155 gr bullets for my .30 Carbine Blackhawk

[jski]

I’ve been developing a load for my .30 Carbine Blackhawk using 155 gr bullets. Charges between 9-10 gr of H110 produce a very comfortable round and consistent load.

I was inspired by Paco’s Long Range Load For the .30 Carbine Blackhawk.

I’m looking for a heavy, slow(er) load better suited to a handgun.

I took my 155 gr Linotype loads to my range and got this at 20 yards (see attached).

No sign of keyholes which is always good.

 

[TX Nimrod]

Interesting idea. Surprising that the bullets seem stabilized with the very slow 1:20 twist. There is a lot of vertical stringing in the photo for 20 yards, were you using the same hold for all shots?

I used the long RCBS 165-grain bullet in my Contender in .30 M1, brilliant accuracy out to 200 meters. But, that barrel had a 1:10 twist and velocity was ~1450 fps.


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[jski]

RCBS Rifle .30 Caliber (.309") 150 Gr. Flat Nose, Gas Check 2-Cavity Bullet Mould
Item #: RC82019 | Manufacturer: RCBS

The one on the left is Buffalo Bore’s 125 gr load. The one on the right is my 155 gr Linotype load.

 

[jski]

The twist rate was and is a concern of mine. But, I’m not trying to push this out to 200 yards. I am curious as to how far can I push this with a 1:20 twist rate?

 

[Unclenick]

In general, if they leave the muzzle properly stabilized, bullets become more stable as they go down range. This is because forward velocity is slowed by drag on the nose pushing into the air, while rotation is slowed by drag from fluid friction with air due to its surface speed of rotation. That surface speed is much slower than forward speed.

In feet per second, the surface speed of rotation is equal to muzzle velocity times the fraction you get dividing the bullet circumference by the rifling pitch where both are in the same units of length (usually inches). So, if you have a .308 diameter bullet going 1000 fps from a 20-inch twist. The fraction is:

pi × .308 in / 20 in = 0.048

So the surface speed of rotation is 0.048 fps for every fps of muzzle velocity in that example, and that's the speed with which surface friction with air will be working to slow rotation. In other words, the surface speed of spin is about 21 times slower than muzzle velocity in that example.

When you see a bullet keyholing, but not immediately, it is usually because the bullet is gradually describing larger circles with its nose with each turn caused by precession until that circle becomes wide enough for the sides behind the nose to catch enough air to initiate tumbling. The only exception I have experienced is with the 168-grain Sierra MatchKing which will maintain match accuracy from a 10" twist barrel until it has passed 600 yards. Then, somewhere out around 700 yards it becomes unstable. Bryan Litz says this is a dynamic instability. In effect, even though the bullet is spinning much faster than it needs to for normal stability, when it starts to drop into the transonic range, where drag bumps up, it overcorrects for air disturbances, causing it to oscillate into instability. This is why the problem shows up in a crosswind, but may not in still air. The same bullet fired from a 13" twist barrel at the same velocity can make it to 1000 yards, even in a light crosswind, so this is a weird case of overstabilization for a particular bullet shape. Other bullets, like the 175 grain Sierra MatchKing, don't do it. The thinking is that it is due to the 13° boattail angle on the 168 vs the 9° boattail angle on the 175. There are a few other shapes that may behave this way out there, but it is unusual.

What is the length of your bullet? What velocity are you actually getting? Be aware that with H110/296 that when the loading density gets below about 88%, there is danger of the loads squibbing out and leaving a bullet stuck in the barrel, which can cause disastrous gun failure if you fire the next round into that obstruction. Hodgdon used to have the warning up on the web site front page, but I don't see it now. If you want to get reduced loads with a magnum-suitable powder, Alliant 2400 is probably the best choice as loading it down simply results in not very complete combustion of a number of grains, but the bullet generally still exits.

 

[TX Nimrod]

I would normally agree completely with unclenick’s concern with the use of H110 in “light loads” but given the considerably reduced case capacity with the long bullet, 10.0 grains may not be so light. Hodgdon’s minimum load with the 110-grain bullet is 14.0, not sure what it would be with the longer bullet but clearly considerably less than that. Their minimum pressure seems to be 26,000 CUP.

Still, a different powder would lessen his stress level and may work better. I used Reloder 7 in my Contender with the RCBS bullet, but loaded the Speer 130 HP with AA-7 and BlueDot for a mild Hunters Pistol load.


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[jski]

Unclenick, Wow, there’s a lot to digest in that posting!

1st, are you saying that my Blackhawk’s 1:20 twist rate isn’t necessarily inadequate? And if so, could be stable much further out than my supposed 100 yards?

2nd, according to my Mitutoyo calipers, the bullet’s length is 0.879”. So this is a plus?

3rd, the 9-10 gr of H110 powder when loaded into the case leave a void in the case that is pretty much what I expect this bullet to occupy when properly seated. So should that alleviate the concern about “ loading density gets below about 88%”?

 

[jski]

BTW, my current stock of powders includes Hodgdon’s H110 & Titegroup, Ramshot’s True Blue, and Alliant’s Unique. Besides the aforementioned H110, are any of the others better suited to my purpose?

 

[Unclenick]

CAUTION: The following post includes loading data beyond or not covered by currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The Firing Line, nor the staff of TFL assumes any liability for any damage or injury resulting from the use of this information.

Jski,

Hodgdon has 110-grain 30 carbine loads at 82% case fill, so I think the smaller case (as compared to .357 Magnum) probably is what allows for that smaller case fill. The primer can pressurize the small space better, so a little more empty space is less prone to lowering start pressure than it is with the fatter magnum revolver cartridge. Using a powder file tweaked to match Hodgdon's performance measurement, I show a maximum charge for your 155-grain bullet at about 11.8 grains, so the minimum will be about 10.8 grains. The heavy bullet will help compensate, but I'd work up to and likely stay in that load range.

The 9-grain load appears to be about 73% case fill and running just under 20,000 psi, neither of which are conditions this powder likes. It was designed to squeeze maximum velocity out of magnum handgun loads by running about as slow as you can burn without reliability issues at magnum pressures. Lower pressure burns it less completely and gives it a harder time staying lit. I try not to run it under about 25,000 psi, and then only with heavy-for-cartridge bullets, as you have here.

Unique is a bit too fast to give you the velocities. True Blue is about like Power Pistol in burn rate. It looks like 6.2 grains should give you the same velocity as 9 grains of 296/H110 and is a more appropriate powder for the task. But it appears to be nearing its limit at 7 grains. Since quicker powders are touchier about the exact maximums, I would approach that cautiously. Unique can do it on paper, but the pressures are getting high enough when you get to that same velocity that I don't trust it's famously difficult dispensing uniformity. I would target True Blue in the 6.2 t0 6.5-grain range, then switching to 10.8 grains of 296/H110 to go hotter.

Regarding stability, the two stability calculators I looked at suggest you have a stability factor of 1.1 to 1.2 with your 20" twist and need a minimum muzzle velocity of 1200 fps if you want to stay above 1.0 (below 1.0 is unstable) in an ICAO standard atmosphere. This is marginal, and while it shouldn't tumble, it may not group well and may have a lower BC due to the bullet catching extra air while it tries to overcome initial yaw. If it works in warm weather, don't be surprised if you shoot it in winter weather when the air is denser, it might tumble or at least throw some slightly elongated holes due to needing extra range to straighten up in flight.

 

[jski]

Unclenick, thanks so much for your extremely thoughtful and helpful postings. I only prepared 24 rounds with the 155 gr bullets with 9.5 gr of H110 for my last trip to the range. Experience has taught me to approach this kind of job slowly and to never over commit myself to the next step, I.e., prepare too many rounds for the next step.

I think I’ll prepare another 24 rounds using your advice going with a charge of 11 gr of H110. This is actually what I was thinking about targeting as I began working my way up with charges.

BTW, does Hodgdon’s Titegroup offer any promise with this load development?

 

[Unclenick]

Tightgroup is pretty quick. I wouldn't get too near maximum pressure with it because small charge errors then are moving the peak pressure value around too much. But 3.1 grains should make about the same peak pressure 9 grains of H110/296 did and give you a workable target load with the same bullet.

 

[jski]

For now, I’ll stick with H110.

One last question, how does the bullet’s length, 0.879”, play into this?

 

[Unclenick]

Length determines how much space is left in the case under the bullet when seated to a particular OAL. The excess volume can affect H110 and it definitely affects your peak pressure, so it is needed for the pressure calculations. Length is also a primary factor in determining whether or not the bullet will be stable at the twist rate and velocity you have.

The 6.2-grain load of True Blue would have been my choice out of the bunch. If you are going to continue with H110, just don't do any fanning or other rapid shooting of the gun. You want to check that each shot makes the same sound and produces the same recoil and that a bullet has arrived at the target. What you are watching out for is the squib Hodgdon warns of. A bullet stuck in the bore could can the next round fired to burst the gun.

The squib problem is one of those statistical things where you could get one with the next cylinder full of cartridges or you might shoot the load for years and think the warning was nonsense, but then get one after all that time. Or you might never get one. No way to tell. The small case volume may or may not be saving you. Just be aware you are using the powder outside the manufacturer's information and warning range so they won't be liable if anything goes wrong. Oh, also with that powder, stick to magnum primers unless they lower your muzzle velocity.

 

[jski]

Unclenick, I’m more than willing to go with True Blue if it’s a better solution. So what measure of True Blue is equivalent to 11.8 gr of H110?