Pressure Issues

[SuperiorRifles]

I was shooting my 7mm LRM hunting rifle on Saturday, first shot of the day was starting with round count 100 from the new barrel. Shilen 1-8 twist, #5 contour, 27", 180 Berger VLD's, 72 grains of H1000, average MV of 3040 fps. Groups were fine as far as accuracy is concerned. 5"-8" groups at 700 yards and 6"-10" groups at 900 yards. The first 5-8 shots showed no signs of pressure, then 9-20 I was getting a sticky bolt lift. Brass showed a light flow into the ejector plunger hole. I have not had any problems with pressure up to this point. Why all of a sudden am I getting a spike in pressure? The temperature wasn't warn at all, morning started off in the 60's and warmed up to about 75 deg. What could cause this spike in pressure?

 

[people]

Your tube was getting hot. let it cool back down everything is fine again.

 

[SuperiorRifles]

Your tube was getting hot. With my 7mmSTW I can fire about 8 shots before the same thing happens to my rifle. When I let it cool back down everything is fine again. Since it is a hunting rifle I never fire any more than three shots before I let it fully cool down. I also tell anyone who barrows that rifle the same thing and tell them the story below.

Right before I swapped out tubes I had about 60 rds to burn up. I loaded and was shooting as fast as I could. I was able to get about 15+ shots before bolt lift was hard. When I had about 20 rds left I just hammered them out as hard as fast as I could. It went from hard to eject to very hard to eject to blowing primers.

I guess its possible. Didn't think I was letting it get too hot, no more than 5 shots in a row at most before cool down. So, are you saying even if I dropped my load down to 71 grains and still let the barrel get hot I will see the same results?

 

[22BRGUY]

I've had this happen in 22BR. Found out that if I shot over 20 or so rounds without cleaning, carbon build up in the neck/chamber area wouldn't allow the neck to expand like it needed to. I now make sure I get all of the carbon out when I clean.