New 33XC work up, confusing data

[Gregg C]

Took possession of 33XC custom rifle recently. Had components ready to roll, found lands, loaded up ten for pressure ladder.
New Peterson brass, FL sized.
250 CCI
250 gr Berger Elite Hunter
.020 off lands

Mr. Tubb shows 128grs H50 BMG at 3260(?), reccomends starting 4 grs lower and working up.

Shot 1: 124grs. 3177
#2. 124.5. 3140.
#3. 125. 3187
125.5. 3152
126. 3189
126.5. 3202
127. 3222
127.5. 3212
128. 3248, and pierced primer.
I have never used this powder before, and am some what puzzled. I expected the velocities to climb in a somewhat linear progression. What's the, in my opinion, wild fluctuations in velocities mean?
Am I seeing a node in 126grs to 127? Speed went up over all three shots, which should be a good thing, not down, and only 33fps. Or am I misinterpreting?
Using a Magneto Speed vx 3.
Would sure appreciate any input here.

 

[tim_w]

I do not have hands on experience with the 338XC.

How was bolt lift and head expansion on the 26gr-27gr?

Did you shoot for elevation check or just powder psi limit?

Personally, as H50 is a extreme line powder, on vel alone, I would investigate 26-26.5 gr. Just give that barrel time to cool between shots. Personally, I only do load dev on cases that have had a med psi fireform load first.

To find pressure limits etc I shoot one single case for all the loads reloading at the range. I know thats not possible for some people.

Did you have any other pressure signs @128 gr? Wondering if it's firing pin gap related?

 

[Gregg C]

Bolt lift was smooth all the way to 128grs, which was a little sticky. No head expansion.
Was only looking for pressure, and a charge to fireform brass, the target was only at 85yds.
It was perplexing to say the least to watch the speeds go up, then down.
Thanks for the input, I'm going to fireform at 126, and then delve more into the rest of the process.

 

[Gregg C]

Firing pin protrusion is .050