Crazy pressure and muzzle velocity

[CSGambill]

I have a DTA SRS A-1. When loading for .338 LM I recently switched to Berger 250gr Elite Hunters. With the new bullets, I'm getting scary high pressure and mv. First test loads expanded the case so much I had to use a dead blow hammer to open the bolt. Not ideal!

After the initial test load I dropped the powder H1000) down to 82.5 gr. I'm still getting a mv of 3000 fps. Very inconsistent accuracy at long range too (yes, it could be me, but if I really thought that, I wouldn't bother with mentioning). The mv seems extremely high for the load as compared to Berger's published load data.

I use Redding Competition dies and thought the neck bushing was too small. Loaded case necks mic in at an average of 0.368" and my neck bushing is 0.367", so that's probably not the culprit. This is in line with Redding's recommendations.

For comparison, using 300gr Lapua bullets with 88.5 gr of H1000 the muzzle velocity is about 2750fps.

Anyone have an idea why I'm getting such high speeds? I want to like the .338 Bergers (work great for the 6.5x47 barrel), but may just stick with Lapua.

Thanks

 

[Bmghunter]

Are the 300gr and 250gr tests from the same lot/canister of h1000? If not, maybe the lots have different burn rates.
Also is the scale calibrated and both loads measured from the same scale? Unlikely to cause this even if they are different scales, but just in case, it had to be asked, maybe your 82.5 gr is much higher in reality if the scale is off.

 

[CSGambill]

Same can of powder. I could drop the volume down some more. I guess I shouldn't complain about using less powder, especially now.

 

[DesartDweller]

Have you checked the zero on what ever scale you're using to weight the charge? If you can trust the Hornady loading manual at 82.5g you should maybe be hitting 2450-2470fps with H-1000. The scale is the first place I would look.

 

[MtnCreek]

Sounds like something is preventing bullet release.

 

[Krob95]

Dumb question. But when’s the last time you cleaned the throat? And has your brass been trimmed back?

 

[CSGambill]

Dumb question. But when’s the last time you cleaned the throat? And has your brass been trimmed back?

Good thought. I am lax on trimming brass, but this is occurring with new and once fired. It's worth checking.

Have you checked the zero on what ever scale you're using to weight the charge? If you can trust the Hornady loading manual at 82.5g you should maybe be hitting 2450-2470fps with H-1000. The scale is the first place I would look.

Yes. I'm confident that the charge weight is accurate. I use a RCBS Chargemaster Lite (calibrated each use), and less often a 10 - 10 mechanical scale. Both read the same. I don't think Occam's razor is right this time.

 

[PinesAndProjectiles]

Are you jamming your bullets into the lands?

 

[MtnCreek]

Take a bullet and insert it by hand into fired cases that showed high pressure. If the bullet freely slides in/out, you can eliminate carbon ring, trim length and neck thickness.

 

[CSGambill]

So bullet comparators are essential, especially when switching bullets that have significantly different geometry. ...Should go without saying I guess.

Turns out I was loading the Bergers 0.15+ longer than they should be. So yeah, jammed way the hell into the lands.

 

[skl1]

So the bullets also could be jamming back into the case, depending on how deep into the lands you were going and neck tension. Would cause a lot of pressure.