Gun physics question?

jski said:

I was talking with my Nevada gunsmith who's smithing my .30 Carbine Blackhawk. We were discussing the .30 Carbine cartridge and, well, all rimless autoloader cartridges. The point he made was interesting.

Without the ability to roll crimp these cartridges, because they're headspaced on the case mouth, you're really not getting all you can from these cartridges. Simply put, the harder it is for bullet escape the case, the more tightly held the bullet is, the more completely the powder will burn in the chamber and barrel. And the higher the pressure level will get.

Now here's the interesting point: he stated that best way to compensate for this is to load heavier bullets. Sound reasonable?

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How does he speculate on going heavier bullet with the powder? Same load? Obviously yes this will increase pressure.... but how safely can one do this?

Easy have him make you one you can use normally and another for use with moon clips and you can crimp them however you wish.

Then post your results for all of us to see.

Your not changing the neck tension by going a heavier bullet. That is why we have different loads for different weight bullets.

Compensate for what? The 30 carbine has a fairly narrow range of bullets and none of them require a roll crimp. That's the way the cartridge was designed, that's the way the guns were designed, and that's the way the bullets are designed. Typically auto loading handgun rounds do not have a roll crimp. Assuming your resizing die does a sufficient job resizing the case neck tension will be good enough. Rifle rounds running 60,000+ PSI don't have roll crimps. I load a dozen different 45 ACP bullets for shooting in revolvers and I use a very light taper crimp or no crimp at all.

The Lyman manual I have save on my computer (#48) has loading data for 1 jacket bullet (110 grains) and 2 lead bullets (115 and 130 grains). I'm sure there is more load data out there but nothing like more popular rounds.

Everything else being equal a heavier bullet will produce more pressure and you will get more complete powder burn, but that applies equally across all cartridges, not just 30 carbine.

My personal opinion, you both are over thinking it and this is coming from someone with years of combustion analysis under my belt. There are plenty of good publications on reloading for both pistol and rifle in .30 Carbine.

The only weight bullets I've seen in the data is 85, 90, 100, 110 grain. Hornady use to offer (I haven't checked of lately) Hornady 100 grain Short Jacket and the 110 grain Round Nose.

To me, one of the fun things of reloading is developing a load that works well in the guns I have have. Try different weight bullets, chargers to find what works best. Besides, this gives me more reasons to go shooting. Looking for that magic load. The .30 Carbine Blackhawk is a fun pistol to shoot.

I think this more a cartridge loading / reloading question than a general discussion question, so I've moved it here.

jski said:

Simply put, the harder it is for bullet escape the case, the more tightly held the bullet is, the more completely the powder will burn in the chamber and barrel. And the higher the pressure level will get .

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Neck tension is what is needed . Heavy for caliber bullets , with slow burn rate powders may help , as the bullet moves further from the case mouth.

Different neck tensions in the 45 acp can require any where fron 40 pounds to over 100 to push a bullet into the case. Simply by changing to different brands of brass.

"...Sound reasonable?..." Nope. .30 Carbine uses very much the same loads out of a hand gun as it does in a Carbine. Makes it an excrement hot magnum like round in a hand gun with 110 grain bullets. Heavier bullets will be slower and you'll have case capacity(lotta 110 grain loads are compressed) and OAL issues.
Suggesting there's a performance difference between a roll crimp and taper is daft too.
Max 130 grain cast loads run 1400ish with IMR4227 and 2400. Rest of 'em are 100 + FPS less.
Use a 110 grain HP.

Gary Reeder shares a similar sentiment. When I was working on a plan for a custom GP100, I explored his 240 and 255 Banshee - in his load data book, he gets CONSIDERABLY more velocity with the same bullet weight, and same parent case, using the 240 instead of the 255. I asked how he accomplished this - his reply:

Gary Reeder in email said:

"The 240 is a bit faster due to the neck being sized down more. The more you size a neck down, the more pressure it builds up, making the bullet a bit faster."

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Basically, a guy can't push the bullet itself hard enough, so adding weight, crimp, or necking down helps build "back pressure".

What folks neglect here, which in doing so makes this principle difficult to understand - pressure curves are dynamic. Acceleration isn't linear, and powder burn rate vs. pressure is a complicated relationship. If a guy applies a heavy roll crimp or necks down even further - in a low capacity, short barrel handgun cartridge at least - they can spike the pressure earlier, generating a broader peak, but not necessarily a higher peak pressure.

jski said:

My ruminating with "Nevada Smith", if you'll excuse the obvious pun, was based on using H110.

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243winxb said:

Heavy for caliber bullets , with slow burn rate powders may help , as the bullet moves further from the case mouth.

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reddog81 said:

Compensate for what? The 30 carbine has a fairly narrow range of bullets and none of them require a roll crimp. That's the way the cartridge was designed, that's the way the guns were designed, and that's the way the bullets are designed. Typically auto loading handgun rounds do not have a roll crimp. Assuming your resizing die does a sufficient job resizing the case neck tension will be good enough. Rifle rounds running 60,000+ PSI don't have roll crimps. I load a dozen different 45 ACP bullets for shooting in revolvers and I use a very light taper crimp or no crimp at all.

The Lyman manual I have save on my computer (#48) has loading data for 1 jacket bullet (110 grains) and 2 lead bullets (115 and 130 grains). I'm sure there is more load data out there but nothing like more popular rounds.

Everything else being equal a heavier bullet will produce more pressure and you will get more complete powder burn, but that applies equally across all cartridges, not just 30 carbine.

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You are forgetting a revolver has a cylinder gap where pressure escapes
That said, crimp is usually for bullet jump, not pressure containment...

No one ever said .30 Carbine was an ideal handgun cartridge, it's a compromise. If it were designed from the get go as a revolver round with a rim and a roll crimp, it would perform slightly better.
Calibers like 9mm do just fine in a revolver with just neck tension because of quick propellants and relatively small chamber size.

Maybe rechamber/rebarrel it to use 327 FED, use that brass and loads. Then you can get that crimp if you think it might help.

FWIW adding a crimp would not be a game changer with that cartridge.

Tilos said:

You are forgetting a revolver has a cylinder gap where pressure escapes
That said, crimp is usually for bullet jump, not pressure containment...

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Haven't loaded much H110 and ran it over a chrony, have you?

Crimp absolutely contributes to burn quality in some powders.

Before_the_bullet_ever_moves,_the_case_is_expanding._That_bullet_has_a_lot_of_inertia_compared_to_the_case.
Life_is_not_what_we_imagine,_but_what_actually_happens.

jski said:

I believe the point Nevada Smith was making is that the work required to push the larger bullet through the barrel will require more time and hence give more time for more powder to burn.

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It's hard for many folk to envision, but a handgun reaches peak pressure in the first 0.25 milliseconds or so, powder burns completely by about 0.5 milliseconds.
During that time the bullet barely moves an inch or two. If you ever get the chance, mess around with computer algorithms that model cartridge discharge.
You'll be surprised that internal ballistics are not exactly the way our mind's eye tries to picture it.

Indeed, incomplete burn is most often associated with a very low powder charge for the burn rate, not bullet weight.

I appreciate that your nice gunsmith is thinking about it, but perhaps he is not fully up to speed on the relationships
among pressure, powder charge, burn rate, bullet weight, case capacity, crimp, primer, and chamber dimensions.
Straight wall handgun cartridges require a taper crimp (no roll crimp) because they headspace on the case mouth.
Nevertheless, as mentioned by other members above, a good taper crimp in those cartridges provide
plenty of case mouth tension on the bullet. Mess with powder choice and powder charge (within published data)
to explore performance in your gun for any specific bullet. You can improve it safely and satisfactorily.

jski said:

Thought it'd be among the slower burning powders.

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It is... for a pistol cartridge.

Powders will shift position with different cartridge cases.

Time down the barrel doesn't count until the bullet starts to MOVE, and that takes time.
It's called inertia.