Neck turning for fire forming BRX

[BryanCO]

Hey guy I’m fire forming some BRX brass from lapua BR brass, I have a neck turn chamber.

My question is when turning the necks down on the BR brass do I go the where the BRX shoulder junction will end up at once fired, or a little more or?

My reamer print shows the BRX neck length at .222 so I’m was thinking of turn the necks of the BR brass to a length of .240 and then fire forming.

Thoughts?

 

[JEFFPPC]

I go to just past where the neck shoulder junction will be. More importantly be sure your throat will let your bullet pressure ring stay north of that point. My bullet of choice when just getting a tiny marking from the lands is half way down the neck leaving plenty of room to go in or out. 90 percent of the time I am in the lands .003 to .009 but have been in much more than that also. Give it what it wants.

 

[NZ_Fclass]

Do you need to turn the necks to chamber the case? I would do it later - I use a "false shoulder" to form brass, but I have a "no turn" chamber and only turn for concentricity.

 

[JEFFPPC]

Do you need to turn the necks to chamber the case? I would do it later - I use a "false shoulder" to form brass, but I have a "no turn" chamber and only turn for concentricity.

Read his first sentence, I believe he is saying he does.

 

[NZ_Fclass]

Read his first sentence, I believe he is saying he does.

That's what comes of reading posts at 6am without yer glasses!

 

[BryanCO]

Ok great, just below the BRX shoulder junction is where I was thinking, the bullets will be jammed about 15k and I’m using 30.5 of Varget, the bullet is seated pretty far out with this chamber so I have about .200 of the bearing surface in the neck, so I believe this will put me above the pressure ring if I am understanding correct?

 

[JEFFPPC]

Pressure ring needs to be above the neck shoulder junction to stay away from any donut interference. With one exception of many barrels shooting 107 gr bullets I have been between 33.0 and 33.4 gr of Varget, puts you around 2970 to 2990 depending on the barrel. Your way light and getting no advantage from the increased case capacity. You can go over 3000 but accuracy drops.

 

[BryanCO]

Yes my current BRX load is 33 Varget at 2990-3000 with a 107smk but 33gn will not fit in the standard br case for fireforming, I will be well above the donut area jammed at 15k

 

[JEFFPPC]

I think I misunderstood you, the 30.5 was in your fire forming load, got it.

 

[Walt Krafft]

I would fire form without a bullet. Pistol powder and a dab of grease in the neck. Then turn as needed.

 

[DJSBRS]

Turn your necks to the correct diameter for your chamber. Turn down on the neck length only enough that an new turned cartridge will just fit your chamber. After firing, it will pull back and expand correctly not leaving a donut.

DJ
DJ's Brass Service

 

[swd]

Ok great, just below the BRX shoulder junction is where I was thinking, the bullets will be jammed about 15k and I’m using 30.5 of Varget, the bullet is seated pretty far out with this chamber so I have about .200 of the bearing surface in the neck, so I believe this will put me above the pressure ring if I am understanding correct?

You want a hard jam more like .060”. 30.5 Varget with a 107 SMK. I use softer Winchester primers for fire forming. Just go to a mid range F Class match and it’s your fault if your not shooting cleans. Sometimes I think fire form loads shoot better than worked up match loads.

 

[rockhound78]

I know in a 7mmTCU MOA pistol I used for IHMSA, it seemed fireforming loads always shot better than my match loads

 

[BryanCO]

You want a hard jam more like .060”. 30.5 Varget with a 107 SMK. I use softer Winchester primers for fire forming. Just go to a mid range F Class match and it’s your fault if your not shooting cleans. Sometimes I think fire form loads shoot better than worked up match loads.

I hear this a lot, do you think it’s because of the excessive jam that these loads shoot so well?

 

[BryanCO]

Turn your necks to the correct diameter for your chamber. Turn down on the neck length only enough that an new turned cartridge will just fit your chamber. After firing, it will pull back and expand correctly not leaving a donut.

DJ
DJ's Brass Service

Ok great, so my thoughts on turn the total length to .235 vs my reamer print .222 (about 10-13k) is too much?

 

[DJSBRS]

I think so. Why not turn to match actual chamber? Then you don't have to jam to fire form.

DJ

 

[BryanCO]

I think so. Why not turn to match actual chamber? Then you don't have to jam to fire form.

DJ

Makes sense, thanks for the info, I’ll give it a try

 

[swd]

I hear this a lot, do you think it’s because of the excessive jam that these loads shoot so well?
The 107 Sierra’s love to be jammed. You can take a 107 in formed brass, seat it out to where the engraving marks are about square, chrono it to 2925ish and it may not be the very best load but it will likely be competitive at mid range. But the fires form loads seem to be just even more magical for some reason.

 

[AlNyhus]

On my BRX, I turned the necks .050 below where the new neck/shoulder junction would end up. This gives a consistent thickness to the upper part of the shoulder....helps against donut formation.

Hard jam into the lands, a top end load of a fast-ish powder for the bullet you f-form with, lightly lube the case and they f-form beautifully. -Al

 

[JEFFPPC]

On my BRX, I turned the necks .050 below where the new neck/shoulder junction would end up. This gives a consistent thickness to the upper part of the shoulder....helps against donut formation.

Hard jam into the lands, a top end load of a fast-ish powder for the bullet you f-form with, lightly lube the case and they f-form beautifully. -Al

I agree except.....dry cases and clean dry chamber for fire forming. Do not fire form with warm/ hot chamber. Case needs to grab the chamber for an even stretch. Yeah I know, but I disagree.