Help Fireform Brass-7mm-08 Ackley Improved

[AROKHUNTER]

My plan is to use Lapua brass and some Hornady 139 grain Interlock bullets to fireform the brass. Was going to load a mid weight charge of Varget, H4350, or IMR 4350 and seat the bullets wherever accuracy is best so I can use fireform loads to hunt with. Planned on starting .010”-.020” off the lands.

Does this sound like a feasible method?

Would it be advisable to prep the brass any differently than I would for a standard 7mm-08?


Any advice or suggestions would be greatly appreciated.

 

[ShootDots]

I am of the opinion that when fireforming brass to either an Ackley chamber or something like a Dasher (blowing the shoulder forward) you need to jam the bullet well into the lands to force the case head firmly against the boltface. This can be eliminated if you create a "false shoulder" to force the case against the boltface. However, doing a Ackley with a false shoulder, to me, seems like a lot of extra work for no apparent gain. So your idea of seating them off the lands is, in my opinion, not the best way. You may very well get misfires and the cases surely will not be exact.
My suggestion is to buy some Berger HUNTING VLD's (which generally like to be jammed) and if in the 140 class weight, try and get some accuracy before going hunting. If you have Varget go from 41.0 to 42.5 grs for fireforming and see which ones form the best with the best accuracy.

 

[KenOath]

I’m no expert and please correct me if I’m wrong but it is my understanding that when Ackley improving a case you will have a very light crush fit (1 to 4thou) at the neck shoulder junction which will push case head hard against bolt face therefore illuminating the need to jam the bullet or use false shoulder.

 

[ShootDots]

I’m no expert and please correct me if I’m wrong but it is my understanding that when Ackley improving a case you will have a very light crush fit (1 to 4thou) at the neck shoulder junction which will push case head hard against bolt face therefore illuminating the need to jam the bullet or use false shoulder.

When P.O. Ackley designed his cases, they were designed so that a factory round could be fired in it and that would also fireform the case. However, I have fireformed MANY, MANY cases to the Ackley 40 degree and before I started using the "hard jam" method, I had more than a few pieces that would not fire. It would strike the primer, which in turn would push the case forward "lightening" the strike, thus causing the misfire. Now I use a neck bushing that is 3 thousandths smaller than a loaded round and jam the bullets 15 thousandths>>>NO misfires..

 

[KenOath]

When P.O. Ackley designed his cases, they were designed so that a factory round could be fired in it and that would also fireform the case. However, I have fireformed MANY, MANY cases to the Ackley 40 degree and before I started using the "hard jam" method, I had more than a few pieces that would not fire. It would strike the primer, which in turn would push the case forward "lightening" the strike, thus causing the misfire. Now I use a neck bushing that is 3 thousandths smaller than a loaded round and jam the bullets 15 thousandths>>>NO misfires..

Im a novice my first experience with ff to Ackley is my current 6BRA, I fire formed 200 cases and out of those I had around 25ish that didn’t fire, they were all jumped.. I will try jamming my next lot which may give me 100% strike rate. Cheers for the info.

Rushty

 

[AROKHUNTER]

Thanks for the input. All of the reasons and points mentioned in the above posts are why I am asking about fire forming. I have read a lot of different opinions and approaches about how to get it done.

 

[dkhunt14]

Im a novice my first experience with ff to Ackley is my current 6BRA, I fire formed 200 cases and out of those I had around 25ish that didn’t fire, they were all jumped.. I will try jamming my next lot which may give me 100% strike rate. Cheers for the info.

Rushty

The firing pin hit still can push the case into the chamber by varying amounts. Almost like partially sizing the case. That's why it's better to also have the bullet in the lands to help hold it back. Matt

 

[KenOath]

Thanks Matt point noted I will be jamming my next lot in the BRA hopefully will have 100% strike rate.

Cheers Rushty

 

[rardoin]

Thanks for the input. All of the reasons and points mentioned in the above posts are why I am asking about fire forming. I have read a lot of different opinions and approaches about how to get it done.

When you close the bolt on new brass (remove firing pin/spring etc. if easily done) do you have to cam the bolt home...ie 'crush fit'? If so I would load up 20 or so and see if they all fire fine. In my 6.5 x55 Ackley shouldered chamber I can ff new brass and it groups well enough to shoot competitively. I have about 275 cases fired with one fail to fire. However, if I was using it to hunt I would only hunt with ff cases to make sure that 1/275 was not on a nice deer.

 

[AROKHUNTER]

I am of the opinion that when fireforming brass to either an Ackley chamber or something like a Dasher (blowing the shoulder forward) you need to jam the bullet well into the lands to force the case head firmly against the boltface. This can be eliminated if you create a "false shoulder" to force the case against the boltface. However, doing a Ackley with a false shoulder, to me, seems like a lot of extra work for no apparent gain. So your idea of seating them off the lands is, in my opinion, not the best way. You may very well get misfires and the cases surely will not be exact.
My suggestion is to buy some Berger HUNTING VLD's (which generally like to be jammed) and if in the 140 class weight, try and get some accuracy before going hunting. If you have Varget go from 41.0 to 42.5 grs for fireforming and see which ones form the best with the best accuracy.

The method of jamming the bullets makes sense to me. I have plenty of Berger bullets to use for this method. Looks like it will be the way to go.

Thanks

 

[Geno C]

I have my ackley chambers all set a little shorter than most people, the does away with the need for false shoulders or jamming. My last 3 barrels were all set .007" short of zero of the parent cases go gauge. I make sure to have lube on my lugs and bolt face though.

I didn't alway do it this way and ran the false shoulder and jammed bullet method. The false shoulder as stated above is extra work that I think could be avoided and the jammed bullet never left me with cases all the exact length.

Try the jammed way first if you haven't set the chamber shorter than considered standard. If that doesn't work to your liking. Try the false shoulder.

 

[Quickoz]

Depends what your reamer print is. My 7mm08AI had the shoulder blown forward so jamming is a must. I fireformed with 45gr 09 and 162gr Amax. Jammed 20 thou and no misfires.

Use the cartridge within its limits and its works well. I ran 180gr for one barrel and was a hummer, but I think 162 to 168gr class bullets are perfect for it running around 2820 mark.

 

[AROKHUNTER]

I have another question. Is there a potential for a donut once the brass is fireformed from any of the methods mentioned?

 

[ShootDots]

I have another question. Is there a potential for a donut once the brass is fireformed from any of the methods mentioned?

There is ALWAYS the potential for doughnuts to form in ANY case, fireforming or not. Under pressure the brass flows to the area with least resistance. The gradual thinning of the case wall as it goes up towards the shoulder and neck will be the area of least resistance, hence doughnuts!!

 

[AROKHUNTER]

There is ALWAYS the potential for doughnuts to form in ANY case, fireforming or not. Under pressure the brass flows to the area with least resistance. The gradual thinning of the case wall as it goes up towards the shoulder and neck will be the area of least resistance, hence doughnuts!!

I hear ya! That being said, what is the best method to eliminate or prevent donuts?

Is there a better method in prepping or forming the brass that will reduce the chance of donuts?

 

[AROKHUNTER]

Depends what your reamer print is. My 7mm08AI had the shoulder blown forward so jamming is a must. I fireformed with 45gr 09 and 162gr Amax. Jammed 20 thou and no misfires.

Use the cartridge within its limits and its works well. I ran 180gr for one barrel and was a hummer, but I think 162 to 168gr class bullets are perfect for it running around 2820 mark.

I took a look at a couple of different reamer prints, and you are absolutely right. Due to the shoulder measurements, each print looks like the chamber would require, or at least work, a different approach to forming.

 

[ShootDots]

I hear ya! That being said, what is the best method to eliminate or prevent donuts?

Is there a better method in prepping or forming the brass that will reduce the chance of donuts?

That is a question that has yet to be answered! If there were a way to prep brass or fireform it to eliminate or even minimize their growth, we would have found it. There is a way to "control" them>>>but to STOP them, it has not been invented yet. You can buy a "cutter-tipped" mandrel from PMA Tool that will cut out most (not the whole thing) of the doughnut out of the case. It works well.. However, eventually they return!

 

[flatlander]

My 7-08 Improved reamer features a 30* shoulder instead of the Ackley 40*. In order to keep cases from being pushed forward against the shoulder by the firing pin strike, then stretching just above the web as the casehead is slammed back into the boltface by pressure, I have to use the false shoulder method. Tried it without, and primers came out looking flatter than a pancake, with obvious thinning of the case ahead of the web. With false shoulder, there was no thinning, and primers with the same load still had a radius out at the edge.

Seems like the easiest way to do it is to start with 308 brass necked down leaving the false shoulder. You wind up with the wrong headstamp, but otherwise, you have to expand 7mm necks up to 30, then size back down to leave the false shoulder. I've yet to try this, so don't know if you'd need to neck turn.

 

[AROKHUNTER]

So, if I were to use the false shoulder method, how do I do that? What is the process and best tools to use to accomplish the false shoulder?

 

[spclark]

So, if I were to use the false shoulder method, how do I do that? What is the process and best tools to use to accomplish the false shoulder?

The idea is simply to use your 7-08 die to bring a 308 neck down to 7mm enough that the bullets will be held in but you haven’t come close to touching the original case’s shoulder. The untouched portion of the 308 neck that touches your 7mm’s chamber’s neck portion is what adds the needed resistance, aka ‘false shoulder’, when it comes time to pull the trigger.

Flatlander’s experience with case stretching brings to mind what I found true a couple of years back with a 308-based 7mm wildcat called 284INCH. I was using many-times-fired 308 cases, had quite a few form that telltale stretch line just at the web/case wall point. This was with me using the COW method too rather than using actual, live loads, which may have been why.

Before I start with a new batch of cases this season I want to find a method that improves on this flaw.