September 20th, 2020The 30 BR cartridge is a wonderful little cartridge. However, 30 BR users will have to neck up 6mmBR or even 7mmBR brass before they can expand it. One of our Forum members expressed concern about the donut which can form at the newly expanded neck-shoulder intersection. Randy Robinett, a respected bullet-maker, offers tips on how you can deal with the “dreaded “donut”.The Forum Member was concerned that he would thin the brass if he twisted his 30 BR necks. “Everything I’ve found on 30 BR cases-forming says simply to turn off the bulge caused by the 6BR shoulder at the base of neck. I expanded my case and measured the neck to be 0.329? The donut is 0.335mm, but the neck is 0.329mm. A groove is visible inside the case… under the donut. It is a known fact that the groove will still be there when I remove the donut and turn the neck? This means that there is now a thin spot ring at base of neck which is.005 thicker than the rest. Has anyone ever experienced a crack in the neck on this ring before? Randy Robinett is one of the “founding Fathers” of 30 BR. He helped prove and popularize 30 BR for score shooting. Randy gives this advice about 30 BR case-forming. While the thinner neck base was one of our initial concerns, unless you cut too deeply into the shoulder, it’s not a problem. In my 30BR chamber I used thirty (30) cases to fire 6,400 round through the barrel. The cases were not annealed and yet there were ZERO failures, neck separations or splits. The case-necks had a diameter of.328″ when loaded round and were sized from the start with a.324″ size. neck-bushing. The best way to avoid the ‘bulge,’ is to fire form before neck-turning. (Several methods have been successfully used). Too much cutting into the shoulder can cause case-neck separation. I have seen this happen, but have not personally experienced it despite having fired thousands of shots and several barrels. The last registered BR match fired with that barrel produced a score of 500-27x and a second place finish. It’s not bad at all for 6K+ shots and over 200 firings in each case.More information on 30 BR Case Forming can be found in our 30 BR Cartridge Guide. Al Nyhus, a benchrest shooter for HBR and score, has provided some tips on that page.
The 30 BR cartridge can be made by necking up 6mmBR or 8mmBR brass. This can be done in several stages or all at once. You can either use an expander mandrel, like Joe Entrekin uses, or a tapered die button. I personally use a Redding 16307 tapered expander. This expands the necks in one pass from 6mm to 0.30 cal. It works as long as the mandrel is lubricated and the inside of each neck. I’ve used the Sinclair Expander Body with a series of larger mandrels but this is more work and the Redding tapered buttons keep the necks straighter. This button can be used with any Redding die which has a large inside diameter that will accept the BR cases without any case to die contact. Do not worry about the necks being straight before you fire them for the first time. They will straighten themselves out when you whack them with 50,000 psi! I recommend not seating bullets in the lands when firing the first time, if there is a light crush-fitting of the case inside the chamber. The Lapua cases are expected to shorten by approximately. 1.550? To around 1.520? After being necked to 30-caliber, I trim to around 1.500? With the (suggested 1.520 length chambers. I don’t deburr or uniform the primer pocket until after the first firing. I use a Ron Hoehn tool to deburr the flash holes. It indexes the tool on the primer pocket and not the case mouth. — Al NyhusSimilar Posts:Tags: 30 BR, 30BR, 6mmbr, Al Nyhus, Case Forming, Fire-Forming, Score Benchrest
