Accurate PC 350 Yds part 1

[OS OK]

Thats pretty much what I expected to hear. Gosh I wish you could buy size sets for these noses like you've worked out. One base die could sport different bushings and bushing retainer screws so I could do .30 cal and the 8MM by changing those two items out and using a corresponding punch whatta great fix.
You managed to get the boolits concentricity correct on the longitudinal axis so that the potential off center balance doesn't make it go off course from it's RPM centrifugal stability...wobble.

I think I have it...huh?

[Bama]

I tried to get a decent pic showing the rifling engagement of the bore rider portion of a PCed Lee 200 gr shot at 2220 fps at 350 yds. The rifling shows equal engagement for the full circumference getting slightly thinner nearing the tip. Before firing the bore rider portion measured .301. Now it measures .304 to .308 and I do not know the effect of impact but the only way it could have uniform rifling engagement is if the bullet was swagged into the rifling on firing similar to a revolver. The rifling marks stopped about 3/16 inch shy of the start of the round nose. There is no indication of any sliding/skipping in the rifling is clean and sharp and other than being dirty the PCed area are in good condition except in impact area. The round disks are all that remains after impact with the AR plate. It makes it easier to understand why size and bore engagement are so critical to shooting accurately with cast bullets at higher velocities.

[popper]

I've heard it called nose slump, obturation but swaging into the grooves works for me. Army data shows even jacketed do that.

[Bama]

I had never seen it occur this close to tip of bullet or to this extent. Would this indicate I need to go harder alloy or a tighter in bore rider section. Any idea what the bullet tip would be doing since it is unsupported?

[OS OK]

You did say that the front section is fitting snug in the lands and grooves, right?
Then I imagine that the tip slumps back centered in the bore as the body of the entire cast round expands out against the bore as it is accelerating with great force.

The same as if you dropped a ball of dough on the floor and it expands in every direction laterally becoming flatter and much more round uniformly.

[Dragonheart]

If a bullet does not have a gap ever so small before it engages the rifling there can be a very large spike in pressure. If the bullet was seated where it did not have a jump then the pressure on the base would be acting like a swaging die forming the bullet in the direction of least resistance. This happens anyway, but a pressure spike would exert a much greater force than normal. My inclination would be to try a thicker coating before a harder alloy since a softer alloy would make for a better expanding bullet.

[popper]

Probably not enough unsupported nose to make a difference. 1-1/4" long boolit with maybe 1/4" unsupported? The 'swaging' also starts engraving in an even manner so the bore section doesn't skid or twist (relative to the base bands) when it starts moving. You don't state your alloy but the added Cu really helps. Our alloys always fail in a shear/plate slip mode. Cu makes the plates like sandpaper - much more force required to slip. Sb gives the alloy 'fibers' between the plates but when they break - they are 'gone'. Sb/Cu forms bigger 'bumps' in the sandpaper. My 2% Cu W.D. boolits actual put a dent in superhard. They shot well too. All said IMO you have the alloy about right, higher fps/pressure might need a little more Cu - accuracy node may change too.
Are the disks just the flattened GC?

[iwottopq]

Hello to all.
This is a great work...I follows...
Nino

[Traffer]

Excellent work. Another plateau reached in the development of rifle pc. Thank you for posting. I hope you have continued success. I particularly like the "like polished glass" after sizing the pc'd bullets. As stated by another, now we need someone making inexpensive tools for this process.

[dverna]

This should be a sticky

[Bama]

You did say that the front section is fitting snug in the lands and grooves, right? --Presently I think I am about .001 smaller for the bore rider portion and I am .002 over sized on the driving ban portion. In a friends gun with custom barrel when a round is chambered and extracted an almost perfect outline of the rifling can be seen on the bullet but will wipe off with no signs of engagement—almost perfect slide fit.

The same as if you dropped a ball of dough on the floor and it expands in every direction laterally becoming flatter and much more round uniformly. – Would it be correct in this case to say a rounded tip would be better than a long ogee ? It seems like a longer one would have more potential to go to one side or the other and mess up the bullet flight.

My inclination would be to try a thicker coating before a harder alloy since a softer alloy would make for a better expanding bullet. –Unless I size down the bore rider section I am limited to the added powder by the bore diameter since This section is inside the bore. With my short throat the point where it goes from .310 at driving bands to .301 hits the throat. I don’t normally like to have engagement but have at least .003 to .004 jump but I have tried both ways and have not detected any difference.

Are the disks just the flattened GC? --Spread perfectly flat but still have the PC undamaged on the back. You can clean the dirt and carbon off and they show no signs of cutting or any melting. This shows the quality of Smokes powders. When I started this project I was using HF red and most of the PC was missing from the recovered GC. I think Smokes powder also plays an important part.

[kbstenberg]

How far towards the driving bands do you nose size?
I was thinking just to the point where the nose no longer engages the bore.

[Bama]

I size all the way to the crimp grove. I normally adjust until the front of the grove is slightly pushed back. The it usually works out with my chamber that the neck just covers the the last driving band. For AR10 I run slightly deeper and use factory crimp to crimp into remaining crimp grove. Runs really well with 170, through 200 gr round noses. With my short throat in bolt gun it insures that almost all the bore rider portion is in the bore to help insure alignment.

[OS OK]

Good question regarding the ogive slumping more than the other because of shape...I'm still contemplating that...can't say, but it seems that the acceleration is so abrupt that there is no time for gravity to affect that small, in weight, ogive area...I'd think it'll slump back straight perpendicular into the body. It would be interesting to measure the length of the cast before and after just to see how much slump is there...I don't imagine it's much at all.

[Bama]

I have been working on bullet and load combinations that would work well with both bolt guns and AR 10. I initially worked with AA5744 in the bolt guns with 180 to 200 gr Lee bore rider type bullets sized .310 on base driving bands and the bore rider portion a light but snug fit (.301 to .302) in the bore. Recovered bullets indicated that all but the last 3/16" of the nose had expanded to full grove diameter (.308) on the bore rider portion. Now the interesting observation. I was trying the Lee 170 with the slight flat tip which I believed would be ideal to run in the AR 10 due to the shorter length and higher potential velocity. The Lyman manual for AR's gives IMR 4895 as one of the recommended powders I guess related to pressure curves. I had tried a function test using the IMR 4895 with 170,180 and 200 gr bullets sized .310/.300 and found no issues so I started looking for load with the 170 gr that would be accurate in both bolt and AR. Tests were made using bolt gun. Initial recovered bullets at lower pressure load showed no indication of forward section of bullet being swagged into rifling and accuracy was no more than 1 1/2" at 100 yds @2291 fps. Accuracy stayed almost the same until velocity hit 2516 fps it was like flipping a switch. Recovered portion of bullet indicated rider section had expanded to full grove diameter. I know that alloy,hardness, powder and barrel twist affect point where bullet is upset but the resulting accuracy is really outstanding. Also noted was barrel was significantly cooler( twice the rounds before having to let barrel cool) using IMR 4895.

[popper]

Lower pressure and slower curve and no slump.

[Bama]

But that is the point, After I had full engagement the accuracy really improved. There was no indication of slip or stripping in the driving band even at the lower loads. I am going to do more testing but everything seems to point out that the most accurate cast bullet is one that totally fills the groves. Bore riders that fit the bore snugly are better pre-aligned with the axis of bore and the slump or swagging which occurs before the bullet moves very far completes the alignment. Before PC this would have resulted in the non-lubed portion of the bullet making hard contact with the barrel which would have caused leading and quickly destroyed accuracy. The PC serves as a barrier to eliminate this issue. One additional item noted was the loads used today were chosen using the Lee formulas for one grain less velocities and pressures. Actual chronograph readings were a little over 200 fps faster than calculated using the formulas.

[Traffer]

Great job. Shows what common sense applied with exacting work can accomplish. You have moved this science further down the road sir.
Thank you.

[Dragonheart]

Bama, once again excellent work. It would appear that you have figured out a way to achieve the bullet concentricity necessary for accuracy by allowing the firearm to form the bullet. I think it is also showing that a lot of the cast bullet designs with a short length of driving bands and narrow tapered body are not going to work.

What you have experienced is what Federal's testing of their line of PC bullets has now proven beyond a doubt and that PC is a superior lubricant. Increased velocity and lower barrel temperature with PC is exactly what Federal has touted.

[Wreck-n-Crew]

I've been following along and now i have a question.

From what i gather a bore rider is more accurate than a bullet that isn't. Seems that 350 yd accuracy with PC is now a doable thing. But the process is longer.

Why use a bore rider? Is it possible to use a different design and forgo the rider sizing and still accomplish the desired accuracy?

Understanding nose sizing is still a required step right?

If nose sizing is the only required additional step it would be done first before bullet sizing in theory correct?

Sorry had a few questions...

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