Possible to do a pound cast of my AR-15?

BHuij

Active Member
I've been sizing my bullets to .225" which seems to be working okay, but I'm flirting with the idea of developing a "super mega accurate even out to long ranges" heavier bullet load for my AR, and I definitely need to know my rifle's internal dimensions if I'm going to do that.

I have read Ian's fantastic series of articles, including the one with pound cast instructions. Are those instructions good for an AR as well, or are they strictly for bolt rifles? I'm a little concerned that the bolt won't hold closed when I'm pounding the lead into shape in the chamber/throat, or if it does, that I will damage it.
 

Ian

Notorious member
The bolt will hold something like 120,000 psi before the lugs shear.

It shouldn't take more than a couple of light taps with a 16-ounce hammer to make a good pound cast if you follow directions.
 

fiver

Well-Known Member
you can always do a sulpher cast of the throat too.
you basically melt the sulpher stir in some graphite and pour it in the camber.
you use a cleaning rod jammed against a cleaning patch to block the barrel, pour the mix in, wait for it to cool then press it out.
 

BHuij

Active Member
Do all the principles of fit apply equally to a gas rifle and a bolt rifle? I'm talking in terms of optimal bullet diameter to fit the throat, bullet design to be well-supported, etc.

Just seems like the action of stripping the next round off the top of the magazine and ramming it home into the chamber might complicate things a bit compared to hand-cycling the bolt. Tougher alloy required maybe, to resist deformation as a result of less-than-gentle chambering?
 

Ian

Notorious member
The challenge of autoloading rifles is not what you are naming, it is something else, particularly in the AR series which have very weak bolt camming strength: You must build in a certain degree of clearance, no hard engraving of the noses, and there must be more clearance of the case to chamber to permit proper functioning. Not an ideal situation for static alignment the way most people are used to doing it.

Tougher alloy and self-aligning bullets are usually required not to withstand the violent chambering, but more for the hard, crooked launches.
 

RBHarter

West Central AR
Look at a 6.8 SPCII chamber drawing and the NOE .278-124 or a 556 and 225-55 . Nether bullet , at least in the rifles I tried them in at mag length , 2.285 were even close to contact .
I size the 278 checks at 280 leaving the bullet .279+ . I think the front band at that length makes or is really close to making contact . That was in a Mossberg M4 style extension and barrel . I saw actual touch marks on the same in an ARP barrel . I know the Mossy wouldn't feed a paper patched but the ARP would . The difference in finish of the ramps , in fact the whole barrel assy , was like the difference between 40 miles of loose gravel washboard dirt road graded with a ripper down and 100 miles of brand new concrete freeway across west Kansas .

I had about the same results with 223 in an ATI . I really needed to have a .227 sizer for it . At .225+ it wasn't fat enough to make contact .
 

Pistolero

Well-Known Member
I would pop the upper off and put the rear of the receiver and back of the BCG against
a hard oak block on a concrete floor to do it. No need to put all those impact loads
into the lower. As far as the bolt and chamber handling it, absolute no problems, as
Ian has said, but the barrel and bolt will be driven rearward pretty hard by each hammer
blow, need to consider the load path, and mitigate unnecessary stresses in the system.

Bill
 

BHuij

Active Member
Sounds good. Hoping to do the pound cast later this week or possibly this weekend.

Ian, if I'm understanding correctly, because the mechanism auto-chambering the next round isn't particularly strong, I basically need to plan on having a little bit more wiggle room in the chamber than the "ideal" perfect static fit I would aim for in a bolt gun?

Or in other words, I can choose between maximum accuracy and no cycling reliability, or very good accuracy (not maximum) and acceptable reliability. Please correct me if I'm wrong.

That being said, for the purposes of my long-range load, I'm wanting to get a heavier bullet (probably something in the range of 70 or so grains). Sounds like bullet design is going to be of paramount importance for me here, even more so than it would normally be, since my bullet has to do the best possible job of compensating for slightly looser than ideal chambering tolerances. Anyone have recommendations on a mold? I would like to be able to push this bullet out to 300+ yards, so a higher BC would be great if that doesn't compromise the alignment or dynamic fit of the bullet.
 

RBHarter

West Central AR
This is for a bolt gun so grain of salt as needed .
The fmj is a factory round with some wiggle room in the mag . It's like 2.23 or close . My mags would have allowed 2.285 . Single fed in the bolt gun the 225-79 can set up on out to touch in one of two and jam a little in the other . I don't have the OAL in hand but 2.465 is on my mind . That oal would be likely with a NATO , US 556 or Wylde chamber with the long leade/throat . Not a problem single fed but not feasible from the mag . Now you're back to case space vs nose length vs hand feeding .
 

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VZerone

Active Member
Another important thing for loading an auto loader is being able to unchambering a loaded cartridge without de-bulleting.
 

BHuij

Active Member
So you're saying it's likely in my .223 Wylde chamber that I'm going to be limited on OAL by the magazine before I reach what would probably be the optimal OAL for the chamber? I suppose that would more likely be a problem using a spitzer design (which is unfortunate since they tend to have the best BC). I wonder if I could get away with a RN, FP, or RF nose design that doesn't add extra length of bullet too small in diameter to support itself well in the throat.
 

RBHarter

West Central AR
I'm only pointing out that the chambers that rely on long leade and throat to lower start pressures of the full tilt bullets will be hard to reach without a bullet that feeds the front band into the ogive . A bullet that hits the top band and is .005 off on the ogive might be THE bullet for your rifle .

Don't be discouraged , try some of several . See if the GI 65,69,72 or 77 gr will shoot well and go from there .

I have a rifle that shot far better seated to the groove than trying to get close to touching . The jump from the crimp groove to lands was over .2" . The rifle also shot consistently 200 fps over data . In reality it shouldn't have shot for snot with anything .
 

Rcmaveric

Active Member
I do a pound cast on mine chambered in the 6.5 Grendel. Just used a hard lead in the case and make pure lead slug to pound on. Gets tricky getting the bolt open. Just gently tap the rod while trying to open the bolt. It will give and not damage the gun.
 

Ian

Notorious member
Just shoulder the rifle, put the rod on a block on the floor, and lean on it while pulling the charging handle. If you tap on the rod while extracting the pound cast it will slug-up the throat part and give you a false measurement.

B, you have it right, but if you get the alloy, bullet design, and powder burn speed right you don't have to compromise much on how well it shoots. The only 70 grain bullet I could recommend isn't made anymore. ACE made a 75-grain self-aligning beauty of a bullet that is absolutely perfect in every regard for the NATO throats and will fit a Wylde and a .223 SAAMI throat as well if you adjust seating depth. Good, universal, self-aligning designs will work very well in a variety of situations.
 

fiver

Well-Known Member
the HM-2 is good also but not that heavy.
I have only seen one of them for sale since the initial run and it sold in 3 minutes.

the problem the AR faces with heavy and cast is you start having trouble in both directions.
the short case neck can only hold so much bullet and the magazine can only hold so much bullet.
this means you need a pretty long drive band length then a rounded 5-6s type nose shape to try and maximize both.
250_250_1370.jpg


this is 63grs and real close to the shape of a 5.56 throat.
set so the base is just below the neck, it is magazine length with a touch of space for 100% feeding.
505796.jpg

put a small flat on the nose and you end up something shaped like this.
add some more length to the drive bands and remove the lube groove then you end up with the jacketed version above, and get close to 70grs.
but your still going to need a fairly hard alloy to take the beating.
take off the gas check and plan on powder coating so you can seat deep in the case and
it will end up looking something like this.
not ideal for an AR, the diameters are off by a couple thou and the nose should slope into that tiny front drive band, it's cog is also too forward.
but it would be something to start with.
Elvis%206.0%20Crimp%20web-500x500.JPG
 

BHuij

Active Member
Is that 225-77 Elvis ideal if I just expand the cavities a bit to fill my throat more? I am concerned about the lack of gas check. I want to avoid powder coating as I tend to achieve my target alloy toughness by heat treating/quenching rather than by adding expensive antimony or babbit. If I can avoid straying from COWW alloy, my cost per bullet remains at $0.00.

Think I'm going to have to play around with a bunch of different "heavy" molds and see what my rifle likes. But step one is doing that pound cast when I have a free weekend.
 

fiver

Well-Known Member
no.
it's actually too big.
.219 sloping to 225 is all you need up there, a .218 nose turning on an ogive like that will help.
cow even water hardened will peter out on you in the 2-K speed range.
it just cannot take the beating when it hits the rifling on the other side of the gap.
 
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Ian

Notorious member
Exactly. Hardened WW alloy just doesn't have the resiliency of a richer alloy (when we use hardened, low-antimony alloy in rifles we're looking for specific qualities, i.e. as much toughness as we can get yet have as much ductility as we need, it's a trade-off best described as TANSTAAFL. The 5.56 needs resiliency far more than it needs ductility, unless it's a bolt-action and you're using a different method of achieving alignment). Hardness/toughness can be the same between a hardened WW alloy and even air-cooled straight, rich alloy, but the two will absolutely not have the same qualities under pressure/impact.
 

BHuij

Active Member
If you were to recommend a Pb/Sn/Sb alloy for best projectile surviveability in the short trip from case neck to rifling then, what would it be? I assume adding antimony would be the preferred method to get the resiliency desired. I can probably work something up by mixing some linotype into my COWW.

Then assuming I get a good alloy mixed up for this application, would you say just air cool it, or would a heat treat/quench be desirable to increase the BHN in addition to using higher antimony-content alloy than straight COWW?

Also; I've been toying with the idea of adding some copper and/or zinc into the alloy for my .223 projectiles specifically, most likely by adding some babbit from Rotometals. A different approach to achieving the ideal alloy strength/toughness that may be cheaper than trying to source antimony I think. Is there somewhere I can read about good bullet alloys containing copper or zinc, specifically for long-range, HV .223 application in a gas gun?

Thank goodness I'm not trying to do anything specific with terminal ballistics... haha. As long as it will put a round hole in paper I'm happy :D