I'm new and trying to sort out a few things in my mind and thought some of you would know my question from your experience. If you take unturned Norma and/or Lapua 6BR brass and seat various brands of 105-107gr. bullets what does the neck diameter come to? I would be interested in various bullets that you may have miked so I can get in my mind what is going on with the various dies, bullets, and unturned brass and neck expansion. Appreciate your knowledge...
Unturned 6BR Neck Diameter?
- Thread starter WhelenMan
- Start date
Fred Bohl
Gold $$ Contributor
Larry,
I use primarily Norma brass and have found the last three lots to have neck walls of 0.0125 to 0.0130 for all lots. I have been using Sierra 107MK, Berger 105VLD,old die), and Lapua Scenar 105 bullets.
For once fired cases, neck sized,0.267 bushing), the finished neck diameters have run 0.2685 to 0.2690 with the Bergers and Sierras but 0.2680 to 0.2685 with the Lapua Scenars.
All three of my 6BR chambers have 0.272 "no-turn" necks.
I use primarily Norma brass and have found the last three lots to have neck walls of 0.0125 to 0.0130 for all lots. I have been using Sierra 107MK, Berger 105VLD,old die), and Lapua Scenar 105 bullets.
For once fired cases, neck sized,0.267 bushing), the finished neck diameters have run 0.2685 to 0.2690 with the Bergers and Sierras but 0.2680 to 0.2685 with the Lapua Scenars.
All three of my 6BR chambers have 0.272 "no-turn" necks.
Thanks Fred, It looks like there quite a variability in the case walls. According to this then I can expect about 5-7 thousandths of an inch of brass expansion each time not including any chamber expansion if any. That I don't know about. This may help me to know what to expect when I get going. Do you regularly mike all of your reloads to check just in case you get one oversize bullet or brass problem that could result in overpressure since even with the no turn neck some cartridges are only .001 or .002 below the neck depending on whether you have 0.271 or 0.272? Thanks again.
That's interesting. Evidently there's quite a bit of variation from one lot of brass to another even within the same manufacturer. I guess when one finds a good lot of brass you need to stock up just in case quality control slips. That last tolerance listed is what I was hoping for in bullets and brass but evidently it does vary going from what Fred saw. Anybody have an opinion on the minute difference between a .271 no-turn neck and a .272 no-turn neck? Maybe one should buy a supply of brass and then neck to match components? New at this and just throwing out ideas....
Fred Bohl
Gold $$ Contributor
Larry,
Fired cases measure 0.270 to 0.271 diameter from my 0.272 chambers with most closer to .270 diameter. I have also found that the wall thickness variance decrease with repeated firings and that almost all are uniform to within 0.0002 after 3 firing and neck sizing cycles.
I have tried tight chamber necks and neck turning,including using a custom collet and mandrel on my lathe) over the years but have not proved to my satisfaction that it was superior to close size no-turn necks without neck turning. In fact, my current no-turn 6BR barrels have delivered my best groups in my 55 years of shooting - 0.190 for my HV barrel rig and 0.085, 0.088 and 0.090 for my Heavy Bag Gun barrel,all in no wind).
I had one combination with turned necks and tight chamber that had a chamber ID 0.001 greater than the loaded turned neck but that needed spotless chamber and finished cartridge neck to chamber dependably. My suggestion would be to design for a chamber ID of 0.0015 minimum to 0.0020 maximum greater than your loaded neck size. That is why I chose 0.272 versus 0.271 chamber neck ID.
Fired cases measure 0.270 to 0.271 diameter from my 0.272 chambers with most closer to .270 diameter. I have also found that the wall thickness variance decrease with repeated firings and that almost all are uniform to within 0.0002 after 3 firing and neck sizing cycles.
I have tried tight chamber necks and neck turning,including using a custom collet and mandrel on my lathe) over the years but have not proved to my satisfaction that it was superior to close size no-turn necks without neck turning. In fact, my current no-turn 6BR barrels have delivered my best groups in my 55 years of shooting - 0.190 for my HV barrel rig and 0.085, 0.088 and 0.090 for my Heavy Bag Gun barrel,all in no wind).
I had one combination with turned necks and tight chamber that had a chamber ID 0.001 greater than the loaded turned neck but that needed spotless chamber and finished cartridge neck to chamber dependably. My suggestion would be to design for a chamber ID of 0.0015 minimum to 0.0020 maximum greater than your loaded neck size. That is why I chose 0.272 versus 0.271 chamber neck ID.
Fred, what you say is exactly what I needed to get straight in my mind. I was planning on building my first rifle to be a 6BR or BRX and thought to go with a .271 or .272 neck and you've helped me see what is happening dimensionally. I really think that Lee has the right idea with their collet dies and it could be a good thing if executed properly. I'll probably get some regular dies like the Redding bushing dies but want to get a couple of sets of the Lee's since they're cheap to play with. I may have to make something myself to get results. I've got a set in 25-06 and they have their limitations. I'm thinking of an adapter to allow me to use my torque wrench in conjunction with my press to get the same pressure each time or go to a fully hydraulic press with gauge or variable pressure relief valve with a homemade collet similar to the Lee Dies but made of steel with a spring load. I like to tinker and look at things for improvements. At one time I was paid to do just that at a nuclear power plant under construction. You're a wealth of information Fred, keep it coming as I'm sure I'll have more questions.
Fred Bohl
Gold $$ Contributor
Larry
In the past I have used Lee Collet Neck Dies including a custom set,send Lee 2 fired cases from you chamber and two sample bullets - also send a sample with a seated bullet for length reference plus $54 and in about 90 days you'l have a custom made set). They produce very strait and concentric necks with minimal working of the neck material.
The limitation I find to Richard's design is in the control of neck tension. Over several reloads, the neck will work harden slightly so that the "spring back/recovery" of neck ID formed on the mandrel will gradually change and with it the neck tension changes. The same happens with bushing neck sizing but I find it far easier to change bushings than to make new mandrels for the Lee die.
In the past I have used Lee Collet Neck Dies including a custom set,send Lee 2 fired cases from you chamber and two sample bullets - also send a sample with a seated bullet for length reference plus $54 and in about 90 days you'l have a custom made set). They produce very strait and concentric necks with minimal working of the neck material.
The limitation I find to Richard's design is in the control of neck tension. Over several reloads, the neck will work harden slightly so that the "spring back/recovery" of neck ID formed on the mandrel will gradually change and with it the neck tension changes. The same happens with bushing neck sizing but I find it far easier to change bushings than to make new mandrels for the Lee die.
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