6mm ARC - Practical Reloading

[gunsandgunsmithing]

My particular rifle is chambered in 6 Predator so I have a bit more capacity than the average 6 ARC. That said it is a tackdriver but with brand new brass and loads using ARC data I get very mild ejector hole and extractor marks. Could this be the product of fireforming the case to the chamber for the first shot? Not all cases show this maybe 5 out of 15. Trying to fireform some 500 cases.

Yes, it can be the new brass being a bit short and slamming rearward into the bolt face that creates those marks. I've seen it many times while fire forming with loads on the stiff side. If that's what it is, it should go away on fired and properly sized cases. A lot of the laua grendel brass is pretty short until formed. I've had it cause misfires as well. Best to deal with it when necking it down, imho...leaving a teeny false shoulder

 

[Laurie]

A lot of the laua grendel brass is pretty short until formed. I've had it cause misfires as well. Best to deal with it when necking it down, imho...leaving a teeny false shoulder

I've also found it short for the original 6.5 Grendel application, and noticed this mentioned elsewhere on other forums. This is most unusual for Lapua for factory applications. I've sometimes wondered if they did this to avoid partial lock-up ignition on semi-autos. In any event, once realised I moved to treating it as a non-factory cartridge fireform operation using bullets I don't rate too highly seated into the lands.

 

[rickt300]

Yes, it can be the new brass being a bit short and slamming rearward into the bolt face that creates those marks. I've seen it many times while fire forming with loads on the stiff side. If that's what it is, it should go away on fired and properly sized cases. A lot of the laua grendel brass is pretty short until formed. I've had it cause misfires as well. Best to deal with it when necking it down, imho...leaving a teeny false shoulder

I have my die set for perfection as far as headspace is concerned with once already fired brass and on new Starline brass the dies doesn't even touch the shoulder just the neck. I would say this leaves around .004 headspace with the new brass. No misfires and surprising accuracy.

 

[rickt300]

I've also found it short for the original 6.5 Grendel application, and noticed this mentioned elsewhere on other forums. This is most unusual for Lapua for factory applications. I've sometimes wondered if they did this to avoid partial lock-up ignition on semi-autos. In any event, once realised I moved to treating it as a non-factory cartridge fireform operation using bullets I don't rate too highly seated into the lands.

I have always disliked that method especially with a semi auto, too easy for the bullet to be pushed back so it doesn't really perform the intended function.

 

[Laurie]

I have always disliked that method especially with a semi auto, too easy for the bullet to be pushed back so it doesn't really perform the intended function.

Very true. I should have clarified this in my post - Howa Mini bolt-action in my case. Gentle bolt operation and lots of neck tension, it works fine.

 

[rickt300]

Well fooled around with the 105 gr. Hornady BTHP, BLC2 and Starline Grendel brass. Primer is the CCI #41. I wanted 2600 fps and good accuracy and I got it. 28.0 grains a load taken from Hodgdons data got me right there . Since I was mostly checking for velocity and pressure signs I wasn't truly concentrating on tight groups yet I put 16 shots into .7 out of 20 fired. Velocity average is 2604 fps.