Fire forming accuracy (6 Grendel)

[Bat Rastard]

I have a big fat new Bartlein barrel in 6 Grendel.
Some groups have clusters and fliers. Some are all fliers.
I hesitate to say I am fireforming, as it was just a neck down operation.
I have been using various amounts of AA2520 underneath 90gr Sierra GameChangers and 103 VaporTrails.
It is the first time through the rifle for the brass, and it is my first wildcat round.
I am going to try Varget next, because I have a few pounds.

My question, Am I going to have better results after the brass has fired through the chamber once?
All help is appreciated.

 

[Hoser]

Gas gun or bolt action?

I am loading 6 Grendel for a gas gun. I size the necks down to where there is a slight crush fit in the chamber when the bolt closes.

After first firing, I bump the shoulder about .002 - .003 and press on as normal.

Varget gave me excellent accuracy, but I ran into pressure problems.

I settled on H4895. Good velocity, good accuracy and low ES/SD.

 

[mopar_4life]

Gas gun or bolt action?

I am loading 6 Grendel for a gas gun. I size the necks down to where there is a slight crush fit in the chamber when the bolt closes.

After first firing, I bump the shoulder about .002 - .003 and press on as normal.

Varget gave me excellent accuracy, but I ran into pressure problems.

I settled on H4895. Good velocity, good accuracy and low ES/SD.

This is my plan also. I'm waiting on my barrel but that's how I already prepared my brass

 

[Bat Rastard]

Bolt gun, Ruger American.
Accuracy is more important for my needs. Unless it's ridiculously slow.

 

[JavmanSTX]

May want to try H335 and AR Comp. ARC hits same POI with the 123amax and 129ABLRs. RAP rifle.

 

[Lougler]

I have a big fat new Bartlein barrel in 6 Grendel.
Some groups have clusters and fliers. Some are all fliers.
I hesitate to say I am fireforming, as it was just a neck down operation.
I have been using various amounts of AA2520 underneath 90gr Sierra GameChangers and 103 VaporTrails.
It is the first time through the rifle for the brass, and it is my first wildcat round.
I am going to try Varget next, because I have a few pounds.

My question, Am I going to have better results after the brass has fired through the chamber once?
All help is appreciated.

Check your neck diameter? My Dad had one built a year ago. Struggled to get it dialed in until he noticed he couldn’t fit a bullet in a fired case. Turned his necks and it came around.

 

[Raptor]

What are you talking for groups?? Have you checked the usual things like action screws, scope, rings and bases barrel making contact with the stock??? How heavy is your barrel??

 

[Bat Rastard]

Its an AMU contour. Things are tight. The free float has room for improvement. Varget shows promise, I neck turned 1/2 my brass tonight and will try to get it out to the range Tuesday,
Three trips to the range today . I ran incrementally up to a FULL case and didn't see pressure. The best 5 were 29.5 grains of Varget under a 103gr Vapor Trail. Tomorrow i will shoot 3 groups of 5 to see if that's the load, or if it was a lucky group. I had a group at .715 and another at .530

My first efforts were running 1-2" with AA2520

I also need to remove the sling studs to ride the bags better.

 

[WyleWD]

Check your neck diameter? My Dad had one built a year ago. Struggled to get it dialed in until he noticed he couldn’t fit a bullet in a fired case. Turned his necks and it came around.

+1^^ This should help, but the OP's sling studs aren't doing him any favors. Accuracy from First round brass is kinda so so. Windflags?? WD

 

[Bat Rastard]

I'm not smart enough for windflags!

 

[Raptor]

My son in law and I just put together an AR in the 6MM ARC and we sized down some Lapua 6.5 Grendel brass and we had the same issue an Lougler described above. We could not get a round in the fired case so all of the brass will need to be necked turned. We hope that we will see some better groups out of the rifle. I know from experience that this can really screw with your accuracy.....

 

[gunsandgunsmithing]

My son in law and I just put together an AR in the 6MM ARC and we sized down some Lapua 6.5 Grendel brass and we had the same issue an Lougler described above. We could not get a round in the fired case so all of the brass will need to be necked turned. We hope that we will see some better groups out of the rifle. I know from experience that this can really screw with your accuracy.....

Necking down doesn't typically cause the donut issues as opposed to necking up...but you're pushing the shoulder back. That thicker brass in the shoulder area is now part of your neck. It had to go somewhere.

 

[Raptor]

Necking down doesn't typically cause the donut issues as opposed to necking up...but you're pushing the shoulder back. That thicker brass in the shoulder area is now part of your neck. It had to go somewhere.

Actually, when we sized down the Star Line brass it stayed the same size......