Powder Charge to Blow out Case to an Ackley

[centershot]

I am going to blow out some .257 Roberts to an Ackley using IMR 4451. The Hodgdon web site says for a regular .257 to use between 41 to 46.2 grains. Would you go low, medium or high? Probably 100 grain bullets. Either that or 17 grains of Trail Boss. Would Trail Boss generate enough pressure to blow it out in one firing?

 

[lightman]

Most of the guys that I know use a max charge for the parent cartridge.

 

[Doug Beach]

Use the high end of the unmodified cartridge’s load data. Without double checking the data you list, I’d use 45-46gr of the 4451. Lighter loads just mean more firings until the case is fully formed.
Also, no need to just blow through these fire forming rounds. Use them for whatever you would use the formed cases for, hunting, targets, whatever. They ought to shoot fine.

 

[Bill Norris]

Most A I owners suggest a full charge of the parent case to blow out cases. I've used that load data for the .223 and 243 A I with good results.

 

[centershot]

Thanks to all. That is what I thought but wanted to confirm that.

 

[linebaugh]

They can be a pain to blow out completely with lower charges. I dont know that trail boss will work due to not enough pressure. I recently tried to go cheap and bought cheap light bullets and loaded lightly in a 221AI and had issues not forming well. I assume I was in the mid 30k range.

Not sure what your gun will be used for but a full load of the parent case and you can produce some superb accuracy while forming at times so you can take advantage of that possibly. If you chrony loads while forming they will come in low, just an FYI.

 

[sundance]

High-end loads have always worked for me. Blows that shoulder right out to a nice Ackley.

 

[Toddy]

I am going to blow out some .257 Roberts to an Ackley using IMR 4451. The Hodgdon web site says for a regular .257 to use between 41 to 46.2 grains. Would you go low, medium or high? Probably 100 grain bullets. Either that or 17 grains of Trail Boss. Would Trail Boss generate enough pressure to blow it out in one firing?

Yes Trail boss works extremely well. I have used it to fire form 284KMR & 6mm Dasher cases. I tweak my charge to get nice square corners at the body/shoulder taper without getting heavy bolt lift. Using trail boss will help to preserve barrel life as it won't wear your throat fire forming. As we know fireforming can still produce great results on target if you choose to use your regular powder.

 

[fyrewall]

I have used 9 grains of HP38 to fire form 6mm Rem to 6mm AI. Any old primer, I use large pistol primers. I wild guess would be 20,000 to 25,000 psi.

 

[centershot]

Thanks for the replies. As of now, I have been waiting 3 1/2 months for the re barrel. Guess everything takes time! Waiting for a f .l. sizing die from Midway for a month. Trying to be patient.

 

[jepp2]

Thanks to all. That is what I thought but wanted to confirm that.

Just a suggestion is to load a range of gr increments. You can see what gives you a nice sharp shoulder and what gives the best accuracy. You REALLY want to be able to feel the bolt close on the case (meaning it is firmly trapped between the bolt face and the portion of the neck it is contacting). When I'm forming 20 Bobcat from 222, I leave a portion of the case neck unsized to help insure the case is forced against the bolt face. On a properly chambered AI, this should occur, but new factory brass can have a significant difference in case head to datum lengths.

 

[JSH]

^^^^
Make sure to keep the lugs well lubed.

 

[centershot]

Just a suggestion is to load a range of gr increments. You can see what gives you a nice sharp shoulder and what gives the best accuracy. You REALLY want to be able to feel the bolt close on the case (meaning it is firmly trapped between the bolt face and the portion of the neck it is contacting). When I'm forming 20 Bobcat from 222, I leave a portion of the case neck unsized to help insure the case is forced against the bolt face. On a properly chambered AI, this should occur, but new factory brass can have a significant difference in case head to datum lengths.

I usually seat the bullet to engage the lands to insure proper head space.

 

[Bill Norris]

I usually seat the bullet to engage the lands to insure proper head space.

That's what I was instructed to do from my builder too.

 

[sundance]

I use my fire forming loads on local prairie dogs .It is a lot more fun that way. And usually, the loads are pretty accurate.

 

[Bill Norris]

I use my fire forming loads on local prairie dogs .It is a lot more fun that way. And usually, the loads are pretty accurate.

My 243 AI shot very accurate blowing out brass. Loaded 10 rds. of 10 different bullets in new un-fired Lapua brass and none of my 3 or 5 shot groups measured over 1/2 inch @ 100 yds.

 

[Dusty Stevens]

I always go halfway between low and max

 

[marchboom]

My 22-250 AI Encore (Bullberry barrel) gave me 5/16" groups while fireforming. Great for varmint hunting.

 

[dgeesaman]

Most A I owners suggest a full charge of the parent case to blow out cases. I've used that load data for the .223 and 243 A I with good results.

Ditto. It used to make me nervous about pressure, jumping right to a “max” load but the brass expansion cushions it fairly well.

I tend to choose one of the faster powders in the usual range.

David

 

[std7mag]

Unless the headspacing was done incorrectly, i wouldn't seat long.
The whole point of the Ackley Improved chamber was that you could use the parent cartridge if for some reason you didn't have the AI cartridge. IE it got stuck in customs or lost if going to Africa or the like.

There should be a slight interference at the neck/shoulder junction when chambering the parent cartridge into an AI chamber.

Seating the bullet long will just raise the pressure. Which you don't need to do.
Especially on the Roberts case.