Hey guys can anybody give me any guidance on whether or not to do a 45 super conversion to my 4566 with the addition of a heavier recoil spring of course?
Thank you!

Yes you can and many have. Its not going to break your pistol. “Conversion” isnt really what happens. You should change the recoil spring. Thats it.
Nothing to “convert”.

Yes, the S&W 45 ACP pistols, especially the 3rd gen versions, are built to take the beating from the 10mm Auto cartridge. They can handle 45 Super and, in my opinion, do it better than your basic Model 1911.

I think the bigger question is why would you want 45 Super? It offers nothing in terms of terminal performance against two-legged vermin that cannot be achieved with the 45 ACP. I would say that the 45 Super might be better against dangerous 4-legged critters, like dogs, mountain lions, and black bears.

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VCDL, GOA, NRA

That is awesome! Thank you!

I know the answer to "why"; it's because I like & I can.

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I set my 4586 up for 45 Super & it functions fine with my full 45ACP & 45ACP (+P) loads, no need to re-spring back to standard unless you go light target loads.

I did a spring test some time back to compare a couple combinations. The results are below.

I run combination #6 in my 4586. Note the 20# spring was cut short by (1) coil because it's too long & the slide bottoms out (stops on) the recoil spring instead of the frame abutment if you don't. Always check any replacement recoil spring for proper fit.

I didn't have a new factory S&W recoil spring to test & compare at the time, but I do now, & will try to update that relative info later.

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Waiting for the break of day

Yes you can shoot .45 Super in a 4566...although it will be a little rougher on the gun than if it was a full sized 4506 since the slide/barrel mass is a little lower. You will need a high power firing pin spring more than you need a recoil spring..Going up in recoil (slide) spring does NOT have a great impact on the final slide energy when it hits the stop...If it makes you feel better just increase the recoil spring to the point that it still operates fine with stardard low powered .45 acp loads and stop there. If you do the math you will see that the mass of the slide/barrel has waaaay more to do with operating at .45 Super than the recoil spring. The gun will operate just fine. Now it WILL be battered more than when shooting stardard .45 acp but I don't see any problem because why would you target shoot with Super rounds. I deer hunt with mine and I probably shoot 30 rounds a year tops in mine. At that rate the gun will live forever. 1050 fps is totally and easily doable with 255 grain hard cast bullets in the .45 Super and you will have no problems with them.

Yeah if it was a 1911 I could just throw a 22# recoul spring and a valkyrie compensator on it like on my 1911. I would love to have a 4506 but I missed out on it and instead found the 4566 tactical my lgd called me about as soon as it came in. Thank you for the great advice

And I like them so much in stock configuration that they are my go to guns if things get hairy. I also have a 4506 and a 645 that I have set up for .45 Super. I think that they are a better fit for the .45 Super round. But hey that is just me. Certainly the 4566 will stand up to the round, no issue there.

Just like in the 10mm round. I really really like the two 1006s that I have. I also have a 1066 that I do not really like as much as my 1006s.

Just sayin!

Here's an interesting, but slightly confounding, article on the affect recoil springs have on timing:

How Balancing Semi-Auto Pistol Recoil Spring Rate with Ammo

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An extra power firing pin spring is always good to have but as you increase the ammo's power &, in conjunction, the recoil spring strength you need to make sure the magazine spring is strong(er) enough to keep up with the faster forward/closing speed of the slide.

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The 5" models 1006/10mm Auto & 4506/45ACP use the same S&W factory (18#) recoil spring (#201610000).

The 4.25" models 1076/10mm Auto & 4586/45ACP use the same S&W factory (17#) recoil spring (#895240000).

So the longer/heavier assemblies uses a recoil spring that's (1#) stronger, not lighter or equal? Hmm...

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Waiting for the break of day

Good article Bluedot! I suspect the lower weight spring on the 4.25 inch guns probably has more to do with the spring length than the one pound diffeence in spring rate. The actual energy absorption difference between these two spring rates is minimal in the end. These two paragraphs from the article are completely correct in my opinon based on the momentum calculations I have done:

Total Cycle Time

The relative speed differences between the three spring weights is more pronounced when looking at the total cycle time. Stronger springs return the slide to battery at a significantly faster speed. The average total cycle time was 57 ms for the 12 lb spring, 48 ms for the 16 lb spring and 45 ms for the 20 lb spring. The total cycle times for the individual springs were extremely consistent within the 10-shot strings, and the extreme spreads did not exceed two milliseconds.

[U]The total cycle times for the full power and reduced power ammunition was nearly identical and did not differ more than one ms for a given spring. This suggests that while recoil springs are sensitive to differences in the power level of the ammunition tested here during the recoil phase, it makes little difference in the overall cycle time.[/U]

The thing we have to keep in mind is the energy absorbed by the recoil spring is dictated by the formula E=1/2K*X(squared) and the absorption of THAT energy deducts from the total slide energy (and thus speed) as it travels back on the frame. However if you run this out you will see that the energy absorbed by the spring is a fairly small fraction of total slide energy and increasing the spring rate (K) has an even smaller part to play. Now this is not the case with low power and low momentum cartridges but with the .45 acp full power loads and .45 Super loads the spring rate just does not have a huge effect on how fast the slide hits the stop. Thanks for posting that article..

I was wondering if the stronger spring on the 5" might be more to insure that the slightly heavier assembly gets back in battery at the same speed/time as the lighter 4.25" assembly does?? Dunno.

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Waiting for the break of day

That is a good analysis I think! Otherwise the cycle time of the 4506 might be longer than shorter gun...