I wonder if the bullet is having nose slump issues past a certain velocity/rpm.
I read on Nosler's site that the ABLR is supposed to open up down to 1300 fps impact speeds. That indicates to me that the nose area is significantly softer than the original AB.
The smaller diameter (.277") ABLR might be more prone to something like nose slump since it has less mass in that ogive.
The sudden and total loss of accuracy seems to me like more than barrel harmonics.
As I was reading this, the first thing that came to mind was, How could a polymer tipped bullet have these problems but then something came to mind that happened to me about 4 years ago.
A customer came up to the shop to do some load development for a custom 300 RUM I had built for him. He was shooting the 200 gr Accubond. Once I got him set up I let him loose loading some test rounds as I did some work in the shop.
After he loaded a few rounds, he came over and asked why the tips kept breaking off the bullets........ He handed me two of the three rounds he had loaded and the white tips were broken off.
I had never seen this before. Went back and I loaded up 5 rounds and one of those tips came out as well. Well, we got a batch of 20 rounds loaded up to test and headed to the range. When he ran the rounds out of the magazine, the bullet tips would hit the feed ramp and break off.
Now, I had used thousands of Accubonds and never had I seen something like this. Even working the bolt very slowly, at least 50% of the tips would break off. We went back to the shop and inspected these 200 gr Accubonds. It seemed that the plastic just under the tip of the bullet, the portion that was in the bullet nose had dissolved for some reason as it had turned into a white powdery compound, not hard polymer.
The customer had brought these bullets with him which he had bought from a local sporting good shop. I grabbed a box of my personal 200 gr Accubonds and we started over, this time without a single problem.
The next day I called Nosler up and explained to them what problems we were having. It was obvious that the Nosler tech knew exactly what I was talking about. He asked me how many boxes I had that were bad and wanted my address. I asked him what was causing this and he said that they had a problem with the flux chemicals they were using. Apparently they used to much and the flux, which bonds the core to the jacket had pressed up around the polymer tip and actually dissolved it causing them to weaken and break off.
Now, we never did shoot any of these 200 gr Accubonds with the bad tips so I cannot say if this would cause a serious accuracy problem but I can say that the meplat on these bullets with the broken tip was HUGE and inconsitant. One would have a partial piece of polymer sticking out, some were broken off even, some were huge HP in appearance. I can see where it could cause some consistency problems.
Not saying this is the problem but hearing the mention of nose slumping made my mind go back to those problems with the Accubonds.
Also want to say that I have seen this in one lot of 160 gr 7mm Accubonds as well but those were the only two lots of Accubonds I have ever seen a problem with.
That does not explain the problems with the Ballistic Tips that the OP was seeing as there is no flux used in those bullets.
If these bullets do not have any structural flaws, they WILL NOT have any nose slump. How do I know this, because I have fired the 120 gr 7mm bullets over 4000 fps, the 140 gr Accubonds to over 3800 fps with no accuracy problems of any kind, in fact, both held 1/2 moa in group size.
Have also fired the 130 gr Accubond in 270 at well over 3800 fps and the 140s at over 3700 fps. Compared to what the OP is pushing the new Accubond, his loads would be a day on the beach for those bullets compared to what I have tortured them at.
If there is a flaw in the bullets though, anything could be possible.
