Difficult ladder

[Keith Glasscock]

Here is a ladder test I shot today at 300 yards (most range available). As you can see, the entire 12 shot, 2.2 grain ladder is 2.5" high and just under 3" wide. Conditions were good with some mirage and winds from 1-3 mph from the left. No attempt was made to correct for wind, but every attempt was made not to shoot ina boil (the boiling was 1/2" or so in image movement).

This is my F/TR rifle and it was shot, prone, from the pod.

I have an idea where the node might be, but I was hoping for a second opinion!

 

[Jay Christopherson]

I don't do ladder tests, so my opinion isn't expert, but it looks to me like you want to be somewhere between 41.5 and 42.1 grains.

 

[mikecr]

I don't see anything useful there.
Something is masking your tune -like bad seating depth.
Possibly poor primer striking.

I would find best seating with one of the mid loads, and return with this to ladder testing.

 

[Terry]

41.5 to 41.7 looks good.

 

[trailrider121]

I don't do ladder tests, so my opinion isn't expert, but it looks to me like you want to be somewhere between 41.5 and 42.1 grains.

Plus 1. I think i would work somewhere around that area.

 

[FroggyOne2]

41.5 to 41.7 looks good.

I concur, after that, seeing that the heavier loaded rounds starting to print lower means you might already be beyond pressure..

 

[Keith Glasscock]

Thanks everybody!

I didn't mention the pressure. The primers are absolutely flat at 43.1 I had a slightly increased bolt lift at 43.3, so both of those are out. (43.1 doesn't group well - tried it because it was OK in the old barrel) I was thinking that 41.7 was better than 41.5 because the impact point of 41.3 was a bit lower.

It was 45-50 degrees outside, and I started with 16 rounds through the barrel. It now has 35. I'm thinking that I don't want to be too high up in the node. Average match temperatures here are above 60, 85-90 on warm days, so I thought I'd give myself some room in case it started making more pressure in the summer.

My plan is to shoot groups at 41.7 and 41.9. If the groups are acceptable, I'll start working the seating depth to tune the load in. I'll also drag the chronograph out so I can get a feel for how fast they are going and if the ES is acceptable.

FYI, the powder is "Varget", but this lot (4920) is so fast that it acts more like H4895 than any Varget I've ever had before.

Mikecr, I agree that the info is "dirty" The mirage was bouncing the aim point around a bit, and all I had to do was chase the mirage image up and wham, 1/2" high. In addion, this was shot off of my Sinclair bipod, and it just doesn't do the same things as a front rest does. On the other hand, it is part of the rifle and I think that tuning should be done with it rather than without. From 41.5 to 42.3 I had .910" of vertical and a horizontal of 1.333". The "group" measured 1.345". Considering that the powder charge change alone should have accounted for 45 fps difference in velocity, I feel pretty good about the vertical there (JBM predicts 0.8" due to velocity). JBM also predicts about 1/2" of windage per mph of wind. I intentionally ignored the wind in this case. Trust me, the shots were not all shot in the same condition. While all of that is great on paper, I agree that the seating depth is not in tune. These are hybrids and while they aren't that hard to tune, they definately tell you when they don't like it.

I figured that this test would do two things for me, first, and foremost, it allowed me to determine the safe range of charges. Second, it gives me someplace to look for the node(s). I intentionally selected a powder charge range that would give me about 125 fps difference. By my way of thinking, there would have to be a node in there somewhere.

 

[rain164845]

I would load up 42 grains and start messing with the seating depth. Shoot 3 shot groups at each depth, then go from there.
I would bet you'll have your load in no time. Then if you want to revisit powder charge, do it with 3 shot groups. Then run an extended string to verify.
That's my method and it involves comparing 3 shots of each changed variable instead of one shot of each changed variable the way the ladder does.
And with all the national championships I have, my method is proven. (My national championships = 0)

 

[Keith Glasscock]

I knew this wasn't an easy one to read, so I decided to try 41.7 and 41.9

My wildest dream was that the thing would shoot both well, and I could get on with the seating depth - not to be. After firing 5 foulers, I set to shooting groups. 2 groups of 41.7 and 1 of 41.9. (these were 5 shot groups - 3's don't tell the story)

All shooting was done at 300 yards.

The 41.9 group printed in good vertical (less than 1/2") with the exception of the third shot. It flew left and low to make the group about 1.25". It wasn't me this time...

The groups of 41.7 were just plain unstable. They exhibited 1.6" of vertical with bullets hitting either at the top or the bottom (none in the middle) The group center also wandered vertically between the groups. I'm thinking that I'm in the barrel swing with this load so, out it goes.

While I couldn't see what the group looked like from the firing line, I thought that the rifle felt better at 41.9. It is a little hard to explain, but I felt like the pressure was very low at 41.7 and it didn't feel consistant. I don't think 41.9 is the node either.

With the 41.9 printing a little better, but still throwing a low flyer, I'm thinking of warming up a little. I'm going to try 41.9 (to verify today's result) 42.0 and 42.1

If nothing jumps out as good, I'll just start the seating depth series with whatever I have going for me.

My last barrel didn't come to life until 200 through the tube. It was an honest 1/2 to 3/4 MOA until then. After that it went to the 2's. Is it possible that I'm just fooling myself trying to find a load with 50 through the tube?

 

[RDavies]

There is a fair chance your new barrel will get a velocity increase between 100-200 shots or so, so your powder load might need changing soon. Trying a few different seating depths until you know if it much prefers jammed over jumped or vice verca. Then you might get more meaningfull info from a ladder test or 3 shot groups.

 

[liltank]

I don't do ladder tests, so my opinion isn't expert, but it looks to me like you want to be somewhere between 41.5 and 42.1 grains.

I concur.

 

[Keith Glasscock]

I'm trying to use the old noggin instead of my normal method of blasting away until I bumble onto the right load.

Here is the idea - shoot holes in it if it doesn't make sense.

I'm taking an arbitrary load and giving it a go - 42 as rain suggested (right in the middle of the 41.5-42.3 flat spot in the "ladder").

I'm going to shoot 3 shot groups at full jam with .001" neck tension, and then move back in .005" increments until I'm only .005" into the lands. I'm going to skip just touching (I think you all would appreciate that I don't want to be chasing the lands inthe middle of a match) and then .005" jump to .015" jump. Any deeper than that and the bullet bearing surface will extend through the neck-shoulder junction.

Here is a question: Has anyone out there had luck with hybrid bullets into the lands or jammed?

I know several people have stated that they weren't able to make them shoot in the lands, but I wonder if that was more because the load was already a touch hot. I also know of people that seem to get almost any bullet to shoot without jumping them.

What do you all think?

 

[280man]

All my experience is with 7mm hybrids and Bartlein barrels. I would skip trying to jam them just load them .010-.015 off the lands and leave it alone. Play with powder charge, primers, neck tension, whatever but in my opinion you are spinning your wheels messing with seating depth.