10 mm

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They made a 6-shot L frame .40- 646. With modern materials, there is no reason why it couldn't be a 6-shot.

10 is only 7.1% more pressure than .40.

True if you go by SAAMI specs. But a lot of 10mm fans insist on ammo with 50% to 60% more power than the same bullet in a 40 can generate. You don't get that kind of power increase from an extra .15 inch of case length and 7% pressure increase.

A 10mm revolver should be strong enough to handle Underwood, Buffalo Bore and reloads from someone that thinks they bought a 41 magnum, not just "weak factory ammo". Anything less and it will be bad mouthed for not being able to handle "real" 10mm ammo.

While everyone that tests ammo on YouTube has a chronograph none of them have a strain gauge to measure pressure. If they did I think, but cannot prove, that a lot of the hottest 10mm loads fall into the +P category and in some cases +P+.
 
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True if you go by SAAMI specs. But a lot of 10mm fans insist on ammo with 50% to 60% more power than the same bullet in a 40 can generate. You don't get that kind of power increase from an extra .15 inch of case length and 7% pressure increase.

A 10mm revolver should be strong enough to handle Underwood, Buffalo Bore and reloads from someone that thinks they bought a 41 magnum, not just "weak factory ammo". Anything less and it will be bad mouthed for not being able to handle "real" 10mm ammo.

While everyone that tests ammo on YouTube has a chronograph none of them have a strain gauge to measure pressure. If they did I think, but cannot prove, that a lot of the hottest 10mm loads fall into the +P category and in some cases +P+.

You can get "real" 10mm rounds within spec. Look at old data, the modern load data is lawyered down to .40 levels.

FWIW I consider "real" 10mm a 180 at 1300 and a 200 at 1200 from a 5" barrel.

However, I don't load my 180 Gold Dots that fast because, from watching YouTube tests, at that fast, it greatly sacrifices penetration. I load them around 1225-1250. Still hotter than a .40. The 180 Gold Dot was not designed to handle that velocity. They should make a 200. I don't trust XTPs.

To the point about pressure- If someone blows the gun up because of roided-up reloads, that's the user's fault. I would think that any factory ammo would be safe. I find it hard to believe that Underwood or BB could stay in business while lying about their pressure levels.
 
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S&W needs an new 10mm. Ruger has a few revolvers and a 1911 out now. Hell, if they sold their RB 4" E-Series in 10, I'd buy one tomorrow.
 
You can get "real" 10mm rounds within spec. Look at old data, the modern load data is lawyered down to .40 levels.
. . .
.I find it hard to believe that Underwood or BB could stay in business while lying about their pressure levels.
I bought a Springfield Omega back in the 80s when it was the first 10mm I could buy and get magazines for. Being younger and poorer the price of factory ammo drove me into reloading. With that gun I found I was never able to get up to the maximum loads without seeing over pressure signs, including a couple of blown primers. In particular I remember trying to work up a load with 155 grain bullets that would generate the biggest splash possible when they hit a plastic milk jug filled with water. The gun mags at the time said AA7 was THE powder to use for 10mm and recommended a max of 13.7 grains as I recall. My 1991 Hornady manual says 13.9. I could only get to around 12 before I started having over pressure signs. The bullets were seated to the recommended depth. I later traded that gun for a 610 and found I could get up to 13.7 grains without over-pressure signs but past 12 grains there was little increase in velocity and accuracy went from tight groups to shotgun patterns. Loading long in the 610 helped.

Much of that was due to the early data recommending the wrong powder in the wrong amounts. Which is why I don't place much value in the early reloading data for the 10mm, a lot of it was wrong. I wouldn't be surprised if the Omega had a tight chamber.

I wouldn't expect +P ammo to blow up a well made gun. Even one not rated for +P. Or in the case of 10mm where there is no +P spec. But I would expect increased wear and reliability problems in guns designed for SAAMI spec ammo. If you look at the BB site or read reviews of BB/Underwood ammo you will see a lot of comments about needing to use a stronger than stock recoil spring, added buffers, etc.

I wish SAAMI would add specs for 10mm +P or 10mm "full power" so manufacturers could sell guns specifically designed for ammo loaded to Underwood power levels. Most people I know with 10mms bought them to shoot strong ammo and the guns should be optimized for strong ammo, even if that means they might not be as reliable with the 40 S&W loads in a 10mm case some ammo makers sell.

If S&W makes a 10mm L frame it should be able to handle the strongest BB or Underwood loads in stock configuration. Which shouldn't be a problem since the L frame can handle 44 magnums. Hopefully they could still get six rounds in but if there is any doubt they should go with 5.
 
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AA9 is good for 10mm. It will get you to full-power. I found it (being ball powder) burns better with magnum primers. The velocity is slightly higher (10-20 fps IIRC) with the magnums.
 

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