Comparing a S&W revolver made with MIM parts to a revolver made with machined parts
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Driftwood Johnson
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I had to stop and think about that for a couple of minutes. I have been called a lot of things, but that is a new one. For what it's worth, Driftwood Johnson is my CAS alias. There is a story behind that, for another time.
Sorry about not weighing the two hammers, it just did not occur to me at the time. At this time the revolvers are reassembled and so I do not anticipate getting any more internal photos or parts photos unless somebody really needs it.
I am impressed with MrBorland's study of hammer mass. How in the world did you calculate the centers of gravity? Did you take CMM dimensions of the parts then model them in 3D CAD? Or did you balance them on something to determine the centers of gravity?
By the way, there will be no comparison photos of the two mainsprings, they are identical in appearance. Just didn't think it worth the while of photographing them.
I did weigh the two revolvers a few minutes ago and took readings of the single action trigger pulls. That information will show up in the report at the end.
Driftwood Johnson said:
Well, I'm not that tech savy, so I did it the old fashioned way.
I took a screen shot of your hammers, printed them out, carefully cut their profile out, then used the plumb line method. I should note that this method determines the CoG based on a 2D image. The CoG differences are likely to be bigger than I determined, since the newer hammer has those cutouts. The weight of the older hammer cutout was only 10% heavier, whereas the older hammer was nearly 30% heavier when actually weighed.Below's a tracing of the 2 cutouts. Interestingly, the bottoms are nearly identical. The top of the older hammer is a bit bigger and canted more forward (which is why CoG is shifted). They look the same when installed in the gun, but upon inspection of the frames, it seems the newer ones come back further to accommodate the newer FP design.
Nom de Forum
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Great stuff Driftwood Johnson! I don't think us THR members can thank you enough for this great comparative examination of S&W technology. So, thanks again!
MrBorland,
Did you by any chance notice any slight difference in the total distance traveled between the two hammer types? In addition to differing mainspring strengths, that would influence lock time. If the older machined hammer traveled a shorter distance it could possibly equal the faster MIM hammer in lock time. The reverse would result in a much faster lock time for the MIM hammer. Regardless of whether there is any difference in lock time it is my understanding that given two firing pins providing equal amounts of energy delivered to the primer, the firing pin with the faster speed is superior for primer detonation. That characteristic is a minor aid to accuracy, and improves reliability in adverse conditions.
Edit: Looking at your post #78 it appears the older hammer may travel a shorter distance, but it would have to be measured when installed in the revolver and at full cock.
MrBorland,
Did you by any chance notice any slight difference in the total distance traveled between the two hammer types? In addition to differing mainspring strengths, that would influence lock time. If the older machined hammer traveled a shorter distance it could possibly equal the faster MIM hammer in lock time. The reverse would result in a much faster lock time for the MIM hammer. Regardless of whether there is any difference in lock time it is my understanding that given two firing pins providing equal amounts of energy delivered to the primer, the firing pin with the faster speed is superior for primer detonation. That characteristic is a minor aid to accuracy, and improves reliability in adverse conditions.
Edit: Looking at your post #78 it appears the older hammer may travel a shorter distance, but it would have to be measured when installed in the revolver and at full cock.
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Driftwood Johnson
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And I thought I was compulsive! Great stuff MrBorland, learn something every day. I have used CAD programs which calculated the centroid of mass, never heard of that great low tech method. Were your cutouts paper, cardboard? I assume you had to give them a little bit of mass to overcome friction and make your method work.
Thanks again for the great idea.
Thanks again for the great idea.
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Driftwood Johnson
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Thumbpieces
Following up on the Cylinder Bolt photo with the Thumbpieces (try spelling that correctly over and over) here are the two Thumbpieces. The different shape of the 617 Thumbpiece is necessitated by clearance for the key to the lock. Not sure why the nut (it looks like a screw but it is actually a nut) for the Model 17 is serrated around its circumference. Perhaps so fingers don't drop it during assembly. Every Thumbpiece nut I have ever seen is serrated like that. Perhaps S&W is using vacuum chucks to position small parts now? Dunno. What ever the case, the 617 nut is smooth on the outside.
Dunno what the marks are inside the Thumbpiece nut hole. Most likely the surface was marred when the nut was torqued in place. I suppose they could be disturbances purposely put there to help lock the nut in place, don't really know.
A word or two about the knurling. Traditionally, knurling is done with a separate knurling tool that rolls across the part under pressure, impressing the knurling into the part. The knurling on the MIM part is very well done. Crisp and sharp, the way it should be. To tell the truth, I do not know if the knurling was cast into the part, or pressed in with a secondary operation. The reason I question it is, in order to be cast into the part the knurling would have to be oriented just right so there were no undercuts. If undercuts are present, the mold would have to incorporate a 'side pull' feature, which would make it much more expensive. Unless the knurling was designed just right so that the part could drop out of the mold with no undercuts. Close examination of the edge of the MIM Thumpiece shows that this may indeed be the case, but I am not completely sure.
Here is a view of the undersides of the two Thumbpieces. The swirling marks around the flange of the milled part are tool marks left by the endmill as it walked around the countour to leave the raised boss behind. These tooling marks are on just about every Thumbpiece I have ever seen, even from the 'Golden Age' of S&W. Testimony that if it does not affect the function of the part, and if nobody is going to see it, it really does not matter all that much.
The orientation feature for the Cylinder Bolt that I mentioned earlier is clearly visible here. I believe the MIM part is hollow to prevent sink marks that may have shown up if the part was solid. Or perhaps it has something to do with the knurling. A couple of letters have been molded into the part, probably some sort of identification. Molding in identifiers like this is very common with MIM parts.
Following up on the Cylinder Bolt photo with the Thumbpieces (try spelling that correctly over and over) here are the two Thumbpieces. The different shape of the 617 Thumbpiece is necessitated by clearance for the key to the lock. Not sure why the nut (it looks like a screw but it is actually a nut) for the Model 17 is serrated around its circumference. Perhaps so fingers don't drop it during assembly. Every Thumbpiece nut I have ever seen is serrated like that. Perhaps S&W is using vacuum chucks to position small parts now? Dunno. What ever the case, the 617 nut is smooth on the outside.
Dunno what the marks are inside the Thumbpiece nut hole. Most likely the surface was marred when the nut was torqued in place. I suppose they could be disturbances purposely put there to help lock the nut in place, don't really know.
A word or two about the knurling. Traditionally, knurling is done with a separate knurling tool that rolls across the part under pressure, impressing the knurling into the part. The knurling on the MIM part is very well done. Crisp and sharp, the way it should be. To tell the truth, I do not know if the knurling was cast into the part, or pressed in with a secondary operation. The reason I question it is, in order to be cast into the part the knurling would have to be oriented just right so there were no undercuts. If undercuts are present, the mold would have to incorporate a 'side pull' feature, which would make it much more expensive. Unless the knurling was designed just right so that the part could drop out of the mold with no undercuts. Close examination of the edge of the MIM Thumpiece shows that this may indeed be the case, but I am not completely sure.
Here is a view of the undersides of the two Thumbpieces. The swirling marks around the flange of the milled part are tool marks left by the endmill as it walked around the countour to leave the raised boss behind. These tooling marks are on just about every Thumbpiece I have ever seen, even from the 'Golden Age' of S&W. Testimony that if it does not affect the function of the part, and if nobody is going to see it, it really does not matter all that much.
The orientation feature for the Cylinder Bolt that I mentioned earlier is clearly visible here. I believe the MIM part is hollow to prevent sink marks that may have shown up if the part was solid. Or perhaps it has something to do with the knurling. A couple of letters have been molded into the part, probably some sort of identification. Molding in identifiers like this is very common with MIM parts.
Nom de Forum said:
I didn't measure them, but I can when I get home from work.
My guess is that there's no significant difference in distance travelled. If you look at the appearance of the hammer spur on Driftwood's pics of intact guns, they appear to be similarly positioned. That means their end-point of travel (I'm ignoring rebound distance) is pretty similar. And since the bottom end of the hammers (which include the sears) are similar, the start-point of travel is pretty similar as well, hence overall distance travelled is pretty similar.
Nom de Forum said:
True. The spring supplies energy. The hammer just transfers that energy. Energy doesn't light off primers. If if did, just slowly lowering the hammer with the trigger back would set off a primer. Power is what sets off primers (because power's good at denting things) and power is the product of energy and speed. As I mentioned earlier, a more powerful hammer strike allows you to reduce spring tension more before getting into reliability issues. I have a 686 I use for match shooting, and I used to have a radically bobbed hammer on it (it's now just bobbed thanks to a new IDPA rule), and even with a light action, it'd set off everything I fed it.
As I also mentioned, the lighter hammer has less momentum, which is a good thing. Momentum doesn't light off primers, but it jars the muzzle upon hammer strike. Check out my coin-on-the-barrel vid for a demo. Shorter lock time might help accuracy, but you also get an accuracy gain when the muzzle's not jarred as much.
As far as reliability in adverse conditions, this is where the "light hammer is better" model needs a caveat: I wrote that a light hammer has less momentum, which is what jars the muzzle. But momentum also what resists internal resistance. At some point, then, a lighter hammer can be more susceptible to an otherwise out-of-spec lockwork, a lack of lubrication or just simply gunk in there.
Apologies to Driftwood for usurping his excellent thread.
Driftwood Johnson said:
LOL. Yep, revolver shooters are a different type.
Driftwood Johnson said:
Paper, but you're right, cardboard would've been better. I used a paperclip, and was sure they were hanging pretty freely, though.
Best would be to use the plumb line method on the actual hammer. One could rig some kind of plumb line setup, then use a digital camera to take pics of each line. Drop them into powerpoint and superimpose the images, and the intersection of the 2 plumb lines would give you the actual CoG. I'll have to play with that.
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Driftwood Johnson
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I would like to revisit the hammers for a moment because I want to mention the knurling on the hammers. I did not take photos of the knurling while the guns were apart, but hopefully these two photos will suffice.
First, the knurling on the hammer of the Model 17. Notice how crisp, deep, and sharp the knurling is. One's thumb will never slip off this hammer spur when cocking the hammer, actually deeper and sharper than the knurling on the old 'long action' hammers. I assume this was done the traditional way, pressed in with a knurling tool before hardening. Or perhaps even cut in with a pair of cutters running on two different axes, the way checkering is done on wooden stocks.
Now the knurling on the 617 hammer. Do not be confused by the photo, it is ever so slightly out of focus. The knurling on this hammer is almost as good as the knurling on the Model 17 hammer, although slightly coarser with less lines per inch. My educated thumb tells me the knurling on the older hammer is slightly sharper, it scrapes the dickens out of my thumb if I drag my thumb across it a few times. Really close examination of the knurling seems to reveal a lack of tooling lines. So I am assuming this knurling was cast into the part. However notice the parting line on the back of the hammer. That shows that the mold parted evenly along the center line of the hammer. This means there surely would have been undercuts created in the knurling. So if the knurling was cast into the part, a more complicated mold with side pulls would have been needed, increasing cost. All just speculation on my part.
Let's look at the knurling on a Colt and Uberti hammer for comparison. The 2nd Gen Colt in the rear has traditional knurling applied with a knurling tool. the really cheesy, smooshed, cast in knurling on the Uberti Cattleman hammer in front pales by comparison. Now look again at the really good knurling on the S&W MIM hammer. Enough said.
First, the knurling on the hammer of the Model 17. Notice how crisp, deep, and sharp the knurling is. One's thumb will never slip off this hammer spur when cocking the hammer, actually deeper and sharper than the knurling on the old 'long action' hammers. I assume this was done the traditional way, pressed in with a knurling tool before hardening. Or perhaps even cut in with a pair of cutters running on two different axes, the way checkering is done on wooden stocks.
Now the knurling on the 617 hammer. Do not be confused by the photo, it is ever so slightly out of focus. The knurling on this hammer is almost as good as the knurling on the Model 17 hammer, although slightly coarser with less lines per inch. My educated thumb tells me the knurling on the older hammer is slightly sharper, it scrapes the dickens out of my thumb if I drag my thumb across it a few times. Really close examination of the knurling seems to reveal a lack of tooling lines. So I am assuming this knurling was cast into the part. However notice the parting line on the back of the hammer. That shows that the mold parted evenly along the center line of the hammer. This means there surely would have been undercuts created in the knurling. So if the knurling was cast into the part, a more complicated mold with side pulls would have been needed, increasing cost. All just speculation on my part.
Let's look at the knurling on a Colt and Uberti hammer for comparison. The 2nd Gen Colt in the rear has traditional knurling applied with a knurling tool. the really cheesy, smooshed, cast in knurling on the Uberti Cattleman hammer in front pales by comparison. Now look again at the really good knurling on the S&W MIM hammer. Enough said.
Noz
Member
Wonderful reading. Keep it coming, please
OK, I did a little measuring, and listed the results below. I measured horizontally from the back of the cylinder to the tip of the hammer spur. For the Single action measurements, I measured at full cock. For double action, I did my best to measure at the point where the DA sear broke (obviously, these measurements aren't going to be quite as accurate). My reference was the measurement with the hammer fully lowered (i.e. not rebounded). Turns out the older hammer does travel a bit further. About 15% further in single action and 27% further in double action (see below)
Earlier, I calculated the new hammer travels 17.5% faster, so we know relative velocity. We now know approximate relative distance, so we can calculate that the relative (lock) time of the older gun is about 34% slower than the newer one in single action, and about 50% slower in double action. Wow. Who'da thunk?
My K-22 is a terrific revolver. It's "shooter grade", but the fit and finish are everything the old S&Ws are known for. It ought to outshoot my newer 4" 617, especially with it's 6" barrel, but the 617 is easily its equal (maybe better) in terms of accuracy. Go figure. Maybe there is something to the lock time thing.
Single action hammer travel, old vs new = 0.85" vs 0.74", respectively.
Double action hammer travel, old vs new = 0.74" vs 0.58", respectively.
Nom de Forum
Member
Hi, Driftwood,
I am not sure how it is all done, but I have no doubt the knurling on those parts was molded in; there would be little savings if they had to machine an MIM part. I am looking forward to the discussion of the trigger; that is where the design for MIM really shines, in comparison with the Model 17 trigger but even more in comparison with the older trigger with its coil spring and machined lever. As for the thumbpiece hole, again they took advantage of MIM to effectively mold a lockwasher into the part. Neat.
I think you are underestimating the capability of MIM; it can be used to produce very complex parts. As I say, I don't know exactly how it is done, but here is a blurb from an MIM specialist company.
"Parts may include cross holes, angle holes, internal threads, irregular shapes, splines, undercuts, side holes or grooves, complex contours, or cantilevers."
That seems to pretty well cover the range.
Jim
I am not sure how it is all done, but I have no doubt the knurling on those parts was molded in; there would be little savings if they had to machine an MIM part. I am looking forward to the discussion of the trigger; that is where the design for MIM really shines, in comparison with the Model 17 trigger but even more in comparison with the older trigger with its coil spring and machined lever. As for the thumbpiece hole, again they took advantage of MIM to effectively mold a lockwasher into the part. Neat.
I think you are underestimating the capability of MIM; it can be used to produce very complex parts. As I say, I don't know exactly how it is done, but here is a blurb from an MIM specialist company.
"Parts may include cross holes, angle holes, internal threads, irregular shapes, splines, undercuts, side holes or grooves, complex contours, or cantilevers."
That seems to pretty well cover the range.
Jim
rcmodel
Member in memoriam
Can't be half as bad as the interweb leads one to think.
http://www.dtic.mil/dtic/tr/fulltext/u2/a521729.pdf
rc
http://www.dtic.mil/dtic/tr/fulltext/u2/a521729.pdf
rc
I really have no objection to mim parts. Seems to me the technology might have had some teething problems years back, but now it's mature and produces consistently good quality. My son is an engineer and in discussions with him, his opinion is that mim is getting better than machining used to be.
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Driftwood Johnson
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MrBorland:
I have never done any comparison accuracy tests between my Model 617 and my Model 17, or one of my K-22s from the 1930s for that matter. But I wonder if your accuracy results might have something to do with the heavy, full underlug of the Model 617. Does your 4" 617 have the full underlug? With rifles, the stiffer the barrel, the more accurate it is. That's why match rifles can have such heavy barrels. Cuts down on sympathetic vibration as the bullet travels the length of the barrel. Does your K-22 have a tapered barrel or a heavy, non tapered barrel?
I have never done any comparison accuracy tests between my Model 617 and my Model 17, or one of my K-22s from the 1930s for that matter. But I wonder if your accuracy results might have something to do with the heavy, full underlug of the Model 617. Does your 4" 617 have the full underlug? With rifles, the stiffer the barrel, the more accurate it is. That's why match rifles can have such heavy barrels. Cuts down on sympathetic vibration as the bullet travels the length of the barrel. Does your K-22 have a tapered barrel or a heavy, non tapered barrel?
I'd completely agree that accuracy is the aggregate of numerous things. "All else equal" never is, so my 617's accuracy could certainly be attributed to it's full underlug, and/or anything else. Could be just a matter of my particular 617 vs my particular taper-barreled K-22.
For this reason, I don't want to get too dogmatic about my 617's accuracy. But the physics at least tells me a 617's hammers ought* to be lighter & faster, which isn't a bad attribute to have.
* Equations and paper cutouts are nice, but we really don't know until it's directly measured.
For this reason, I don't want to get too dogmatic about my 617's accuracy. But the physics at least tells me a 617's hammers ought* to be lighter & faster, which isn't a bad attribute to have.
* Equations and paper cutouts are nice, but we really don't know until it's directly measured.
the heavier barrel will reduce "muzzle rise". and the smaller the rise, the less variance in that rise, which should increase accuracy. probably why the bull barrel ruger 22s do so well in bullseye competition. my opinion, of course
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Pudge
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What a remarkable thread. Thank you, those of you who have contributed, for providing information I just wouldn't otherwise be exposed to.
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Driftwood Johnson
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Side action molds are possible with MIM technology. Side action or side pull is what it is called when a feature that would lock the part in the mold is molded. Very common with plastic injection molding. This little animation explains it pretty well. In the case of the hammer, the parting line is down the center of the part. If the knurling was done using a side action mold, that portion would pull out perpendicular to the knurling.
http://www.protolabs.com/resourceimages/united-states/smaller_picture_296_wide.gif
A side pull mold increases the cost of the mold, so it would increase the cost of the part too. But probably not as much as pressing the knurling in as a secondary process with a knurling tool.
http://www.protolabs.com/resourceimages/united-states/smaller_picture_296_wide.gif
A side pull mold increases the cost of the mold, so it would increase the cost of the part too. But probably not as much as pressing the knurling in as a secondary process with a knurling tool.
Madcap_Magician
Member
Thanks for the thread! Great work.
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Driftwood Johnson
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Rebound Slides
In the next three photos, the MIM Rebound Slide is on the left and the conventional part is on the right. The pin protruding from the side of the rebound slide is what actuates the Hammer Block. Notice that in the conventional part, the pin is a separate part, pressed into a hole in the main body of the part. Since no extra material is needed to hold the 'pin' in place on the MIM part, it is the uppermost portion of the part. The marks for the ejector pins can be seen on the backside of the MIM part. That is the side that rides on the frame. Placing the ejector marks there may also cut down on friction against the frame.
I may have been a little bit overconfident when I took apart the 617, not paying as much attention as I should have. At one point I looked down on the bench and there was an extra pin there and I did not know where it had come from. After a bit of quick detective work (on the S&W Forum) I realized that the pin was the trigger stop. Just like on some N frame guns. The pin sits inside the Rebound Slide spring. It limits the motion of the trigger by limiting the motion of the Rebound Slide. The pin bottoms against the inside of the hole in the Rebound Slide. When the rear of the pin contacts the Rebound Slide Stud, it prevents the stud from moving back any further, which in turn prevents the trigger from moving back any further.
In this view the hammer is cocked. The Trigger Lever (the plunger that shoves the Rebound Slide back) has almost pushed the Rebound Slide back until the pin inside the spring has contacted the Rebound Slide Stud. There is just enough motion left so that the trigger can rock back a tad further to release the hammer. Any over travel of the trigger will be prevented by the pin contacting the stud. The last coil of the Rebound Slide Spring is visible pressed against the Rebound Slide Stud.
Here is the other type of Trigger Stop in the Model 17. The stop is a small piece of steel that is held in place by the end of the small screw in the photo. There is no hole in the Trigger Stop, the screw simply clamps it in place. And since the Trigger Stop tends to rotate slightly as the screw is torqued down, it is a little bit fussy to position just right. Simply done by eye. I suppose in the factory there would have been a gauge to determine the proper position.
There are Trigger Stops like this in the Model 17 as well as a Model 14-3 and 19-3 of mine. There is also one in a K-38 from 1940s. As somebody said before, typical of S&W target revolvers. My K22 and M&P Target Models from the 1930s do not have this type of Trigger Block in them. Guess I will have to take them apart to see what the story is.
Once all the dimensions are known and properly toleranced, making the pin type of trigger stop within the Rebound Slide work in mass production is no problem. And quicker and easier to install. You just have to remember to pop it into the Rebound Slide and Spring, with the flat end to the rear, before putting the Rebound Slide in. Anybody who has ever wrestled with a Rebound Slide knows that this can be a bit of a pain.
In the next three photos, the MIM Rebound Slide is on the left and the conventional part is on the right. The pin protruding from the side of the rebound slide is what actuates the Hammer Block. Notice that in the conventional part, the pin is a separate part, pressed into a hole in the main body of the part. Since no extra material is needed to hold the 'pin' in place on the MIM part, it is the uppermost portion of the part. The marks for the ejector pins can be seen on the backside of the MIM part. That is the side that rides on the frame. Placing the ejector marks there may also cut down on friction against the frame.
I may have been a little bit overconfident when I took apart the 617, not paying as much attention as I should have. At one point I looked down on the bench and there was an extra pin there and I did not know where it had come from. After a bit of quick detective work (on the S&W Forum) I realized that the pin was the trigger stop. Just like on some N frame guns. The pin sits inside the Rebound Slide spring. It limits the motion of the trigger by limiting the motion of the Rebound Slide. The pin bottoms against the inside of the hole in the Rebound Slide. When the rear of the pin contacts the Rebound Slide Stud, it prevents the stud from moving back any further, which in turn prevents the trigger from moving back any further.
In this view the hammer is cocked. The Trigger Lever (the plunger that shoves the Rebound Slide back) has almost pushed the Rebound Slide back until the pin inside the spring has contacted the Rebound Slide Stud. There is just enough motion left so that the trigger can rock back a tad further to release the hammer. Any over travel of the trigger will be prevented by the pin contacting the stud. The last coil of the Rebound Slide Spring is visible pressed against the Rebound Slide Stud.
Here is the other type of Trigger Stop in the Model 17. The stop is a small piece of steel that is held in place by the end of the small screw in the photo. There is no hole in the Trigger Stop, the screw simply clamps it in place. And since the Trigger Stop tends to rotate slightly as the screw is torqued down, it is a little bit fussy to position just right. Simply done by eye. I suppose in the factory there would have been a gauge to determine the proper position.
There are Trigger Stops like this in the Model 17 as well as a Model 14-3 and 19-3 of mine. There is also one in a K-38 from 1940s. As somebody said before, typical of S&W target revolvers. My K22 and M&P Target Models from the 1930s do not have this type of Trigger Block in them. Guess I will have to take them apart to see what the story is.
Once all the dimensions are known and properly toleranced, making the pin type of trigger stop within the Rebound Slide work in mass production is no problem. And quicker and easier to install. You just have to remember to pop it into the Rebound Slide and Spring, with the flat end to the rear, before putting the Rebound Slide in. Anybody who has ever wrestled with a Rebound Slide knows that this can be a bit of a pain.
Nom de Forum
Member
Improved lock time is only a small part of the numerous things that contribute to mechanical accuracy. I don’t see how the more rigid barrel on the 617 could not aid mechanical accuracy. Vibration reduction through rigidity is a key factor in mechanical accuracy. You also have the shorter bullet time in barrel with the 4”. Of course the longer sight radius of the 6” barrel should technically aid human accuracy potential but that is affected by an individual’s shooting characteristics. Some people just shoot 4” barreled guns better.
I telephoned S&W Customer Service twice. Initially I got nowhere because the customer service persons did not understand the unusual technical question about differences in hammer design affecting lock time. Then my call was transfered to a gentleman who is an old hand at S&W. He is not an engineer but a former fitter and revolver competitor who began his career decades before the conversion to MIM. He agreed that a 617 hammer moving faster results in a faster lock time. So this is a performance characteristic that a comparison of physical differences in material and design identified. I wonder what other performance characteristics Driftwood Johnson’s comparison will identify? By the way, the gentleman I spoke to opined that the MIM guns may be more uniformly accurate. Anyone have any experience or ideas about this?
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