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.300 blackout brass jig.

13K views 12 replies 8 participants last post by  elkbow 
#1 ·
Yes, I own a 6.8 SPC, actually two. Please be gentle.

A buddy got a .300 BO, and got me to build one as well. Still waiting on my barrel, but otherwise it is essentially complete. Brass isn't an issue for me since I have 5k+ in LC and other 5.56 brass, so I looked around at other sites to see how folks were doing it and I found this jig hooked up to a Harbor Freight mini chop saw.



Saw a few things I liked, and didn't like, and proceeded to build a repeatable jig that just cuts brass.

Added a piece of UHMW for the end block for a definite measurement on each case.


Screwed the jig board to the base of the saw AFTER squaring it to the blade. A bit of trial and error.


Made a few more for my buddies with .300 BO's, including a "witness case" to align the saw.


I omitted the "shoulder drop hole" from my design, as it caused a few jams in my trial tests. Went for 15 minutes and was able to produce 318 cut off cases, all the same length, give or take .005".
 
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#2 ·
That's the way to do it. Are you anealing too after removing that portion of the brass?
 
#6 ·
I trimmed them to the proper length for my die set so that once they were sized, no further trimming was needed. Chamferred and deburred, then ran them through my Dillon 650 to size them. Final act was to swage the primer pockets.




Investment was $27 for the saw. Between my son and I it took us two hours to process the brass. Did LC brass for supersonics, and FC brass for subsonics.
 
#10 ·
1/2" round bit on my router table.

I cut well below the shoulder to the proper length where with MY DIES, and I have to do is chamfer and De-bur, and the cases are at the spec trim length. I played around with the length a bit until I got it set correctly. Your jig needs to be set to your dies. You can set it a bit long, and then add an adjustment screw through the UHMW cap to adjust as needed.
 
#8 ·
Ok I am a little confused. How far down do you cut the brass? Below the shoulder? Then the resizing die resets the shoulder?


Sent from my island villa by carrier pigeon.
 
#9 ·
Ok I am a little confused. How far down do you cut the brass? Below the shoulder? Then the resizing die resets the shoulder?

Sent from my island villa by carrier pigeon.
Yes! In the attached video link in the OP it shows cutting the length at 1.375 inches. Generally you want to cut the length as close as possible, but not too short, to avoid having to spend too time trimming to get the correct length. In some of the other conversion vids I have viewed some just simply cut off just below shoulder. But then you still have to trim to proper length. Depending on the tools you have available trimming to length vs cutting close to begin with may take up a lot of time. After cutting to length(close) you then chamfer and debur then size. After sizing you can then trim to length. At least that's the way I plan on doing it for initial brass cuts.
 
#12 ·
I use my Harbor Freight chop saw set up to cut them at 1.380" and finish trimming
them with my Dillon RT1200 trimmer on the press. I finish trim my brass to a 1.360"
length with the variances at about +-.002". Then I remove any burrs with a quick
twist of the inside and outside deburring tool.

I just don't trust the chop saw enough to use it as a "FINAL CUT" to length jig. To
me a + -.005" is pretty loose on the tolerances. When I cut mine on the chop saw,
my lengths are all over the place.
 
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