M&P M2.0 Accuracy Issues, do to dwell time?

[Walt Sherrill]

The fellow with whom I spoke in one of the armorer recerts mentioned that in the original M&P's the slide & barrel started to unlock when the bullet was typically only up to several inches out of the muzzle, but in the 2.0 the bullet is significantly further. He offered some numbers, but I don't think I wrote them down, as that sort of trivia is unnecessary from an armorer's perspective, albeit sometimes interesting trivia for owners and enthusiasts.

That explanation (his, not yours) sounds like the work of a BS-artist hard at work! -- as whether barrel unlocks when the bullet is just a few inches out of the barrel, or when it's traveled farther, if the bullet is gone BEFORE the barrel unlocks, barrel movement (unlocking) should have no effect on accuracy. The bullet is gone at that point.

If the 1.0 barrel was starting to unlock just as the bullet was leaving the barrel, even THAT ought not affect accuracy IF it acted in the same manner with each shot! Consistent behavior (with the gun locking up with each shot, or -- if it's unlocking early -- consistently doing so) is what leads to better accuracy.

As others have noted, something other than an increased lock time must be responsible for better performance.

 

[Fastbolt]

That explanation (his, not yours) sounds like the work of a BS-artist hard at work! -- ...

Or, it might be that the over-simplified explanation he was given leaves out some salient info that would have some relevance to the discussion.

I remember when a former Glock employee (sales rep) was quite certain that Tenifer was a "coating". When he was explaining something about a similar process (working for another gun company), i asked for some specific details. He said he'd have to call engineering to ask, and would get back to me. He did, and clarified that he'd apparently not had all of the correct information (from when he'd been working for Glock), and was able to now provide some more detailed info he'd just gotten from engineering. It was obviously different than what he'd first said, and apparently what he'd been telling and teaching when working for Glock. He was a little chagrined, and somewhat annoyed with what he'd first been given to tell people.

Sometimes people are told things that could be more precise or better explained to them, and sometimes they may not understand all of what they're told (even if they think they do).

After so many years of talking with folks at some of the different gun companies as an armorer (reps, LE/CS contacts, repair technicians, armorer/training instructors and even an occasional engineer), I've adopted the cautious practice of listening to what any one of them says, but to wait and hear how the info may be repeated, or different, when heard from others within the same company.

Naturally, the higher in the food chain, corporate structure or technical (engineering) area the person may be, the more willing I may be to give weight to what they say. However, I've been told by a senior engineer that something a less experienced engineer told me wasn't quite precisely the case. Apparently (obviously) not all engineers may be privy to all the info on everything having to do with the products.

 

[Randy Lee]

Since I designed the barrel, I figure I should chime in.
So that we are on the same page, I use the classic definition of dwell time to mean: "time spent in the same position, orientation, area or stage of a process."
This means that the barrel should maintain the same lock up position relative to the slide and frame (and therefore mechanical barrel pre-tension forces) until the bullet is clear of the barrel.


I hear people refer to early unlocking all the time, but rarely do any two people define the term in the same way. As in the video, the narrator demonstrates unlocking in a fairly gross and rudimentary fashion by pulling the slide to the rear a considerable distance. To be clear, that much movement ONLY occurs after the bullet has left the barrel and chamber pressures have dropped to a safe level. The physics of the event would not allow the barrel to tilt while the bullet is pulling the barrel forward and the brass is trying to push the breech face to the rear.

What IS happening is that the barrel is becoming destabilized while the bullet is in the barrel. To bring a more common frame of reference, by destabilized I mean that the forces acting on the barrel are not the same from shot to shot. In the case of the 1.0 and to a much lesser degree in the M2.0, the slide stretches at the weakest point- near the rear of the ejection port each and every time you fire the pistol. The brass is pushing the breech face to the rear while the bullet is pulling the barrel forward as I mentioned above.

Pretty common physics equation: force forward=force rearward. This does not contribute to the destabilization because the forces cancel eachother out. What does contribute to the destabilization is the slide stretching phenomenon (which realistically is less that a couple of thousandths of an inch, if that).

As the brass pushes the breech face rearward and the slide begins to stretch, the force that the recoil spring is exerting on the slide/barrel interface (the barrel hood extension against the breech face) becomes variable and is dependent on the pressure curve of each individual cartridge. Since the barrel's only vertical support is the angled surface that contacts the round surface of the takedown lever, the change in force due to the slide stretch allows the barrel move randomly. You can test this by pulling the slide a few thousandths of an inch ( you don't need to retract the slide any more than the thickness of a business card) to the rear and seeing how much you can wiggle the muzzle end of the barrel as well as the chamber area visible at the ejection port. To test this fairly, do not apply downward force on the slide as you pull it to the rear. This reduces the vertical slide to frame clearances, and negates the validity of the test.

In many 1.0 and 2.0s, there will be detectable movement. The M2.0 slide has thicker sidewalls,which reduces the degree of slide stretch. That coupled with the other improvements greatly improves not only their accuracy, but their shootability.



There are other contributing factors, but this is what we have found to be the biggest cause of variable accuracy.

Or, I could be totally wrong.

 

[Smakmauz]

Since I designed the barrel, I figure I should chime in.
So that we are on the same page, I use the classic definition of dwell time to mean: "time spent in the same position, orientation, area or stage of a process."
This means that the barrel should maintain the same lock up position relative to the slide and frame (and therefore mechanical barrel pre-tension forces) until the bullet is clear of the barrel.

Thanks Randy, for the clarification! That helps a lot to understand why these are so great.

Now when are those 2.0 trigger kits coming?!

 

[Walt Sherrill]

What IS happening is that the barrel is becoming destabilized while the bullet is in the barrel. To bring a more common frame of reference, by destabilized I mean that the forces acting on the barrel are not the same from shot to shot. In the case of the 1.0 and to a much lesser degree in the M2.0, the slide stretches at the weakest point- near the rear of the ejection port each and every time you fire the pistol. The brass is pushing the breech face to the rear while the bullet is pulling the barrel forward as I mentioned above.

Pretty common physics equation: force forward=force rearward. This does not contribute to the destabilization because the forces cancel eachother out. What does contribute to the destabilization is the slide stretching phenomenon (which realistically is less tha[n] a couple of thousandths of an inch, if that).

That addresses an issue that nobody has mentioned before -- that the slide itself is an integral part of the problem (due to the fact that metal will stretch and return to it's pre-stretch state if it's NOT stretched TOO far!)

Do ALL semi-auto slides demonstrate this same sort of accuracy-affecting behavior or is this a characteristic of the basic M&P 1.0 lockup design? It appears that the 2.0 version may incorporate design changes that make it less of an issue. (All that said, I've got an M&P Pro in 9mm and I've found the accuracy impressive, so I'm not criticizing M&P accuracy.)

You address PART of the question of "why" accuracy can be affected in your following comments.

As the brass pushes the breech face rearward and the slide begins to stretch, the force that the recoil spring is exerting on the slide/barrel interface (the barrel hood extension against the breech face) becomes variable and is dependent on the pressure curve of each individual cartridge. Since the barrel's only vertical support is the angled surface that contacts the round surface of the takedown lever, the change in force due to the slide stretch allows the barrel move randomly. You can test this by pulling the slide a few thousandths of an inch (you don't need to retract the slide any more than the thickness of a business card) to the rear and seeing how much you can wiggle the muzzle end of the barrel as well as the chamber area visible at the ejection port. To test this fairly, do not apply downward force on the slide as you pull it to the rear. This reduces the vertical slide to frame clearances, and negates the validity of the test.

That you can "test this by pulling the slide a few thousands of an inch" and wiggle the muzzle doesn't seem entirely convincing -- since the forces being applied to the barrel, slide, and recoil spring when the bullet is moving down the barrel under intense pressure would seem to make that whole assembly more rigid and less easily moved in a random manner than in your "test" example. I understand, however, that the "test" shows that the potential for movement exists. That a bullet spinning down the barrel may apply forces most of us have have never considered, and such subtle changes in the bullet loads can also affect accuracy, is also interesting.

To this non-gunsmith layman, all of this might suggest different ways to offset these "random" barrel behaviors, including barrel bushings, a different lockup design or, as you mention in passing, tighter vertical slide/frame clearances.

I appreciate, however, that when you do all of that, you've begun to build a different gun with what may be different design objectives -- maybe trying to create a target pistol and not a service pistol -- designed for a different role, different reliability objectives, and much different production costs.

Some very subtle, almost invisible M&P 2.0 changes are probably a far more realistic approach.

Thanks for your informative response -- now I've got more to think about!

 

[Christopher67]

Since I designed the barrel, I figure I should chime in.
So that we are on the same page, I use the classic definition of dwell time to mean: "time spent in the same position, orientation, area or stage of a process."
This means that the barrel should maintain the same lock up position relative to the slide and frame (and therefore mechanical barrel pre-tension forces) until the bullet is clear of the barrel.


I hear people refer to early unlocking all the time, but rarely do any two people define the term in the same way. As in the video, the narrator demonstrates unlocking in a fairly gross and rudimentary fashion by pulling the slide to the rear a considerable distance. To be clear, that much movement ONLY occurs after the bullet has left the barrel and chamber pressures have dropped to a safe level. The physics of the event would not allow the barrel to tilt while the bullet is pulling the barrel forward and the brass is trying to push the breech face to the rear.

What IS happening is that the barrel is becoming destabilized while the bullet is in the barrel. To bring a more common frame of reference, by destabilized I mean that the forces acting on the barrel are not the same from shot to shot. In the case of the 1.0 and to a much lesser degree in the M2.0, the slide stretches at the weakest point- near the rear of the ejection port each and every time you fire the pistol. The brass is pushing the breech face to the rear while the bullet is pulling the barrel forward as I mentioned above.

Pretty common physics equation: force forward=force rearward. This does not contribute to the destabilization because the forces cancel eachother out. What does contribute to the destabilization is the slide stretching phenomenon (which realistically is less that a couple of thousandths of an inch, if that).

As the brass pushes the breech face rearward and the slide begins to stretch, the force that the recoil spring is exerting on the slide/barrel interface (the barrel hood extension against the breech face) becomes variable and is dependent on the pressure curve of each individual cartridge. Since the barrel's only vertical support is the angled surface that contacts the round surface of the takedown lever, the change in force due to the slide stretch allows the barrel move randomly. You can test this by pulling the slide a few thousandths of an inch ( you don't need to retract the slide any more than the thickness of a business card) to the rear and seeing how much you can wiggle the muzzle end of the barrel as well as the chamber area visible at the ejection port. To test this fairly, do not apply downward force on the slide as you pull it to the rear. This reduces the vertical slide to frame clearances, and negates the validity of the test.

In many 1.0 and 2.0s, there will be detectable movement. The M2.0 slide has thicker sidewalls,which reduces the degree of slide stretch. That coupled with the other improvements greatly improves not only their accuracy, but their shootability.



There are other contributing factors, but this is what we have found to be the biggest cause of variable accuracy.

Or, I could be totally wrong.

Great post, thanks for sharing!

 

[Randy Lee]

That addresses an issue that nobody has mentioned before -- that the slide itself is an integral part of the problem (due to the fact that metal will stretch and return to it's pre-stretch state if it's NOT stretched TOO far!)

Do ALL semi-auto slides demonstrate this same sort of accuracy-affecting behavior or is this a characteristic of the basic M&P 1.0 lockup design? It appears that the 2.0 version may incorporate design changes that make it less of an issue. (All that said, I've got an M&P Pro in 9mm and I've found the accuracy impressive, so I'm not criticizing M&P accuracy.)

You address PART of the question of "why" accuracy can be affected in your following comments.



That you can "test this by pulling the slide a few thousands of an inch" and wiggle the muzzle doesn't seem entirely convincing -- since the forces being applied to the barrel, slide, and recoil spring when the bullet is moving down the barrel under intense pressure would seem to make that whole assembly more rigid and less easily moved in a random manner than in your "test" example. I understand, however, that the "test" shows that the potential for movement exists. That a bullet spinning down the barrel may apply forces most of us have have never considered, and such subtle changes in the bullet loads can also affect accuracy is also interesting.

To this non-gunsmith layman, that might suggest ways to offset these "random" barrel behaviors could include barrel bushings, a different lockup design or, as you mention in passing, tighter vertical slide/frame clearances.

I appreciate, however, that when you do all of that, you've begun to build a different gun with what may be different design objectives -- maybe trying to create a target pistol and not a service pistol -- designed for a different role, different reliability objectives, and much different production costs.

Some very subtle, almost invisible M&P 2.0 changes are probably a far more realistic approach.

Thanks for your informative response -- now I've got more to think about!

Thanks for keeping me thinking too, Walt.

Before I started making parts, I was a starving pistolsmith, so I had the good fortune to work on your everyday run of the mill 1911s, Glocks, XDs, Browning HPs, Sigs etc. Most of them have more robust slides, particularly at the ejection port region where the stretching phenomenon is most likely to occur. I believe the added material reduces the effect.

The M2.0 has considerably more material on the slides, and if you look on both interior walls just in front of the extractor and the vertical wall on the side opposite, you will see a noticeable step. While this is present on the 1.0, the M2.0 has about .008-.009" more material protruding inward towards the chamber sidewalls of the barrel. This does two things:

First, it adds thickness to the areas where the stretching occurs and second it increases torque lock of the barrel to the slide as the bullet rotates its way down the barrel. This coupled with the 1:10" twist rate greatly improves accuracy potential in the 9mm.

"That you can "test this by pulling the slide a few thousands of an inch" and wiggle the muzzle doesn't seem entirely convincing -- since the forces being applied to the barrel, slide, and recoil spring when the bullet is moving down the barrel under intense pressure would seem to make that whole assembly more rigid and less easily moved in a random manner than in your "test" example."

Walt, the force being applied only helps to lock the barrel and slide along the axis of the bore. This means that the only contact point being stabilized is the top locking ledge of the barrel against the mating surface at the front of the ejection port. When the slide stretches, vertical forces acting on the barrel become variable. I believe it has a greater affect on the M&P pistol due to the way they designed the system. Other pistols like Sigs, 1911s Browings and my favorite 3rd Gen Smiths use a mechanical means to apply vertical force to bottom lug of the barrel. The M&P simply does not. Given that it is a service pistol, perhaps it isn't really a big concern for most.

Our barrel is different because we have the bottom lug of the barrel mate to the locking block- this is what provides the consistent vertical support as the slide stretches. It is not new magic or snake oil. This is the way the Sig P series TDA pistols have done it for decades, and custom built 1911s usually have the bottom lug cut so that the barrel is not only vertically supported through the dwell phase but beds the barrel's top lugs against the slide lug recesses. In all cases, for optimal accuracy the barrel must be mechanically fixed relative to the slide until the bullet leaves the bore. For the M&P, this requires the barrel to be supported by the frame locking block.

 

[CB3]

Thanks Randy for taking the time to detail for us what is really going on. It's a wonderful feeling to be properly "schooled".

I love my Apex Gunsmith Fit barrel Apex put in my M&P 1.0 last spring. Thanks!

 

[Randy Lee]

I hope that my babbling adds knowledge to this forum. There is a lot of mis-information out on the internet and quite frankly even in our industry.

CB3, I'm glad you like our barrel!

 

[Smakmauz]

I can't speak for everyone, but I love it! I'm a technical detail nerd and I love reading about this kind of stuff.

 

[Walt Sherrill]

Walt, the force being applied only helps to lock the barrel and slide along the axis of the bore. This means that the only contact point being stabilized is the top locking ledge of the barrel against the mating surface at the front of the ejection port. When the slide stretches, vertical forces acting on the barrel become variable. I believe it has a greater affect on the M&P pistol due to the way they designed the system. Other pistols like Sigs, 1911s Browings and my favorite 3rd Gen Smiths use a mechanical means to apply vertical force to bottom lug of the barrel. The M&P simply does not. Given that it is a service pistol, perhaps it isn't really a big concern for most.

I had assumed that the fired round's casing was staying TIGHTLY pressed against the chamber walls until pressure dropped (as the bullet exited the barrel). IF that was happening, it would seemingly make slide stretching a non-issue. But that may not always be the case.

I understand that with fixed-barrel semi-autos like .22s, Makarovs, etc., the casing DOES move before the pressure drops -- so it makes sense that it could also happen less dramatically in some versions of the Browning Short-Recoil Locked Breech design. Maybe only SOME BSRLB guns have non-stretchy slides, and most of us assume all do. (This is another aspect of a subtle and dynamic process that I've not seen addressed in prior discussions.)

If a little "stretch" was a characteristic of the original (1.0) design, adding extra material to the slide for the 2.0 version seems like an elegantly simple and relatively inexpensive fix.

I keep learning new things in this discussion, or find new ways to look at old things differently.

Thanks again.

 

[ScaryWoody]

Any pistol is a poor performer compared to a finely tuned rifle. Many think that their pistol should perform as a target pistol. It wasn't designed for that. Know it for what it is, a get off me gun. My needs are simple, to go boom when the trigger is pulled. Anything beyond that is bonus.

 

[Fastbolt]

A friend of mine just took his brand new M&P 45 2.0 to the range to function test it. Using 230gr loads (didn't ask which brand/line) he checked it for basic accuracy at 7yds, cold, just to see how it would do. He said he put 25 rounds into a hole the size of almost a quarter. Not too bad.

 

[Smakmauz]

A friend of my just took his brand new M&P 45 2.0 to the range to function test it. Using 230gr loads (didn't ask which brand/line) he checked it for basic accuracy at 7yds, cold, just to see how it would do. He said he put 25 rounds into a hole the size of almost a quarter. Not too bad.

There's a thread from just last week here where the OP posted pics of 25yd testing of his 2.0 .45 with his home made ransom rest and that thing looked like it was shooting sub 1-1/2 groups. pretty damn accurate and much improved over the 1.0's.

 

[stavey]

I have a post on here where I tested 15 loads in my m2.0 45acp. Accuracy is as good as it gets . I shoot 4 , 6 round groups at 25 yards . Minimum of 4 groups to get an average. Then eliminate the first flier per group which is due to inconsistent hand racking of the first round into the chamber.
Worst groups were 1.5" average. Most were under 1 inch my pet load averages .617" These were all shot using ? X fired brass.
That's as good/better than ANY 45 I've had in the ransom besides my p227.
I've tested the gen 1 9mm they are 3-4" guns before the apex upgrades. I could go on all day but if you want astounding accuracy you won't beat the m2.0 45acp.
My ransom is not homemade.
All I tested were 185g zero's and 185 xtp's Those are all I shoot for good reason-ransom rest proven
Today or tomorrow my new edc gen 1 m&p 45c is going in the ransom.

 

[Fastbolt]

There's a thread from just last week here where the OP posted pics of 25yd testing of his 2.0 .45 with his home made ransom rest and that thing looked like it was shooting sub 1-1/2 groups. pretty damn accurate and much improved over the 1.0's.

I have an early production '08 FS M&P45 in DE w/thumb safety that shoots startlingly good groups, even when it had the older striker assembly and a heavier trigger. Out to 50yds it rivaled my accurate '05 Colt XSE Govt. That was with an assortment of a couple types of duty loads and ball.

Considering the acceptable +/- 2lb trigger pull tolerance spec in the standard "1.0" line (I haven't been to a 2.0 armorer class yet), it's not surprising that some guns might be capable of surprising accuracy, for a service-grade gun, than some others. I've certainly handled my fair share of Glocks of which that could be said, and the listed allowable tolerance spec difference in trigger pull mentioned in their classes, and the newest armorer manual, has as good bit of "wiggle room".

When I have the time to get back out to our range, I plan to try a couple of the newer 2.0's, just to get some hands-on. (They aren't on the CA roster for non-peace officers, so it's not like I'll be ordering one now that I no longer have a badge, so my 9 year old M&P 45 will probably have to do. 0

 

[bsmiley]

Former starving pistolsmith Randy Lee said "Or, I could be totally wrong."
Ha-ha! Talking about slides stretching and still keeps a healthy sense of humor.

 

[Christopher67]

A friend of my just took his brand new M&P 45 2.0 to the range to function test it. Using 230gr loads (didn't ask which brand/line) he checked it for basic accuracy at 7yds, cold, just to see how it would do. He said he put 25 rounds into a hole the size of almost a quarter. Not too bad.

Thanks for sharing! It appears he pulled his video down on his Youtube channel now....

 

[Randy Lee]

In my experience, the 45 and 40 S&W caliber M&Ps have never suffered from the accuracy complaints that the 9mm gets on the internet. In fact all the 45 M&Ps I've ever tested have shot as well as some high end custom 1911s.

The question is why does the 9mm not display equivalent accuracy standards as the 40/45s given that the lock up design is the same?
From what I have been able to determine, it boils down to torque.

A general rule of thumb is that the larger the diameter of bullet, the greater the amount of torque it will apply to the barrel (surface area of the bullet and twist rate also play roles in this too). The larger torque values "torque lock" the barrels to the slide, at least moreso than the 9mm.
The factory changed from a 1:18.75" twist rate to 1:10" some years ago in the M&P 9mms. While there was a lot of speculation, the end result was that the number of complaints about accuracy dropped.

The changes implemented in the M2.0 definitely improve the accuracy in the 9mm guns we've tested.

 

[Walt Sherrill]

A general rule of thumb is that the larger the diameter of bullet, the greater the amount of torque it will apply to the barrel (surface area of the bullet and twist rate also play roles in this too). The larger torque values "torque lock" the barrels to the slide, at least moreso than the 9mm.
The factory changed from a 1:18.75" twist rate to 1:10" some years ago in the M&P 9mms. While there was a lot of speculation, the end result was that the number of complaints about accuracy dropped.

Is the slide of the .45 model thicker (reinforced) in the ejection port area than the 1.0 versions of the 9mm or .40/.357 SIG models?

This makes me wonder whether the higher pressure of the smaller caliber rounds [9mm, .40 S&W and .357 SIG] might also play a role in this, IF the cases in the chamber DO move a bit to the rear as the bullet goes down the barrel...