4 inch barrel revolver VS 4 inch barrel semi auto.

[Oldshooter]

Which one looses more pressure / power? The gap or the slide ejection! or is either one inconsequential?(does it matter) The bullet is supposed to be gone when the slide pulls back for ejection, so does that make the semi auto more efficient? I have always been amazed by the flash of a 44 mag model 29 S&W coming out of the gap(at night or low light).

[irold]

I can tell ya my 5" 1911 gets higher velocity than my 5 1/2" Bisley with the 45aco cylinder installed.  Must be the cylinder gap ?

regards , irold

[Oldshooter]

I have been thinking on these lines for a while, but I have no real scientific proof. The gap in a revolver has to be like a relief valve, but is it enough to matter. Wonder if anyone has tested it on a chrony?

[Lloyd Smale]

a semi auto will about allways give better velocitys with the same load

[Mikey]

Oldshooter:  the cylinder to barrel gap on a revolver is usually .003-.006 inches - pretty small unless you are escaping gases from a cartridge detonation but this is not a factor in semi-auto pistols where the bullet is fired from a closed chamber.  In the semi, all the power from the burning powders powers the bullet down the barrel with the recoil of the cartridge creating the forces to cycle the action.  In a revolver, some of that power is lost through the cylinder to barrel gap.
 
Regrettably there are few valid comparions that can be made but you can make them with 22lr, 9mm and 45 acp.  All three rounds can be fired from both revolvers and semi autos.  In the 45 you will need a 5" barrel as on the Colt and S&W M1917s for a better comparison with the 4" barrel (rifled part) on the 1911s; the 9mm fired through one of the S&W snub nosed revolvers might be more favorably compared to a short barrelled 9mm auto, and the 22lr can be had in both revolver and semi and finding those that could compare most favorably should not be difficult. 
 
It would make a interesting comparative analysis I think.

[SHOOTALL]

Remember a 4 inch auto has the chamber included where a revolver barrel does not.
 Does it matter to  me no. but cyl. gap varies from gun to gun. And depending on pressure it might matter less at higher pressure. The gap is what it is and will only pass a certain amount of gas thru. it At some point more pressure will not cause more gas to escape the gap can only pass a certain amount. Does the pressure vs. gap get to that point ? Don't have a clue and it would depend on the particular gap involved. If this is hard to understand ( and in refrigeration class it is a big deal it was hard for most to understand) but consider a cyl. blowing apart on a revolver even though the bullet goes out the cyl into the barrel in most cases the gap won't vent the pressure of an over load fast enough. Can't get it out because only so much can pass thru. in a certain amount of time.
Thing is in an auto you are  restricted to a point by timing and too much pressure will batter the gun and cause wear or malfunction and too lite a load won't work the action. So the revolver works over a wider range of pressures .

[spruce]

I think it's safe to say that generally the auto has a slight edge, but probably not enough to make any practical difference in regards to the bullet's effect on target.
 
Like was mentioned above a 4" barrel auto is not the same as a 4" barrel revolver because of the standard way of measuring barrel length.  Not to forget that guns of the same make, model, caliber, and barrel length will also vary in average velocities.  There are many variables besides barrel length that affect velocities:  chamber dimensions, forcing cone dimensions, barrel dimensions to name a few.
 
Trying to  eliminate all the variables would be a tedious and expensive project to say the least.
Maybe the most practical way to compare would be to take a 5" auto, a 4" auto, a 4" revolver, and a 4 1/2" revolver, all in the same caliber, then get at least a 10 shot average from each to make the comparison. 

[Lonegun1894]

I think that unless you are comparing the same caliber in both types of gun, you are comparing apples and oranges.  Having said that, assuming the same caliber and barrel length, I think the semi will have a slight advantage.  However, the revolver, in the same size overall package as your chosen size of semi-auto, will be available in more calibers at least some of which will be of higher performance than the chosen semi-auto chambering, which in turn is limited due to the timing, and pressure curves, and other factors that have been brought up already.  For example, I will personally take a .357 Mag with it's heavier and faster bullet over a 9x19, and would in fact choose a .38 Spl over a 9x19, also for the heavier bullet with the flatter nose which won't feed in most semi-autos.  Same as my 4 5/8" Ruger Vaquero in .45 Colt firing a 255gr Keith-type SWC at 1150fps outperforms my 5"1911 .45ACP firing a 230gr HP which is pretty much limited to about 900fps due to the semi having to be able to cycle the rounds from the magazine into the chamber without beating itself to death.  And I am not trying to talk trash about either because I love both guns and both work very well for what they are intended to do, but they just have different jobs.  Both are the approximate same size package, same bore size, and same barrel length, but the revolver is more versatile regarding the range of loads it can handle.

[Oldshooter]

So a guy shoots a 10 mm Glock  with a 6 inch bbl designed to shoot cast bullets. Will a S&W 610 shooting the same ammo with the 4 inch barrel have the same firepower.(is that a fair comparison) I'm thinking the revolver is not as "hot" , but is it a measurable difference. I thinking pig hunting here. I know what I need to know for defense. I'm  just curios about the difference for a hunting and penetration.

[SHOOTALL]

At one time I could shoot a 10 mm Delta Gold Cup, Glock 20 and a 610. You would have no problem feeling (recoil) and seeing (impact on steel targets) between the pistols and revolver.

[Oldshooter]

So between the 610 and the Glock 20, would you have a preference as which to take into the brush after a big pig?

[SHOOTALL]

Good ? , The Glock 20 and it is the one I carry hunting these days , It was the most weather resistant and it never failed to feed and fire. It held the most rounds making a spare mag unnecessary. The other two are gone . The other two are good guns , both SS both accurate , both had better triggers but the Glock was simple and easy to maintain. It was also the least expensive so adding a second gun would be less expensive. I ride a 4 wheeler in mud , rain , snow etc why mess up a nice Smith or Colt ? I started carrying the 10 when we started running into Bear and Mt lions.

[1911crazy]

Enough said, Elmer Keith made a 265yard shot with a s&w m29 with  4" barrel. My point is how far can the auto shot? I can ping small rocks on the berm at 100yards using 3' of Kentucky windage with a 9mm CZ 85DB. Hickok45 on you tube made the same 265yd shot with the same gun.


I think the bullet is long gone past the cylinder gap by the time the flames are seen.

[irold]

Oldshooter ... When working up my loads for my 1911 , I went through a lot of variables ( powder, bullets , etc ) I finally settled on two loads ,  185 gr Nosler over bullseye and 200 SWC over W-231.  I'm not looking at my data nor am I at home where I can look ... that being said ..I'm thinking the 185 gr was clocking at just under 1000 and the 200 SWC was mid 800s ... Last summer when I purchased my Blackhawk convertable ... with the 45 acp cylinder , I was using the same loads and was getting about 100 fps less.  The Range Officer has a 5 inch barrel ... the Blackhawk is a 5 1/2 incher.  Not sure what , if anything ,this proves ...but that was my findings.

regards , irold 

[Oldshooter]

Thanks, thats interesting info, and makes sense. I dont know if the difference matters much, but I just cant get the gap thing outta my head.  Sometimes my head makes me crazy. 

[reliquary]

In an old reloading manual (Speer number 9), on page 435 in the table called Handgun Velocities, it shows the chronographed muzzle velocity of a .45ACP cartridge from a 5" Colt ( 1911?) to be 840 fps and the same load from a Ruger 71/2 " to be 889 fps, a difference of 49 fps. 
 
Other tables in the same manual show the effect for a given barrel length of the same handgun on the same cartridge to be a variation of approximately 50 fps per inch of barrel length.  So, if a Ruger 5" barrel revolver was to fire the same cartridge as a Ruger 7 1/2'' barrel, one should expect approximately125 fps variation, ignoring barrel-cylinder gap.
 
The variation between the "demonstrated 49 fps between the 1911 and the Ruger revolver"  and the "expected 125 fps variation between two Rugers" should be explained by the barrel-cylinder gap on the revolvers that doesn't exist on the 1911?
 
In other words, we lose something, but not much, from the barrel-cylinder gap?

[Oldshooter]

The 45 acp lower pressure may not lend itself to much of an increase in velocity in a longer barrel. I have not tested it but I did get a 6 inch bbl for my 21 just to see if it made a difference in accuracy at longer ranges, but I'm told that the longer barrel will not produce any significant increase in velocity. The link below says from a 5 inch to a 16 inch bbl a 230 gr hydro shok will increase from  895 to 994fps a little less than 100 fps for an increase in 11 inches.
 
http://www.ballisticsbytheinch.com/45auto.html

[RevJim]

 I have had both, and I too feel a lot has to do with the cartridge pressure. I do feel the cylinder gap makes a bit of difference, but none I could ever tell in the field. Again, I never had a revolver/auto in the same centerfire round, so I can't say for sure. I always chose a revolver if I wanted (a) accuracy foremost or (b) heavier caliber. I always chose autos for (a) firepower for self defense (b) followed by reliability/accuracy. In .22 , it's all the same, ha.
For pigs, I think the Glock in either 20 or 29, set up right, is "Eye-Dinktum", lol. For sitting over corn from a blind, a revolver can "finesse" him, but for wading into the puckerbrush, with pigs running everywhere/over you, it would be hard to beat a powerful auto with 15rd mag! I always felt well armed with any 1911 and Buffalo Bore +P 230 FNFMJ rounds. I was surprised at how accurate my G29 (with standard G29 length LW bbl & 21# RS) is, and it shoots the DT 230 hardcast faster than my 5" 1911 did the +P 230 FNFMJ...HUAHHH!

[MePlat]

To keep a level playing field my 4 inch Jerry Michelek 45 Auto revolver with cylinder and barrel is 5.625 inches long.  Not comparable to a 5 inch Auto.
To be comparable to a 5 inch auto the JM revolver would have to have a barrel of 3.375 inches.
Then there is the flash gap to take into consideration.

[Basicguy]

  One other factor is that all semiautos are not the same. My testing of a blow back 45 (hi-point) gives less velocity than my 4" barreled 1911. About 50fps less.

Have to agree that barrel length should be measured the same way in revolvers and and semiautos.

[Groo]

Groo here
 One of the big time barrel makers [1911] stated that 90% of the bullet speed was developed in the first 2 to 3 inches of barrel.
 so porting could only reduce that speed by 10%.
 As the porting of a 1911 barrel is much greater than the BC gap of a revolver, the reduction in bullet speed
 must be due to the cylinder length --- less than the 2 to 3in range.
 allowing the pressure to bleed off before the ideal pressure is reached.
 This would explain the large difference between the auto and revolvers speeds when barrels measured they same way are clocked.