Please help: Question regarding pressure signs, barrel breaking in?

[spladi]

Background: I have a newly re-barreled Christensen Arms 280AI with approximately 145 rounds through it. I completed the 50 round barrel break-in as they recommend. I have 100 pieces of Pettersen brass and fireformed all of it using older Hornady bullets (half was used for the break-in). Having all brass once fired in new barrel, I began load testing. I loaded 4 different bullets (4 groups of 3 each) with powder increases of half grain between groups. Fortunately of the 16 groups, every one was sub MOA with 5 being sub .5. I had no signs of pressure and velocity was about what I expected. Obviously I was very please with these results and the next time out I loaded up more groups with the most promising from the first session. I also moved up in powder chares hoping to maximize velocity. The bullets I was using were all mono's ranging from 140-152 (yes, I live in the commie state). The two powders were H4350 and RL23. The next trip to the range was surprising, the rifle was still shooting very good groups, but with the same loads as the week earlier, several started showing signs of pressure and velocity was up between 55-95 fps. I was unable to try several of the hotter loads as I was hitting pressure.

The outside temp was actually 10-15 degrees cooler than the first trip out and nothing else was changed with the loads. The brass was also all once fired?????? I'm guessing the barrel must be smoothing out and getting broke-in. What do you guys think, am I missing something? Obviously I'm going to back things off and avoid pressure, will this get better or worse as the brass gets more firings in this barrel? For info the pressure signs were very slight bolt lift and slight ejector marks. Neither were significant, but I don't like pushing it. Any advise appreciated

Possibly case lube on the outside of the case.

 

[Rflshootr]

With it being an Ackley, I doubt it, but check the case length to make sure you don't need to trim your brass.

 

[coop2564]

Could be copper build up. New barrels sometimes foul up quickly. Did you clean the barrel between shooting sessions or leave it fouled? If you were cleaning between groups per breakin. And now stopped it maybe truly not broke in yet and copper fouling on you?

 

[Bassnbow]

Could be copper build up. New barrels sometimes foul up quickly. Did you clean the barrel between shooting sessions or leave it fouled? If you were cleaning between groups per breakin. And now stopped it maybe truly not broke in yet and copper fouling on you?

Yes I thoroughly cleaned between sessions and the barrel is cleaning much quicker now that it has 150 rounds through it

 

[Mike Matteson]

The neck might be a little thick. You have gotten some great input from above. Glad to see that you are annealing too.

 

[coop2564]

So if its none of the things mentioned. Did you load this later set of rounds after the first set or were they loaded at same time? Could you of loaded this later set to a hotter load than 1st? might pull a bullet and double check.

 

[Bret GRAVELINE Graveline]

How are you cleaning the barrel, my first thought is you may have excessive Copper building up in the bore, I got my bore scope in the early 90's, it was not uncommon to find severe copper fowling in bore that I felt was clean, copper can become work hardened in small pockets along the bore while this does not always affect accuracy it can cause pressure spikes, did you get pressure signs as soon as you started shooting or did the signs start showing as you got further in the shooting process?