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  #1  
Old 11-05-2019, 09:08 AM
GlenS GlenS is offline
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Barrel length measurement

Why is the measurement of barrel lengths different on revolvers vs semi-autos? Revolvers seem to be measured just the barrel and not the cylinder. Semi-autos are measured from the breech face to the end of the barrel. Revolver cartridge length does not count for barrel length. Semi-auto the chanber is included in barrel length.

I hope I am getting this clear enough. If not, sorry!
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  #2  
Old 11-05-2019, 09:10 AM
quintessetialman quintessetialman is online now
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Because with simiauto the chamber is part of the barrel, in revolvers the chamber is in the cylinder.

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  #3  
Old 11-05-2019, 11:57 AM
Randall M Randall M is offline
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Yeah, I have a S&W 625 with a 5" Bbl.
and compared to a full size 1911 5" bbl. the 625
has approx. 1" more inch of twist/power spplied to the bullet

Go back to 1900 and ask why they measure differently

R- --
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  #4  
Old 11-05-2019, 12:03 PM
1911_Kid 1911_Kid is offline
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Kinda like how a square is nothing more than a special rectangle.
Revolvers are kinda "special", they have "articulating" chamber(s)?

Probably just done that way for ez sake. Technically the full length is down to where the bottom of round is located.
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  #5  
Old 11-05-2019, 12:54 PM
dakota1911 dakota1911 is offline
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Think about it. I have a couple Ruger Blackhawk convertibles with what Ruger calls its 4.62 inch barrel I think. Each has two cylinders. One shoots 10mm/40S&W and the other shoots 357mag(38Special)/9mm.



Or think of the S&W Governor where one can shoot 45Colt and 410 shotgun or with moon clips one can shoot 45ACP.
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  #6  
Old 11-05-2019, 01:31 PM
Randall M Randall M is offline
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dakota1911 Multiple cartridge versatility has nothing to do with
barrel length measurement.
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  #7  
Old 11-05-2019, 02:11 PM
PolymerMan PolymerMan is offline
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I have mention this in other threads years ago that a 2.5 inch snubby has an effective (semi-auto) barrel equivalent of 4 inches. You can add an 1 to 1.5 (cylinder length depends on caliber and make of revolver) inches to ballistics table to get a rough idea when you must compare revolvers to pistols using the same cartridge and load.

It is not precise or exact, but close enough and some of the tables at http://www.ballisticsbytheinch.com/ (Ballistics by the Inch) indicates this approximation to be true. There is also a cylinder gap where gas pressure is lost, but when the bullet traverses from the cylinder through the forcing cone, the bullet seals the gas in until the entire bullet is in the barrel.

Below I compare my Charter Arms Pitbull .45 ACP (2.5 inch BBL) with my Ruger Commander size (4 inch bbl). I tried to place the tape measure at the breech face so you can see that the projectile has the same length of travel in a 4 inch semi auto as it does in a 2.5 inch revolver.

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  #8  
Old 11-05-2019, 05:27 PM
drail drail is offline
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Because the cylinder's chambers are NOT part of the barrel. A semi auto barrel has the chamber attached.
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  #9  
Old 11-05-2019, 06:20 PM
subscriber subscriber is online now
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Quote:
Originally Posted by Randall M View Post
Yeah, I have a S&W 625 with a 5" Bbl.
and compared to a full size 1911 5" bbl. the 625
has approx. 1" more inch of twist/power spplied to the bullet

Go back to 1900 and ask why they measure differently

R- --
Sorry Randall, but the advantage of that extra inch, is lost due to your revolver's cylinder to barrel gap.

As for twist; the bullet does not skid in the rifling (unless it is grossly undersized). Thus, one inch of barrel is enough to impart spin. Yes, the velocity will be reduced if it that short.

To see how much barrel length matters by caliber for rifles, pistol and revolvers, browse ballistics by the inch: http://www.ballisticsbytheinch.com/
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  #10  
Old 11-05-2019, 06:23 PM
1911_Kid 1911_Kid is offline
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Originally Posted by drail View Post
Because the cylinder's chambers are NOT part of the barrel. A semi auto barrel has the chamber attached.
I think this was the OP's argument. Why is a detached chamber not part of the barrel system? Yes, a cylinder is considered part of the action, but the question is still valid.

Maybe barrel length should be where rifling starts and ends (for rifled tubes, etc)?
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  #11  
Old 11-05-2019, 06:29 PM
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Glen, the reason is convention. Probably because, when a barrel is put into inventory in a factory, that part number and bin are labelled with a certain barrel length. A worker reaching into the parts bin for a given contract would use a ruler to verify that he has the correct barrel length. Having a 1911 barrel labelled as a 4.1" when it measures 5" on his rules is going to be confusing. Simple as that.

If you feel cheated because your AR pistol really only has a 6" barrel, then buy something else.

All joking aside, non-magnum handgun calibers have pretty spiky pressure profiles and losing an inch off a "standard" barrel does not lower the velocity as much as one might think it should. Certainly, shorter barrel carry pistols don't have the same performance as their longer counterparts. However, they are intended for short range only.
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  #12  
Old 11-06-2019, 01:02 PM
Randall M Randall M is offline
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Originally Posted by subscriber View Post
Sorry Randall, but the advantage of that extra inch, is lost due to your revolver's cylinder to barrel gap.

As for twist; the bullet does not skid in the rifling (unless it is grossly undersized). Thus, one inch of barrel is enough to impart spin. Yes, the velocity will be reduced if it that short.

To see how much barrel length matters by caliber for rifles, pistol and revolvers, browse ballistics by the inch: http://www.ballisticsbytheinch.com/
Subscriber I'm well aware of the Barrel to Cyllinder gap
it varies a lot from Revolver to Revolver.

I've refereneced/used BBTI for years.

Question does the barrel length listed 18" down to 2" include
the length of the cartridge as measured in Semi-Autos? If Not
you may be comparing incorrectly

R-
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  #13  
Old 11-06-2019, 02:56 PM
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Originally Posted by Randall M View Post
Question does the barrel length listed 18" down to 2" include
the length of the cartridge as measured in Semi-Autos? If Not
you may be comparing incorrectly

R-
Pretty sure that a 3" .223 barrel means the rifled portion is only 1" long...

I emailed BBI to confirm.
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Old 11-06-2019, 02:57 PM
buck460XVR buck460XVR is offline
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To confuse you even more, in my state, to determine minimum barrel length for hunting with a handgun, revolvers are measured thru the cylinder to the recoil shield.
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Old 11-06-2019, 03:01 PM
drail drail is offline
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As usual the people who make up the laws have absolutely no idea what they're talking about. Just like "assault rifles". These people are dumb but they've been put in charge. The length of a barrel is the actual length of a barrel - there is no such thing as a "barrel system". Just a barrel and a chamber - attached or not.

Last edited by drail; 11-06-2019 at 03:05 PM.
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  #16  
Old 11-06-2019, 03:05 PM
PolymerMan PolymerMan is offline
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Sorry Randall, but the advantage of that extra inch, is lost due to your revolver's cylinder to barrel gap.

As for twist; the bullet does not skid in the rifling (unless it is grossly undersized). Thus, one inch of barrel is enough to impart spin. Yes, the velocity will be reduced if it that short.

To see how much barrel length matters by caliber for rifles, pistol and revolvers, browse ballistics by the inch: http://www.ballisticsbytheinch.com/
The cylinder gap pressure loss is actually insignificant. In fact, very insignificant, in my humble opinion.

http://www.ballisticsbytheinch.com/gaptests.html

http://www.ballisticsbytheinch.com/docs/GapCompare.xls

I had exchanged email years ago with the owner of BBTI about the matter and he later included some ballistic data on different revolvers with different clearances in the gap. It varies by revolvers but it has a much less effect, especially on shorter barrel guns than one would think. Don't forget... the bullet SEALS the gap as it transverses from the cylinder though the forcing cone. Think of it as a gasket. The gap then releases gas after the bullet clears the cylinder gap. But gas also escapes through the rifling forward of the projectile. I have seen some ultra-slow motion videos of guns being fired and in almost every video, there is a fireball that precedes the projectile as well as afterwards. Rifling depth and bullet design and malleability probably has more effect on gas pressure leaks than the gap, some copper clad bullets aren't soft enough to seat themselves all the way into the rifling. But that is my educated (or uneducated) guess.

Also keep in mind, much of the powder burns outside the muzzle. A .357 magnum has enough powder to burn in a rifle length barrel (16 to 20 inches), so does a .38 spl and just about every pistol caliber cartridge. If you look at the tables at BBTI, you will find optimum barrel lengths for various loadings and caliber.

Just about every single pistol caliber cartridge has enough powder to accelerate a projectile in a 16 to 21 inch barrel and that is indicated by the muzzle velocity continuing to rise as barrel length increase. At some point, the projectile does lose velocity if the barrel is too long and all the propellant as been extinguished within the barrel.

But the point I make, the bottom line is that the gap has some small effect on pressure, but far less than one would anticipate.
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  #17  
Old 11-06-2019, 03:06 PM
drail drail is offline
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+1 Excellent explanation.
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Old 11-06-2019, 03:38 PM
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Don't forget... the bullet SEALS the gap as it transverses from the cylinder though the forcing cone
So what? The major leak at near peak pressure starts as soon as the bullet base clears the gap. Then the leak lasts at diminishing pressure, while the bullet travels all the way up the barrel.

As for estimating cylinder barrel gap leakage power loss; compare velocity of a .44 mag when fired from a revolver VS a carbine. The reason why the velocity is so much higher in the rifle is not just barrel length, but that there is no cylinder barrel gap to leak. Which as you stated, is magnified by barrel length.

The volume of gas ahead of the bullet is tiny, compared to the volume behind it. Find some high speed video and compare the volume of the gas balls. A diameter difference of 5 fold is actually a volume difference of 125 times. A rifle with an oversized chamber throat will leak more gas ahead of the bullet than one with a tight throat.
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Old 11-06-2019, 04:06 PM
PolymerMan PolymerMan is offline
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So what? The major leak at near peak pressure starts as soon as the bullet base clears the gap. Then the leak lasts at diminishing pressure, while the bullet travels all the way up the barrel.

As for estimating cylinder barrel gap leakage power loss; compare velocity of a .44 mag when fired from a revolver VS a carbine. The reason why the velocity is so much higher in the rifle is not just barrel length, but that there is no cylinder barrel gap to leak. Which as you stated, is magnified by barrel length.

The volume of gas ahead of the bullet is tiny, compared to the volume behind it. Find some high speed video and compare the volume of the gas balls. A diameter difference of 5 fold is actually a volume difference of 125 times. A rifle with an oversized chamber throat will leak more gas ahead of the bullet than one with a tight throat.

Well, I disagree. Look at the excel spreadsheet off of the BBTI website that I linked to. They tested 0 mil, 1 mil and 6 mil, gaps.

The difference between 0 mil and 6 mil was not more than 10-20 fps. The difference between 1 mil and 6 mil was something like 2 or 3 fps.

There were I believe if I recall correctly 6000 rounds fired in their test so they could rule out statistical anomalies.

There is far more variation in velocity of a given barrel length due to things like variations in batches of ammo.

Like I said... yes, there is a pressure loss, but it is so minimal that it is negligible.
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Old 11-06-2019, 06:04 PM
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Well, I disagree. Look at the excel spreadsheet off of the BBTI website that I linked to. They tested 0 mil, 1 mil and 6 mil, gaps.

The difference between 0 mil and 6 mil was not more than 10-20 fps. The difference between 1 mil and 6 mil was something like 2 or 3 fps.
I disagree back at you: A zero mill flash gap is not the same thing as a contiguous barrel, without meeting faces. With two faces meeting at a zero gap, the frame still stretches and it still leaks.

They should have tried this with a Nagant, with regular and short cartridges...

https://en.wikipedia.org/wiki/Nagant_M1895
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Old 11-06-2019, 06:11 PM
WaterDR WaterDR is offline
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It’s amazing how a simple question can cause so many arguments 🙂

I think it’s pretty simple. Early guns were revolvers. The barrel is the barrel. It’s a part. The barrel can be removed. A cylinder is not a barrel so ergo if you want the barrel length, it’s the length of the barrel and not the cylinder.

On a semi auto, the barrel is also the barrel. It’s a separate part regardless if it also includes the chamber. So the length is the length.

Performance questions are altogether different. A 9mm fired from a 3” revolver I suspect might have more velocity than the same round through a 3” barrel in a semi. But in the end, it doesn’t matter as long as you are comparing apples to apples and oranges to oranges.
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Old 11-06-2019, 08:36 PM
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The difference between 0 mil and 6 mil was not more than 10-20 fps. The difference between 1 mil and 6 mil was something like 2 or 3 fps.
Depends on which caliber, barrel length and load you are looking at. This one seems to have a much larger difference than the load you chose to look at for 8" barrels : http://www.ballisticsbytheinch.com/federal.html


I am not sure I trust all their measurements. How do you explain the spike in the blue line, here, at a 16" barrel length: http://www.ballisticsbytheinch.com/blackhills2.html
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Old 11-06-2019, 09:33 PM
PolymerMan PolymerMan is offline
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I disagree back at you: A zero mill flash gap is not the same thing as a contiguous barrel, without meeting faces. With two faces meeting at a zero gap, the frame still stretches and it still leaks.

They should have tried this with a Nagant, with regular and short cartridges...

https://en.wikipedia.org/wiki/Nagant_M1895
Oh there are a zillion variables no doubt.

You can also argue that in semi-autos, in either straight blow back or short recoil action (lug and tilting barrel) or any kind of semi auto, gas pressure is also used to cycle the action, taking away pressure from driving the projectile. There is also gas escaping against the breech face. Those chambers, brass cartridges and breech face are not sealed hermetically during ignition.

Some of the hardest carbon deposits is often found on the breech face of semi autos, which tells me there is some really hot plasma gasses getting back in there, similar to the deposits (carbon rings) I get on the cylinder face of my revolvers.

subscriber, the point is that revolvers don't lose that much pressure through the gap... it is certainly not equal to the loss equivalent to 1 inch of barrel length like you suggested in post#9 with Randall. It just isn't that large of a loss. I would say that it is closer to 1/10 of inch, certainly not a full inch.
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Old 11-06-2019, 09:36 PM
PolymerMan PolymerMan is offline
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Itís amazing how a simple question can cause so many arguments 🙂
By now you should know if there are 1000 active forum members that there must be at least 1000 opinions...
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Old 11-07-2019, 09:11 AM
1911_Kid 1911_Kid is offline
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As usual the people who make up the laws have absolutely no idea what they're talking about. Just like "assault rifles". These people are dumb but they've been put in charge. The length of a barrel is the actual length of a barrel - there is no such thing as a "barrel system". Just a barrel and a chamber - attached or not.
Don't forget what I had said numerous times.

Govt is moving in a direction from "Govt of the People" to "People of the Govt".

Govt used to be about fundamentals like water, air, energy, jobs, innovation, security. Nowadays govt wants to tell you how it has redefined what COTUS means, arrest you for using certain words, allow illegals in, tell you what health insurance you can have or must buy, collecting data about you, red flagging you, etc etc etc.

For those who are 45-50yrs old, you are right in the middle of the transformation. Give it another 50yrs and the Krats will have crossed their finish line. Just look at VA and KY as examples of what transformation looks like. Look at CA NY NJ to see it completed. Muslim somali's are taking office all over (aka "the cancer").

American Patriots are becoming the minority, but why? Because 1) immigration (both legal and illegal), and 2) Millennials and Snowflakes have been well indoctrinated to believe the Krats are good for America.
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