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Old March 14, 2013, 01:58 PM   #1
Jim March
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Understanding semi-auto calibers in full-length revolver chambers.

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Old March 14, 2013, 02:49 PM   #2
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How is accuracy affected by the bullet hitting the throat and rifling at comparatively high velocity?
That is, if the cases of the two cartridges had a greater length disparity, say, shooting .45 GAP in a revolver with a cylinder long enought to accommodate .45 Colt, will the faster-moving GAP bullet be deformed, or otherwise suffer from having been accelerated to higher velocity while still in the cylinder?
If there were no issue in that regard, why does S&W make shorter cylinders for shorter cartridges? I've seen some custom .45 ACP-chambered revolvers with cylinders that appear to be only about 2/3 the length of other cylinders in the same frame size.
I suspect that while velocity could benefit from the longer "throat" in the cylinder, accuracy will suffer.
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Old March 14, 2013, 03:25 PM   #3
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Quote:
I've seen some custom .45 ACP-chambered revolvers with cylinders that appear to be only about 2/3 the length of other cylinders in the same frame size.
Right, I know what you're talking about. In a setup like I have (second image is pretty close) the bullet is hitting the back of the barrel (called the forcing cone) at a high rate of speed. Does that hurt accuracy? Dunno. Obviously, it might...on Maurice's barrel I did a fairly deep forcing cone and polished it to a mirror finish on a lathe, plus it's a very good barrel to start with (Douglas Premium, true .355").

Now...are the target revolvers in 45ACP benefitting from using shorter cylinders and set-back barrels? Dunno. And unfortunately I haven't had time to wring peak accuracy out of Maurice - I do have reloading gear in 9mm but the ammo/component shortage has been brutal in 9mm and I don't have the cash or time to fully pursue what Maurice can do. *Preliminary* testing with crap ammo looks good though, at least as good as it was as a stock 357.

And since this is still a defensive piece I want big velocity as long as accuracy isn't crap.
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Old March 14, 2013, 03:50 PM   #4
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re:

In the summer of 2007, a friend and I designed an experiment.

He brought a pair of RG .38 revolvers with 2-inch barrels. For those who've never had the pleasure, RG barrels are ridiculously easy to remove. Knock out the crosspin and pull the barrel out of the frame. The barrel is no more than a steel tube with a pot metal shroud pressed over it.

I set the barrel/cylinger gap to as close to identical as I could, and replaced the barrel. There was just enough rifling in the leade to stabilize the bullet.

Then I lopped off one barrel flush with the frame and reinstalled it. We bought a 50-round box of 158-grain lead RN standard velocity ammunition and set up the Chrony 15 feet distant. The morning was perfect for chronographing with no wind and a light overcast with an ambient temperature of approximately 80 degrees.

We carefully fired three five shot groups from each revolver...averaged the results...and compared.

There was a 58 foot per second difference between the one with the 2-inch barrel and the one with a quarter-inch barrel with barely any rifling.

Then I figured what the hello...the Chrony was old and I wanted an excuse to buy a new one...so we removed the lopped-off barrel completely...and chronographed another five rounds just for giggles

It lost another 11 fps to the 2-inch barrel. A piece of cardboard behind the chronograph showed that the bullets barely keyholed instead of flipping 90 degrees and destroying the Chrony like we expected.

69 feet per second difference between 2 inches of barrel and no barrel...with the bullet yawing between the screens.

More...an uninterested party was drafted to fire the guns in a back-to-back blind test to see if he could discern any difference in recoil. He couldn't.

Interesting.
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Old March 14, 2013, 04:17 PM   #5
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Yeah, but...you're assuming the original barrel was any good. On an RG...wow, I wouldn't bet on it.

Put another way: you can see pretty serious speed advantages with a newer S&W revolver (current production 686) over an old classic like, say, a late 1960s model 27. Now, that 27 was a superb gun but the barrel didn't shoot as fast as a current type or for that matter a Ruger GP100, and this is with all guns wearing 4" barrels.

Maurice's barrel is very, very good stuff but I don't have a handle on how fast it shoots. Has a gleaming mirror finish inside though...
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Old March 14, 2013, 09:20 PM   #6
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I think it's academical at best. I do like my old Smith 25-2 45 ACP Revolver, but I use Full Moon Clips. I don't like to rely on headspacing on the case mouth on a revolver.

I bought a Ruger Blackhawk with a 45acp cylinder, and found it to be very finicky on the brands of factory loads I could use, do to poor headspacing, with several brands going to deep into the chambers and causing jams, high pressures, etc. Maybe quality control was bad on that gun, I don't know, I know I have had plenty of problems with Rugers on Quality control, so maybe that was it, but apparently there was a problem.

A 1911 seems to handle the problem of head spacing ok, but I sometimes give the extractor some credit for helping with headspacing. I like the idea of using the 45acp rounds in the Ruger, but gave up on it.
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Old March 15, 2013, 09:40 AM   #7
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RG Goodness

Quote:
Yeah, but...you're assuming the original barrel was any good. On an RG...wow, I wouldn't bet on it.
True that, but I forgot to mention that we ran a baseline test with both revolvers with handloaded ammunition, and the velocities were close.

Consider this for a minute.

Assuming that velocity increase with barrel length is hypothetically linear...

With a 5-inch 1911 barrel, there is approximately .900 inch of chamber and 4.1 inches of rifled section. Let's simplify it and just call it 4 inches even.

If we assume 35 fps gained or lost per inch...which is pretty close for standard pressure .45 Auto and 850 fps mv...we get 140 fps of the total in the barrel. When/where was the other 710 fps produced?

If we then assume that the missing velocity was produced in the first half-inch of bullet acceleration...we gain about 122 fps in the remaining 3.5 inches of barrel...and 728 fps in the first half-inch.

Later, I ran another experiment with an old, badly pitted 1911 barrel by boring it out to a full half-inch ID all the way to the chamber shoulder. I didn't use a chronograph, but instead compared penetration depth in dry newsprint with the depth before the barrel was altered. The unaltered barrel, firing the same lot of ammunition...230-grain RNJ with 6 grains of Unique...gave a tick more than two inches more penetration than the bored barrel...and the bullet from the bored barrel gave indication of a slight yaw.

And, yes. The slide cycled at what appeared to be normal speed, and the empty case landed at about the same distance from the gun. If anything, in the test with the open barrel, the slide's cycle felt more brisk, and seemed to hit the impact abutment a little harder.

In other words...hardly enough to flip a coin for the practical difference.

With one of the quicker powders like Bullseye...I'd be willing to bet that the unaccounted for velocity is realized before the bullet base clears the case mouth.
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Old March 15, 2013, 03:40 PM   #8
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The described RG and 1911 tests are interesting. However, Jim March wrote in the original post:
Quote:
An S&W factory 9mm snubby with a 2" barrel will produce 9mm bullet velocities on par with a good 4" barrel semi-auto like the Glock 19
Please explain this quoted text which appears to fly directly in the face of everything we know to typically be true?

Are you saying that this free-bore section of the cylinder allows for this, and it not only makes this happen, but it erases the loss of the cylinder gap -AND- it doesn't account for the known slight up-tick in velocity that you may often see from an OEM Glock barrel that is polygonally rifled?

Is this simply data from a single Smith & Wesson 9mm chambered snub revolver compared to general quoted stats from Glock 19 pistols?

I'm not trying to be argumentative, I'm just trying to get to the bottom of the claimed velocity advantage of 9mm in a snubbie revolver -- because it doesn't jive with all the "conventional" velocity arguments from handguns.
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Old March 15, 2013, 04:19 PM   #9
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I chrono'd rounds through a Smith 625 with 2.5" or 3" barrel, and a Commander-length - 4.25" - Nighthawk 1911, and the rounds went faster through the revolver.
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Old March 15, 2013, 05:54 PM   #10
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re:

Quote:
An S&W factory 9mm snubby with a 2" barrel will produce 9mm bullet velocities on par with a good 4" barrel semi-auto like the Glock 19
You'll need to open your mind and get ready for something else to fly in the face of conventional wisdom.

10...maybe 12 years ago...there was an article in one of the gun magazines where a guy decided to provide the definitive answer on how much barrel length affects velocity.

In order to eliminate all the variables possible, he used the same rifle for all tests...starting with 26 inches and lopping off an inch at a time and recrowning. He fired all loads with 26 inches...cut and crowned...fired them again at 25, then 24...lather/rinse/repeat until he stopped at 18 inches.

He used the same lot of bullets throughout the test, and several different powders that were recommended for the .308 caliber.

I believe that it was IMR 3031 that gave up some interesting results. He found that he got more velocity in 21 inches than he did at 22 inches...and a little more still with 20 than with 21.

Proving what I suspected for years...

With quick powders...depending on barrel length...it's entirely possible for the bullet's velocity to be higher at some point in the barrel than at the muzzle.
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Old March 15, 2013, 06:07 PM   #11
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Velocity

One last story. Sometimes a combination of boredom and curiosity leads me to do things just because I can.

A friend of mine gave me 50-60 rounds of .45 Schofield brass that he'd gotten in a shipment of .45 Colt by mistake. A little time spent with the caliper and Jethro Bodine cipherin' gave me an idea. I decided to increase the magazine capacity of my Winchester Trapper carbine by one. By trimming the Schofield cases to SAAMI minimum length, I could just squeak in an extra round.

I wanted to retain the cast 250-grain bullets I'd been using, so I adjusted for the reduced case capacity and loaded up with 7.5 grains Unique...figuring that the velocities would be roughly equal.

Wrong. I'm talkin' real bad wrong.

From the soft recoil, I knew that something was amiss on the first trigger pull, so I broke out the trusty little Chrony and compared the new stuff with the old standby.

I'd lost a full 300 fps. Too much to be explained away with 1.5 grains less powder. I bumped the charge up a half-grain at a time until I got to the original 9 grains...and I was still almost a hundred fps shy. At 10 grains, I was almost there. I stopped.

The only thing that really changed was the length of jump/freebore in the too-long chamber.

Go figger.
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Old March 15, 2013, 11:44 PM   #12
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the shorter cylinder is a manufacturing standpoint for the most part. overall length of gun stays same,but you can put in some more barrel length. less cylinder weight can increase longevity of action. easier on the joke/crane assembly. saves sw money. its cheaper to properly machine a 9mm sized cylinder then machine a standard 357 cylinder blank to size. that freebore section costs money to make.
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Old March 15, 2013, 11:49 PM   #13
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So here's a credible report of somebody getting 1,217fps from Winchester 127gr +P+ Ranger-T ammo out of a Glock19:

https://www.youtube.com/watch?v=zSY018CXRi8

And here's a credible report of the same load doing 1,198 from an S&W 940 (2" barrel 9mm factory revolver):

http://www.stoppingpower.net/forum/p...TOPIC_ID=16691

That same report also shows a 9mm Ruger SP101 3" barrel doing 50fps LESS - but I have also heard reports that the 9mm Ruger uses a standard .357" barrel from the 38/357 series guns, which could easily explain that issue.

This particular load is, in my opinion, a good one to do a comparison with because it is marketed for law enforcement and hasn't changed much over the years. It is also a very hot, very high quality carry load.

Something else: if you read reports on the 940 you hear about issues with sticky extraction. I can tell you that Maurice is NOT having any such issues . In fact the first time I shot it with 9mm the gas-powered auto-extraction worked shockingly well...the 357Mag shells had been gently swatting my goatee whereas 9mm was whacking me in the cheek hard enough to hurt . I had to do the hammer-mounted shell deflector STAT. I think that David Manson finish reamer had a whole lot to do with that particular result .
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Old March 16, 2013, 04:11 AM   #14
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Quote:
You'll need to open your mind and get ready for something else to fly in the face of conventional wisdom.

10...maybe 12 years ago...there was an article in one of the gun magazines where a guy decided to provide the definitive answer on how much barrel length affects velocity.

In order to eliminate all the variables possible, he used the same rifle for all tests...starting with 26 inches and lopping off an inch at a time and recrowning. He fired all loads with 26 inches...cut and crowned...fired them again at 25, then 24...lather/rinse/repeat until he stopped at 18 inches.
I've seen similar testing done in magazines several times.

The good fellows at Ballistics by the Inch have done the same sort of testing also, using a T/C Encore barrel and cutting it down an inch at a time.

Their results are published here:
http://www.ballisticsbytheinch.com/9luger.html
The results tend to follow conventional wisdom.

They've also done some testing with regards to cylinder gaps. A lot of interesting bits of data on their site. Good guys, too.

There are some chrono results in a magazine I just read the other day from a couple of 9mm revolvers. I'll post what I see in there after I've chased down that magazine.

I find this topic is quite interesting.
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Old March 16, 2013, 04:56 AM   #15
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Topic

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I find this topic is quite interesting.
Ballistics discussions always catch my attention. Many interesting things emerge for those with a drive and the means to experiment. Sometimes the results are in agreement with what we think or believe...and some go in the opposite direction. I've had both to happen during my "Mad Scientist" moments.

One of our own performed one such experiment several years ago, and I duplicated it just to see for myself.

He threaded the muzzle section of a 1911 barrel...used a steel rod, cut to length and form-turned to match the shape of the nose of a 230-grain hardball bullet so as to prevent any movement of the bullet...installed the barrel into a pistol...loaded it and fired it...and nothing happened.

One would have expected the pistol to imitate a fragmentation grenade, but nothing at all happened, and when the set screw and rod were removed...the gun was fired, and it functioned normally. My duplication produced exactly the same results. The only thing that happened was the pistol sat there and hissed as the gases vented out through the breech area.
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Old March 16, 2013, 11:03 PM   #16
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That is a nutbar experiment, and one that I have conjured in my own head many, many times. Always wondered what would happen!

Another experiment I've always wondered about was the whole "let's neck a .50 BMG down to .224" (or smaller, .20, .17, etc) I believe it's been done, but IIRC, you end up having a difficult time building a slug that can survive the experiment. Of course, it pushes the mind to even more outrageous places... what about one of those crazy Naval war ship deck guns?! Let's neck that down to .22 cal!

Tuner, have you followed any of the posts in the handloading & reloading area by gun-killer Clark? First time I saw one of his posts, my knee-jerk was: "oh, he's crazy." Then it was "oh, he's just trying to make people think he's crazy." But I've read a lot of what he's done and I'm quite sure neither of those is accurate. In fact, Clark is willing and driven to spend his money finding the true limits of different chamberings and calibers, and wrecking guns is merely a cost of that adventure. I've said before after some of his posts... I don't know how I'd make use of some of the results of his adventures, but I always enjoy seeing what he has to say.
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Old March 16, 2013, 11:05 PM   #17
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In the spirit of that post about Clark, same thing with Jim March. I can't personally imagine any road that would lead me to wanting to replicate this whole Maurice trip he's on, but it's pure entertainment to see little blips and nuggets of his obvious passion on the subject, and I know I'm a little richer because he's shared it.

I can only imagine how many times that handgun (!) has made someone, somewhere drop a jaw a bit and say, "uhhh, what in the ____ is that?! "

That's pretty cool.
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Old March 17, 2013, 09:28 AM   #18
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Sevens, the Encore thing is a totally different animal. That platform does not have the pressure venting cylinder gap of a revolver or the pressure absorbing recoil mechanisms of a semi auto.

I had no revolver to do back to back comparisons with a 460 S&W but I did run factory loads across a chronograph. The Hornady 200 gr SST carries a suggested velocity of 2200 fps out of a revolver. My 15" Encore ran those across my chrony at an average of 2696 fps.

I do have a 1911 and a S&W 25-2 in 45 ACP. I could do velocity comparisons between the two but the revolver has a bit longer barrel.
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Old March 17, 2013, 10:33 AM   #19
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What .45 LC are you refering to for the judge, I may want to test this.
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Old March 17, 2013, 10:49 AM   #20
Jim March
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This stuff:

http://www.venturamunitions.com/lehi...-me-12-rounds/

Personally, I think the odds fo getting all four of those petals to stick "straight out" and form 2" or so of wound channel(!) are...low. More likely they'll fold back, or possibly fail to expand. And at 800fps, even if it does expand it may go only 5" deep or something?

Interesting concept though.
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Old March 17, 2013, 12:23 PM   #21
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My personal experience is that anything less than 100fps difference can be attributed to the individual gun/ammo combination.

The precise fit of the bullet in the chamber and barrel is an individual thing. While most guns will have their velocity with a given load fall in a fairly narrow range (with equal barrel lengths), if you test enough guns you will find ones that are noticably "faster" or "slower" than the average. And while a difference of as much as 100fps is unusual and uncommon, it is not impossible.

I have seen a "fast" 4" clock slightly higher velocity than a "slow" 8" revolver. It's rare, but it does happen.

So,don't get your knickers in a twist if gun A is 50fps faster than gun B, or a 3" gun shoots faster than a 4" one. Those differences are insignificant.
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Old March 17, 2013, 02:32 PM   #22
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Sevens, the Encore thing is a totally different animal.
I understand these things of course, I am quite familiar with them. My post regarding the T/C Encore and the testing of barrel length done by BBTI was in response to 1911Tuner's own testing by cutting down a rifle barrel. A very similar test.
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Old March 17, 2013, 04:22 PM   #23
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Encore

Quote:
Sevens, the Encore thing is a totally different animal. That platform does not have the pressure venting cylinder gap of a revolver or the pressure absorbing recoil mechanisms of a semi auto.
There isn't any pressure-absorbing mechanism in a semi-auto, either, and there is no difference in the way that a locked-breech autopistol functions during the acceleration/recoil phase.

With a locked-breech pistol, the slide and barrel assembly is the gun. The frame is essentially the gun mount. Here, the gun is mounted on rails, with a spring that returns it to battery.

Because the breechblock...the slide...is mechanically connected to the barrel for a brief time...just like the barrel and breechblock on a single-shot TC Encore, when the slide is driven backward by recoil forces, it grabs the barrel by the locking lugs and hauls it along with it.

The Encore...or a revolver...does exactly the same thing, except that it doesn't drop the barrel.
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