I have heard of such misshapes with H-110 and 2400 and breach seated bullets so I have never considered using them. Detonation is a possibility with all that air space, a fast burning powder and possibly a crimped or hard seated bullet?

I know been using it for years with no problems and he probably has been doing the same. If you look at Alliant's online reloading guide a substantially slower burning powder Reloader 10 would have possibly been a better choice?

True detonation cannot take place in any charge of smokeless powder.   The molecules are too stable.

I ran a simulation in Quickload, 26 grains, seated .424 deep, using a bullet weight of 3000 grains, to simulate a bullet jammed in the throat.  (Generally acknowledged now as the mechanism behind the so-called S.E.E.)   Pressure 60,000 PSI.     Probably not enough to do what happened to that Marlin.   

Another simulation with 405 grain bullet weight, but a double charge of 2400 (52 grains).   Double charge occupies only 95% of available powder space.  Pressure 106,000 PSI.

My money's on a double charge.   

Agree that 2400 is too fast for that application.  He might have picked it because of his short barrel, I suppose.   RL-7, RL-10, or 4198 would have been better, in hindsight.  All have more that 50% load density, so a double charge would have been noticed.

ClaMar wrote on Apr 12^th, 2015 at 10:37pm:


A friend of mine once loaded some ·357 Mag, and there were a few ·38 Spl cases in the batch. He noticed, and put the ·38 Spl ones in the pocket of his work jacket and - forgot them.

Months later on the range he found them, and didn't remember how they had got there, so they went into the chambers of a ·38 Spl revolver...

Blew one side out of the cylinder and jacked-up the top strap.

I have the cylinder somewhere. That is not a pretty sight either.

The friend was an engineer, and he straightened the strap and put in a new cylinder (I can't remember what make the pistol was). It shot just as well as it had done previously.

I can't think that a ·357 Mag load is anywhere near double the ·38 Spl (I'm in a café ATM, so I've nothing to check with), but there's a moral here somewhere, viz: don't make mistakes, and if you do (and know you have done so), correct them immediately.

--
Aonghas

A few weeks back I was helping out with a few youngsters on our 25 metre sighting in range from a local scout troop that had camped out overnight on our range. 
We had closed off three of the lanes for them to shoot 22 rf when out of the corner of my eye I saw smoke a few lanes away.
This guy had just put down two shots with his 7mm Rem Mag. had a new silencer and a new scope to sight in.
After firing his third shot when he opened the bolt on his Remington rifle he found out he had just fired a 270 in it. The case had split but the rifle looked fine.
They were not his reloads and said he had just bought the new packets a few days before.
Didn't have time to talk to him.