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Strange extraction behavior. Two different revolvers.

This is a discussion on Strange extraction behavior. Two different revolvers. within the Reloading forums, part of the Firearm Forum category; 357 magnum load 15.3gr Win 296 Winchester small pistol magnum primer Hornady 158gr XTP bullet Starline brass The Hodgdon website lists 15gr as the starting ...


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Old March 2nd, 2017, 01:11 PM   #1
 
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Strange extraction behavior. Two different revolvers.

357 magnum load
15.3gr Win 296
Winchester small pistol magnum primer
Hornady 158gr XTP bullet
Starline brass

The Hodgdon website lists 15gr as the starting load and 16.7gr as the max load. Hornady 10th edition has 16gr as max.

Through a GP100, the extraction is very light. In a S&W 627, I do feel some resistance. I don't have to bang on the ejector rod, so it's not like the cases are stuck. I can still eject the cases just using pressure from one finger, it just has more resistance in the S&W compared to the Ruger.

Primers look flat. To be honest, even factory American Eagle rounds (357 magnum - 158gr JSP) get flattened primers in my 627. However, factory rounds did extract easier.

Cases look good. Combustion of powder is fairly clean, not overly sooty. Chambers in the 627 are smooth and shiny.

Is the increased extraction force normal in this case, or am I starting to get an over pressure sign from the 627?



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Old March 2nd, 2017, 02:31 PM   #2
 
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What C.O.L. are you reloading at?
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Old March 2nd, 2017, 02:51 PM   #3
 
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Quote:
Originally Posted by zaster View Post
What C.O.L. are you reloading at?
1.585" (pretty much seating to the middle of the cannelure). Hodgdon lists a COL of 1.580". Hornady lists 1.590".
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Old March 2nd, 2017, 03:45 PM   #4
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Red9, If you are using a Hornady XTP bullet, you need to set them to Hornady's recommended depth .... which is a COL of 1.590". Anything shorter is sure to cause an increase in chamber pressure. Your powder charge is well under max.

357 Magnums are rated for a max chamber pressure of 35k psi .... which is a lot. What you are seeing is an obvious sign of pressure but NOT necessarily a sign of over pressure. One thing worth checking is your cylinder throats. If they are too tight, chamber pressure will increase .... possibly to dangerous levels. You should be able to push those XTP bullets nose first from the front face of the cylinder though all six throats with nothing more than slight finger pressure. If your throats are too tight, have them reamed to .358".

BTW, I just finished working on a S&W Mod 686 (357 Mag) that had tight throats. The largest pin gauge that would pass through the throats was .356". The owner had tried everything to prevent bore fouling with .358" lead bullets but nothing worked. After I reamed them to .358", the lead fouling mysteriously went away. Because jacketed bullet are way harder than lead bullets, they don't deal well with tight throats .... it just increases chamber pressure. I'm not saying your throats are too tight but it is certainly worth checking.
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Old March 2nd, 2017, 05:57 PM   #5
 
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I did the cylinder throat check using the XTP bullet. Oddly, the 627's throats weren't as tight as those on the GP100.

I'll go and pull the remaining rounds so I can redo them to Hornady's specs. I know you said that what I'm seeing isn't necessarily a sign of over pressure, but better safe than sorry.
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Old March 2nd, 2017, 05:59 PM   #6
 
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Iowegan, thanks for the help and info. I learned something new about cylinders and throats.
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Old March 2nd, 2017, 07:23 PM   #7
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Red9, You're welcome! It's always better to be safe than sorry.

I just ran your load (15.3gr W-296, Hornady 158gr XTP) through QuickLOAD. It predicts a mere 26,685 psi chamber pressure when the COL is 1.590". Hornady's max load, 16gr of W-296 is estimated at 31,094 psi .... still conservatively well under the SAAMI max of 35,000 psi.

Here's something that I have noted .... not all brands of cylinders expand and contract the same when firing the same exact ammo. Here's what happens .... when the cartridge develops peak pressure, the bullet has traveled just .5" .... and has not yet left the cylinder throats. The walls of the cartridge will expand along with the walls of the cylinder's chamber. As pressure drops, the cylinder will contract and will squeeze the expanded brass case. Normally, this will result in a case that extracts easily .... but not in all guns. It's not the cylinder thickness alone, it's the properties of the metal used in the cylinder that make it somewhat elastic. Here's where the difference comes in .... S&W uses a very hard forged alloy for their cylinders that is not very elastic ..... Ruger uses a softer alloy that is cast, not forged and is very elastic. The difference is very notable when you ream these cylinders .... Rugers ream very easily whereas S&Ws are very hard to ream. The two companies have chosen different solutions for the same issue .... controlled expansion. Some people may argue that one alloy is better than the other but in reality, they both work amazingly well .... far beyond SAAMI pressure standards.

At the working pressure for your loads, the S&W cylinder must not be expanding much and is clamping the expanded spent brass cases. That said, at different operating pressures, the exact opposite may happen where the Ruger cylinder is harder to extract spent cases. This is exactly why you should never try to judge chamber pressure by hard/easy extraction. Same for primers .... even factory 357 Mag cartridges will have flattened primers .... just a sign of pressure but not a sign of over pressure as with your extraction issue.

Reloading manuals subscribe to SAAMI specs and in fact pressure test all their loads with SAAMI approved equipment and procedures. Listed loads are always on the conservative side .... never exceeding SAAMI specs and usually well under the max limit. Factory ammo is notably hotter .... almost always right at the SAAMI limit but not over. If you are afraid to shoot max pressure loads, you better stay away from factory ammo. If you have any gun that is made in the USA, it will be designed to handle SAAMI max pressures for the specific cartridge. As such, you can rely on reputable reloading manuals to keep your loads well under SAAMI max pressures and not worry about misleading pressure signs.
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Old March 3rd, 2017, 03:32 AM   #8
 
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Or, one revolver simply has a slightly rougher cylinder and could use some polishing.

I really don't think you'll see ANY pressure change from a 0.005" COL difference, as that is well within the normal COL variation cartridge-to-cartridge.

I have found that at LOW chamber pressures I sometimes get flattened primers and they go back to normal as I work the load up.
Finally, I don't like 296/H110 as there are too many references to NOT going below 2% of max load as you can occasionally leave a semi-molten wad of powder in the barrel, and the range of max loads in various manuals exceeds that 2% range. Also, I find that 2400 gives me better accuracy and I only lose about 50 fps from the max 296/H110 load.
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