Dynamics of very soft bullets and revolvers


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Sundles
April 10, 2007, 01:10 AM
Folks,

Firing very soft squishy bullets out of revolvers creates several dynamics that cause accuracy and consistancy problems. These problems apply strictly to revolvers.

First, When the primer and powder ignite, that soft bullet is instantly under pressure and will slug up to fill the diameter of the chamber throat. A harder bullet wont do this. Lets say we are talking about the 38 SPL cartridge. Your chamber throats are supposed to be sized about .359 inch, but in some revolvers they are bigger or worse yet in some revolvers they vary from chamber to chamber--some throats may be .359 while others may be bigger, much bigger, perhaps .362+ in the same gun. When those soft bullets slug up to differeing throat dimensions, it causes a huge inconsistancy in accuracy and in extreme velocity spreads, BUT WE ARE JUST GETTING STARTED.

Second, When those soft bullets move out of the cylinder and hit the forcing cone, they again slug up to fill the forcing cone, (some forcing cones are huge) but then, as they enter the grooves and lands, the barrel has to size the bullet back down to barrel dimensions. This is a lot of gyrating for that poor bullet and it causes accuracy and more extreme velocity spread problems. So, it is very difficult to get a soft bullet at pressures above 14,000 cup, to shoot as accurate as a harder bullet. We could (and have) fire that same soft bullet out of a rifle or a semi auto handgun and have none of the above dynamics and normally get much better accuracy.

While we want soft expanding bullets, for all their terminal advantages, shooting them out of revolvers is always a compromise. Ive never been happy with the accuracy of our super soft 158gr. bullet, especially at our +P speeds, but they have always been accurate enough for the inteneded purpose. While I tend to want every thing perfect in regards to my ammo, some limiting factors end up requiring a less than perfect solution. No super soft bullet will give consistantly wonderful accuracy out of a variety of revolvers. The good news is, they are accurate enough.

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Jim March
April 10, 2007, 01:22 AM
Huh.

<scratches head>

Interesting. So far I've tried Winnie and Remmie 158+Ps in my New Vaquero and accuracy was nothing to write home about...3" to 4" range groups of six at 25yds bench-testing. Speer's 135gr jacketed in 38+P ran 3", the same slug in 357 did 2", still the best I've seen in this gun.

Ruger changed the manufacturing process on the cylinders in the New Vaq and 50th Anniversary 357 Blackhawk. Larger-frame Ruger SA cylinders were drilled in one shot with six reamers going at once. The New Vaq/50th357 cylinders are done one bore at a time by the same reamer in sequence, so we're seeing absolutely identical chambers on all six bores. This has helped accuracy a lot.

I had kind of assumed that the single-reamer-in-sequence system was more common. Tim, are you saying that's not the case, and that variances between bores are fairly common across all makes?

---

What sort of group size differences are you seeing between the 150 hardcasts and the 158 softs?

Sundles
April 10, 2007, 01:30 AM
Jim,

Variances in chamber throats are all over the board. It varies from manufacturer to manufacturer and from gun to gun within the same make. Gun companies go through stretches of bad QC from time to time. I remember the sloppy S&W revolvers of the 1970s.

Some revolvers of all makes have very uniform chamber throats, others do not. The best I've seen are FA revolvers which are super consistant and thier accuracy shows it.

Sundles
April 10, 2007, 01:33 AM
Ooops, almost forgot to answer your question. The 150gr. wad cutter almost always out shoots the 158gr. bullet in a very wide variety of revolvers. I have probably at least 25 different 357s and 38s here at the factory and the wad cautter is more accurate out of all but one of them.

One factor that helps the accuracy of our 158gr. bullet is that gas check. Not only does it stop leading, but it helps the obturation effects in the throat and forcing cone.

Z_Infidel
April 11, 2007, 10:28 AM
These recent threads on .38 Special ammo have been very interesting. Mr. Sundles, thanks for posting this info.

I recently purchased a new production S&W Model 10 and have been trying some different commercial loads to see which it likes best. So far I'm having good results with the Federal 158 gr LSWCHP+P rounds, but am also looking at the Georgia Arms semi-wadcutters and am very interested in the Buffalo Bore offerings. I've never tried full wadcutters, so that might be an interesting option to explore.

The Federal rounds are pretty affordable though... hmmm, lots to think about.

vanfunk
April 11, 2007, 10:40 AM
Fascinating! Thanks for the insightful information. I look forward to reading more on this subject. I love to get a "peek behind the curtain" with ballistic issues such as this one. What a great site we have here...:)

Thanks,
vanfunk

PzGren
April 11, 2007, 11:09 AM
Soft lead bullets, swaged in general, are not known for their accuracy at elevated velocities.
Interesting that you bring the gas check up, they were actually intended to avoid the base of the bullet being damaged by hot gases but have the benefit of helping to avoid leading.

Now, what I always wondered, is that the gas check scrapes the lead basically out of the barrel after the bullet has passed. This is little different from shooting a jacketed bullet through a barrel to clean out the lead.

Am I missing something in my assumption?

19-3Ben
April 11, 2007, 11:23 AM
Mr. Sundles, you are a remarkable resource to have here on this site. Thank you so much for sharing your knowledge and experience with us.

Sundles
April 11, 2007, 11:47 AM
Folks,

Thank you for the kind comments. Being in this business, I learn something new almost every day.

PzGren,

In my opinion the gas check helps stop leading a couple ways. As you mentioned, I do think it sort of scrapes lead build up from the lands and grooves as it travels down the barrel, just like a jacketed bullet does, only to a lesser degree because of its small size. For decades Ive been shooting jacketed bullets down my barrel to clean out lead deposits after a long shooting session with soft lead bullets. Second, that gas check keeps hot gasses from melting/eroding the base of the bullet as it travels down the barrel. The base of the bullet eroding, will leave lead deposits in the barrel. So, no, I dont think you are missing anything.

go_bang
April 11, 2007, 12:03 PM
Tim, have you seen this issue you mention happening with plated bullets?

loplop
April 11, 2007, 12:29 PM
Very interesting information, Mr. Sundles. Thanks for sharing.

Jim March
April 11, 2007, 05:51 PM
Second that: Tim, you're a good man to have around here.

CB900F
April 11, 2007, 08:12 PM
Fella's;

If you use the copper-washed lead bullets, such as Ranier, or Berry, be aware that they are not, repeat not, to be treated as jacketed bullets. The lead under the electroplated copper is quite soft. If you overdrive these bullets, they will suffer exactly the problems have been detailed above. Furthermore, if you really overdrive them, the base of the bullet will quite possibly expand in the cylinder gap & you will note little lunettes, think a little lead parenthesis, around the front of your cylinder, hitting your hand, found on the bench where you're shooting, etc.

If you don't ask how I know this, I won't tell. Or something like that.

900F

Smith357
April 11, 2007, 10:12 PM
I use soft lead 158 grain SWC with excellent results in my 14-4, but then I keep velocity under 750fps. For +P velocity's I use JHPs, not so much for accuracy as for lead fouling.

Sundles
April 12, 2007, 12:50 AM
I have little experience with those soft plated bullets, so I dont know.

PzGren
April 12, 2007, 07:04 AM
Sundles,

thanks for the reply - and it's exactly what I wanted to hear from an experienced source.

Nematocyst
April 13, 2007, 05:31 AM
1) THR continues to be the best, most informative gun forum on the Internet.

2) Sundles (Tim) thanks for contributing. I'm reading with much interest.

3) I'm most interested in SD rnds for my 642 snubbie. The 150gr. wad cutter almost always out shoots the 158gr. bullet in a very wide variety of revolvers. Does that apply to snubbies?

These recent threads on .38 Special ammo have been very interesting.4) Here's another thread - a poll - on .38 spl ammo. (http://thehighroad.org/showthread.php?t=269258)

Y'all come vote. :cool:

Nem

1911Tuner
April 13, 2007, 09:45 AM
Sundles wrote:

>First, When the primer and powder ignite, that soft bullet is instantly under pressure and will slug up to fill the diameter of the chamber throat. A harder bullet wont do this.<
*****************

To better understand the dynamics, it's necessary to understand that nothing happens instantly. Everything takes time, and...no matter how miniscule that the elapsed time is between powder ignition and bullet obturation...there will always be a little gas cutting past the sides of the bullet unless the bullet is sized large enough to tightly seal the gas.

Softer bullet alloys bump up quicker and more readily than hard alloys. As a long-time caster and mad scientist given to experimenting just for the sake of satisfying my curiosity and proving/disproving theories...I found out that in certain applications a harder bullet will usually produce more lead fouling than a softer one if the bullet to bore sizing is less than optimum. F'rinstance, with my go-to pistol bullet alloy, I can drive a 150-grain .357 bullet to beyond 1300 fps with zero "hard" fouling...but the same alloy will lead the barrels when cast to .452/225/800 fps and fired in .45 ACP pistols. This alloy is a bit softer than the standby Lyman #2 that's composed of a 90/5/5 percent mix of lead/tin/antimony.

In another .357 revolver with a .0005 larger groove diameter, they might lead badly. In another .45 pistol barrel with a .0005 tighter groove diameter, they may not lead at all. Accuracy and the tendency to hard lead fouling is more closely related to sizing than alloy hardness or lack thereof. Of course, beyond a certain velocity, a bullet that's cast too soft has a tendency to skid across the first inch or two of rifling when the pressure impulse boots it in the butt, and cause all sorts of fouling and accuracy problems. Quicker powders tend to make skidding/stripping more likely to happen with a given muzzle velocity than slower powders, but the difference in burn rate has to be
fairly radical in order to see any real difference. Something like IMR 3031 and 4350.

Alpacca 45
July 18, 2009, 07:37 PM
F.W. Mann had a series of photos of .30-40 jacketed bullets fired from a barrel which he progresivly shortened. When he got to around 2 inches (It is about 20 years since I read that part so I may have a few mistakes), the mid section and base of the bullets was dramatically mushroomed.

Sundles interpretation is exactly right. As the bullet starts to move, the force of acceleration is sufficeint for weight / inertia of the lead at the front of the bullet to plasticly deform the lead in the mid section.

In a one piece barrel & chamber, the barrel contains the sloppy lead, and I suspect that the mid section and probably also the base of the bullet is bearing on the bore with pressure at least equal to the pressure of the gas behind it, otherwise, I think we'd see a lot of gas cutting past the bullet.

In a revolver, we make that accelerating bullet jump into a funnel that it is supposed to somehow get pushed down the middle of. Think of doing the same thing by hand with jelly....

1911 Tuner, Does the microscopic roughness of the bore have much effect on the leading you have seen? I have a pet theory that jacketed rifle bullets ride partly on metal to metal contact and partly on flash heated gas that was trapped between the high points on the bore surface and the bullet.

RatDrall
July 18, 2009, 07:55 PM
I've fired touching groups, at 50', with Remington 158gr LHP+P "FBI Load" out of a 4" S&W K frame.

Jim Watson
July 18, 2009, 08:34 PM
Ive never been happy with the accuracy of our super soft 158gr. bullet, especially at our +P speeds,

So you sell bullets or ammunition?

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