Velocity-Pressure...When to Stop?

truck driver · Oct 14, 2018

Scotty my M70 300wm does the same thing with medium loads and I have found pieces of brass around the ejector plunger. I think I have a burr that wasn't cleaned up at the factory. Every piece of brass I have fired in it has that mark thinking it could have also been the Winchester brass I have since the base and rim doesn't look perfect to my eyes.
I would have disassembled the bolt to get a better look at the ejector button but I hate dealing with small springs under heavy tension.

SJB358 · Oct 14, 2018

truck driver":3pvcmf0g said:
Scotty my M70 300wm does the same thing with medium loads and I have found pieces of brass around the ejector plunger. I think I have a burr that wasn't cleaned up at the factory. Every piece of brass I have fired in it has that mark thinking it could have also been the Winchester brass I have since the base and rim doesn't look perfect to my eyes.
I would have disassembled the bolt to get a better look at the ejector button but I hate dealing with small springs under heavy tension.

Yes sir, but it is still a sign, it’s all about the combination of these along with speed that’s tells me what I’m doing. Don’t underestimate a shade smaller or larger barrel. Either one will show signs before the other. We’ve said it a million times, but two rifles coming off the same floor at the same time can be different. That button, cutter or whatever is used to rifle our bores wears a bit each pass, so I’d imagine the 100th barrel that day might be a shade tighter than number one.

Sharp edges do give false signs. Remington and Win push feeders can show pressure that you wouldn’t see on an otherwise smooth bolt face. My 264 drags a bit with everything since the face is a bit rough. I have to rely on other signs and the chrono readings or I’d stop at 6.5 CM speeds thinking it’s the max. Great topic though. Love reading about this stuff.

Elkman · Oct 14, 2018

Just looking at that primer, would make me halt and back off a touch. The other marks could be as already discussed pressure or rough machining. But for me the primer tells the story.

truck driver · Oct 15, 2018

Scotty the bolt face on my push feed M70s will collect enough brass to look like it was plated with extended use shooting at the range if I don't brush it off after each session. Roughest bolt faces I have ever seen.
One reason I watch the chrony velocity and measure the web area to see what is going on. I'm too cheap to take them to a gun smith and have the face polished, I would do it myself but don't want to mess with the plunger spring.