6.5CM pressure signs in Lapua small primer brass

[9sigman45]

Having some concerns with the initial load development with my new AIAX in 6.5CM and asking for opinions.

I'm experiencing faint pressure sings (ejector swipe) with new Lapua small primer brass on every charge I've tried. Did 50 rounds, five rounds each in 0.3 grain increments from 40.0 to 42.7 grains. Obvious accuracy nodes were between 40.3-40.6 and 42.4-42.7 but I'm concerned with the higher charges based on what I'm seeing. I loaded another 5 at 40.6 and ran across the chrono and they averaged only 2,417 fps with the 140gr Amax and that just plain sucks. Am I just paproid? Should I focus more in the 42.4gr area and just expect fewer loadings on the brass?

Here's a pic of the faint pressure sign, semicircle thought the "LA" in Lapua.
And a pic of my groups, 5 rounds at 100 yards (those labeled 41.4 & 41.7 are actually 42.4 & 42.7, I'm a moron).

 

[918v]

AI bolt faces produce these semi circles with any load. It’s not a pressure sign.

 

[Darkside-Six]

I’ve gotten some faint marks like those on my Lapua as well with my AX and my load was 42.7 running 140’s about 2800. No over pressure issues though and never had any real issues. I don’t think it will be a “thing”. I’d say you’re fine.

 

[9sigman45]

Thanks for the feedback guys!

 

[BlueLacy]

Check the difference in length between the new brass shoulder to the once fired. New brass is often much shorter than the .001 to .003 we resize our brass back to. New brass with the shorter headspace often show false pressure signs as it stretches out to fit your chamber. Your primers look nicely rounded , and your velocities are not near the redline for that cartridge.

I would guess your brass probably strecthed out considerably which is normal on first firing of virgin brass.

Just a possibility

 

[r.tenorio671]

...might also want to check if your ejector has a "square edge" as opposed to a slight radius....

 

[9sigman45]

Good call Blue.
My fired brass is measuring 0.007"-0.008" longer in base to shoulder datum dimension than the unfired brass.

 

[918v]

It’s going to continue making these marks even after you fireform.

 

[Dead Eye Dick]

Another way to check pressure is to fire factory rounds and compare the dimension of the diameter of the case just above the head compared to the same measurement of your reloads.

Still, velocities less than 2500 FPS in a Creedmoor seem awful light. I have a rifle of another brand, that shoots great with loads just above starting level of more than one reference, and that rifle leaves marks very similar.

 

[rustyinbend]

I've found that especially with my 6.5-CM rifles (I have 3 of them), more so than my 300-WM and 300-PRC ... it's virtually impossible to get rid of that ejector mark and still have a charge weight that gets to something reasonable for velocity (>2600). I've given up trying, and watch for heavy bolt lift and primer craters as the real pressure signs in my 6.5-CM.

 

[9sigman45]

What barrel length? That's still only moving along at 2600'ish. Maybe you'll pick up 50-75fps over the next 100rds, but that's still pretty slow

26" AI factory barrel

 

[9sigman45]

I did a bit more testing and loaded up to 42.5 grains of H4350. Here's the data, better but still not what I'm looking for:
AVG = 2,619
ES = 22
SD = 8.0

This was a 10 shot string fired as two 5 shot groups, both measuring around 0.625" @ 100 yards. Most of the cases looked good, but one had a significant swipe and by the chrono it was the extreme low round at 2,609. Go figure.

Now that I have the new brass fire formed to my chamber I think I'm goon try a different bullet, maybe the 147 ELD-M.

 

[Cynical]

You may have a really slow lot of powder, or old powder that’s degrading.

 

[918v]

What chrono are you using?

 

[Mike Casselton]

What chrono are you using?

That would be the same question I would ask

 

[9sigman45]

You may have a really slow lot of powder, or old powder that’s degrading.

It is older. I "found" a case (2 kegs) that I purchased 6-7 years ago buried in my stash.

 

[9sigman45]

That would be the same question I would ask

It's an older CED with the rabbit ears that you shoot through.

 

[Mike Casselton]

Make sure you're shooting close to the optical sensors and not 8-12" above them.
You'll get much more consistent readings.

Set it up and then pull your bolt and look through the barrel to ensure your not gonna send a bullet through the unit face plate.

 

[918v]

It's an older CED with the rabbit ears that you shoot through.

Get a magnetospeed for accurate velocity readings

 

[9sigman45]

Nope, I have a buddy with a LabRadar, so no need for me to invest in a new chrono. My old stuff has worked well in the past and I typically validate electronic data at distance. I'll try to do that this weekend.

 

[9sigman45]

Over the last few weeks I purchased some 147gr ELDs and and have started playing around with different powder charges. Keeping all other components the same, 41.5 and 42.1 appear to be grouping nodes. Today I finally got beside my buddy's Labradar. Only had a few rounds of each of those charges loaded up; boy was I pleasantly surprised with the speeds. 2775 and 2820 fps respectively. The slower of these two has a slight grouping edge, so I'm thinking I'll focus there and take it easier on my brass. Will try to get out to 600 prior to making a final decision though.