S&W 66-7 Two Piece barrel question

DRADW · #1 03-10-2011, 10:15 AM

The newer model 66 now incorporates a two piece barrel. Does this in any way lessen the propensity for forcing cone cracking.

handgunner356 · #2 03-10-2011, 10:35 AM

I don't think it would make any differece as the problem comes from the cylinder size and the clearance cut at the bottom of the barrel. That's probably why the went to the L-frame size when they replaced the 65/66 with the 619/620, to get a full size forcing cone all the way around the barrel.

DRADW · #3 03-10-2011, 10:43 AM

Thanks Handgunner, What is the alleged purpose for the two piece barrel, is it cheaper to produce, easier to service or possibly stronger. I know about the MIM parts like the hammer and others, but since the model was being phased out why make such big changes?

colt_saa · #4 03-10-2011, 12:26 PM

Quote:

Originally Posted by DRADW

Thanks Handgunner, What is the alleged purpose for the two piece barrel, is it cheaper to produce, easier to service or possibly stronger. I know about the MIM parts like the hammer and others, but since the model was being phased out why make such big changes?

The purpose of a tensioned barrel is not alleged. It is to improve accuracy. This has been proven time and again over the last four decades.

DRADW · #5 03-10-2011, 12:33 PM

Again thanks for taking the time to reply. Maybe alleged was too strong a word.

dfariswheel · #6 03-10-2011, 09:21 PM

The purpose of the two piece barrel is cost savings.

The old barrels started off as a rough lump of forged metal.
In the older barrels, even the front sight was part of the forging.
The bore was drilled and rifled, and the outside was machined and threaded.
If anything went wrong at any step, the barrel was scrap and all the previous cost of work was lost.

The new barrels have inner tubes that are rifled and threaded.
Modern high speed turning equipment is used that seldom makes a mistake.
The outer shroud can be a cast part that's virtually finished when it comes out of the mold.
If the shroud is less than perfect, it can simply be re-cast.

Fitting the barrel is much faster and easier, since the shroud is just slipped onto the frame and the inner barrel is tightened in place.
The old one-piece forged barrels required extensive hand fitting and adjusting.

So, the new barrels are much faster and cheaper to make, and require little hand work or fitting. Human labor runs the price up, so anything that can be done to limit that costs less.

DRADW · #7 03-10-2011, 09:32 PM

Dfariswheel
That was very informative, my compliments on your knowledge. I happen to really appreciate S&W revolvers. I don't think the older pistols, although excellent considering the manufacturing abilities that were available at the time, I think we have better more precise weapons available now. I've never worn out a quality handgun, and hopefully I'll never need a super capacity semi auto. The explanation of the production methods concerning barrels will stay with me. My 66-7 Is beautiful and utilitarian. What more can you ask for.

scooter123 · #8 03-10-2011, 11:07 PM

Quote:

Originally Posted by dfariswheel

The purpose of the two piece barrel is cost savings.

The old barrels started off as a rough lump of forged metal.
In the older barrels, even the front sight was part of the forging.
The bore was drilled and rifled, and the outside was machined and threaded.
If anything went wrong at any step, the barrel was scrap and all the previous cost of work was lost.

The new barrels have inner tubes that are rifled and threaded.
Modern high speed turning equipment is used that seldom makes a mistake.
The outer shroud can be a cast part that's virtually finished when it comes out of the mold.
If the shroud is less than perfect, it can simply be re-cast.

Fitting the barrel is much faster and easier, since the shroud is just slipped onto the frame and the inner barrel is tightened in place.
The old one-piece forged barrels required extensive hand fitting and adjusting.

So, the new barrels are much faster and cheaper to make, and require little hand work or fitting. Human labor runs the price up, so anything that can be done to limit that costs less.

Having spent nearly 30 years as a Manufacturing and Design Engineer I'll dispute your claims. The fact is that on the surface the 2 piece barrels APPEAR to have a cost advantage. However, when you factor in the quality requirements in terms of fixturing, inspection, record keeping, stock tracking, and inventory control, you'll probably find, as I suspect S&W has, that making 2 precision parts costs more than making one precision part even if the one piece part requires a bit more fitting. I suspect that's the reason why every single steel K & L frame that featured a tensioned barrel has been dropped from the catalog, they cost more to make that initially thought. The only remaining tensioned barrel S&W's are the Scandium models and I believe the 460 and 500 Magnums, all of which cost far more than the 66, 67, or 620's did when they were being made with tensioned barrels.

As for the accuracy benefit of the tensioned barrel, do a bit of reading on the accuracy of the Dan Wesson line of revolvers, almost all of which used a tensioned barrel. In addition, take a look at Guns & Ammo's testing of the M&P R8. They mounted a scope on one and shot a near 1/2 inch group at 50 yards from a bench rest using off the shelf Commercial SD ammo. I've personally managed to group my 620 to 1.75 inch at 35 yards and if I were to mount a scope on it could probably get it under an inch on one of my good days. Simple fact is that tensioned barrels are more accurate.

As for the OP's concern, as previously noted the K frames have that flat machined to clear the gas ring on the cylinder. Because of this, it's best to consider that the weak point in the design and treat it as such. On a positive note, what you have is a really superb 38 that can occasionally be used with the 357 Magnum if you limit yourself to 158 grain loads.

minconrevo · #9 03-11-2011, 12:22 AM

There have been some reliability issues with the two-piece barrels in the newer series 67's. Do a search on it on this forum.

Dpris · #10 03-11-2011, 12:34 AM

Scooter,
I can guarantee you that S&W did not try the two-piece barrels for improved accuracy.
They are, as D said, strictly a cost-saving proposition.
S&W is moving away from those barrels to a degree & has dropped at least three models that used them.

I've seen photos of the flange broken off at the muzzle & of the rear end broken off at the threads.
I would suspect the discontinuance of the Model 67 & 64 with two-piecers was due to failures encountered with the system, more than anything else.

S&W has modified production methods to eliminate as much of the human touch as possible in revolver assembly. The two-piece barrels are a part of that business plan.

Those who point out that tensioned barrels CAN be more accurate CAN be correct, IF the method used is done correctly. The Dan Wessons were famous for their tensioned barrel accuracy, but those used a quite different system.
Denis

scooter123 · #11 03-11-2011, 01:07 AM

I've seen the posts about the cap failing on the tension barrel and I've also seen posts about one piece barrel shearing off at the frame. IMO the cause in both cases is simply bad metalurgy in those particular barrels. Basically, stuff happens and S&W cannot afford to x-ray inspect every single bar of steel they use and we couldn't afford the guns if they did do that.

However, I do find it odd that that nobody seems to remember that cantelever mounted barrels have been snapping off at the frame of revolvers for over 100 years but everyone wants to blame the "new" system for a few isolated failures. Wasn't too long ago that a member posted images of the 686 that he shot the barrel off of. It snapped off right where any Engineer would expect it to, at the stress riser created by the transition from the mounting extension to the full profile.

As for the accuracy benefit of the tensioned barrel, I've seen it first hand. I have 3 revolvers equipped with reflex sights that I shoot an longer ranges with and the 620 is clearly the most accurate. Unfortunately it also has the most recoil so I'm still working on shooting to it's potential.

Srigs · #12 03-11-2011, 02:09 AM

Quote:

Originally Posted by handgunner356

I don't think it would make any differece as the problem comes from the cylinder size and the clearance cut at the bottom of the barrel. That's probably why the went to the L-frame size when they replaced the 65/66 with the 619/620, to get a full size forcing cone all the way around the barrel.

The 66-7 does not have the clearance cut on the bottom. Here is my 66-7.

Dpris · #13 03-11-2011, 10:23 AM

A while back I worked with a two-piece Model 67.
Accuracy was no better or worse than other Smith .38s I've shot over the years.

OK, but nothing remarkable.

And it's not a cap, it's a flange.
A cap implies a different type of separate part.

Denis

dfariswheel · #14 03-11-2011, 09:43 PM

"I've seen the posts about the cap failing on the tension barrel and I've also seen posts about one piece barrel shearing off at the frame. IMO the cause in both cases is simply bad metalurgy in those particular barrels. Basically, stuff happens and S&W cannot afford to x-ray inspect every single bar of steel they use and we couldn't afford the guns if they did do that."

There appears to be more to the two-piece barrel problems than just a bad barrel or bar of steel.
As I recall a number of guns purchased by an East coast prison system suffered a number broken barrels in Model 64's.
There have been a number of other verified reports of barrels breaking off, and flanges failing.

To be fair, these seemed to be from early production guns made when the two-piece barrel was still new.
I'm rather surprised no company or custom gunsmith has brought out a Dan Wesson-like interchangeable barrel system for the new S&W revolvers.

Dpris · #15 03-12-2011, 12:20 AM

D,
Considering the relatively lackluster sales of the On Again/Off Again DWs over the years, there probably would not be much money in the idea.

Denis

Gearhead Jim · #16 03-14-2011, 09:28 PM

Quote:

Originally Posted by Srigs

The 66-7 does not have the clearance cut on the bottom. Here is my 66-7.

How would the 2-piece barrel allow them to eliminate the clearance cut like that, unless the entire forcing cone is thinner instead of just the bottom?

As I understand it, the clearance cut is to allow space for the crane to get into place, going to a 2-piece barrel shouldn't change that.

Confused...

Srigs · #17 03-15-2011, 02:03 AM

Quote:

Originally Posted by Gearhead Jim

How would the 2-piece barrel allow them to eliminate the clearance cut like that, unless the entire forcing cone is thinner instead of just the bottom?

As I understand it, the clearance cut is to allow space for the crane to get into place, going to a 2-piece barrel shouldn't change that.

Confused...

Everything I have found says it was part of the -7 engineering change. The picture posted shows it. My 3rd gen of S&W book from 2006 does not even show a -7 engineering change and the one shown based on serial # is 2004-5 vintage.

DRADW · #18 03-15-2011, 03:16 AM

My 66-7 does Not have the forcing cut relieved at the bottom.
This has been the most informative post I have ever experienced,
The knowledge I have gained and the respect I have for members of this forum is awesome. I'm proud to be a member, thanks guys.

blujax01 · #19 03-15-2011, 04:21 PM

It's all due to the IL and MIM parts. You see, a gun when fired sets up a resonant frequency. With the hole in the frame, that resonance gets corrupted, sending a shock wave back through the barrel. The forged trigger and hammer used to buffer that shockwave but then they put in the MIM parts ...

Dag-nabbid new-fangled gadgets will be the end of us, I tell 'ya ...

Gearhead Jim · #20 03-17-2011, 10:36 AM

Quote:

Originally Posted by Srigs

Everything I have found says it was part of the -7 engineering change. The picture posted shows it. My 3rd gen of S&W book from 2006 does not even show a -7 engineering change and the one shown based on serial # is 2004-5 vintage.

We know it was part of the engineering change, but what was it in the change that allowed them to eliminate the cut?

Quote:

Originally Posted by blujax01

It's all due to the IL and MIM parts. You see, a gun when fired sets up a resonant frequency. With the hole in the frame, that resonance gets corrupted, sending a shock wave back through the barrel. The forged trigger and hammer used to buffer that shockwave but then they put in the MIM parts ...

Dag-nabbid new-fangled gadgets will be the end of us, I tell 'ya ...

Cute. I wish it were true...

MTKTM · #21 03-17-2011, 01:36 PM

All this technical stuff is making my head ache!

I have a 66-7, bought it circa 2005 when I heard that S&W was going to discontinue the model. I'd had a couple of 19s and one 66 in the past and always liked the K platform, so picked one up. I used mine fairly extensively for a few years shooting IDPA in SSR division. I have found it to be a perfectly good, serviceable revolver, no issues or problems whatsoever. I don't shoot a lot of hot loads through it, probably never will, but I'm of the opinion that if I shoot a gun enough to wear it out, I've had a lot of fun and it's time to go get a new one!!!

Gearhead Jim · #22 03-18-2011, 01:04 PM

Still trying to figure out what they changed, to eliminate the relief cut on the bottom of the barrel.

Whatever it was, must not have been fully successful; or they would still be producing the 66-7 and probably some other .357 K-frames.

dentkimterry · #23 04-09-2011, 10:48 PM

I just looked at my newly acquired model 66-7 and it also does not have a flat spot on the bottom of the forcing cone. I bought it from the original owner who purchased it in 2005.

I went to the store already and got a box of 357 mags. Just looked at them and they are 125gr. Is it going to be wise to shoot these or should I leave them on the shelf and get some 158gr.?

scooter123 · #24 04-10-2011, 12:17 AM

There are two things that could have been done to eliminate the flat on the barrel. One is to reduce the entire diameter of the barrel stub that extends inside the frame, the other would be to reduce the gas ring on the cylinder. I suspect that what was done is to reduce the diameter of the barrel stub to that which matches that on the J frame revolvers.

From an Engineering standpoint not having that flat will produce a slightly stronger barrel even when the diameter is reduced. The reason is that any time there is a "change in section" this creates an area where stresses will "accumulate". It called a stress riser and the effect of just a simple flat such as featured on the K frame can cause in increase in localized stresses of 5-40% depending on the depth of that flat. Personally, I think that using your 125 grain load for defense is probably somewhat safe but I certainly wouldn't guarantee that. Bottomline, I'd put that ammo up for the day you get a 686 and purchase some 158 grain loads for your model 66. Quite simply just because it's probably safe, why risk it.

whoisavner · #25 04-10-2011, 01:17 AM

I was shooting 125gr silvertips out of my 66-7 the other day no problem. love the gun, it shoots great, and I like it better than the 586 I used to have.

I normally shoot the 158gr magnums but some hot loads every so often won't hurt it. S&W beefed the gun up in these latter iterations, to take more magnum loads. I hardly ever fire 38s thru mine.

dentkimterry · #26 04-11-2011, 02:27 PM

I went to 3 guns stores today, no one had any 158gr 357's. So I got some 142gr, I thinking these should be OK until I can find some 158gr. I only bought one box of 50.

71vette · #27 04-11-2011, 09:53 PM

Strictly going off of what I've read, anything over 140 grain should be O.K. Also, I've got a 66-7, a 66-5, and a 66 no-dash in addition to my 19's. I'll have to get the calipers out but to my Mk1 eyeball it looks like they made the barrel stub thinner on the -7 than the -5. The -5 still has the one-piece barrel and the flat. The -7 has no flat and a two-piece. I've got a 360 with the two-piece barrel and will check the diameter of the stub against the -7.

ETA: just measured the 360 and the 66-7. The barrel stub is the same diameter.

Does the fact that the stub is J-frame sized affect a 66-7's ability to handle 357 loads?