A.I. Fire Forming Tip of the Day

[Pdvdh]

Fireformed 50 Nosler 270 Win cases today to 280RCBS Improved. I used CCI 200 primers, IMR SR7625 powder, tissue between powder and cream of wheat, capped off with tissue paper.

I wouldn't have predicted what I experienced could happen. Despite my engineering background.

I wasn't sure how large a powder charge would be required to set the shoulder fully forward. Loaded 15.5gr on the first casing. Lubed the exterior of the casing and my chamber with some super slick oil I purchased from LUBRI-KIT.com
Touched it off and then measured the case head to shoulder dimension and it was fully formed. 0.001" longer than my fully prepped hunting shells. Perfect!
I bumped the powder charge up to 16.5gr for the second case for good measure, since the pressure on the 15.5gr charge was very moderate. Lubed the case exterior, fired it off. Measured shoulder and again it's perfectly formed. This is too easy, I'm thing to myself, smuggly.
So I load the rest (48 more cases) using 17.0gr powder. I want them fully formed the first fireforming. So I fire all 48 remaining cases over a duration of about 2 1/2 hours. No sweat!
Back in the reloading room I'm dumbfounded to find the majority (46) of the case shoulders are 0.004" - to 0.009" shy of fully pushed forward. WTH?
As I was bemoaning my failure, I kept trying to think of what could have gone wrong. I hate having to do things over a 2nd time to get them "right".
Finally the light dawned... I only lubed the chamber once, and then the first two cases with oil. The oil in the chamber persisted during fireforming of two additional cases, and then the case shoulders stopped blowing forward fully. I measured all 50 cases with a dial indicator. The dryer the chamber became, the less the shoulders formed.

If you want to help ensure your case shoulders blow fully forward, and with a lower pressure load, then lightly lube the exterior of the cases prior to fireforming.
I had read that lubing the cases helps allow the shoulders to blow forward. I've also read others scoff at the notion. Now I can tell you it works.
I'll be re-fireforming 46 cases. This time they'll all be lightly lubed with oil. The lube allows more complete fireforming of the shoulder with a lower powder charge and lower chamber pressure.

 

[Rich Coyle]

Thanks.

 

[just country]

morning, I fire form 223AI Winchester brass. I hunt with brass I am forming.
I also target shoot while forming brass. never had a problem. GBOT TUM

 

[Predator 22]

Have you sectioned a case to make sure your not stretching all the extra material out of the case head?

 

[Pdvdh]

I expanded the case necks with a .308 mandrel and all cases were headspaced tight with a crush fit upon bolt closure. There is no case head stretch.

 

[Pdvdh]

morning, I fire form 223AI Winchester brass. I hunt with brass I am forming.
I also target shoot while forming brass. never had a problem. GBOT TUM

Yes, that's another option. I chose the Cream Of Wheat option, so the game and targets would have to be pressed up against my muzzle to either hunt or target shoot with them.

 

[Pdvdh]

I'm not certain why the lube oil made the difference. And I've pondered the theories for a good while. Anyone able to explain this - I'd like to hear it.

I think I know why... I think the lube allows the casing sidewall to slip backward when the case head is slammed back into the bolt face. Instead of the stretch at the case head which leads to the common case head separation over time, I think the lube allows the casing sidewall to slip backward against the chamber wall. The result is the casewall stretches/elongates farther toward the shoulder, where the case wall is much thinner and weaker.
Remember, I'm seeing less than 0.010" gap remaining for proper case head to shoulder spacing with the unlubed cases. I think when the firing pin slams the primer, the cases are moved slightly off the bolt face (<0.010"), and then as the pressure builds, the case tries to expand to fill out to the full chamber dimensions. The lube allows the sidewall to slip back and stretch out to full length away from the case head, where the wall is thinner.
Without the lube, the case wall is locked tight to the chamber, and the pressure on my COW load is insufficient to stretch the thicker brass at the case head, where we normally see case stretching with full power loads.

Of course, the more common solution is a higher powder charge and the higher pressure! Enough pressure to stretch the case wall "wherever" in order to reach full chamber headspace dimensions on the cases.

 

[gohring3006]

I did the old Jam and slam method when I fireformed 22-250 Lapua brass into 6.5 Creedmoor.
The brass appeared to be formed fully on the first firing, but I necksized for two more firings just to be sure.
I did lube the cases with imperial wax and left it on the cases.

 

[Predator 22]

Interesting. I was forming some 6.5ss cases for my Dads rifle, doing just like you were. Expanded to 7mm then part way back down to 6.5mm leaving a false shoulder leaving a very small amount of lube on the case. I was using unique powder at around 15gr. and cci primers. After forming around 30 pieces I noticed a ring around the case just below the case shoulder junction. Upon closer inspection and sectioning a few cases it appeared the case was grabbing good around the head and part way up the body then stretching just in the one spot. I droppd my charge a few grains and removed all the lube and all was well with the reloading Gods again. But maybe if I had lubed the cases the full length I wouldn't have had the problem? Or maybe it would of stretched in the web area with as far as the SS shoulder is being moved? Tests are in order! Thanks for the report.

 

[Pdvdh]

I've added my theoretical explanation to my post #7.
It's the only and best explanation I can think of.
If true, we'd all be better off lubing the case exteriors when fire forming with Cream Of Wheat.

 

[Pdvdh]

No doubts about the benefit of pre-lubing both your cases and your chamber, if you fireform using the Cream Of Wheat (common acronym = COW) method.
I further tested the methods this morning fireforming some Norma 280 Rem brass into 280RCBS 30-degree Improved cases.
For the first two cases, I lubed the exterior of the cases only. Both cases expanded to within 0.001" of the case head to shoulder measurement of the measurement I load my full power loads to. In other words, fully formed for all intents and purposes of moving forward with load development.
For the next five cases, I lubed each case AND also lubed the chamber with the oil I purchases from LUBRI-KIT.com. Each of these five cases formed more fully than full pressure loads in my rifle firing bullets. When I lubed the chamber walls in addition to the exterior of the casings, I measured about 0.002" further case head to shoulder expansion shooting the identical COW loads compared to the 2 loads where I only lubed the exterior of the cases. Futhermore, the bolt lifted with some obvious resistance, indicating an overpressure load, even though the pressures were nowhere's near maximum operating pressure. The lube simply allows the case walls to more easily slide and stretch in its contact with the chamber, helping to ensure a fully form improved casing. If you lube the exterior of a full pressure round loaded with a bullet, or prelube the chamber walls, you'll also experience high pressure symtoms, in that the bolt will commonly lift with some added force while ejecting the fired casing. The pressure is not any higher than had the cartridge been fired with an unlubed exterior/chamber. But more force is exerted against the bolt face because the cartridge casing slides backward under recoil much less restrained, because the coefficient of friction between the case wall and the chamber has been greatly reduce.

This nice part of this practice when COW fireforming is that you can use a lower pressure load and still obtain complete case forming to your wildcat chamber.
Anyone that says differently is welcome to their opinion. Everyone has the 1st Amendment right to be wrong, as frequently and as many times as the desire.

Test it yourself. As long as your chamber isn't scared and marred with poor chamber quality surface, you'll obtain the same results I did. I also polish my chambers with Flitz. Some gunsmiths believe the chamber surface should not be overly smooth/polished/slick. As if this could overly strains the bolt lugs under full pressure loads. I am not in that camp. The rifle action and bolt are designed above and beyond the maximum SAAMI pressures, as a safety precaution. If a smooth/polished chamber surface results in damage to the firearm, then the bolt or action were defective in the first place. I want the bolt lugs to receive the load. Not my casing sidewalls!

If I had pre-lubed all my Nosler 270 Win brass casings, I wouldn't now be forced to prep them and fire them a 2nd time using the COW method. Bummer for me. Live and learn. My plan is to re-lube the chamber also, after about every 8 casings fired, at the same time I run a nylon bore brush down the bore to remove the caked/cooked Cream Of Wheat from the chamber/throat area. However each and every case will absolutely be lubed prior to fireforming.

 

[Pdvdh]

Interesting. I was forming some 6.5ss cases for my Dads rifle, doing just like you were. Expanded to 7mm then part way back down to 6.5mm leaving a false shoulder leaving a very small amount of lube on the case. I was using unique powder at around 15gr. and cci primers. After forming around 30 pieces I noticed a ring around the case just below the case shoulder junction. Upon closer inspection and sectioning a few cases it appeared the case was grabbing good around the head and part way up the body then stretching just in the one spot. I dropped my charge a few grains and removed all the lube and all was well with the reloading Gods again. But maybe if I had lubed the cases the full length I wouldn't have had the problem? Or maybe it would of stretched in the web area with as far as the SS shoulder is being moved? Tests are in order! Thanks for the report. View attachment 84755

If I saw those incipient separation rings, I'd anneal the shoulder area and I'd lube the case exterior AND the chamber, prior to any further fireforming. Then you'd definitely be able to use a lower pressure/less violent charge of powder and still obtain complete fireforming to your wildcat chamber dimensions - without the risk of damaging any of your parent casings.

 

[JSHKS]

I will add a bit to this from fire forming with COW.

This was quite a few years ago. TC contender was the platform, 7-30 waters was the cartridge. 7-30 brass was and still is hard to come by. I had some virgin 30-30 I necked down to crush fit when closed.
I think I used 700 or 800X under the COW.
This particular barrel was their 12" hunter with a brake.
Third or fourth round sucked the brake right off, sent to parts unknown. They are silver soldered on.

I have pretty much only used COW method for forming brass as a last resort.
As the city has encroached on me, I can no longer step out the back door.
Also if I am going to kind of sorta load a case, may as well make it worth while. I use a cast bullet if at all possible. If not, I use odds and ends of jacketed cull bullets.
As mentioned above forming loads can be accurate. I have fired several thousand rounds of various TCU calibers over the years with good accuracy.

Want to scratch your head?
I had a 7 TCU barrel that shot forming loads better than formed brass! I tried everything imaginable to get it to shoot as good with formed brass.
Jeff

 

[Pdvdh]

I don't deny there are additional options for fireforming parent casings to fit a wildcat chamber. Sometimes the parent case will headspace properly without any fireforming, which is what Ackley intended for many/most/all of his A.I. designs. Simply chamber a factory round and pull the trigger. But such is not the case for my two rifles, and a great many other wildcat cartridges.

The parent casings I'm fireforming do not headspace in the chambers properly. The chamber headspace is way excessive using the 270 Win cases. And still excessive with the 280 Rem cases. I could proceed to fire bullets provided each bullet is jammed hard against the rifling, and then hope that my case head stays in full contact with the bolt face when the firing pin strikes home. And I could load bullets into the cases after the temporary shoulder has been formed on the enlarged case neck. But those bullets would have high runout, and the cases would lack substantial volume. Not the way I want to proceed with load development.

So I choose COW. I don't waste money on bullets and I don't waste bore life sending bullets down the bore at much higher pressure. Importantly, I don't have to load develop with bullets jammed into the rifling, when I don't plan on jamming bullets into the lands with my final hunting loads. There's no load develop benefit to firing bullets while fireforming my parent cases in my wildcat chambers, from my perspective.

But there are alternative options to fireforming cases to wildcat chambers. Not denying that.