how much jump is to much for an AR?

[GRH]

I don't know that it would be a problem unless it's short enough that it would come out of the case, except for accuracy reasons. Bullet jump will "effectively" increase case capacity and generally lower pressure. The bullet jumps against the lands and stays there until the powder develops enough pressure to start engraving and push the bullet down the barrel. So it's artificially creating a longer case with greater capacity.

Using GRT the projections sometimes don't coincide with real world chrono results, adding the measured bullet jump to the model often times brings FPS within exceptable percentage of the chrono results.

So yes bullet jump does have an effect, you just need to find the closest node that still fits in the mag and feeds reliably.