300 BLK subsonic mould for PC

[Spindrift]

Was it unstable, as in scatter groups with the buller hitting sideways, or just slightly oval holes?
The MP-BLK made slightly oval holes when shot through a 1:10ROT at subsonic velocity, but still grouped pretty well.

A long, marginally stable bullet that tumbles on impact could have some interesting terminal ballistic properties even without expansion. Unless you need linear, predictable, deep penetration. But, as someone told us years ago, «only accurate rifles are interesting».
Best of luck with your shooting, and please keep us posted, Ian!

 

[Ian]

Elliptical holes, about two calibers wide. First group with solids, including cold dirty bore flyer was 1.5" at 100 yards. The lafhe-hp'd group had two with tight necks and those both went supersonic and out of the group, the first one was out to the left, and the two that felt and sounded good were touching in the bullseye but still yawing. My lathe HP job wasn't perfect, either.

 

[fiver]

bullet looks bent.

 

[Ian]

It is very slightly bent.

 

[Will]

I assumed the bent bullet was from it being long and going from close to 1000 FPS to zero in a couple feet.

 

[Ian]

Yep. The corner of the gas check shank got dinged, too as the bullet bounced around in the box past the catch media. The engraving marks are uniform all around so I'm quite sure the bullet didn't get bent, crooked, or "slump" inside the rifle.

 

[CWLONGSHOT]

MP 220 HP cast in 20:1 fired at 25' into wet news print. Velocity was +-1000 fps penetration was 9-10"



Trying 30:1 next.

CW

 

[Ian]

I have the original BRP version of that design with one cavity hollowpointed, it does well with 2.5/2.5 alloy at about 2K fps mv.

Those look good from 20:1 but looks like you could size them down about .002-3" more before loading and save your coating on the bearing surface.

The .30-caliber hollow points are a whole 'nuther thing to get to expand. I'm going to try straight roofing lead next.

 

[popper]

1) bullet trajectory has nothing to do with weight.
2) decrease in bullet fps is all about BC and slow has poor BC.
3) length/shape determine stability. rockets have little spin or velocity at launch (no steering) but are stable!
4) heavy bullets have more momentum to allow penetration at same fps (sometimes).
5) An old NASA demonstration for kids was to cut a cardboard 'bullet' shape, attach a string at the CG and spin it. Good 'bullet' BC would actually straighten and fly right when up to fps. If you could ever get it going fast enough. No spin involved. It demonstrated the aerodynamic effect on SHAPE.
6) spin stability is determined by length and dia. and SHAPE! Rotational momentum is different for cylindrical vs pointy objects (moves from CG). Center of pressure is somewhat irrelevant below Mach 1. Basically a heavy (for caliber) sub with point nose is tail heavy and needs more spin to fly straight.
basically old buffalo hunters were throwing heavy rocks at long range so gravity and weight caused the damage. Good old 32 ft/sec^2.
Chuck Hawk had a pretty good write up on SD vs animal size for penetration.
Just some observations.

 

[Ian]

Center of pressure is somewhat irrelevant below Mach 1.

I did not realize this. This bullet has the CP very close to the CG which is usually detrimental to yaw correction >mach 1.

I have observed subsonic bullets having boat tails and bare check shanks tend to wobble more, I figure the CG/CP is closer to the same and the smaller surface area out in the drag current at the base means less tendency to get "pulled" into the line of flight.

My solutions to stability are:

1. Move the CG back (point the nose, lighten the nose [hollow point], mill out the gas check shank to full size).
2. Move the CP forward (thin and point the nose, hollow point with lightweight "ballistic tip", remove gas check shank).
3. Shorten the bullet considerably and point the nose (for 10" twist).

Am I on the right track? Miller says should be stable in 10" ROT as-is and they do group so-so [1.5 MOA @100], they just yaw a lot more than I'd like.

 

[popper]

Primarily as the small dia. doesn't create much pressure wave until approaching and exceeding Mach 1. Per the NASA thingy, until you get fps up you can't get any stability. There is pressure wave, just not much. Just as MOVING shock wave messes up going trans-sonic. IIRC trans-sonic per NASA is a wide range .8-1.4 Mach.

 

[popper]

As an aside: Why heavy SS in BO?
1) military has a purpose, very close range 'hunting'.
2) I can do it?
3) equivalent to slug deer hunting? due to restriction by Gov.
I'm running a 170PB @ 850, fun and cheaper to shoot and would serve #1. It will puncture a hog @ 50. Obviously same on a deer @ 100. But a 150 will too. Dreaded 'knock Down' theory says you get maybe 50% max improvement but how much do you need? Gun games use power factor to make the game competitive. Chicken & pigs to make sure target goes down when hit. Shot some umc 220 subs at first, so?
Seems to me we are spening extra $ and work - any realistic reason? Am I missing some important/advantage point?

 

[CWLONGSHOT]

I bought a 311284 here a while Back. From Brad I think... Expressly for My 300's. He or someone hollow pointed the mold with a fair dia and deep HP.
It ahoots very well but to date has not been shot tbru the bullet box!! Need to get on that!!

CW

 

[Ian]

Popper, my carbine-length AR fas systems won't cycle with 200-grain bullets and remain subsonic (1030 fps MAX for least bullet flight noise). 220 is reliable, 230 worked very well with the Lee bullet weight-wise so why quit a winner? The Lee bullet is so undersized in most of the front that it yaws because the nose goes crooked right at launch and the flight path traces a spiral.

I can shoot whatever for subs in my .308 bolt rifle, this is more of an exercise in learning what does what and where the limits are since I already have the mould.

The problem with the blackouts is feeding, and I'm about convinced it's the magazines. Gonna try the Lancer 300 blk mags next, but before I get too carried away I'm gonna try some 100-yard groups with the BLKs and see how good they are, where they print relative to 50 yds, and how round the holes are.

 

[Ian]

another reason for heavy bullets is I want to engineer an expanding nose somehow and it will need mass to drive it through whatever needs a big hole in it.

 

[CWLONGSHOT]

I loaded and shot all the heavy 30's I had.

none shot to my expectations with powders I used. ALL where useable if range was kept short.

Only the 311284 was a HP.

 

[Ian]

Did they all feed and function in an AR? Were the holes round past 50 yards?

 

[CWLONGSHOT]

Did they all feed and function in an AR? Were the holes round past 50 yards?

Yes ALL fed & functioned!! Target was 50 yards worst was 4/5" best was about 1.5-2". Thats three different AR a single shot & bolt gun. Need to revisit, side tracked cause deer season coming fast!!
CW

 

[RBHarter]

Maybe this is the place for that .220 meplat on a really long bore ride TC of secant ogive .

 

[popper]

CW what is that 'nut' shaped device in your pic?