Quote from: sparkyv on December 04 2021 05:38:45 PM MST
So does a second cylinder require hand-fitting?  Does the end require tweaking?

Technically, yes... 

I haven't tried to fit mine yet, but I'm hopeful that modern CNC machining means it won't actually need much fitting or shimming. 

S&W is apparently now selling these...

https://usagunsandgear.com/products/smith-wesson-revolver-n-frame-model-610-cylinder-10-mm

I bought one (and their only?) from Midwest Gun Works last week:

https://www.midwestgunworks.com/page/mgwi/prod/412310000

I was hesitant to ream my cylinder for 10mm Mag, but it was actually quite easy... 

If you really want more oomph, then go for it. 

Caveat:  I wasn't able to replicate the velocities that Taffin reported (not even close). 

I lost interest in going further when I started splitting cases with 200gr Gold Dots at ?1,200fps. 

Some of that may be due to my sloppy DIY reaming job, but some of that is just the limits of a 6-1/2" barrel.  (IIRC, Taffin was testing using an 8" autoloader.) 

Quote from: VRoth on October 13 2020 07:20:55 PM MDTI ran some numbers and the chamber pressures seem to be within tolerances, at least for 10mm auto.

I'm skeptical...  I reamed my 6-1/2" barrel S&W 610 out to 10mm Mag.  Eighteen grains of 2400 under a 200gr bullet yields barely 1,200fps. 

How they're going to get 1,600fps out of a 6" barrel, I dunno...

I did it myself...

See this thread:

https://10mm-firearms.com/10mm-revolvers/smith-wesson-610-3-to-10mm-magnum/

Quote from: jthoresen on August 30 2020 08:05:22 AM MDTIf you look at the target on the left, it looks like 5 shots, it's actually 6. One key holed.

Terminology:  That's not a "keyhole," that two shots in one irregular hole.  "Keyholing" is when bullets tumble and hit the target sideways (usually because they aren't stabilized, or because they've hit something else beforehand). 

I'm really happy with my new (since last December) S&W 610.  I adjusted the mainspring (with a set screw) and replaced the rebound spring, and the trigger is sweeeeet.  A fiber-optic front sight and a Hogue grip makes it easier to shoot, too...  Boring it out to 10mm Mag was a slam dunk.

Quote from: Jtigertic on August 23 2020 06:03:17 PM MDTI think the difference could be the barrel...

This would be my guess, too...  Different barrels and guns (even with the same length barrel) can produce significantly different velocities with the same ammo. 

Velocities were about the same... 

I loaded a big batch with 16.5gr, and I put a touch of crimp on the cases after seating, so that the mouths measured 0.421" or so.  (That's about the same as factory .40/10mm.) 

The crimp didn't seem to make much difference in terms of velocity or SD. 

Having fired 10+ rounds of each: 

16.0 = 1,081Avg.,  34SD

16.5 (crimped) = 1,141Avg., 48SD

17.0 =  1,159Avg., 19SD

18.0 (only 6 rounds) = 1,193Avg., 50SD. 


Looking at these numbers 17 grains seemed like a sweet spot (low SD, good velocity).  Eighteen grains seems compressed, and SDs were too much, and all for only 34fps more. 

So, I loaded up another 300 rounds with 17 grains, and now I have a decent supply of ammo. 


Now I'm going back to loading .40S&W for my Glocks and .30 Mauser for my uncle's Broomhandle... 

Another update...  I shot my 10mm Mag, again. 

I tried 16, 17, and 18gr of 2400, and didn't have any cases split or other problems. 

I think I remember that when I shot the 18gr last time, I had difficulty chambering the moon clipped rounds, and then found a piece of copper shaving in one cylinder...  Maybe it's possible that one ill-fitting round caused the split case? 

Quote from: 357_Sig on July 06 2020 03:22:45 PM MDTThe buffer tube/spring came as a kit from PSA and is the KAK Shockwave.

Hmmm...  Dunno about that. 

I'm still guessing there some obstruction or something that's preventing your buffer from going all the way to the rear of your buffer tube. 

It shouldn't take you more than about 3 minutes to (1) remove the rear take-down pin and separate the rear of the upper from the lower, and (2) remove the buffer and spring, and (3) see whether the buffer and BCG fit in the buffer tube. 

Quote from: mr.revolverguy on July 06 2020 08:11:58 AM MDT
Thank you for sharing I am still thinking about taking this journey but sending my cylinder off to a gunsmith/machine shop.

Right, in retrospect, I guess I should've done that...  Or taken the time to buy a drill press and learn to use it. 

FWIW, I've been reading up more on bulging brass, and the famous "Glock bulge" is often 0.432" or so, so my chambers aren't THAT oversized, after all. 

Also, the SAAMI numbers are ± 0.005", so technically most of my chambers are in spec, and only the one oddball (oops!) that's 0.437" is really out of spec. 


I'm still mystified that velocities were so slow and pressures so high...

OK, so I shot my 10mm Mag reloads in my newly reamed 10 Mag S&W 610, and I'm afraid the results were disappointing... 


I had loaded 16gr, 17gr, and 18gr of 2400 under 200gr Speer Gold Dots. 

Average velocities were 1,124fps, 1,172fps, and 1,212fps...  Nowhere near what I was expecting based on Taffin's data using 2400 and 200gr XTPs (1,421;  1,503;  and 1,569fps). 

Taffin was using a 8-inch automatic, but my 6.5" revolver is also 8+ inches from muzzle to breachface, so I was expecting similar velocities.

As is, 200gr at 1,212fps is only 652ft-lbf, and that's not even as much energy than the (admittedly, crazy hot) Underwood 165 Gold Dot at 1,380fps (698ft-lbf). 


Worse:  there were already pressure signs at these velocities:  the primers look smushed to me, especially the 17 and 18gr versions.  In the first photo, the 16, 17, and 18 are left to right.

Worst of all:  one of the cases with 18gr split lengthwise...   See the second photo. 


I did some quick research on split cases in magnum revolvers, and one cause is oversized chambers...  You guessed it:  I literally got a little sideways doing my reaming and bored out the rear of the chambers, too. 

SAAMI says 10mm Auto chambers should be 0.429, tapering to 0.424, but mine are all at least 0.432 on my micrometer, and one is 0.434, and one is .437. 

I measured the spent cases as I removed them from the moon clips, and they follow the same pattern...  Most are at 0.429, but one in each cylinder is 0.433" and another is .435". 


This isn't a catastrophe, because this gun is really a range toy (and I'll be shooting mostly 155gr SWCs through it at 700fps from .40S&W cases), but I take back everything I said about how easy it was to ream chambers...


In the meantime, I'll stick with 16grains of 2400 and the 200gr Gold Dots, or maybe I'll see what I can do with 165gr bullets.  Even this "light" load is equivalent to a decent 10mm Auto load, at 550+ ft-lbf. 

 










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The photos of the cartridges in the cylinder...

And yeah, I know the front of cylinder is filthy.  That's some nasty burned-on black stuff! 

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Update:  I finally got around to loading some 10mm Magnum cartridges, and I'll shoot/chrono them on Wednesday. 

Following Taffin's old data, I loaded 16, 17, and 18gr of 2400 under a 200gr Gold Dot.  18gr of Gold Dot just about fills the case to where the bullet seats, so that's not a compressed load, but it's close.   

Specs say length should be 1.555", but I loaded them at 1.570", because that looked right and there's plenty of space in the cylinder.  (I measured/figured max length to fit in the cylinder could be 1.660", but given that the Starline brass actually measures only 1.245", I only have 0.315" of bullet in the case.)

I'm attaching photos, compared with 10mm Auto... 

NB:  Notice how the 10mm Auto cartridges are barely visible in the cylinder (from the front), and the 10mm Mag cartridges are much closer (with 0.090") of the front of the cylinder. 

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First, go straight to M4Carbine.net and ask there...  (I think that whoever told you to cut the spring was an idiot.)

My guess:  Your buffer is too long for your pistol lower. 

Aren't pistol receiver extensions and buffers shorter than carbine, which are shorter than rifle-length? 

Try this:  Remove the spring.  Now see if your buffer and BCG both fit in the extension.  I bet they don't.