Ejector smear with Sig Cross 6.5

[Nomad88]

I have a sig cross that started as a 308, I bought a factory 6.5 barrel from Sig, direct swap... easy enough.

I tried my handloads for my RRP in it and it shot amazing. .3 moa 5 shot group, but was getting pressure signs and bad ejector marks.
That was 41.5 gr of h4350, 142SMK. seated .052 off the lands.

I tried 41gr, got pressure, and just tried 40.5, same thing... ejector marks.

Anyone have an idea of whats going on here?

 

[shoot4fun]

What brass are you using?
Alpha? Peterson?
Do you have a blade mic to measure case head expansion? That would give you an idea if the ejector swipe is actually pressure of something else.
Could there be a headspace issue with the new barrel?
Many opportunities for blame without more info.

 

[Nomad88]

What brass are you using?
Alpha? Peterson?
Do you have a blade mic to measure case head expansion? That would give you an idea if the ejector swipe is actually pressure of something else.
Could there be a headspace issue with the new barrel?
Many opportunities for blame without more info.

I measured in the groove,
New measures .399
Sig cross is .399
Ruger precision .399

I checked headspace,
Sig: 1.560
Rpr: 1.559

Seems the chambers are almost the same.

Using Peterson brass

 

[Walt Krafft]

Try some Sig factory ammo and let us know how it shoots.

 

[Clancy]

Peterson holds less powder than Lapua, and guess what….

THIS IS WHAT HAPPENS WHEN YOU START AT MAX!!!

But…..

I’m noticing a pattern amongst friends with factory chambers and PETERSON brass. I think it’s too soft to take that first slam into the bolt face. It works great in my custom barrels though.

Try a starting load with a decent amount of jam and work your way up with a that same jam. That would give the brass a chance to fireform without a lot of stretch in the wrong places. Then just start backing up until it shoots to your liking.

That’s just a maybe though, hard to say if that’s the problem without more info.

P.S. Don’t start at max loads.

 

[shoot4fun]

I measured in the groove,
New measures .399
Sig cross is .399
Ruger precision .399

I checked headspace,
Sig: 1.560
Rpr: 1.559

Seems the chambers are almost the same.

Using Peterson brass

@Clancy has hit the nail squarely on the head!
Peterson Brass has way less internal volume than other brands.
Also, measuring the groove diameter is useless. The pressure shows up the case head near the .200 line.

 

[Nomad88]

I have some starline brass, I’ll load it today and see how it does.
If it were the brass, why does it do fine in 2 other rifles?

 

[Pres100]

Every chamber/rifle are not the same... different reamers, reamer wear, different chambering methods, etc etc etc. Ammo for one gun doesn't always perform the same in another.
You mentioned the barrel was a direct factory replacement ... was it checked for headspace when installed?

 

[565tinfitter]

Bore diameters can also be a factor to consider when you have pressure, even if the chamber dimensions are close in tolerance.

 

[Webster]

I have a sig cross that started as a 308, I bought a factory 6.5 barrel from Sig, direct swap... easy enough.

I tried my handloads for my RRP in it and it shot amazing. .3 moa 5 shot group, but was getting pressure signs and bad ejector marks.
That was 41.5 gr of h4350, 142SMK. seated .052 off the lands.

I tried 41gr, got pressure, and just tried 40.5, same thing... ejector marks.

Anyone have an idea of whats going on here?

Pressure is the only thing that makes ejector swipes. The brass is getting pushed into the ejector pin hole.

 

[dantiff2]

Pressure is the only thing that makes ejector swipes. The brass is getting pushed into the ejector pin hole.

^^^This^^^ end of story. doesn't matter what length barrel you have or what brand of shaving cream you use. Pressure is the answer. Some brass will flow at a lower pressure than others. I have witnessed Hornady brand brass flow when other brands would not but you have to consider internal capacity also. Less volume causes more pressure.