Fireforming wildcat (6mm Grendel) when brass will grow .0125?

[Winny94]

I started trying to find a charge weight on my 6 Grendel, and quickly realized ill need to fireform the brass before moving on to that step. For those that fireform wildcats, do you typically find a fairly hot or mild charge to fireform?
I was doing some reading over on Accurate Shooter, and it was reccomended that since the brass will grow so much (.0125" base to shoulder) based on the half a dozen rounds I did fire, I should jam into the lands by about .020" to prevent the case from moving in the chamber - has anyone here done that?

Thanks for any advice

 

[SupressYourself]

Which 6mm Grendel variant are you using again? I thought most used same chamber dimensions as the 6.5 (minus the neck).

 

[Supersubes]

Is this an AR or a bolt gun? Just curious.

To your question, just shoot them. Not going to be a huge difference, you can still find the bullet and powder it likes, and do a minor tweak to your charge on fired brass as the load will be slightly hotter.

Also, since you’re necking down, just don’t neck down so far, leaving a small portion of your neck a slightly larger diameter thereby creating a false shoulder. No need to jam billets.

 

[Bradu]

Is it a 6 grendel or something based on it? If you are just necking down from 6.5 to 6mm, it's no different than shooting any other round. .012" growth isn't unheard of when firing new brass.

 

[Winny94]

Is it a 6 grendel or something based on it? If you are just necking down from 6.5 to 6mm, it's no different than shooting any other round. .012" growth isn't unheard of when firing new brass.

6mm predator (aka 6 grendel, 6mmAR, 243 LBC)

 

[Winny94]

Is this an AR or a bolt gun? Just curious.

To your question, just shoot them. Not going to be a huge difference, you can still find the bullet and powder it likes, and do a minor tweak to your charge on fired brass as the load will be slightly hotter.

Also, since you’re necking down, just don’t neck down so far, leaving a small portion of your neck a slightly larger diameter thereby creating a false shoulder. No need to jam billets.

Its a semi auto.
I may do that for the next batch, but this one is already done necking down.

The reason I'm asking is because during my first range trip, I was getting very early pressure signs. I didn't have my brass catcher, so I turned the gas off to not lose expensive Lapua brass. I got extractor swipes and very difficult extraction by 27gr (most loads in this cartridge w/ same bullet/ powder combo end up b/w 27.5 & 28). I was told it may have been impacted by excessive headspace, so jamming the bullet and fireforming with a milder load may help.

I've never done wildcat development, so looking for any advice, even if it's contrary to what others are saying - as long as it's not dangerous, more than 1 way to skin a cat I'm sure

 

[mcfred]

Since you're necking down 6.5 Grendel brass you can leave a "false shoulder" where your chamber's 6mm neck will headspace on a high-spot you leave when you neck it down from 6.5mm. This is frequently done with Ackley wildcats. Basically, just leave an oversized bit of brass at the neck/shoulder junction to headspace on and use a load between the starting and maximum load to fill out the shoulder. I don't think that getting ejector swipes while fireforming is a good practice.

That said, .012" sounds like a lot of stretch to me, but that could just be what you get with your chamber vs your lot of brass. The false-shoulder method should not result in that much stretch and I'd wager it can be more reliable than jamming bullets heavily in the lands. In your AR you can also remove the spring-loaded ejector(s) to reduce the forward pressure on the case to try and keep the case-head in closer relation to the bolt face.

 

[Bradu]

I doubt you are but you don't have the die setup to bump the shoulder any when necking down? I don't worry about jamming the bullet when necking down. You will be fine loading a lighter load that won't show any pressure signs. It will still move the shoulder forward. You are correct that it can cause pressure signs.

 

[TonyTheTiger]

Almost sounds like you have the wrong bolt face depth.

 

[Yondering]

Almost sounds like you have the wrong bolt face depth.

No, I encountered the same thing with some Lapua 6.5 Grendel brass; it was .010" too short for my minimum spec chamber. Maybe Lapua sized it for the wrong bolt face depth...

 

[Winny94]

I doubt you are but you don't have the die setup to bump the shoulder any when necking down? I don't worry about jamming the bullet when necking down. You will be fine loading a lighter load that won't show any pressure signs. It will still move the shoulder forward. You are correct that it can cause pressure signs.

Nope, it took awhile to get the die set, but I was meticulous to make sure the shoulder didn't bump

Almost sounds like you have the wrong bolt face depth.

The bolt is a matched bolt to the barrel from the MFG (ar15 performance), so barring something extraordinary, that shouldn't be the issue.
Counting myself, I've now read 3 cases of Lapua Grendel brass being very short. Not sure if thats normal from them, or if it was one lot we all bought from.

 

[TonyTheTiger]

Maybe Lapua sized it for the wrong bolt face depth...

 

[Yondering]

LOL

Lapua definitely got it wrong on my batch of brass anyway. .010" too short in two different chambers, one from BHW and one I chambered myself with the bolt there in hand.

I'm sure they were just trying to make sure it'd fit every chamber, but they went too far on that batch IMO. I'd have been less surprised if it was Winchester or Remington or even Federal.

 

[MarinePMI]

Were it I, I would either try for a false shoulder (which you may already be past this option in case forming), or as someone told you, jam the bullet (lightly) and use a moderate, but full power load. I'd also disable the gas system while doing this step, so as to not be yanking on the cases while they may still being trying to form to the chamber after ignition. Your previous pressure signs were likely due to the case moving in the chamber as the firing pin impacted the case, and then it (violently) slamming back against the bolt face as ignition occurred. Any residual case forming wax (like Imperial) left on the case will magnify this effect.

Welcome to the wonderful world of wildcatting. Where there are no hard and set rules, and minor variations in components (or reloading process) can cause major changes in pressure and performance. It's a disease at times, but certainly fun figuring out.

TBH though, I have to scratch my head at times. Isn't a 6mm Grendel basically a 6mm PPC?

 

[Winny94]

Were it I, I would either try for a false shoulder (which you may already be past this option in case forming), or as someone told you, jam the bullet (lightly) and use a moderate, but full power load. I'd also disable the gas system while doing this step, so as to not be yanking on the cases while they may still being trying to form to the chamber after ignition. Your previous pressure signs were likely due to the case moving in the chamber as the firing pin impacted the case, and then it (violently) slamming back against the bolt face as ignition occurred. Any residual case forming wax (like Imperial) left on the case will magnify this effect.

Welcome to the wonderful world of wildcatting. Where there are no hard and set rules, and minor variations in components (or reloading process) can cause major changes in pressure and performance. It's a disease at times, but certainly fun figuring out.

TBH though, I have to scratch my head at times. Isn't a 6mm Grendel basically a 6mm PPC?

Thanks for the reply. So I've gotten different opions as to what would qualify as a moderate load - most say 26.7-27.2 is moderate, but that gave me very noticeable signs. However, if jamming the bullet or false shouldering fixes that issue, then I can run a little hotter. Should I load another 10 load ladder with the jam (since Ive already necked sized the whole batch) and see if/when pressure signs start, then load the rest at whatever charge I find, or should I load them all at say 26 or 26.3, which was fine the first time out, and jam and shoot them all?

And yea, this cartridge is very similar to the PPC. The only dimensional difference I recall is the Grendel variant will have a .070 longer neck.

 

[MarinePMI]

My preference would be the 26.3gr load (known moderate load without pressure signs) and seat the bullets lightly into the lands (only a couple thousandths is really needed). And then fire form them. Once formed, then I would do a ladder test to find a good node with the fully obturated case. remember, you're just trying to give the case support (minimal movement front to back) as the pressure increases to the point that it blows the case out and bullet is sent down range.

JMTCW...

 

[Yondering]

And yea, this cartridge is very similar to the PPC. The only dimensional difference I recall is the Grendel variant will have a .070 longer neck.

Actually the main difference in the cartridge itself is the shoulder of Grendel brass is .070" farther forward than the PPC, for more case capacity. Otherwise, the cartridges are very similar. The Grendel case came from the PPC case, which in turn came from the 220 Russian and 7.62x39 cases.

The chamber is different as well though; most PPC chambers are/were intended for lighter bullets, while the Grendel and most of it's wildcat descendants are throated and twisted for heavier bullets. The capacity for heavy bullets, no turn neck, and slightly increased capacity are the differences between a 6 PPC and a 6mm Grendel wildcat.

 

[Winny94]

Actually the main difference in the cartridge itself is the shoulder of Grendel brass is .070" farther forward than the PPC, for more case capacity. Otherwise, the cartridges are very similar. The Grendel case came from the PPC case, which in turn came from the 220 Russian and 7.62x39 cases.

The chamber is different as well though; most PPC chambers are/were intended for lighter bullets, while the Grendel and most of it's wildcat descendants are throated and twisted for heavier bullets. The capacity for heavy bullets, no turn neck, and slightly increased capacity are the differences between a 6 PPC and a 6mm Grendel wildcat.

Thanks for the clarification - all I could remember is the .070 number, but couldn't recall where that difference was.

 

[MarinePMI]

Actually the main difference in the cartridge itself is the shoulder of Grendel brass is .070" farther forward than the PPC, for more case capacity. Otherwise, the cartridges are very similar. The Grendel case came from the PPC case, which in turn came from the 220 Russian and 7.62x39 cases.

The chamber is different as well though; most PPC chambers are/were intended for lighter bullets, while the Grendel and most of it's wildcat descendants are throated and twisted for heavier bullets. The capacity for heavy bullets, no turn neck, and slightly increased capacity are the differences between a 6 PPC and a 6mm Grendel wildcat.

<chuckle> I guess my playful sarcasm was a bit too subtle. My question was a bit tongue-in-cheek, as I am very aware of the history of the .220 Russian case, and all the child cartridges that it has given birth.

 

[Yondering]

Yeah, chuckle, because the answer to your "tongue in cheek" question is no, the 6mm Grendel wildcats are not basically a 6mm PPC. They are superficially similar but functionally very different cartridges, as I explained above.

Do you even own or shoot one of the 6 Grendel wildcats?

 

[MarinePMI]

LOL! Methinks someone is feeling butt hurt.

And yes. I do. But I think this conversation has reached it's viable end, since I'm not about to get in a penis measuring contest on who is the saltiest wildcat reloader. Life is just too short.