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Military Firearm Restoration Corner

On 300 Aac Blackout


Dr.Hess

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No, I haven't.  I have some 30 cal jacketed bullets for 30-06, but mostly big heavy round nose stuff that my big Mauser likes, and those cost me like 30 cents each 25 years ago.  The 300BO is kind of a strange round.  The bullet needs to be long and pointy to feed right.  If you look at a store-bought 300BO 220GR round, like the box of SIG stuff I bought at about a buck each, the bullet tapers off real fast after the neck, but the loaded round is as long as a 223.  I did look for bullets like that at Midway and Brownells, but I couldn't find anything.

 

Using a sizing die as a crimper has been working out really well.  No problems at all with the bullet coming apart or not feeding.  I should take some pics. 

 

Midway got the Redding 300BO taper crimp die in stock yesterday.  Just for the hell of it, I ordered it.  I've spent so much time and money on this project, what's another forty bucks?  I know I've cast, powdercoated, loaded and shot well over 1K rounds trying to get this right.  I've never developed a load this thoroughly before.  It is pretty handy to load up 5 or 10 rounds in the evening, walk outside and dump them into a tree stump to test, then go back to the loading bench and try something else.  Much handier than the way I used to have to do it:  Load up a bunch, drive to the range, set up, shoot, take down, drive back home, think about changes to make and wait for another opportunity to test.

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  • 3 weeks later...

So, the Redding taper crimp die worked OK.  I would not say the results were any better than with the Lee sizing die and I switched back to the sizing die for the "crimp" station.  I figure that would put less strain on the bullet, giving less chance of those rings coming off.


The bullets are working well now.  I powder coated a couple hundred more this evening. 

 

Next problem:  Failure to go into battery because... wait for it... unburnt powder.  Lots of it, all over the upper and in the chamber.  Seems to me that AK's never have that problem.  Oh well.  Some Google-Fu points to there not being sufficient pressure to fully light off the H335.  I'm working with a several 300BO's here now, the original 16" carbine upper and two pistols, one 10.5" and one about 7".  I am primarily playing with the 7" pistol, which has the folding receiver extension thingie.  Because it's cool.  Anyway, according to teh Intr4w3bz, y0, a stronger crimp will lead to less unburnt powder.  It also leads to damaged cast boolits in this experiment.  So, back to the drawing board for the powder.

 

I dug the Win 296 back out.  10.3GR of 296, the 230GR cast (water dropped) powder coated bullet gave just the start of some pressure sign, that is, some flattening primers but not "ZOMG" levels or "oopsie" levels, but "full power" type levels.  10.6GR was approaching TOO MUCH.  And the 10.3GR charge locked the slide back in the pistols, both of them.  The 2 have the same barrels, but I cut the one down.  The other one (10.5") has the original size gas port and a non-adjustable gas block.  The 7" has the larger gas port and an adjustable gas block on "full open."  I have only run about 20 rounds through, but I am not seeing unburnt powder with the 296, even in the 7".  The H335 charge in the carbine didn't have much unburnt powder.  A little, but not near as bad as the 7".  In the 7", complete flakes of powder only discolored to a slight yellow tinge were all over.  The 10.3GR 296 does not have enough gas to lock the slide back on the 16" carbine.  I suspect it may be "undergassed."  I may break it down and bore the gas port out the next size larger.  I feel like replacing the upper receiver on that one anyway.


I think I'll load up a hundred rounds with the 296 powder and run them through the 7" pistol. 

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So far, the 10.3GR 296 has been working out well in the pistols.  I mean, really well.  No problems at all.  More recoil than the 13.7GR H335 noted too.  In the carbine, it won't lock the slide back.   I'm thinking of reducing the mass on the buffer.  I have a couple extra buffers around.  I might take one apart and see what I can do to drop the weight.  There seems to be a roll pin holding on the plastic end, and they seem to have something loose inside.  Shouldn't be too hard to make lighter.

 

Here's a tech tip for the powder coated boolits:  When sizing them, put some lanolin on your fingers like you were sizing a shell casing.  Just a bit.  The transfer to the boolit when you pick it up is plenty lube and it makes running them through the sizer much easier.  I bought a large tub of it on amazon for like ten bucks.  You can also get it at Walmart, sold in the infants section as "nipple cream."  100% pure food grade lanolin.

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On the Carbine, I reduced the mass of the buffer from 86 grams to 66 grams.  I did this by driving the roll pin out, taking the plastic end off and inside there is a steel cylinder.  I chucked it up in the lathe and drilled a hole through the middle somewhere between 1/4 and 3/8".  I just kept drilling it bigger, putting it back together and trying it, taking it apart and drilling bigger, etc.  With the 66 gram total mass, it seems to be locking the slide back on the 10.3GR 296 rounds about 90% of the time.  I'm calling that good enough.  I'll use that buffer only with these 300BO rounds.  I have another buffer to use with regular 223 if I put another upper on it.

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  • 11 months later...

Whoa!! Forgot about this 300 BO thread. Just curious Doc have you used gas checks on powdered bullets? Best I can tell from the photos looks like there's enough taper to seat the checks. Another ? if you know. Does one powder coat before or after installing gas checks? I can't guess if it even matters before or after and likely a difficult task if you're not sizing. I had bad luck years ago using home cast lead bullets in a M-1 Carbine without gas checks leading the barrel. I gave it up after the bullet lube worked its way into the gas piston. I had to buy a tool to remove the piston to clean it properly. I assume using coated bullets the chances of plugging up the gas piston would be far less than using conventional 50/50 bee's wax/Alox lubes. I thought about trying cast bullets coated in Lee goo but decided I'd try and find a lightweight 30 cal round nose mold using a gas check. Lee made one many years ago but it has been long discontinued. Found one on EBay but the previous owner reamed the taper out. 

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I experimented with gas checks on the powder coated bullets.  Some people do use gas checks on the PC'ed bullets.  They put them on after the powder coating.  That 230GR Lee bullet on the left has a place for the gas check.  My conclusion was that accuracy was better without the gas check and there was no difference in barrel condition.  I size them to 308 in a Lee sizing die (really good product) and use a tad of pure lanolin on my fingers to provide a little lube for the sizing process.  I have probably run a thousand rounds or more of those through that barrel.  It is just as clean as if I ran FMJ's through it.  The 7mm's I ran through my Spanish Mauser, as I still experiment with it, and those are at a significantly higher velocity than the big 300BO's, and there is no leading at all in that.  Or the 44MAGs in the Desert Eagle.  This powder coating thing is really the way to go with cast bullets.  And using the shake and bake technique, tool outlay is virtually non-existent.

 

 

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8 hours ago, Dr.Hess said:

Yeah.  Used up what I thought was a lifetime supply of lead casting those and some 230gr 45's.

Know the feeling well. My what I thought was a lifetime supply ran out a few years ago. Casting heavy 45's for 45/70 and powder puff loads for 458 Winnie went fast. Strangely the 450 and 500gr home cast slugs print 100 yard clusters using mild powder data for the Trap Door Springfields. At the time I was working with a group buy on scrap lead. After a scrap dealer turned flakey, everybody was refunded but the group no longer exists. Another local scrap dealer will trade lead for aluminum cans for lead scrap but his last batch was loaded with Zinc and Steel wheel weights. I probably disposed of at least 15 or possibly 20% of a hundred dollars worth. According to the scrap dealer, all scrap prices are constantly climbing because the Chinese are buying all they can get. Obozo regulated USA lead mines and processing plants out of existence, saving the planet and Polor Bears.

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