Seating depth affect pressure

[I hunt_dm3]

I am working on loads for my Christensen Ridgline in 6.5 PRC and have been getting pressure signs on multiple different powders before reaching book max. I am shooting Berger 156’s and seating them to 2.950 coal. I am using Lapua brass and 210M primers and have tried Retumbo, H1000 and N570. All are producing cratered primers at mid to max book loads. Could seating depth play a part in that?

 

[Pharmseller]

Short answer, yes.

Pressure will be higher if the bullet is jammed into the lands. Pressure will decrease as the bullet is seated deeper, but will begin to increase when the combustion chamber gets small.

What does the chronograph say?




P

 

[rayporter]

think Weatherby

 

[I hunt_dm3]

Short answer, yes.

Pressure will be higher if the bullet is jammed into the lands. Pressure will decrease as the bullet is seated deeper, but will begin to increase when the combustion chamber gets small.

What does the chronograph say?




P

I got higher speeds when the bullet was seated deeper and and more pressure signs, and greater variance in speeds.

 

[Axlrod]

It could be a tight bore. Christensen has had a few like that over the years.

 

[Pickettpuncher]

What do your primers actually look like?

 

[I hunt_dm3]

What do your primers actually look like?

I don’t have a picture but it is raised around where the pin hits, you can see it from the side profile easily. Also slight extractor marks on some and tight bolt lift on some. I find it odd because not all shots have tight bolt and extractor marks but all primers look the same.

 

[Pickettpuncher]

I don’t have a picture but it is raised around where the pin hits, you can see it from the side profile easily. Also slight extractor marks on some and tight bolt lift on some. I find it odd because not all shots have tight bolt and extractor marks but all primers look the same.

What you describe is fine as long as the primer edge is still rounded and not flat.

 

[I hunt_dm3]

I’ll have to double check but I believe they are still rounded.

 

[willfrye027]

My buddy’s Christiansen 6.5 prc makes all kind of “pressure” marks on the brass at low medium and high pressure loads. Same with my buddies Christiansen 7mm mag. I think the machining is rough..both are very accurate though.

With your gun I would just aim for a safe load at reasonable fps and not worry about some potential velocity left on the table. With that bullet I’m sure you will be above 2000fps impact at some pretty extreme hunting distances.

 

[SDHNTR]

What brass? Thicker brass will show pressure earlier.

 

[I hunt_dm3]

Lapua brass

 

[SDHNTR]

Lapua brass

Not surprising then. Book max just means where they hit pressure in THAT barrel, with the stated brass. Your powder lot is different, your brass is different, your barrel is obviously different. It’s unrealistic to expect the same results. So you hit pressure somewhere between mid to max… that doesn’t mean there is anything wrong. I have several rifles that hit pressure before any book. What are your speeds? That will tell you a lot.

 

[I hunt_dm3]

Not surprising then. Book max just means where they hit pressure in THAT barrel, with the stated brass. Your powder lot is different, your brass is different, your barrel is obviously different. It’s unrealistic to expect the same results. So you hit pressure somewhere between mid to max… that doesn’t mean there is anything wrong. I have several rifles that hit pressure before any book. What are your speeds? That will tell you a lot.

I get that my setup is different, and I do not expect to have the exact same results. But for the handful of guns I have reloaded for, I have never seen pressure issues at book max, I can usually squeak out an extra grain or two before seeing sings. The fact that I am at mid book is wild to me. My speed is good, I have dropped 3 grains and have only lost 100 fps with N570. With Retumbo and H1000 the speed is pretty bad with pressure signs, like 150 to 200 below states book speed. And I am not trying to chase speed, I am looking for an accurate load with moderate speed, would like to keep it in the 2900 range.

 

[I hunt_dm3]

My buddy’s Christiansen 6.5 prc makes all kind of “pressure” marks on the brass at low medium and high pressure loads. Same with my buddies Christiansen 7mm mag. I think the machining is rough..both are very accurate though.

With your gun I would just aim for a safe load at reasonable fps and not worry about some potential velocity left on the table. With that bullet I’m sure you will be above 2000fps impact at some pretty extreme hunting distances.

I am starting to wonder if it is a Christensen thing. It had to be sent in and rebarreled when I first got it.

 

[Pickettpuncher]

Cratered primers alone is not a good indication for pressure. All it takes is a slightly oversized firing pin hole. Ejector marks are concerning but I’ve noticed faint marks on anemic loads.

 

[bmart2622]

Whats the chronograph say? I have an ultra mag that hits pressure well under book max but its still pushing a 230 Berger 2950 fps. See what it does even if its not where the book says max is, maybe it will shoot well and produce the velocity you want.

 

[I hunt_dm3]

Whats the chronograph say? I have an ultra mag that hits pressure well under book max but its still pushing a 230 Berger 2950 fps. See what it does even if its not where the book says max is, maybe it will shoot well and produce the velocity you want.

175 to 100 fps lower then stated book speeds

 

[SDHNTR]

It does happen. I had a barrel like that. The chamber was tight and it annoyed me. It doesn’t exist anymore.

 

[The_Whitetail_Kid]

Same story in mine. Gets ejector marks no matter what load basically. Even on loads I know aren’t pressure. H1000 and H4831 showed this. I just shoot mine as is.