Re: First time doing a ladder test...
Here is an explanation of my way of doing a ladder step by step.
My methodology is after I have done basic research to determine, bullet,primer, and powder combo I want to use/test for each ladder. Now this might be many reloading manuals, others recommended loads, Qload, etc, but I find a "suspected" powder, primer, bullet and case and then work a load that is normally about 2-3 grains below max to 1-2 grains over at .2 to .3 increments depending on case size. Normally this is 15-25 bullets only with 4-5 extra of the lowest charge for initial zero on the other target.
I use the smaller increments as I am looking for a node that often is only .5 to max 1.0 wide and this gives me a easier way to determine it. If you go .5 grains you can jump right over a node and never see it unless you are in the 338 lapua size cases.
1. Shoot ONLY in early morning or evening in no wind conditions.
2. Minimum of 300 yards prefer 400. I have found that seems to be the ideal distance for enough vertical dispersion as the bullets walk up and close enough to see each separate bullet impact with good spotting scope on white target. Shorter makes it to difficult to determine impacts and longer makes it too difficult again to see any impacts. You are wasting your time and bullets at 100.
3. 35P chrono is used. MV grouping will match the accuracy nodes.
4. I have a minature paper target at bench to plot each round and another sheet to write down each MV for each round. That way I do not lose track of any bullet shot as each is numbered on plot sheet and anytime I go down range to verify impact. I also mark each shot on the 35 P paper as it is shot.
5. Minimum of 1 minute between shots from starting dirty bore, I usually zero at that distance on another target at the side to confirm accurate zero for bottom of ladder target which is normally large plain white cardboard with 1" aiming dot near bottom. I use .3 grain for most magnum cases and .2 for smaller cases as increments. Anything 338 Lapua and above you can do .4
6. If I am not 100% sure of bullet location, I either walk down or I often use use colored magic markers(4-5 colors) alternating on bullet tips which show up on target. No they will not vary impact points on target. That is used all the time at 1K BR to identify any crossfires on your target.
7. MV as you go up will be linear (ie roughly same FPS each bullet) until you hit a node and then it tends to decrease dramatically for that 2-4 shots and then jump linear again. You will see 3-4 rds with small MV variances normally in the node and then jump dramatically again. You can see on a magnum a jump of 20-25 FPS and then 3-4 bullets around 6-8 fps along then it will jump again back to around 20-25. This is only an example, not always.
Here is the real key: Use a combination of bullet AND MV grouping confirms node and is usually easy to see when you compare the two, not just grouping!! You will have multiple bullets with similar vertical impacts and very low dispersion on MV.
8. I pick the middle of the node, shoot groups to confirm basic accuracy and ES, SD nodes. I normally find 2 mabye three nodes, and one will be in the MV range I am looking for. Many times the top one is at the starting of high pressure point, so I often do not use that one. By using the middle of the node for powder, gives me enough variance on temps and other factors that I am not out of the node on any given day. I do not focus on the lowest solely on ES/SD. Once I find a node then it is an "acceptable ES/SD and tight grouping that is confirmed. I normally shoot for single digit ideally but low teens is acceptable with the grouping.
I determine pressure by stiff bolt for the top end and case head expansion measured with a blade mic, primers (but not always accurate as some are softer than others) etc. It is a combination of everything that leads me to determine I am at high pressure. I take it until is see firm signs of pressure and then stop even if I have not shot all the shots IF I am at an acceptable MV and see good nodes.
9. I then try groups at various seating depths at my best grouping and see what depth it likes. For a single shot gun, start .010 in the lands and come out. Magazine gun, start at max magazine COAL and in from there. I start .010 in, come out at .030, .050, .080 and .120 IF a single shot gun. One will be much tighter and then work in between to find the place normally down to .010.
10. If the gun will not shoot 1 MOA, that makes shooting a ladder a little difficult as you do not know what is the real vertical or 3-4MOA grouping "inability", so IMO it is not for every gun.
11. If a gun will not shoot with all this, then another ladder with another powder or bullet combo.
I have proven this is repeatable and capable of taking a new rifle to winning in competition in under 50 rds fired.