[ajacobs]

Today I was doing a couple of dry fire exercises in the woods along with reloading drills while I was walking the dog in the woods. And it got me thinking about a few construction questions I had on my 642. I can never hope to to know as much as the collective knowledge of the board so I thought this was the place to ask for these purely acadademic questions.

1. I only have one revolver at my current location so I can't compare to to my others which are several hundred miles away in my safe but I was wondering why the front site on my 642 is higher than the rear. All of my autopistols have sites of the same height. It of course is not just a little difference either, it is almost twice the heights. it shoots just fine and point of aim is point of impact for me, I am just wondering why there is this difference with the 642 and is it present in allot of other firearms as well? It does not have any thing to do with a difference in height between the top of the frame, ie. I am not refering to the actual sights heights I am saying that the top of the notch of the rear sight is lower to the bore than the top of the blade of the front sight. Why? IF it was the same on my 1911's etc, I would be shooting rather low.

2. The 642 is a 38 spc and the 640 is all steel. Yet the 642 comes with a 1 7/8 in barrel and the 640 a 2 1/8" barrel. I am wondering if there is more logic to this than just a matter of prefference in the designs. I remember reading on the winchester ammo site about differences in guns chambered in 556 and 223 and it talked about using them interchangably and the different barrel/chamber lead (a unrifled portion of the barrel) and it's effect on accuracy. I looked at the 642 and it appears that although there is a little bit of a coning in the cylinder end of the barrel the whole thing is riffled. So probally by faulty logic I put 2 and 2 togegether and though that on the 642 maybe it can afford to have the shorter barrel as the extra room in the cylinder serves as the lead section of the barrel and on the 640, given the longer round and same cylinder size that the barrel of the 640 might have had to have some lead in it. Then I looked at a 1911 and a Khar and saw that they appeared to have no lead so maybe it was just that a little bit of extra barrel was needed to stabalize the 357.

Maybe I think to much. What are your thoughts.

[caz223]

Lead(e) (The distance between the forcing cone and the rifling) is only really necessary in revolvers.
The bullet is given a little time to stabilize before it hits the rifling because the cylinder and the barrel in a revolver don't line up perfectly every time.
The barrel in an auto is one piece with the chamber, and the concentricity is more uniform, making the lead(e) unnecessary.
Good accuracy in rifles is usually obtained by seating 'long' because the bullet contacts the rifling, and 'waits' for a second for pressure to build up.
This makes the load a smidgen more consistant.
Also, the typical rifle and the typical auto puts more emphasis on the shoulder/mouth of the case, headspacing on the case mouth (sometimes the shoulder as well.).
Revolver cartridges are usually rimmed, headspacing on the rim, making crimp more important, and the lead(e) stabilizes the bullet making sure that it seats squarely in the bore before it engages the rifling.

I'm sure that I just confused you more than informed you, so I'll leave it up to my forum friends who are ten times better at explaining stuff like this.

[Jim March]

On point one:

Your 1911 barrel is the same way: pointed a bit downwards in order to get a horizontal shot off. You can't see it because the barrel is in the slide, which is itself horizontal.

All handguns work this way. Rifles too. The gun begins recoiling while the bullet is still in the barrel, so there's a "timing problem" - you want the gun to start out nose-down and then be brought horizontal by the recoil during the flight-time-in-barrel. For the same reason, a very lightweight, fast but low-recoil round will often shoot low, where a big heavy slow slug will shoot high. Of late, people have been selling big heavy-slug loads of 325grains or more in 45LC cases, which has caused a small aftermarket to boom in taller front sights for Ruger Blackhawks and whatnot...the gun needs more "starts-point-downiness" for those loads :).

Point two:

Sounds to me like S&W is doing a very light version of the "Taylor Throat" process. See also:

http://www.angelfire.com/ga/alphaprecision/revolveraccuracy.html

As to why the slightly longer barrel on the 357 snubbies?

Hmmm. Make everybody buy new holsters?

:scrutiny:

[BluesBear]

The 642 has a noticable higher front sight than the 640 because the lighter weight alloy frame of the 642 allows the muzzle to rise just a tiny bit more in recoil before the bullet leaves the barrel. If the sights were the same height the 642 would shoot a little higher than a 640 with the same loads.

As for the difference in point of aim between heavy and light bullets... Yeah to what Jim said.

[bountyhunter]

And if you buy a laser bore sighter you will find your revolvers all sight in to point of aim with the bore aimed a couple of inches low at 15 yards. Autos sight a lot closer to dead on because the moving slide acts as a recoil absorber and the muzzle doesn't rotate upward as fast compared to a revolver for a comparable bullet weight and loading.

[ajacobs]

Thanks for the help on the site issue.

I do now understand the lead as it relates both to revolvers and other firearms, but it does not answer my question in regard to why the longer barrel on the .357. maybee as I suggested in my first post it is just about longer length needed to stabalize the round.

[DJJ]

Why the longer barrel on the .357?

For the longer ejector rod stroke, maybe.

[BluesBear]

I believe, that the S&W J-frame .38 special revolvers (with the expection of the 300 series) still use the 1 7/8" barrel with exposed ejector rods, while the newer .357 magnum J-frame models use the new 2 1/8" barrels with fully shrouded ejector rods.



"Well..... dat's what I tink!" (A.D. Clay 1990)