Changing to 4.25 barrel length in M2 4"

[OldLefty]

I would like to replace the 4" barrel with a 4.25" barrel
in my MP9 M2 Compact 4".
It seems to fit just fine.

However, I saw another forum says the barrels are flared and will not lock up with the slide (maybe P.C. guns).

Another oddity. Seller measured the barrel as 4.22". I believe they forgot to include the bullet case in the measurement. But sure enough, the barrel sticks out only .22" in front of the slide?

 

[Beju]

S&W weirdly lists most M&P full size barrels as 4.25" and LE SKU M&P full size barrels as 4.22." Both are over Canada's 105mm length minimum, so I'm not sure why.

 

[Saudade]

The barrels on the 1.0 are "flared" (a slightly larger O.D. at the muzzle). The 2.0's are straight.

As far as the "difference" in length, MGW lists the length as 4.22" (4 11/15" in the description, quite amusing).

Smith & Wesson M&P 40 M2.0 Barrel, 4.22": MGW

Now I have to ask, why?

 

[OldLefty]

.. and MGW shows M&P 9 M2.0 Compact Barrel, as 4.07".

Went to the range and the 4.22 fired fine.
Although it shoots significantly higher than the 4".

Now I have new questions. Is there a way to 'adjust' fixed sights (or do shooters just make a mental note)?
(assuming the barrel is not bent?)


And, should I change the RSA spring weight?

 

[OldLefty]

Cleaned the new barrel after my trip to the range and noticed two things:
Original 4.0" barrel has concentric circles on the crown vs a flat face on the 4.2"
The number 29 or 62 is stamped on the 4.2". I assume it means nothing.

 

[Jim Watson]

Official barrel length is measured with a rod down the barrel from muzzle to breech face. See what that gets you.

You can drift a fixed sight in its dovetail to correct windage but to change elevation you would have to modify or replace one or the other. Dawson Precision sells front sights in a wide range of heights. You are striking high so you need a TALLER front sight. Dawson shows the math for figuring out how much taller.
Smith & Wesson(R), Gun Sights


Sight Calculator

 

[Equus]

Cleaned the new barrel after my trip to the range and noticed two things:
Original 4.0" barrel has concentric circles on the crown vs a flat face on the 4.2"
The number 29 or 62 is stamped on the 4.2". I assume it means nothing.

Those concentric circles on the muzzle are just where the lathe tool was starting to dull (probably a very small chip in the tool) when the barrel was faced to length.

 

[OldLefty]

Couple of photos:

 

[minconrevo]

Cleaned the new barrel after my trip to the range and noticed two things:
Original 4.0" barrel has concentric circles on the crown vs a flat face on the 4.2"
The number 29 or 62 is stamped on the 4.2". I assume it means nothing.

There are several ways to induce tool chatter in the barrel manufacture process. Some makers have lots with more chatter than others.

The numbers mentioned make sense to the barrel maker. They might be heat treat lots, material lots or something other.

There will be small variations in barrel OAL; just part of manufacture.

 

[hardluk1]

I would leave the sights alone and just get use to it . Hang the target by your gun bench and remember Kentucky windage had looong history of working well .

 

[ken158]

Maybe a 6 o’clock hold will give you the poi you seek.

 

[Gman556]

I would leave the sights alone and just get use to it . Hang the target by your gun bench and remember Kentucky windage had looong history of working well .

Your kidding right?

I hope?

Maybe my sarcasm meter is bent?

 

[Jim Watson]

Sounds like a lot of trouble but an extra .15" is just so uber kewll.