Need Help with Velocity/Pressure Spike.

[archp625]

I need some help again. I have 126 rounds through my barrel. I cleaned the barrel 86 rounds ago.

I did a pressure/velocity ladder. Figured out where my node was.

Next I loaded for 3 shot groups in the ladder test. I did notice a 60 FPS increase when I did this. Still not a big issue. No hard bolt lift and no swipe on the case.

I'm shooting a CA Ridgeline in 6.5 PRC, 147 grain ELDM 0.020" off lands. Reloader 26 powder And Fed 210M primers. The powder charge is 54.7 grains at 2950.

I loaded 10 rounds of what I found to be the ideal load so I could shoot two 5 shot groups, one to see what size group and to get my final ES and start loading more at that for distance.

Everything was great shots 1-5. Es was 7. Shot 6 was 22 FPS fast than 5. I thought that's weird. Maybe something I did on that charge. Shot the 7th 5 FPS faster than the 7. Shot 8 - 9 and started getting a swipe. And climbed 50 FPS faster than the first 5. I didn't shot the 10th. Something isn't right. It climbed to 3000 FPS with swipe on brass.

Here is a picture of my 5 shot group before shot 6 went wild.

What are your guys thoughts?

The only thing I can think of is either one my barrel speed up quiet a bit or I need to clean really good and my pressure/velocity will go back down.

 

[SilverbulletMAG]

On the shots that were faster, did you maybe keep the round chambered longer between shots? i.e. cook the round leading to more velocity and higher pressure? Or barrel and things just heating up in general? RL26 is said to spike pretty quickly over 85 degrees.

 

[archp625]

On the shots that were faster, did you maybe keep the round chambered longer between shots? i.e. cook the round leading to more velocity and higher pressure? Or barrel and things just heating up in general? RL26 is said to spike pretty quickly over 85 degrees.

I would say not any longer than the first five or what I would do in general. I did let it cool down after the first 5. I have shot all the shots between 43-62 degrees.
I think my barrel has just speed up and I need to redo my pressure/velocity ladder.

 

[Mram10us]

I'd be surprised to see the barrel speed up in a 6.5prc after 126 rounds. Any borescope to check for carbon ring?

 

[Lefty7mmstw]

I'd be surprised to see the barrel speed up in a 6.5prc after 126 rounds. Any borescope to check for carbon ring?

Mram10us hit the nail on the head... 86 rounds on an overbore like the 6.5prc is a bit much.
6.5 prc is a rather fast stepper... I would say you (the OP) are fouling and need to clean. I would also say you (the OP) need to back down a few percent if you are on the edge enough that a bit of extra fouling sends you over the edge on pressure. I've got a buddy running a 300roy with 220 sierra's and 7828; he only cleans when the groups fall off (or he remembers it's been a while- usually my prodding as to whether he's cleaned his rifle this year)... He's never seen a high pressure case from fouling or high temperature. I set him up doing 2750 fps with his 220's even though he could have gone 100 fps faster; the thing is a tank and won't puke no matter the conditions now.