M*CARBO Brotherhood

Pistol Caliber Blowback AR pistols and carbines

Hello, All
Just posted over on the 308 forum in the PCC/PDW section a lot of information and photos on buffers in blowback operated ARs.
Worth a look if you are planning a build or just interested.

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Some great info. Sounds like you could maybe fill that niche left by QC10 and maybe make a buck or two.

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I would help a brother out for sure but not really set up for mass production. Size and shape is easy, but the bore is the tough part. 3 drills 1/4- 1/2- 17/32, boring bar to final diameter, and then a long reach end mill to flatten the bottom. SS is a pain to drill, even the 303. Have to push hard and take enough material so it doesn’t work harden, but not so hard that it gets hot and work hardens…

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i went to using one of these on stainless and titanium, now i use it on everything, even keeps copper from growing while you cut.(that crap is alive LOL) makes for a perfect Knurl. no mess like with coolant, no moisture/rust on the machine. was worth the investment…

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Looks pretty COOL.
I have been going over to indexable bits in the lathe, big improvement over the solid carbides or cobalt/HSS in stainless. The only cooling issues I have are the deep bore drilling where I can’t force coolant or air in that deep. Almost thinking of drilling the pilot hole all the way through and then feed the coolant through the spindle. I’m getting a pretty clean bore with no lube and the long indexable boring bar, but drilling to size leaves a poor finish. Long reach endmills tend to wander in a lathe. So its drill, drill, drill, bore, move to milling machine and bottom. Thinking you should be able to flatten the bottom with a boring bar but at these small diameters can’t get the cutter to center of bore.

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you cutting with tool steel ,carbide insert or solid carbide?ive ground what they call a tray panning point to dive bore smaller holes and not get chatter due to circumference. I have quite a few what we called pocket cutters, you would drill to depth,machine to fit,and then last step was use the cutter to flat machine /finish the bottom of the blind hole they were precision ground on sides to fit what ever diameter we were machining to. depending what we were mounting. it would cut the blind end within .00001 ± true. what size hole are we talking about in decimal.

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Carbide indexable inserts are giving me a really nice finish. Bore diameter I’m shooting for is 0.566 to 0.572 and 3" - 4" deep. The largest boring bar I can use is 3/8". I could hit center with a 1/4" boring bar but don’t see one available that I can secure in the tool holder and still project enough into the bore, need about 6" total tool length.

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Checking these out, need a lot bigger air compressor then I have now. The 611 looks like it runs 15 SCFM, I think my biggest compressor is 10 CFM @ 90 PSI so probably 6-7 SCFM?

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what tool holder you using?

Im running a similar setup to this, except i bought a IR 2 stage compressor pump, and a 10 HP motor, and mounted it on a 80gal Black max tank, that i have hooked Siamese to a second 80 gal tank, 175 PSI 35 CFM, had to play with pulley’s to get my speed right on the motor, came out about half the cost with double the volume…

I did 3 phase cause My old van norman is 3 phase, so i already had a rotary phase converter, that i wasn’t running 1/4 of the capacity on…(rotary will do multi tool unlike static converters) made by Phase o matic run mine thru a dryer, and have a snap in oiler for tools. cant ever go too big or too much with air.

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Looks like this but 3/8" x about 6" long.

Nice compressor setup.
Way outside what I will probably ever have.

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why i built my own setup. at that time I was blasting a lot, running a minimum single stage 220, and after i grenaded 2 of em in 2 years i went the home brew route.i had the tanks already.

my old atlas Lathe runs rounds, but i think i might have some hex’s in the box i will look. get some pics of the ones i bore with tomorrow

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