In my 26", 1-14 twist Hart, with minimal freebore
55g Nosler ballistic tips
IMI cases(tough)
CCI BR-4 or Remington 71/2 (tough primers)
26.0g of N135
very tiny groups
right at 3500 fps
No pressure issues other than cratered primers and I fixed that issue by sending the bolt to Greg Tannel of Gre-Tan rifles to get the firing pin bushed
I am not the only one that shoots this load, either.
This is a bolt gun load and you should work up to that load
things that increase pressure:
1-9 or tigher twist
going to a flat base bullet with more bearing surface and/or different bullet
Different lot of powder
different barrel that could be a tighter bore
Different brand of brass with less powder capacity than IMI
I have no problem shooting the above load in my rifle. In my 223 AI that has a 27" 1-12 twist, I shoot the 55g Noslers at 3650, bushed firing pin on that bolt also. These are real world velocities checked with an Ohler 35P that is two chronographs.
N133 with the 50g(3600fps) and N135 with the 55's are a world apart in accuracy and speed compared to probably the next best powder which would be toss up between H335 and Benchmark.
Be advised, work up in your rifle with caution, and if you have a 1-9 twist...all bets are off, that twist really jacks up the top end pressure on loads like this causing it to "spike" quicker. I had a 22 PPC, 223 AI, and 223 all with Hart SS bbls with mimimum SAAMI Match chambers with minimal freebore in 1-9 twists and they all caused pressure spikes quicker than the 1-12 and 1-14 twists with 50 and 55g Bullets.
What happens on the pressure spikes are as you would suspect, the bolt is very hard to open(Scuffed case head), cases with not so tight primer pockets blow the primers out(then you have to try and find the primer's anvil somewhere in your action along with the primer cup), not to mention the flyers.
So, work up your loads carefully, and take into consideration super hot weather if you shoot in that kind of weather(don't leave your ammo in the sun).
Good luck