Mushroom Free 6XC Cases

From Left to Right
22-250 Case - Once Fired Winchester
22-250 with shoulder pushed back using 308 Die
6XC Case Formed after prebumping shoulder back
Mushroomed 6XC formed using just the 6XC Die

Summary of Mushroom Free Process
1. Formed necks are longer and closer to 6XC design length
2. Cases necks appear to be more concentric
3. Turning necks after 6XC forming may yield less donuts
4. Cases look better before fire forming
5. Fireforming should be easier, just expanding the shoulder out. You are not trying to smooth out a reverse wriggle in the case shoulder..
6. Case trimming may be required at some point

11-13-2005 Update
Trigonometrically speaking backing the shoulder down the 0.064 is wrong or slightly too much. The shoulder diameter on the 22-250 case is 0.414 in diameter and the case side slope is something like 57.16 to 1. Therefore, the shoulder diameter on the set backed 22-250 case should be about 0.4162, which is still much smaller than the finished 6XC shoulder diameter of 0.455 inches. Therfore, the bumped shoulder on the 22-250 with the smaller diameter shoulder should sit about 13 thousandths higher into the 6XC forming die than finished shoulder after fire forming. Therefore, the total amount of pushing into the 308 die may be closer to 0.051 thousandths than 0.064 thousandths as mentioned above. I have tried one 22-250 with a 20 thousands washer and it worked without any mushrooming and had a more pronounced 30 degree shoulder. The magic number may be 18 thousandths, anything less than 16 thousands I have gotten mushrooming. The math on this will drive you nuts. Just remember the main point here is 22-250 cases may be prebump and then formed using the 6XC die and not have any mushrooming on the case head. Anyone doing this should run a few test cases for the amount of prebumping which will work best with your brass and fired chamber. The one 22-250 once fired case I tried with no washer or just pushed the case flush to the bottom of the 308 die still mushroomed. I will mention again that I do not have my Tubb Gun yet to work out correct amount of set back for my chamber. Hopefully by the time I get my Tubb Gun, enough of you other Tubb 6XC users will have tried this and have some actual prebumping barkpark numbers for new 22-250 brass from various manufacturers.

11-18-2005 Update
Case length. This process also produces longer necks on the formed 6XC cases. In fact you can control the case length. The amount of pre-bumping will affect the overall case length. As you approach the minimum amount of pre-bump for a mushroom free case, the overall length of the case reduces. I am going to use a pre-bump that will yield me an overall case length that is slightly above the trim to length of 1.900. This will allow me control the length of the case neck before neck tuning. Just trim all the long range cases before neck tuning. I have received my neck turning and neck expanding mandrels. While turning a couple of mushroomed cases in notice excessive wobble in the neck while holding the neck turning tool. I did not notice this on any of the non-mushroomed cases that I neck turned. The mushroomed cases with the wobble were not evenly mushroomed, i.e., they were mushroomed more on one side than the other. These cases caused the neck-turning tool to wobble in my hand. Therefore, the pre-bumping process may produce more concentric cases.

11-28-2005 Update
I have received my 500 Winchester 22-250 Remington cases so I may now start making my 6XC cases. My goal is to have mushroom free 6XC cases ready when I get my Tubb Gun. I have sent some formed cases to a friend that has a Tubb 2000 to measure and compare to his fired cases. This will give me a starting point for my die set up. My first attempts at making 6XC cases using once fired 22-250 brass indicated that I may have some control over the final overall case length. Therefore, I would like to have the formed 6XC pre-fire formed cases just over the trim length of 1.900 inches. I would like to have trimmed cases before neck turning.

I plan to use the Redding competition shell holders in all die set-ups. I will start with the Plus 10 Shell Holder and see what I get using the 0.268 Tubb bushing. I screwed the 268 bushing down tight as I could into the 6XC die and locked it. I also screwed the 6XC die as hard I could use channel locks and a small piece of leather so not to mar the die to the top of the raised ram with the plus ten-shell holder. If I change shell holders, I will repeat the tightening the die down hard on the new shell holder.

Using the 0.268 bushing the first case I pre-bumped using a 16 thousands washer. The first new case had some slight mushrooming. The case measured 2.068 inches with my Tubb Gauge with an overall length of 1.900. My target headspace dimension is 2.064 inches with an overall dimension around 1.904 inches. I was able to get 1.908 with some of the once fired cases. Therefore, I am hoping for the overall case length to be just long enough to do some trimming on. Next, I tried the plus six-shell holder on the same case and ended up with 2.0615 inches for the headspace measurement. I should have tried the plus eight first. The next case I changed to a 20 thousands washer and back to the plus ten-shell holder. The table below shows the various washer thicknesses and shell holders sizes I used to achieve the various results.

Case Number	Washer Thickness	Shell Holder Number	Gauge Headspace	Case Length
1a	0.016	+.010	2.068	1.900
1b	0.016	+.006	2.0615	1.894
2	0.020	+.010	2.0675	1.901
3a	0.020	+.010	2.068	1.901
3b	0.020	+.008	2.0645	1.900
4	0.021	+.010	2.0685	1.900
5	0.0215	+.010	2.0675	1.901
6	0.022	+.010	2.0665	1.901
7	0.023	+.010	2.068	1.901
8	0.025	+.010	2.0675	1.901
9	0.027	+.010	2.066	1.903
10	0.0285	+.010	2.065	1.899
11	0.031	+.010	2.0665	1.904
12	0.031	+.010	2.065	1.905
12a	0.031	+.010	2.068	1.904
12b	0.031	+.010	2.0645	1.902
12c	0.031	+.010	2.0685	1.901
12d	0.031	+.010	2.0655	1.902

Now I have come back to the 0.031 thousandths washer and time to see which cases will chamber okay. Now off to friend house with Tubb Gun to test the above cases. I think the cases using the plus 0.010-inch shell holder are to long, however, I am hoping that the cases may still chamber okay since they are slightly long just at the very top of the shoulder. The cases using the plus ten shell holder chamber okay. There was some resistance. However, if I did not try the bolt on an empty chamber first I would not have noticed it. The resistance was minimal. I also measured his go gauge with my gauge bushing and some fired cases.

Cases numbered two through eleven were pre-bumped using a 0.020 washer and shim washers to change the amount of pre-bump. Cases numbered 12 where done using a new 0.031 thick washer glued on top of the flat shell holder. I did five cases in all with the new washer to check the variances in gauge length and overall length. Everything looks like a go for these settings. Picture of finished cases below.

The basic procedure I used to form 6XC brass from 22-250 brass is as follows:

Step one - Pre-bump the 22-250 shoulder using the 20-degree shoulder angle of a 308 win full sizing dies. I used 0.031-inch think washer to push to 22-250 case slightly into the 308 die. No lube was required and all but two of the 500 cases fell freely out of my Redding 308 full sizing die. Two required a tap with a pipe cleaner to get started.

Step Two - Form 6XC cases using the Tubb 6XC sizing die with the 0.268 neck bushing. I also used the Redding Plus 0.010 inch competition shell holder. Gauge length of formed cases 2.0665 inches.

Step Three - Expand necks using K&M expanding 6mm mandrel.

Step Four - Trim cases to 1.900 inches. I modified a 243 Lee Trimmer.

Step Five - Inside taper and de-bur neck using K&M 7 degree taper tool. I chucked the case in my hand lathe and then used the K&M 7-degree taper tool. Doing this before neck turning, I think it helped the flute mandrel on the neck-turning tool enter the cases easier.

Step Six - Turn necks using K&M Neck Turning tool. I set the cutter for 0.012 cut wall thickness using feeler gauge. Lightly de-bur outside of case mouth and steel wool case mouth end. First tried fourteen thousandths and completely missed the neck. Thirteen thousandths setting cut some of the neck but not enough. The twelve-thousandths setting looked good and I stayed with it.

Step Seven - De-bur flash hole inside case using K&M tool and letter B drill. Just made sure that the K&M tool would easily rotate in the flash hole and do it with the letter B drill. I notice some of the holes had burs on the inside of the hole and required to be drill out with the K&M tool. The letter drill cuts a 118-degree angle and not a 60-degree angle like the K&M tool.

Step Eight - Uniform the primer pockets. No, I will be using the K&M primer pocket uniformer to clean the primer pockets after firing and after about three firings, it will stop cutting and just clean the primer pocket.

Step Nine - Solvent Rinse, three stage process.

Step Ten - Sort by weight and box in MTM-100 boxes.
Box One - 156.7 to 157.4 grains
Box Two - 157.4 to 157.8 grains
Box Three - 157.8 to 158.4 grains
Box Four - 158.4 to 159.1 grains
Box Five - 155.7 to 156.6 grains plus 159.1 to 161.0 grains plus cases used to develop process and three with fixed rims.
Thirteen of the new cases had split necks out of the bag.

Now the big wait begins. I am going to have to get some fired cases to practice on next.

Case Forming Summary

The 0.031 pre-bump worked allowed me to trim almost all of the cases some. While most cases just a partial cut, it was enough for a good stop during the neck turning process.

No lube required during the pre-bump step and I only lube the case neck inside during the 6XC die-forming step. I slopped enough Imperial Wax on the neck outsides to keep the neck bushing lubricated.

The Winchester brass seemed to have consistent neck wall thickness. The 0.012 wall cleaned up all the cases. The few I set aside for incomplete cut, I sorted by weight back into the whole group. For all practical purposes, they were 100 percent cut. I did not have any lopsided cases, just a few with split necks.

12-17-2005 Update
Godday Larry,
See attached photo of 6XC shell holder. Works like a charm. The only alteration is the width of the extension area which is 9.6 mm in diameter. (Why 9.6 mm - because that is the diameter of a .223 case rim - also no problems with "stuck" cases due to die contact with shell holder). Why don't you add this to your 6BR article as an update. Notice on the far left is the original mushrooming of the 6XC. The two cases on the right are using your method. Chambering is perfect and your height dimension is optimal. A picture paints a thousand words.

Cheers

Mike

2-10-2006 Update

Here is a picture of the final washer constructed Shell Holder I used to pre-bump the shoulder on the my new Winchester brass. Washer height is 0.031 inch. The shell holder was filled with epoxy under the washers to prevent any dimpling of the washers.

Great to have a friend with a lathe. Here is a picture of a very nice machine shell holder made to pre-bump the 22-250 cases. Height of pre-bump is 0.036 inch.

June 2006
I finally got my Tubb Gun and here is a picture on a fired case next to a loaded muchroom free case. Cases are fire gorming complete using 35 grains of H4350 and bare Sierra 107 MatchKings. My fired cases are only three or four thousandths shorter.

Picture below shows a loaded Mushroom Free case that I resized for 6XC alone side a fire formed and resized case.

Mushroom Free round next to a fired and resized case

Using my Top-Secret Pattent Pending Inspection Lighting Systems, allows you to see minor changes in surface contours. Note the small cut in the top of the shoulder on the Mushroom Free Case on the right. That small portion of the case is actually a few thousandths longer in headspace and chambers easy. The small portion on the base of the neck not neck sized is barely visible on the resized case on the left. The little bumping on the shoulder is also using the lighting system.

Larry Medler
anyrange@comcast.net

Rifle Silhouette Shooting

Silhouette Ballistics

Any Questions or
Web Page Comments
E-Mail

Released - November 8, 2005
Revised - September 2, 2006

Author's Rifle Silhouette Shooting Home Page with Shooting Tips