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jwtharpe

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I have been working on this for a little while now and its finally coming around. The reason for it is to have the correct case length in order to use longer bullets and still be able to fit them inside a mag. The old standards ( 6mm-223, 6x45, 6TCU etc. ) all have difficulty when trying to use non varmint bullets at mag length because of the nose length.
I chose to use a 40 degree shoulder in order to keep the neck length close to caliber size for all of the reasons longer length necks are good. The steep shoulder also allows the body of the case to be longer relative to 23 degree and 30 degree shoulder angles. This along with the decreased body taper allow the case to have nearly the same useful capacity as the 6-223 case despite it being .050" shorter.
Since the case has the same body taper and shoulder angle as the 6TCU, I use a modified 6TCU die for forming and resize.

I'm not good at writing, so here is some pictures and data.

Here are OAL to the lands of some different projectiles

SIE 70MK        2.270"
HOR 95SST     2.300"
BAR 80TTSX    2.318"
NOS 90BT       2.320"
NOS 90AB      2.345"
HOR 105BTHP 2.353"
HOR 105AMAX 2.390"
BER 95VLD     2.434"
BER 105VLD   2.442"
NOS 107CC    2.430"
NOS 105CC    2.443"

There is really no way to design a chamber that will be perfect for every projectile. You have to make compromises in order to make it work for your desired projectiles. I wanted to use 90 grain noslers for this with a mag. Knowing they like between .030, and .050" jump I set the freebore and case length where it is. (body might be just a little too long, .020 shorter would have been perfect IMO.)

I have a boat load of 105AMAX, so I used them on the first loads shot from the barrel.
Here are the results from the last strings I shot. This was on new brass that was not completely formed. Cant shoot these from a closed front mag.

Case- Lapua
Primer- BR-4
Bullet- 105AMAX
Trim- 1.700"
Powder- CFE223
Barrel- 26" 4G,8T Edit 12-21-2015 this chamber is longer than the production barrels
OAL-2.385"

27.0gr.
1-2710-av-2702
2-2699-es-11
3-2699-sd-6

27.5gr.
1-2760-av-2751
2-2754-es-17
3-2743-sd-7
4-2749
5-2760


6mm before first firing not fully formed
20150620_211110-1[1].jpg 

6mm compared to 223
20150622_201531-1[1].jpg 

5 shot group 27.5CFE 105AMAX @ 80 yds
20150621_185431-1[1].jpg 


More to come......

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JBFA

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Reply with quote  #2 
Very nice JW! You truly are a very busy guy
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RangerJoe

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I like it!!  I built a 6x45 back in 1983 or so; it really wasn't as good as I hoped.  Need to use light bullets to fit mag, which somewhat defeated the purpose.  THIS looks interesting!
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BIGGDAWG

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Reply with quote  #4 
Looks sweet Jw great velocity and accuracy can't ask for more.
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jwtharpe

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Reply with quote  #5 
Shot this today. 107 Nosler CC's  Mowed the range this morning. Distance was 100yds.
6mm-107gr-HPBT.jpg 

6mm target.jpg Screenshot_2015-06-27-10-43-41.png 


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MDWS

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Reply with quote  #6 
...and 28 grains wins. We are going to have a lot of fun with this. What do you think the best "varmint" bullet will be?
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RangerJoe

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Reply with quote  #7 
Quote:
Originally Posted by MDWS
...and 28 grains wins. We are going to have a lot of fun with this. ...

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jwtharpe

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Reply with quote  #8 
Quote:
Originally Posted by MDWS
...and 28 grains wins. We are going to have a lot of fun with this. What do you think the best "varmint" bullet will be?


No idea, I got some lighter bullets ordered but they have not come in yet. I might be wrong, but I don't think they will shoot any better than the heavy weights. Still have about a grain or two of capacity left with fire formed cases. This thing will be a killer on the 600 line.
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jwtharpe

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Case- LC-12
Primer- 450
Bullet- 87 V-MAX
Trim- 1.700"
Powder- TAC
Barrel- 26" 4G,8T  Edit 12-21-2015 this chamber is longer than the production barrels
OAL-2.315"  (.005" into lands)

New brass seated .005" into lands for fire forming. No accuracy data due to rain.

26.0gr.
1-2818
2-2849

26.5gr.
1-2812
2-2849

27.0gr.
1-2892
2-2879

27.5gr.
1-2898
2-2943

28.0gr.
1-2962
2-2969

28.5gr.
1-3016
2-3037

29.0gr.
1-3086
2-3079

29.5gr.
1-3115-av-3095
2-3093-es-36
3-3079-sd-18

30gr. starting to get into compression, had to turn seater in .005 to make length
1-3174-av-3207
2-3220-es-54
3-3228-sd-18

30.5gr. This is starting to show some pressure, slightly cratered primers, turn seater in .016" to make length
1-3284-av-3246
2-3267-es-95
3-3189-sd-50

changed to fireformed case, and load length to 2.275" .040" off lands. will fit in a mag at this length. Ran out of light before string was done.

29.0gr.
1-3058-av-3075
2-3079-es-64
3-3108-sd-24
4-3086
5-3044

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RangerJoe

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Reply with quote  #10 
Very impressive!  Too bad I can't rechamber my old 6x45.  What are you going to call this new 'cat?  "6mm Turtle Thumper"?  "6mm Tharpe"?
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coondog

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Reply with quote  #11 
Not bad numbers JW. In my 22inch 6mmARP barrel with a 90grAB set to 2.295 with VV N530 I can run about 2950 in Hornady brass. At 3000fps I blow primers. I need to try the same load with Lapua brass.
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jwtharpe

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Reply with quote  #12 
RJ, we would have to set your old barrel back around .080" to make it work. Then your gas tube would be too deep into the carrier key. I have not come up with a name. All of the good ones have been taken. Lol. Sent a PM

Coondog, that was Lake City brass. I'm liking it better than the lapua. The necks are thinner where they meet the shoulder after forming and don't have to be turned. I was going to turn some after turning lapua brass and the turning tool went all the way to the shoulder without cutting anything. Lapua has to be turned, it makes a step where the shoulder gets pulled up into the neck. The shoulder is much thicker on lapua brass. 
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coondog

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Reply with quote  #13 
One of the loads that worked good for me was with 60gr SMK and LT-32 powder. I tried to get to 3300fps but never made it. In the Grendel/Lapua case necked down I still had plenty of room for more powder but the pressure went to high. Lt-32 acts a lot different in the small boars.
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MDWS

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Reply with quote  #14 
6mmJW.
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jwtharpe

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Reply with quote  #15 
I'm going to try some LT-32 with some 70SMK's next time out. 
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coondog

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Reply with quote  #16 
Quote:
Originally Posted by jwtharpe
I'm going to try some LT-32 with some 70SMK's next time out. 

LOL I bet it was the 70gr SMK I used. 60gr just did not sound right.

One thing I like about your 6mm is the case size. Seems once a case gets bigger than a 6.8 case, you run into cycling issues. Running as long as you can with the bigger cases really helps.
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jwtharpe

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6mm primers.jpg 

That's a pic of the last 8 rounds shot today. The three on the left was 30.5gr load, and the five on the right were 29.0gr. with fireform case mag length. You can see some slight craters but other than that, they look good. Brass not bulged out close to the head, no flow into the ejector/extractor. Most military 855 cases look worse than this from most of my 5.56's.
I probably wont use TAC much because of the terrible es/sd that it always gives. 8208, and AR-Comp will probably be what I use for bullets in this weight range. Its going to give up some velocity compared to 2230/TAC, but it will be more consistent

One of the reasons I started on this is the brass. 5.56 brass is everywhere.  I have seen 6.8 brass and 6.5g brass become hard to find. Also both of those are expensive compared to surplus Lake City brass.

They should run real well in metal mags. Magpuls will probably need to have the inside rib shaved down a bit to prevent tilting. The steel mags from CPD, and ASC will give the longest load lengths. Im going to cut the fronts out of a couple for those rounds that I want to run out past mag restricted length.  


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RangerJoe

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Reply with quote  #18 
Quote:
Originally Posted by jwtharpe
RJ, we would have to set your old barrel back around .080" to make it work. Then your gas tube would be too deep into the carrier key. I have not come up with a name. All of the good ones have been taken. Lol.  
My 22" 6x45 barrel was custom made by SGW/Olympic Arms back about '82 or '83.  GREAT accuracy with light bullets (55-70gr).  This was long before the craze for heavy bullets in 5.56... so a 60~70gr bullet from an AR was considered "heavy". I bought a bunch (~1k) of 90gr FMJ-BTs to try, but they proved too long.  I don't recall the twist - but I'd guess 1:12 or 1:11. Guess I'll keep it as a "safe queen" experiment.

6mm ThunderCat   6mm Badger   6mm Ripper

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jwtharpe

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Reply with quote  #19 
Quote:
Originally Posted by RangerJoe
Quote:
Originally Posted by jwtharpe
RJ, we would have to set your old barrel back around .080" to make it work. Then your gas tube would be too deep into the carrier key. I have not come up with a name. All of the good ones have been taken. Lol.  
My 22" 6x45 barrel was custom made by SGW/Olympic Arms back about '82 or '83.  GREAT accuracy with light bullets (55-70gr).  This was long before the craze for heavy bullets in 5.56... so a 60~70gr bullet from an AR was considered "heavy". I bought a bunch (~1k) of 90gr FMJ-BTs to try, but they proved too long.  I don't recall the twist - but I'd guess 1:12 or 1:11. Guess I'll keep it as a "safe queen" experiment.

6mm ThunderCat   6mm Badger   6mm Ripper


I guess we can name it after we see if it works or not
Going to turn the gas on this weekend hopefully. It might not cycle/feed. If it dont, then I will have a good safe queen. 
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jwtharpe

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Reply with quote  #20 
6-Mongoose case making process
Starting from left to right.
1st shoot up some 223's and save the brass.
2nd case, clean up and deprime your 223 brass.
3rd case, resize the clean 223 case.
4th case, trim resized case to 1.690", add primer, powder and bullet of choice, and shoot making sure that load has enough pressure to push out the shoulder and walls.
5th case, you now have properly formed cases for maximum effort loads, resize and trim to 1.690" max.
6th case, load your favorite 6mm projectile and powder. This one is a 80TTSX @ 2.285" it is .035" off the lands. The case mouth is in the middle of the crimp groove, you have +/- .020" to play with either way to tune load and keep mouth in the groove.
 

6mm MDWS casees.jpg


It has a name now! Took Mark a while to make up his mind.....

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RangerJoe

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Reply with quote  #21 
I think I'm in love... again.  [love]  When is JBFA going to offer prepped and RTL brass?
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coondog

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Reply with quote  #22 
Looking good JW. I see the birth of a new cat here.
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talonxracer

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Reply with quote  #23 
That is a cool round
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coondog

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Reply with quote  #24 
How about the 243WLV
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MDWS

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Reply with quote  #25 
JW wanted it to be associated with MDWS in some way originally.  I wanted to name it the 6mmJW but he wouldn't have it.

So, 6-MDWS it is.  Or some variation thereof.

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We are charged with upholding the constitution, from all threats, foreign or domestic, and we will bear true faith and allegiance to the same.

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