what dies Cooper 6mm BR?

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kenickie22

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My dad is trying to load for a new Cooper 6mm BR. The neck diameter of a loaded round is 0.266". When we use a 0.264" neck bushing in a Wilson die on once fired brass, we are getting a "doughnut" below where the bushing stops sizing. This causing the rounds to not chamber. We are using Lapua brass. Does this indicate that the chamber diameter is excessively large? Should we be using a non-bushing type die with this gun? What die would you recommend? Thanks.
 
kenickie22 said:
My dad is trying to load for a new Cooper 6mm BR. The neck diameter of a loaded round is 0.266". When we use a 0.264" neck bushing in a Wilson die on once fired brass, we are getting a "doughnut" below where the bushing stops sizing. This causing the rounds to not chamber. We are using Lapua brass. Does this indicate that the chamber diameter is excessively large? Should we be using a non-bushing type die with this gun? What die would you recommend? Thanks.
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Wilson neck size dies only size a portion of the neck leaving the bottom of the neck unsized. This shouldn't have any effect on whether your brass will chamber or not. Try this, put a fired case that was fired in his rifle back in the chamber. It should chamber with no problem. Next size the case in the Wilson die and see if it will chamber. If the first one will chamber, the second one should as well. Now seat a bullet, no powder or primer and see if it will chamber. If you are running into a problem from a doughnut, it will be caused by neck turning and will be at the bottom of the neck where the neck turner quits turning and not caused by the Wilson neck size die. The doughnut will be inside the neck of a fired case. If you seat a bullet into this area of the neck, it will push the doughnut to the outside of the case neck making it to where the case will give problems chambering. If that's the case, then the solution is to turn the necks farther in towards the shoulder to keep a doughnut from forming or use a shorter bullet so that the bottom of the bearing surface of the bullet is above the bottom of where the neck turning stopped. You can also inside neck ream the neck to remove only the doughnut at the base of the neck. Hopefully, that will help solve your problem.
 
What is neck diameter of fired round? Cooper's chamber necks are on the large side. The fired round neck will be about .001 smaller than the chamber neck. It may be the .264 bushing is pushing brass toward the shoulder causing an external donut. The fired round should have the same neck diameter from mouth to near shoulder. Neck turning will correct the external donut. Try a .265 and .266 bushing to see if donut occurs. If your loaded round is .266 the neck brass is .0115. Check thickness the full length of the neck to see if brass is thicker or is bulging from sizing.
 
The neck diameter of a fired round is 0.274". An unsized fired round will chamber with no resistance.

A sized case measures just over 0.265" with no bullet (0.264" neck bushing). The unsized portion of the neck tapers from 0.270" to 0.278" near the neck/shoulder junction. This case will not chamber.

Zimmden, you are suggesting neck turning to 0.266" after the first firing, correct? I would need to neck size the cases and then run an expander thru the neck before turning, right?

Thanks for your help!
 
It's probably because your chamber neck is so much larger than the bushing that you are using that when you try swaging the neck down with the bushing the brass below the bushing is swelling out from the pressure sizing the neck. I don't think neck turning will do you any good. I think Wilson can make the die size all the neck instead of just part way down the neck. I've used Redding type S dies with .272" necks and unturned brass and not run into the problem you are having. I'd bet your chamber neck is at least .275" and you're getting .001" spring back on the fired case giving you the .274" fired neck diameter. All the Wilson dies I used were used with tight necked chambers with the brass turned for the most .002" clearance and never ran into the problem you're having. Try having the Wilson die adapted to size all the neck or get a type s full length bushing die and use it sizing all the neck and see if that will solve your problem. Either would be less expensive than having the barrel rechambered for a tighter neck. I haven't run into this before so am not sure what the best way to fix the problem would be. At least, the best at the least expense.
 
Ken...im not shure what ur doin...but it sounds like your turned the necks too thin for a NO turn chamber....the bushing is squeezin the neck too far down and it is balooning out to much larger near the bottom of the neck ---what a mess---try some brass that is NOT turned and use a .265 or .266 bushing ...and remove the expander ball......they shuld load around .268-.269......the clearance is built in beacause of the huge neck dia. of the factory reamer!!!....let us know what helps...Roger
 
The brass is unturned Lapua. Would a Redding type S die be capable of sizing the entire neck? Maybe the Wilson die only sizing a portion of the neck is the issue (along with the large factory chamber).
 
With a .274 fired case neck I would want a brass neck thickness of .0145. This will give you a loaded round of .272. This gives you .002 to .003 clearance when chambered. The brass will wear out very quickly from firing and resizing the neck with more clearance from thinner necks. I would not turn necks thinner than this. You are correct when you suspected the chamber neck was large. Factory cut chambers have to be this way so all ammo fits and fires safely. Custom chambers (tight neck) require neck turning to give .001 to .003 clearance. If your brass is not thick enough to have .0145 necks, you will need a sizing die that does not bulge the neck. Use a small amount of Imperial Sizing Wax on neck.
 
Check to see if the case is growing in length. I had a problem like that. Yous a full length sizer with bushing.
Good luck Max
 
Let's do a little math. If we figure the unturned neck at about .0145 per side and you bullet at .243 (perhaps .0003-4 more if it has a pressure ring) your loaded round should be roughly .272. Which would call for a neck bushing of .270. I suggest that you obtain a bushing of that size and give it a try. Why did you pick the .264 bushing in the first place?

Added later: It may be that with the fired neck being so much larger than the bushing ID, that the neck is too large to be properly accomodated by the lead in chamfer of the bushing, and that this results in excess pressure on the end of the neck as is starts into the bottom of the bushing, distorting the case. What brand is your bushing, and do you have the size number on top?
 
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A loaded round measures 0.266". That's why we chose the 0.264" bushing. It's a Wilson bushing, and the number side is up.
After talking to Redding, I've decided to order a standard (non bushing type) full length die. I think my chamber is too large to use a bushing die with the brass I'm using.
 
If you are using unturned Lapua brass then your loaded round should be measuring in the .272" range. This is considered a "no turn neck" thickness. I don't understand why your loaded rounds are measuring .266" if you haven't neck turned. Did you buy this brass new? What are you measuring the loaded round diameter with and is your measuring device calibrated or zeroed? Something isn't adding up somewhere.
 
There's no such thing as the chamber neck being too big to use a bushing die. You just order the correct bushing size. I've got a 6 BR with a no turn neck and have no problem with rounds chambering when sized with a Redding bushing FL or NS die. Unturned Lapua brass as stated above should be ~0.272" over the bullet in the neck. I doubt that a manufacturer would sell a relatively mass market rifle with a chamber requiring neck turning. They don't like getting letters from lawyers representing irate customers who just got a bolt stuck in their eye because one of their rifles came undone.
 
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