6 MM BRX problem

[Bob3700]

Gents,

I have a newly chambered 6mm BRX bbl. I ordered new Lapua brass. Decided after much reading that I wanted to use the false shoulder method of fireforming.

The necks were necked up to 25 cal and then placed in the 6 MM BR FL sizing die. As I kept sizing the neck down to 6mm, the case was inserted into the chamber looking for the point where the bolt would just close. It never would. I have the neck completely resized back to 6MM and the bolt still would not close.

I took a factory case that had been FL resized and attempted to chamber it in the gun. No dice. Now I am concerned. I actually took the factory case and with some coaxing, got the bolt to close. When I extracted the case, the mouth of the case was crimped.

Now I am really getting concerned. Got the print out of for the reamer. Also measured the OAL of a new case.

New Case 1.558"

Reamer print on chamber length 1.550"

What gives? This reamer is supposed to be a no turn neck. Just create a false shoulder and go fireform.

Now it would appear that I have to trim the case neck shorter to get it to chamber. There has never been any mentioning of trimming the brass shorter in order to get it to chamber when fireforming brass for a 6 mm BRX.

As I see it, there are only two possible issues here.

First, the cases need to be trimmed shorted to get the brass to chamber.

Second, the reamer is ground with a neck area that is too short.

What are the neck length of your reamers?

Thanks for the imput.

Bob

 

[sparker]

Hi Bob.

Call me tomorrow after 4pm pacific.

Scott Parker

661 364 1199

 

[Rustystud]

You have not told us if this is a no neck turn,.272) chamber or a smaller necked chamber. If your chamber is a neck turn chamber you will have to turn the necks on your brass first. I have never had any problems fire forming 6mmBRX from Lapua 6mm BR brass. Don't waste your time or money with any brass other than Lapua. The brass just has fit the chamber. 29 to 30.5 grains of Varget and your bullets jammed into the rifling .010 to .015 has been an old standby load to fire form this brass. It is so accurate you can shoot it in matches out to 600 yards. The fire formed case will have the same overall length. The shoulder will be blown out .100 and the neck will shortened. If you are using a neck turn chamber the case will have to be turned to just below the neck shoulder juncture or you will have a donut. If you are using 6mm BR dies to load the 6mmBRX you will need to get or make a body die. I use a FL died backed out .098 to size the necks and shoulders. I use a body die to size the shoulders back to the case head. This can be done by taking a 6mmBR body die and boring out the die top so the case can pass through and the die allowing it to work the web area of the case. You may have to take a few thousands off the die face to get it down over the 200 mark of the 6mmBRX case. The 6mmBR brass is thinner than a .308 and the 200 mark really is a false web line. With the Lapua 6mmBR brass the web line is closer to the case head. Your chamber should be polished to allow for case to slide in and out without resistence, if not you will have extraction issues. I don't know if this has answered any of your questions.
Rustystud

 

[expiper]

HI Bob...if the print is correct and the chamber is correct and the math is correct ....it sounds like you gotta shorten the cases..!!!! I wuld shorten 1,one) to 1.550 and see ....shuld take 5 min...would asnwer a multitude of ????....let us know...Roger
PS,,,I have found most ctgs. shorten after fireforming...that is why lots-0-dasher chambers are 1.555...just enough jam on the case mouth to hold it in place and after forming the cases are aprox..1.535 ...just rite....this is why the chamber is cut short...you can jam the case mouth and hold it for fire forming,no bullet) and usually not have to create a false shoulder in the neck....try one and see.

 

[Dubya]

Hey Bob,
If you have the reamer print, what does it show for neck diameter? If it's a no turn neck should show .272, if it shows smaller than that, you will indeed need to turn the necks.

Gary.

 

[Bob3700]

Gents,

Thanks for your replys.

The reamer is a "No turn" .272 so turning brass should not be an issue. Brass is new lot Lapua.

The print states that the OAL of the chamber is 1.550 and this is the same as Bob Crone's,sp) original according to Dave Kiff.
My current lot of Lapua brass has an OAL of 1.556, which is part of the problem. It is too long to chamber. I'll have to trim .008" off the brass before I can begin to chamber a case for fireforming.

I agree that at this time, the only option is to trim a case back until the bolt closes and that will be the max OAl for the case. My complaint/concern is that at no time has anyone written that these "No Turn" cartridges must have the brass trimmed to a shorter length befor you can fireform!

So there is some misinformation out there on the ease of creating the cartridge as well as neck length dimensions. Now I am looking at trimming to length a whole bunch of cases before I can begin to shoot/form my brass. That is not a show stopper, but certainly another step that must be accomplished.

Perhaps there are also issues with Lapua Brass being different length,slight variatios) depending upon the lot that you have purchased.

RGDS

Bob

 

[expiper]

Hi agin bob....you ar rite...there is a lack of info on the internet....and a lack of knowledge of the way to make/form/fireform various AI/Improved/Dasherized versions of various cal....in the case of the BR and various wildcat children one simplification of the process involves the chamber length dim. that "fits" most Lapua virgin brass...thus when forming without bullets the problem is negated and when the cases shrink after forming they are short enuff to not require trimming at that time.....some gunsmiths that ar not shooters and some shooters that dont have access to reamer drwaings are in the dark....Im glad you are gettin a handle on it and are about to shoot one of the finest cal. out there .....good luk and keep us posted on your ctg and load development....Roger

 

[sparker]

Hi Bob.

I measured new brass and found brass from 1.550 to 1.560 in length.


I measured fired brass and one batch measured 1.550 to 1.560,no false shoulder)

I measured another batch at 1.530 to 1.540, false shoulder).

Your case length on your chamber is too short.

Scott Parker

 

[Bob3700]

Scott,

What is the case length that your reamer print calls out?

Bob

 

[Dubya]

Hey Bob ! How about posting your reamer print! It may help in the discussion of your problem.

Gary.

 

[Bob3700]

Gary,

I believe that I have found the problem.

The length of my reamer neck is 1.550". It should be 1.565" to work with standard Lapua 6 mm BR brass.

New Lapua brass measures 1.550 to 1.560 out of the box.

The reamer needs to be reground.

RGDS

Bob

 

[Dubya]

Bob, you are headed in the right direction, but your reamer should be set to chamber to 1.570. SAAMI specs. require .020 clearance for expansion.
My old lot of new Lapua brass measure 1.550. I have built three 6BRX since 2004 and about to build a fourth, great shooter,
and I'm sure you will enjoy it when you get things straightened out.
I will try to PM you a print of my reamer.
E-mail sent.
Gary.

 

[mrjdasr]

explain how you plan on regrinding a reamer to add length to the neck

 

[Bob3700]

The body of the reamer is much longer than the section that actually cuts the chamber.

The reamer grinder can regrind the whole reamer to make the dimensional adjustments.

Bob