Carbon covered cases, but getting high velocity

[MikeMcCasland]

SO62 seems to be the powder your usung? https://www.lhs-germany.de/en/powder/smokeless-powder/lovex/s062/View attachment 1182852

Yes. That data is for a 140gr bullet though.

 

[243winxb]

it would seem the bullet is wrong for the slow burn rate powder?

 

[MikeMcCasland]

Looks like the Shooter's World powder passed. Any unfired ammo of same load available to pull bullets & weigh charges? Did all same load ammo have black stuff deposits?

By mechanical ejector - is this a spring loaded, blade like ejector that pops up into a slot in the bolt when the bolt is retracted to hit the back of the case causing ejection as opposed to a plunger type ejector located in the bolt face? I would not expect to see plunger ejector swipes or ejector slot swipes at 60K and lower pressures. I don't know how brass is ejected from your rifle.

If the pressures generated were in the 60K range, as per Hodgdon data, there would be little or no primer cratering unless the fit between firing pin & hole in bolt face was sloppy. Was the diameter of the hole in bolt face & diameter of firing pin measured? Little primer flattening would be expected with lower pressure loads but at 60K there should be a degree of noticeable primer flattening .

Getting into the obduration stuff - any comparisons of neck diameters between cases having black stuff and clean cases assuming equal neck wall thickness?

Hard jamming bullets into rifling would jump pressures but minor differences in seating depths should result in minor variations in pressure.

It kind of looks like the pressures shown in the Hodgdon data using Varget & 107 Si MK bullets up to 60K psi were not reached for any number of reasons.

Kelblys style "blade like ejector that pops up into a slot on the bolt". The point I was trying to make is that the action makes it impossible to even see pressure signs via the ejector. I don't think I'm in 'over pressure' territory though.

The more I've thought about this, the more I'm convinced either serious tension or (more likely) upping the charge will fix this. I'll have to mock up a dummy tonight to get the true OAL of the round, but I'm guessing you couldn't magazine feed them, they were pretty long (I was using a bobsled, and they were most defintiely over the 2.7xx OAL the book wants them seated at). My suspicion is that by seating it out that far, I gave it a ton more powder capacity than you'd typically find in a CM; that combined with the already light for caliber bullets may just mean I get hyper velocities out of the thing...I don't know.

What I am confident of is that it's not a brass, powder, gun issue etc.

Again, I loaded up 120gr bullets during the same loading session, loaded them .020" off, and had a slightly higher charge weight (long story), and got good burn there. I'm thinking I may actually get 3200-3300FPS out of these things before I see pressure.

I won't get a chance to test for a couple of weeks as matches are picking back up, but I'll post what I find. Just something I hadn't come across before.