Simple Ballistics Question: Point of Impact with a Longer Barrel

[neven]

The following question has been bugging me for several days.

1) If you replace a barrel on a revolver with a longer one (e.g., Dan Wesson)
the revolver will shoot lower.

2) If you put a longer barrel into a plasticy semi-auto (e.g., Glock), it will shoot higher.

Why the different behavior between a revolver and a plastic framed bottom feeder
when the barrel is extended?
(Only the barrel length is increased. All other variables remain unchanged.)

Any thoughts would be appreciated.

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[3MTA3]

The following question has been bugging me for several days.

1) If you replace a barrel on a revolver with a longer one (e.g., Dan Wesson)
the revolver will shoot lower.

2) If you put a longer barrel into a plasticy semi-auto (e.g., Glock), it will shoot higher.

Why the different behavior between a revolver and a plastic framed bottom feeder
when the barrel is extended?
(Only the barrel length is increased. All other variables remain unchanged.)

Any thoughts would be appreciated.

WAG's but:

Revolver: Adding mass to the barrel of a revolver will reduce barrel jump so it shoots lower. The biggest drawback to a revolver design is the leverage created by the height of the barrel relative to the shooter's hand.

Pistol: Note that as you move the slide to the rear the barrel angle increases. If the bullet doesn't clear the barrel while it is still parallel the sights it would shoot higher. Perhaps a longer barrel causes this to happens it takes slightly longer for the bullet to clear the barrel.

 

[P7M13]

WAG's but:

Revolver: Adding mass to the barrel of a revolver will reduce barrel jump so it shoots lower. The biggest drawback to a revolver design is the leverage created by the height of the barrel relative to the shooter's hand.

Pistol: Note that as you move the slide to the rear the barrel angle increases. If the bullet doesn't clear the barrel while it is still parallel the sights it would shoot higher. Perhaps a longer barrel causes this to happens it takes slightly longer for the bullet to clear the barrel.

I like your WAGs.
While both answers make sense, I would ask the OP, "what basis do you have to frame the question?" Is there statistical data from controlled experiments, or is it anectdotal from one person's experience?

 

[EPS]

WAG's but:

Revolver: Adding mass to the barrel of a revolver will reduce barrel jump so it shoots lower. The biggest drawback to a revolver design is the leverage created by the height of the barrel relative to the shooter's hand.

Pistol: Note that as you move the slide to the rear the barrel angle increases. If the bullet doesn't clear the barrel while it is still parallel the sights it would shoot higher. Perhaps a longer barrel causes this to happens it takes slightly longer for the bullet to clear the barrel.

I will agree with this heavy gun less recoil and barrel rise and the auto the barrel change 's Point's up when the slide is back .my old P89 when the slide is back the barrel is pointing at a very odd angle lol it's amazing that that gun is pretty accurate

 

[neven]

Thank you all for your comments.
3MT's answers/guesses make sense.
The pistol was really the one that I had no explanation for.
The only plausible answer seems to be that the barrel starts moving upward relative to the frame before the bullet is out.

To answer P7's question, it is just something that I observed when playing with both revolvers and pistols. I often change barrels on my Glock and the loger barrel always shoots higher. (I hope that this is something that other people can confirm.)
I also have a Dan Wesson revolver that is extremely accurate (easy 2 inch groups at 25 yards off hand).
Recently I changed the barrel from 6 to 8 inches and the groups moved down a good 4 inches at 25 yards. I was surprised at first since it takes more time for the bullet to exit the longer barrel so I thought that it would rise more.
Then I worked out the physics. For those that are interested, the angle of upward movement of the barrel is approx. proportional to the sqrt( barrel_length) because of the bullet propagation time but it is also inversely proportional to the moment of inertia ( related to the mass and shape).
Further, the moment of inertia is approximately proportional to the barrel_length squared.
This means that the moment of inertia wins and the loger the barrel, the less the muzzle should rise.
Now the Glock went against my theory and that was no good.
3MT's answer will allow me to sleep again at night.

 

[EPS]

I forgot I have this you could try one like this is a STORM LAKE PORTED BARREL I use it some time's but usually have my lone wolf barrel in my gun the longer barrel could be a problem when carrying

 

[neven]

Thank you for the idea and the pictures EPS.
It looks like such a ported barrel will push the muzzle downwards just after the bullet passes the slot (port).
I think such barrels must be longer than the slide to be effective. Otherwise, they will start spitting gases/unburnt powder inside the slide cancelling the downward push and making the inside of the slide dirty in the process.
(No ports for me. The easier it is to clean, the better ).

 

[etrain16]

Reading through this thread and seeing some slow motion videos of bullets leaving guns, I don't think barrel length or porting would have much, if any, impact on where the bullet will impact the target - at least on the first shot. In the videos I've found - pistols and rifles, it appears the bullet always clears the barrel before any recoil forces start to act on the gun/shooter.

Where extra weight/length or porting would make a difference is how quickly you can get back on target for a follow-up shot - and that 2nd shot, I would also guess, is not likely to hit the exact same point, unless you're really good.

Here is a video, actually put together by the Oregonian of all people, showing several different angles and speeds of bullets leaving a Sig SP2022. In each case, you can see clearly, that the bullet is gone from the gun before the recoil forces start acting on the gun:

 

[Certaindeaf]

The longer barreled revolver yields higher velocity, ie the bullet has left the gun sooner than the slower shorter one, allowing less pivotal recoil moment to affect that high axis design.
So the faster bullet prints lower out of a revolver.

 

[Greenbug]

The longer barreled revolver yields higher velocity, ie the bullet has left the gun sooner than the slower shorter one, allowing less pivotal recoil moment to affect that high axis design.
So the faster bullet prints lower out of a revolver.

Beat me to it!

 

[Certaindeaf]

.
Recently I changed the barrel from 6 to 8 inches and the groups moved down a good 4 inches at 25 yards. I was surprised at first since it takes more time for the bullet to exit the longer barrel so I thought that it would rise more..

Bullets start slowing immediately after leaving a barrel. Longer barrels very often yield higher velocities than shorter ones.
Obviously the faster bullet is in the barrel for a shorter amount of time.

 

[3MTA3]

Bullets start slowing immediately after leaving a barrel. Longer barrels very often yield higher velocities than shorter ones.
Obviously the faster bullet is in the barrel for a shorter amount of time.

In this case it's actually in the barrel longer - the bullet would exit the shorter barrel when the bullet in the longer barrel has just passed the same distance. The reason the bullet in the longer barrel is faster is because there is more time to allow for more gunpowder to burn increasing both pressure and velocity.

 

[Certaindeaf]

In this case it's actually in the barrel longer - the bullet would exit the shorter barrel when the bullet in the longer barrel has just passed the same distance. The reason the bullet in the longer barrel is faster is because there is more time to allow for more gunpowder to burn increasing both pressure and velocity.

I understand there's some calculus involved.

 

[dangerranger60]

This is just a guess, but here goes!
I don't think the barrel length has much at all to do with it. its only the barrel itself that has changed. Differences in fit may be where the change comes in. If you ever wanted to prove this, you would have to start with an extended barrel and cut it shorter in even increments to see a trend. swapping barrels give too many variables. DR

 

[etrain16]

I understand there's some calculus involved.

I thought it was triggernometry

 

[EPS]

I thought it was triggernometry

DON'T matter trggernomtry or Calculus I'm not doing eather one lol I didn't buy that longer barrel for any of these reasons I bought it because I was drinking shopping on the internet and thought it would look cool LOL DON'T DRINK AND SHOP ON THE INTERNET

 

[EPS]

I been doing some experiments with my glock I took the stock sights off after my first trip to the range with I put on trjjicon night sites they are good but last week I put on these XS SIGHTS

 

[EPS]

They have a big Front sight and the rear site only has the one line in the middle of the notch I like they part as long as you have you sights lined up like a i your good no three dot line up stuff but the front sight is so big I shoot low every time so I mixed and match put the trjjicon small front site back on and left the XS REAR SITE ON lol find out on Wednesday when I go back to the range

 

[dmack]

Not sure you can say for sure that the barrel length on the revolver is the only factor. A slightly different front sight height between barrels will also affect POI.

 

[EPS]

Not sure you can say for sure that the barrel length on the revolver is the only factor. A slightly different front sight height between barrels will also affect POI.

I didn't shoot mine with the long barrel in last week just the new sights and I'm almost 100% sure that large front sight was what was causing me to shoot low I guess with more time I could have got used to it but I'm going to try the mix match thing on Wednesday see what happens