New Rifle Pressure Questions

[erle1139]

I recently purchased a Christensen Arms Ridgeline in 300 wsm. Doing their recommended barrel break in of 50 rounds, I bought a 20 rnd box of 165 Norma Oryx, a 20 rnd box of Armscor 165 NAB, and I loaded 10 rnds for a pressure test for future load development. I followed their break in procedures, shooting two 3 round groups, then cleaning. With the first box of factory Norma Oryx I noticed pressure signs of sticky bolt and ejector marks. The next 20 Armscor rounds with Winchester brass had no issues. I loaded the 10 rounds for pressure test off the Hodgdon data center for Winchester staball 6.5 powder with new Norma brass, 180 gr Swift Scirocco .030 off lands using ogive measurement, CCI 250 Magnum large rifle primer. Hodgdon data uses the 180 scirocco and shows starting charge 61.5 gr (2,720 mv) and max charge 68.0 gr (3,019 mv). I loaded the following for the pressure test and immediately had stiff bolt (worse than the factory Oryx) and noticeable ejector marks and primer cratering on all loads:

1. 64.8 gr, 2975 mv
2. 65.2 gr 3012 mv
3. 65.2 gr 3029 mv
4. 66.1 gr 3039 mv
5. 66.5 gr 3069 mv

i stopped after the fifth round. Powder was measured on my Franklin Arsenal Intellidropper that I use for other loads and velocities were measured with magneto speed chrono. What could my issues/causes of factory Norma having pressure and loads more than 3 gr under max having pressure issues and high velocities?

 

[jdubrr]

I had a similar issue with my Ridgeline in 300 PRC, after break in I started to do some load development and got pressure signs early. Turns out the rifle had developed a carbon ring after only about 30ish rounds. Boretech C4 took care of the problem. Did you clean the barrel good after the break in? You might have a carbon ring too?

 

[erle1139]

I had a similar issue with my Ridgeline in 300 PRC, after break in I started to do some load development and got pressure signs early. Turns out the rifle had developed a carbon ring after only about 30ish rounds. Boretech C4 took care of the problem. Did you clean the barrel good after the break in? You might have a carbon ring too?

I cleaned it exactly like their manual says, using Barnes copper solvent. ran dry patches til they came out clean. I'm only 45 rounds into their 50 round recommended break in. I don't think that would explain the pressure signs (bolt stick, marks on case head) on the very first 20 rounds with factory ammo though? I'm by no means an expert reloader. While I've shot a ton of rifles with factory ammo, this is only the 3rd rifle I've loaded for (1st new rifle) and never had these issues.

 

[rayporter]

carbon rings are bad but i dont think thats your problem.

 

[erle1139]

I tried inserting a bullet into my fired brass. In the fired Norma factory loads I'm not able to to get a bullet in. In the fired Armscor Winchester brass I can freely insert, in the fired new Norma brass I loaded, I can insert a bullet, but it has a little resistance. I did full length size and chamfer the new Norma brass with an RCBS full length die before loading the 10 rounds.

 

[Trippy]

I tried inserting a bullet into my fired brass. In the fired Norma factory loads I'm not able to to get a bullet in. In the fired Armscor Winchester brass I can freely insert, in the fired new Norma brass I loaded, I can insert a bullet, but it has a little resistance. I did full length size and chamfer the new Norma brass with an RCBS full length die before loading the 10 rounds.

Just to fill my curiosity, you have a tool to measure the wall thickness differences?

You didn't happen to measure MV speeds of the factory loads did you?

 

[erle1139]

Just to fill my curiosity, you have a tool to measure the wall thickness differences?

You didn't happen to measure MV speeds of the factory loads did you?

I just have a set of digital calipers, which from what i've read is not a reliable way to measure wall thickness? and no I didn't measure the factory load mv unfortunately.

 

[B23]

Measure the case capacity in water to the very top in the Norma brass and Winchester brass. It wouldn't surprise me if there is a fairly large difference in case capacity between the two with the Winchester brass being the bigger of the two.

Smaller case capacity will show pressure sooner.

 

[Trippy]

I just have a set of digital calipers, which from what i've read is not a reliable way to measure wall thickness? and no I didn't measure the factory load mv unfortunately.

It's not perfect but it's something to see if there is a big difference. Water method works too like @B23 wrote if they have primers still in them or you have the plugs available. Guess a last method would be load a dummy round of each brass with same bullets then measure the OD of the necks.

 

[MThuntr]

Looking at the info on Hodgdon and the info you gave, I'd guess that it is the capacity of the brass as suggested. You reached way over max at 1.5 grains lower than book max with similar velocity. I'd suggest starting over with Hodgdon's min (61.5) and work back up to a safer max.

You could be in the same boat as I am with my 300WSM. My chamber is on the tight end of SAAMI and all factory ammo was too hot. My rifle is basically a spicy 3006 which is not why I bought it but it does kill things.

 

[JakeSCH]

Christensen makes tight chambers and I think this comes up a lot. On my PRC it actually made swipe marks when closing the bolt, 1x fire brass had zero problems.

 

[erle1139]

Thanks guys, I'll definitely check the case capacity of each since I haven't deprimed any of them yet.
@mthuntr I load my buddy's 30.06 for him and he's getting 2800 fps with a 180 gr NAB over RL 17. When we were both shooting at the range yesterday and I started having these problems, the same thought you mentioned crossed my mind...a "spicy 30.06"...but in my case minus the "spicy".

 

[erle1139]

Christensen makes tight chambers and I think this comes up a lot. On my PRC it actually made swipe marks when closing the bolt, 1x fire brass had zero problems.

That's good to hear. I'll start at minimum load with some once fired Norma and work my way up again

 

[Cahunter805]

If you can’t insert a bullet into your fired case I’d think you have a combination of a tight neck chamber and thicker necks on the culprit brass.
As a reamer wears out it begins to cut chambers that are on the “tighter” side also. Not sure how often Christensen replaces them either.

I would FL size the Winchester brass and load it with your pressure test again and see what those results are.

 

[Lawnboi]

Sounds like the chamber on a Christensen 300 I had. It’s gone now.

 

[B23]

Not being able to slide a bullet in the neck of a fired case isn't always an absolute. I have some that I can and some that I can't and the ones that I can't I know it's not because they're lacking neck clearance.

 

[erle1139]

i checked case capacity with water, 2 different empty brass of the factory Norma Oryx, Armscor winchester brass, and new Norma brass i loaded:

factory Norma - 79.6 gr, 79.5 gr brass length 2.091, 2.089
new norma - 79.2, 79.1 brass length 2.097, 2.098
winchester - 81.8, 81.6 brass length 2.093, 2.097

normas weighed about 20 gr more empty than winchester

I’m not sure how significant that is.

i also measured neck wall thickness with my calipers
factory and new norma were .017”
winchester .015”

I appreciate everyone’s input and learning

 

[rayporter]

i dont believe 20 gr. is a big deal on that case. mmmmm winchester brass is 2 thou thinner and has no pressure? and it holds more so it is thinner.

you need a good mic and you need to mic loaded rounds. in the end loaded is all that counts anyway.

but some of those cases not accepting a bullet is something to think on. especially since you have plenty of pressure. if it was a light load with no pressure signs things would be different.

i know you dont have the stuff to turn necks but that is what i would do to a few to prove the necks were not too thick for the chamber.

it is beginning to look like you need a chamber cast.

 

[CCooper]

Christensen has been known to make a “tight barrel” on occasion as well.

 

[Cahunter805]

Not being able to slide a bullet in the neck of a fired case isn't always an absolute. I have some that I can and some that I can't and the ones that I can't I know it's not because they're lacking neck clearance.

Please explain this? Brass will always expand until it hits the chamber walls/neck walls. There will be a little spring back but usually only about .001.