On a standard chamber, no , besides neck tension may affect accuracy and velocity a bit, it will not cause pressure spikes unless the case is long enough the case mouth enters the leade and camming the bolt jams it into the throat binding the bullet.
It can happen with tight necked chambers if the brass is not neck turned.
Brass is very soft, it conforms to the chamber before the bullet gets fully into the rifling.
RR

The wife has a Krieger barrel on her rifle. which she reloads for. This does not mention the the pressure spike, but worth reading.

If the shoulder on your brass is pushed back too far, at ‘best’ you will have accuracy issues, at ‘worst’ you can have a failure to extract or failure to fire because the cartridge is pushed too far into the chamber. Or, it could fire, stretching the brass too far, too fast, and you could split or separate a case. If it is not sized back far enough for the chamber in your rifle, you can have a failure to feed or completely close the bolt. Depending on the length and the rifle type, this could result in firing out of battery and can be extremely dangerous!

http://www.kriegerbarrels.com/Proper...246-wp7875.htm

Well Uncle, I've been to several other reloading boards to see what others had to say... Every one of them said that your right... They said that if the case chambers without any problems the shoulder shouldn't be causing a pressure issue.

That's also one of the issues the guy that was teaching me checked, and there were no issues when loading, or extracting the cases.

Some have suggested that there may be some issue with the chamber itself. Which wasn't something that my gunsmith considered, or at least never mentioned. If that was the case at this point I'll never know because I've since had the receiver/barrel/bolt squared, and the headspace was set to the minimum factory specs. Well, it's actually .001 under the factory specs.

The work was done by the same gunsmith, and he never said anything about any chamber abnormality's, but he did have an apprentice, so I don't know who did the initial work. Or even if the apprentice did all of the work, and my gunsmith checked it at the end.

At this point I'm left scratching my head... I physically went threw all of the steps I described in the other thread, And I personally witnessed the change in fps on the chrony as I went threw the steps. I also saw the growing heaspace on the cases with the precision mic.

I'm thinking that I'll have to do some back tracking, and re-checking. I've not gone threw those steps since I've had the chamber squared. I figured that I had found the issue, and have since always fully resized the cases after the second firing.

Edit: I should also add something that I re-learned in my research... Some bullet, and powder manufacturers don't put out any load data for the 7mm RUM because of the pressure issues with the cartridge. Though I haven't found any info yet as to what was causing the problems.

At the end of the day all that matters is that you have solved the pressure issues and ended up with good and safe loads. All rifles are different and if anyone ever really understood the all of the mystery (not me) they would shoot .00" aggs (certainly not me).

Good hunting.

I am wondering if you have a tight bore or tight chamber. I have run into this before with a few of my rifles. The chamber is match, and the bore, instead of being .277 was actually .272. This caused blown primers and massive case swelling on Speer book upper end loads. Not max loads, but getting up there. The starting loads were pretty warm in this instance. Try neck turning and maybe try a chamber cast and see what that tells you. Only other thing that comes to mind is that the neck is being pushed into the lead and being crimped into the bullet, which will definately cause massive pressure problems. Hope that you get this problem solved, because an explosion 4" from your face is not a good thing.

Yes, give us some specs, is it a factory barrel? If not is it cut or button rifled, is it a a custom chamber cut to min. Specs?.
Let me give you an example, my 7 AM with lapua brass goes from 3510 to 3630 fps from the first to the fifth loading of the brass, if you load it the 6th time the brass is so work hardened it springs back so much, they chamber hard and the bullet slips in the neck, after annealing they are back to 3510 with .02 neck tension. Most probably spring back is your pressure problem. Many rifles chambered in high intensity rounds have this problem. Brass is about 85% copper! which gets brittle as you work it! learn to anneal.
RR

Ld, your original post stated that you discovered this problem when you chronographed your loads. Basically, a chronograph measures the elapsed time that the shadow of the bullet makes between the sensors in the chronograph, then it converts that et into velocity.

In a perfect world, the velocities of each shot, everything else being equal, would be the same, and every bullet would fly into the same hole. Unfortunately, we don't live in a perfect world, and the shot to shot velocities vary, for whatever reason.

I don't recall that you ever said what the velocity deviations of your loads were. A velocity deviation of 50 fps is not that unusual in some loads. I normally shoot several .22 lr shots over my Chrony at the start of each chronograph session. I have recorded as much as a 100 fps difference in the velocities of .22 lr ammunition from the same box, from the same manufacturer, and shot from the same rifle, at the same chronograph session.

How much were the velocity "spikes" that led you to believe that you had pressure problems?

I was trying to dig up the data... I finally gave up... The info was from 2006 when I started loading, and I no longer use the powder, I was using then, H1000, and H870, which I still have some of, but is no longer available. I was also using Nosler partitions at the time which I also no longer use.

If I'm remembering right, which I believe I am, the jump was 200+ fps. with the same powder charge, and seating depth.

It initially happened using the H1000 with my friend. After I bought my own chrony I got cocky, and had the same thing happen using H870.

Wasn't the shoulder, was lack of neck tension, brittle brass sprung back, so you bumped the shoulder, prolly about .005 so the brass would chamber, but the neck was still too large so at almost no pressure the bullet moved foreword jammed the lands and hung there till the pressure built high enough to send it down the barrel, have saw it before.
RR

Interesting theory. One of the things I wanted to try based on my early readings was to figure out a seating depth by setting the bullet close to the lands.

We tried to determine that by putting a bit of a dent into the neck of a fired factory case. We then slightly seated a bullet into the case and chambered it. We couldn't get the bullet to move no matter how far out we tried to set it... To quote a statement I read early on from a loader that experienced something similar with a particular rifle/cartridge combo, this rifle/cartridge seems to have an "epic free bore". The comment of course pertains to the distance the bullet travels from the time it leaves the case, until the time it hits the lands.

Based on my own measurements, I've shortened that distance by about .005 since I've had the action worked on.

So if I'm reading you right RR. The large amount of powder I'm using with this cartridge is affecting the neck of the cases. Heating up the neck, and making it brittle, therefore not gripping the bullet as it should.