Once the potential sweet spots are determined then load up 10 identical rounds or so with that powder amount for each potential sweet spot & head back to the range to see which one results in the best accuracy. So in a couple of trips to the range you’ve identified the best bullet/load combination for your rifle.
For a lot more details & better description of ladder testing, including the benefits, see the following link: https://www.6mmbr.com/laddertest.html
Wayne