Grendel to ARC, frustrated.

[KMW 1954]

This is the third time I've sized down 6.5 Grendel to 6ARC. The first time went well other than I found out not to anneal before I resized it. Last batch I ran into a problem with pierced primers and hard extraction.

This time after processing 30 pcs I loaded a couple pcs and tried chambering it. No go! So I went thru it all again and all put two pcs sat all the way down into my Hornady case gage. Then I tried chambering raw brass into the gun, no problems, with feeding or extraction.

From there I loaded 2 more and they wouldn't seat into the gage, neither would they chamber in the gun.

Checked everything again, case length, comparator measurement, BTO, neck measurements. All measured the same as the 6ARC loaded Hornady brass. Stumped.

Finally started pushing back the bullet, as that was all I could come up with. Pushed it back .045" from where I was normally seating this bullet and now it chambers? WTH? Been loading and shooting this gun for over a year. Now wanted to try the Grendel brass as I've acquired a good bit of it.

 

[Oso]

You are necking down cases, which means thickening the neck wall thickness. In addition, the 6ARC has a shorter case (body) so you are bumping back the shoulder, which means that some of the 6.5 Grendel’s shoulder material (typically thicker) is now being converted into the lower portion of the newly formed neck on the converted 6ARC cases. This is the perfect setup for forming a Doughnut. This would explain the pressure spike and hard bolt lift that you are experiencing when using converted 6.5 Grendel cases.

>What is the Neck O.D. of your newly converted 6ARC?
>What is the Neck O.D. of the newly converted case after seating a bullet in it?
>What is Neck O.D. of store-bought Factory 6ARC Ammo that has been fired through this rifle?

How do these numbers compare???

The metallurgy of the brass may also contribute to springback (trying to return to 6.5 Grendel dimensions). What is the headstamp on the Grendel Brass?

 

[KMW 1954]

OK, makes sense but doesn't explain why seating the bullet deeper corrected the bolt not closing. As for the Factory numbers. This rifle hasn't seen a Factory round since the first week it was shot over 18 months ago.

 

[SeabeeKen]

Sounds like you were jamming the bullet into the riflling or between a donut and rifling.
When reforming, hold the case in the die for 5 seconds to allow it to adjust and settle into its new shape. Works for me

 

[KMW 1954]

Sounds like you were jamming the bullet into the riflling or between a donut and rifling.
When reforming, hold the case in the die for 5 seconds to allow it to adjust and settle into its new shape. Works for me

Had loaded this same bullet out to the original length before while using 6ARC brass. Standard practice id to load slow. Not a race when trying to load Match use ammo.

These bullets are 105gr Hornady loaded light to fire form this brass. Thankfully I haven't processed a bunch of this stuff. So if it tuns into this much trouble I'll find something else.

 

[Bronsin]

If you decide to try something else, get some Alpha 6PPC brass, load the bullet into the lands, fireform it and be done with it.