Fire form 7.62x39 ??

[GrendelHunter]

I know in the grendel you can fire form 7.62x39 with the only difference being large primer and internal case complicity slightly changed.

Any chance im making a mistake by trying this with the arc??

Size, rough trim, light load, and shoot??

[Lemonaid]

I've gone down this path with my 6PPC trying to save money. You need the Redding form and trim dies plus a Wilson inside case reamer as the neck o.d. will be over large. You can do it but it is a pain.
In this time of small rifle primer drought I am seriously considering going back to it so as to be able to use available Large Rifle Primers. If it was just to get some brass I would test the Grendel to ARC route first, It's working well in my 6PPC, much easier to form, and I can barely get by without inside neck reaming.

[GrendelHunter]

Inside neck reamer yep didn't think of that. And ya im short small rifle primers as well. But remembered I do have 7.62 brass.

[Lemonaid]

Or if you are set up for case neck turning you can do with out the inside neck reamer.

[GrendelHunter]

Well I sized 50 pieces and was surprised to find after seating a bullet that my neck size was in spec. So at least for now Nosler 7.62 sized should work fine with no turning. Now to fire some and see what happens to case size and length. I'm in a bind though ranges have time restrictions with covid and my buddy's place is out as I'm so close to Kenosha, WI to not bring attention firing rounds at his place. GOD DAMN RIOTING!!! Im using cfe223 im thinking 28-29ish Gr. to fire form and 90gr eld-x.

[Lemonaid]

I would suggest making one dummy round and see how it chambers, or if you can safely do it with your loaded rounds. If they wont chamber or are very hard to chamber you may have to adjust the sizing die to the maximum. If your are working with new unfired brass you should be o.k.
Another cause of hard chambering could be oversize neck o.d.
Hope it works out for you, Large rifle primers can increase velocities quite a bit so factor that in.
It is amazing how fast the world has gone crazy!

[GrendelHunter]

Well I think I F****D up ... Or the  throat in this Barrel was cut wrong... Possible but idk they don't list the 90gr ELD-X in the load data at all Only the GMX...

Part 2 I loaded 50 and didn't check them before hand. I got way to over excited. Some will chamber and others won't but allllll of them smash into the lands!!!
          So seat them deeper? Or pull them and use another option on my shelf?

[Trashy]

Have you measured the chamber for the bullet you are using? Have you measured the headspace on your formed cases? Max headspace on the 6 arc is 1.190. Is the neck thickness ok or do they turning? Hope this helps.

[Lemonaid]

Looks like a candidate for the black marker routine. Measure oal of one of the lands marked rounds, seat it 5 or 10 thou deeper, color with marker and chamber and eject (safely!). Observe if lands still mark bullet. Repeat until no marks are observed and that is the max oal for that combination of components.
The ones that would not chamber need to be pulled and resized or neck turned depending on what is the problem, you might be able to observe on the brass where it is rubbing, either the neck or the shoulder.

[GrendelHunter]

Ok pulled all the rounds apart
Resied all 50 with 1/4 turn (with decaping pin removed)
Checked case overall length and chamber fit trimmed case length to 1.491 ish
I then lowered the previous powder charge from 28.3 thrown to 26.2 thrown
Using your sharpie trick seated bullets to 2.180 to be just off lands .010 thou ish
Rechecked chamber fit, all chamber and extract (some extract stiff (suspect neck thickness))

So I'm wondering if I must cut the necks down to safely shoot them or can I fire form, resize, and recheck thickness??

Big shout out to Lemonade and Trashy for the help.

THANK YOU FOR THE SHARPIE SHORTCUT AND THE HEADSPACE NUMBERS!!! HELL YA.

[Trashy]

I would drop that cfe223 charge down as low as I could. If there is a neck thickness issue you can get into trouble quick with cfe223. The saami chamber spec for the neck is .275 and the cartridge neck is .274, measure the necks of a couple and see where you are before pulling the trigger on one just to be sure.

Edit: max case length is 1.490 so get those cases trimmed to about 1.480.

[GrendelHunter]

Yep shot all 50 rds at about 2pm. All went well. With case trim length at 1.490 and during firing it shrank. 1.480 new case length. I used 26.2gr thrown cfe223 and my upper shoulder is not crisp and defined still a little round. Ill post pics later. Now I'm going to start working up a 90 gr hunting load that's I hope .5moa load. And see how far this 16in barrel can be pushed in the long distance game.

[GrendelHunter]

Newly formed case.

[Trashy]

Well done GH! Glad to hear you got those cases working for you. Now you have another option other than the elusive small rifle primer.

[Lemonaid]

A few observations that may apply. Case capacity was decreased a grain and 1/2 or so with my converted cases but velocity gains from the large rifle primer made up for that, sometimes exceeded.
Before going to large scale conversion, note that in the early Grendel days when brass was scares some converted 7.62x39 brass to make Grendel cases. Many experienced loose primer pockets in 3 to 4 reloads. I'm not sure how hot they were pushing them for that to happen and it may be dependent on what brand of 7.62x39 brass they choose to start with.
I am also going back to large primers as I stocked up on them on the last shortage (Fed 210M's were gone for years).

[GrendelHunter]

Good notes are those numbers for 6.5 Grendel or 6mm ARC?

[Lemonaid]

7.62x39 to 6.5 Grendel.  I may use the ones I converted now that small rifle primers are unobtainable.

[GrendelHunter]

Im curious whats the case capacity of a 6 ARC.... One quick google search later and the answer is 34.0 of water. Ill measure my converted brass tomorrow.

[GrendelHunter]

Yep I'm late I know but 33.6 it the number for a twice fired nosler 7.62x39 formed case.

[StoneHendge]

GH, did you get anything resembling accuracy on your fireforming loads? Enough to use them for something like practicing offhand shooting IPSC targets at 100 yards? I'm thinking of trying this just because I have a glut of large rifle primers and that sort of practice is something I'm going to be doing anyways - normally with a .223, but that would be using small rifle primers.  And I'd be using the bullet and powder anyways.....