First go with the 300 BLK

[Ian]

Got back from a trip late last night and had a few minutes this evening to put together a test load for my new AR Frankenrifle. Brass is a handful of home-made stuff courtesy of L1A1Rocker, I have some factory-new Federal stuff on order. After managing to dumb-down the alloy enough to make NOE 247 Whisper bullets cast small enough on the nose to fit my SAAMI-minimum Blackout chamber, I loaded five with ten grains of H4198 and headed to the range with my Mageto-Speed chronograph. Shot them into one hole at 15 yards but had a little yawing going on. I think the points all went through the same hole but the bases made it about 3/8" total diameter with daisy-petal marks radiating around. Velocity was average 1002 fps with a horrific SD of 23.4. This load would neither lock back the bolt nor feed the next round, but ejected empties just fine (carbine-length gas system, 16" barrel, no silencer).

I'm probably going to try 10.5 grains and maybe switch to Reloder 7 for a little more gas volume and hopefully some better consistency. One thing's for sure, I wouldn't want to shoot these yaw-riffic things through a can until I figure out how to make them fly straight. Any suggestions?

 

[Brad]

Would a shorter bullet work? Maybe try the 190X or the MP 30 sil.

I don't know enough to help much otherwise. I can offer the really obvious answer, spin the bullets faster!

 

[Ian]

It's an 8 twist, shoulda been fast enough. Same bullet shoots great even slower at 100-yards out of my 12-twist .30-30s, but I never checked the stability at 15 yards with that one, it might be yawing like crazy at close range.

The problem with going lighter is making the rifle function while keeping it subsonic. I bought a Lyman 311299 to try, hoping the nose was the classic undersized and would fit my .298" bore, but I haven't cast with it yet. Got another heavyweight mould on the way to try, I'm just fiddling with what I have on hand and trying out the gun for the first time. Main thing is it didn't blow up and the headspace seems correct.

A side note is the barrel was brand-new, never fired, had the parkerizing bronze-brushed about 100 strokes and swabbed out with Ed's Red, then dried with a couple clean patches and just these five SL-68.1-lubed bullets fired. Not a trace of lube anywhere in the gun, not on the crown, flash suppressor, gas system, nada. Bore looks pristine. Gotta love the soap lubes.

 

[L1A1Rocker]

If you'd like to try some 1680 or 5744 I can hook you up.

 

[Brad]

If you lived closer I have a few pounds of 1680 I haven't found a use for.

For a first run the fact it all worked properly and didn't spontaneously disassemble it is all good.

 

[Ian]

Seems like I've been told to use AA1680 or 5744 for the cast subsonic heavies.....but dangit I don't have any. I might take you up on just a small sample of it, L1A1, if I can't make something else work. Right now I'm trying to use up some odd stores of powder and streamline my inventory, not add to it.

 

[Brad]

Ah, the reduce inventory goal. Been there, done that. Seems I just buys lots of a few powders instead of little bits of a bunch of powders.

My wife isn't gonna like it but you are irritating that itch that is a 300 BLK. I may just have to scratch that itch someday. Got 2 ARs so I just need an upper.

Dammit Ian, it is getting awful ex

 

[Ian]

You might look into buying an upper from Radical Firearms in Houston....They have uppers less charging handle and BCG for something like $309. With some pretty classy FF handguards, too, and they don't have a reputation for building junk. You have the rest of the stuff to make them run. Then of course you'd have to scratch that NFA itch......more money! Actually, for a range toy I'd say screw it and just shoot lightweight supersonic cast bullets with gas checks. Mine will be a working rifle for destructive critter management, mostly.

 

[Josh]

I know my bolt gun has a 1-7 but like you I have shot the super heavies in 1-12 twist bores. I am not sure what is going on with the tipping, but that NOE is a VERY nose heavy design, the C.P. & C.G. may be screwy.

Once you get the Lee copy I can't wait to see the results, I am also going to send off some of my 260's which have the same OAL as the 235's

 

[SwedeNelson]

VERY nose heavy?

311-247-FN
CG 46.15%
CP 48.49%

311-202-RN (311299)
CG 43.94%
CP 46.23%

311-214-RN (311284)
CG 46.78%
CP 49.02%

311-218-RN (311331)
CG 46.67%
CP 49.06

I don't understand

 

[Ian]

Fairly nose-heavy. Like the Lee CM it might take 50 or more yards of travel for the yaw to dampen out. It was just a test, I'm not using that bullet full-time because it doesn't fit the AAC throat at all, another reason it may be yawing (launch damage). I had some cast up, managed to get them to chamber, and shot them. The mould I'm buying from Josh looks like it will be a dandy fit.

Al, did you ever make a mould for the 300 BLK SAAMI chamber?

 

[300BLK]

Ian,
For shooting subs you have the carbine length gas working against you even with maximum gas port diameter. What you have is perfect for shooting supers, but you could get full function with even lighter bullet subs by going with a lightweight BCG, lighter spring, and lighter buffer.

It sounds like your 16" is chambered like my 10.5" pistol barrel. I'll be hard pressed to get .310" in it, but my 16" barrels both accept .311".

 

[Ian]

Thanks for weighing in, 300BLK, I'll keep that in mind. I'd like to have the best of both worlds in case I want to shoot supers, and supposedly the carbine system in a 16" barrel will support both if I build the loads correctly. 220-240-grain bullets with 11.5 +/- of AA1680 for subs and 110-125 grain with 15-15.5 H110 for the supers are the ballpark areas I'm told to work in....for jacketed. Looks like I'm under-gassed for heavy cast subs and H4198 and might not make it cycle before going supersonic using the parts I have.

Interesting about the BCG and buffer weight, I didn't want to monkey with that stuff at first, and drilling the port hole (it's .093" now) may be a last resort. If I can't get happy with powder, I'll pull out the buffer weights and try again. Lightening up the bolt/buffer mass may not be the best way to overcome an under-gassed system, though, and I like the positive chambering that standard weight parts gives. Lots to play with here to get it right. Subsonic function with heavy cast bullets is still the #1 priority.

It's a tight chamber, with about a .310" diameter freebore section of the throat. My Lee dies size brass right to the SAAMI maximum at the case head and just behind the shoulder, and brass is a hard press-fit in the chamber. A chamber pound cast revealed that the chamber itself is about a thousandth tighter in the body dimensions than the minimum allowed. I have some Remington factory cartridges that will chamber but are very snug on the case body and leave scuffs all around and up and down. Also, I got a bag of Federal new brass which is right at the minimum for brass body dimensions so will work well. Also picked up an RCBS AR-series 300 BLK small base die, which hopefully will solve all my problems with reloads provided that it sizes the body below the shoulder small enough, like at least .360" if not .359". We'll see tonight when I get home.

The help is much appreciated, I just hate reinventing the wheel!

 

[L1A1Rocker]

Ian, you should be able to get it to run with the 1680 or 5744. If you want to swing by I can give you a bit to get you going. I also have a good supply of 220 Matchkings if you'd like to try those. Also, as you know, I've got the stuff to build my own silent capture springs systems. I don't know when I'll get around to it, but I might be able to do an extra one. And when you have time I'd like to bounce some ideas off you and how best to fabricate one peace on that thing.

 

[Ian]

L1A1, you're a gentleman and scholar! I'll stop by tonight but gotta make it quick because I'm in charge of cooking supper tonight.

 

[300BLK]

In regards to BCGs, the M16 variety is the heaviest, AR15 lighter and then there are the purposely lightened varieties. I don't know which you have, but you could use the same bolt and just switch carriers for different purposes.

.093" sounds small for carbine length gas, and maximum port size is the ID of a gas tube, so closer to .125". The larger port diameter will get you more gas, but whether or not the pressure will be high enough is another question.

I've used RCBS dies exclusively and the only chambering difficulties have been with the pistol barrel being too tight at the neck (with .311" bullets). Your chamber sounds ridiculously tight.

 

[Ian]

Just shot five more at ten grains of RX7. Average velocity 1002, SD 5.9. Same bolt behavior, ejected empties just fine but not stripping a fresh round or locking back the bolt. It does recock the hammer, same way with the H4198. So basically the same except more consistent, the more consistent part being the only thing I predicted since RX7 burns pretty uniformly at very low pressure. The load is definitely anemic but brass is obturating the chamber and there are only a few mummies in the bore. I can go up to 10.5 or 11 grains and see what happens, or switch powders since L1A1 loaned me some 1680 and 5744 to try. Then there's that keg of Herco I have.....

 

[300BLK]

Herco will be of no use unless you want to manually cycle the action.

You might want to read this:

http://micromoa.com/300-blk-port-size-testing/

 

[Elkins45]

8-9 grains of 2400 is worth trying, as is 7.5 grains of 800-X or 7 grains of Longshot if you have any. Of course these recommendations are from a 10.5" suppressed gun with a pistol gas system so the charges may be a little light for a carbine length gun with no extra back pressure.

I think my subsonic load for the heavy gun in a 16" carbine barrel is somewhere around 10 grains of 2400, but I would have to check that.

 

[Ian]

That Micromoa report was quite interesting, considering I have a .093" carbine port. Like you wrote before, not the best for what I'm doing.

On another note, I tried the RCBS AR small base .300 dies and they put the case body nicely below the chamber size. My fired cases come out about .3615" on the front part of the body and .3755" about 1/16" forward of the extractor groove, the resized casea are .358 x .372", respectively. Perfect.