Tungsten vs stainless M&P guide rod which one to go with?

[jsneff]

I am looking at the stainless and tungsten guide rods. Does the tungsten really reduce recoil?

[Dave Gundry]

Yes, it does - in that it weighs more, which absorbs some of the impulse of the recoil transmitted to you.

But, that being said, I would think the tangible difference is fairly small or negligible, but I have yet to try one.

Tungsten GR also makes the M&P illegal for Production division.

Edited March 15, 2008 by Krautwagen

[RIIID]

Kraut,

Since when does a Tungsten guide rod make a gun illegal for Production?

[DaG]

I thought Tungsten was legal as long as you don't go over the 2oz. factory weight....????

DaG

[double_pedro]

Do you have an idea how much weight either of the two guide rods add to M&P (i.e. how much more do they weigh than the stock guide rod to be repllaced)? If you can tell me this, I can estimate how much of difference each should make in muzzle flip. The stock guide rod is already fairly heavy so I am curious how much additional weight a stainless or tungsten rod will have. The good news is that the moment of inertia of the M&P is fairly low to being with so the difference may be relatively large as a percetage. If someone out there has one, thow it on a scale and let me know. Also, do the same for the stock rod it will be replacing.

[Dave Gundry]

Kraut,

Since when does a Tungsten guide rod make a gun illegal for Production?

Since I read the rules wrong, of course

[kend]

The stainless steel guide rod weighs 273.1 grains (0.62 oz.) and the tungsten weighs 508.8 grains (1.16 oz).

[double_pedro]

The stainless steel guide rod weighs 273.1 grains (0.62 oz.) and the tungsten weighs 508.8 grains (1.16 oz).

I weighed the stock guide rod in my 9mm M&P. The stock rod (with captive spring) weighs just under 26 grams. A Wolff spring I have weighs 7 grams, so I estimate the stock guide rod for the M&P is about 19 grams. Coverting the guide rod weights you give above, I find the SS guide rod weighs 18 grams and the tungsten rod 33 grams. So it would seem that the SS rod is actually lighter than the stock rod it replaces - that's not going to help recoil.

To quantify the effect in any case, what one needs to know is how much the additional mass changes the moment of inertia of the pistol. Moment of inertia is the physical quantity that characterizes how hard it is to rotate something (just like mass characterizes how hard it is to move something in a straight line). Moment of inertia depends not only on the mass of an object, but also how the mass is distributed from the axis of rotation (mass far from the axis of rotation makes something harder to rotate) - this is where additional guide rod mass comes into play to flatten recoil.

In the case of pistol recoil, a reasonable example to consider for comparison purposes is the rotation of the pistol about an axis just under the beaver tail (i.e. at the top of the grip). The moment of inertia of the entire pistol would be a bit complicated since it is irregularly shaped and non-homogenous. However, it can be determined by measuring the angular acceleration that results from the application of a known torque. I've done this for a few different pistols (including the M&P) (link). For the guide rod, one can calculate the moment of interia directly since it is basically a uniform rod of mass M and length L rotating about an axis that is a distance R from the nearest end of the rod. The moment of inertia of the rod in this case will be:

I_ROD=(M/3L)*((〖R+L)〗^3-R^3)

and for the M&P, approximate values for L and R are L = 3.2" (0.081 m) and R = 3.5" (0.089 m).

So the question at hand comes down to what is the moment of inertia of the stock, SS and tungsten guide rods and how large of a part is this to the entire moment of inertia of the pistol (rotating about the same axis just under the beaver tail). The following table summarizes this information based on my measurement of the stock M&P moment of inertia (0.0056 kg*m^2) and the contribution of additional guide rod mass based on the above formula. The percent change in moment of inertia (bigger being better) will give a good idea of how much reduction in muzzle flip the change in guide rod will yield. The SS guide rod in question, apparently being close to the same mass as the the stock rod will result in no change, while the tungsten rod will reduce muzzle flip by about 4%.

Edited March 16, 2008 by double_pedro

[dcarter]

God, I think my head hurts!

[ChrisStock]

God, I think my head hurts!

you and me both

I actually did replaced my captive GR/spring with one from Kend for the sole fact that I can now change recoil springs in seconds, and tailor them to my loads to get the slide speed right where I want it. Perceived recoil was not an issue, but slide speed was way too sluggish with some of my lower powered loads.

[jsneff]

Thanks for the info! I am going to get a recoil guide so I can switch springs. Hmmm, 4% huh?