Im curious if your sml is like the MLII? The primer slides loosely into a slot on the bolt face of those.
Smokeless 10ml problem
- Thread starter cmn
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Smokeless
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- Jul 16, 2015
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Headspace is important and when set properly can solve or avoid many issues.
Anatomy of a breechplug.
Flame channel = The area between the vent and primer. This area volume is important. Too little can cause swollen primers. Too much and ignition performance will suffer. Should be cleaned periodically with a 5/32" driil bit.
Vent = The tiny hole in the nose, typically .030" to .040". This hole keeps powder from falling thru the primer hole when when loading powder before priming. It also serves as a metering device to slow the building of pressure in the flame channel. This orifice opens up gradually due to flame cutting by the flow of superheated gasses. Fast powders, like n110, imrsr4759 tent to erode it fastest. Hotter loads of slower powder can do the same thing. The breechplug can be modified to accept a carbide bushing, to replace the ventliner, that will likely outlast the gun under normal hunting conditions.
Primer pocket = The space that holds the primer cup and seals the primer cup to the breechplug.
After ignition, pressure builds in the flame channel the entire time the bullet is in the barrel. This is referred to a "barrel time". Like water thru a nozzle, a given amount will flow at a given pressure. The flame channel fills at that rate. a larger or worn vent or a small, carboned up flame channel will build pressure faster and to a higher pressure. A clean flame channel or a tight vent will build pressure slower.
The remainder of this discussion will follow the photo below.
Top breechplug standing on end, New and never used. Notice a small shelf or ring down in the primer area. This is a very narrow shelf that is approx .280" into the primer pocket. It just so happens that a Winchester 209 primer measures right about that length. The primer to the right of that plug is a Winchester 209 primer. Notice the bulge in its diameter, That is what helps seal it to the plug in a Savage plug. The middle plug is an unmodified plug. I pushed the primer into it by hand. It is not seated on that little shelf. It is just tight in fit. The bottom plug has a shim installed in the primer pocket that makes the pocket .180" deep. This allows the primer to seal on its face AND not be allowed to be driven further into the plug by the firing pin. So, a properly set up Savage plug has a shelf for the primer to seal against and the inside diameter sized for the primer you intend to use. (Federals are hotter but are straight, not always round, and do not seal as well as Winchesters).
So, to recap, All Savages seal on the sides of the primer cup and have a tendancy to be driven in by the firing pin. Primer cup tension fit in the plug is very ticky, making one rifle stick where another does not. So, when the firing pin strikes the primer, it is driven deeper into the plug, leaving a void between the primer cup and the bolt face. Then when pressure builds in the flame channel, the gold part of the primer inside the cup is driven out of the cup into the bolt face. This causes the primer to stick in the bolt face. By properly supporting the primer, proper headspace is achieved and the gold part of the primer cannot be blown out of its cup because the cup is sandwiched between the bolt face and the primer shelf in the plug giving the gold part nowhere to go.
Yes, my LRMP modules are slip fit in the bolt face.
And the picture below is of a slip fit savage rifle action bolt face with a savage plug and a winchester 209 primer inbetween. It is set up for maximum primer insertion into the plug for added support to stop primer cup swelling with higher pressure loads.
Below is a single shot 45-70 converted to sml with a Savage plug. It also has the primer nose supported. The typical rifle firing pin is set to .055". Proper headspace is a must for proper firing pin strikes.
Anatomy of a breechplug.
Flame channel = The area between the vent and primer. This area volume is important. Too little can cause swollen primers. Too much and ignition performance will suffer. Should be cleaned periodically with a 5/32" driil bit.
Vent = The tiny hole in the nose, typically .030" to .040". This hole keeps powder from falling thru the primer hole when when loading powder before priming. It also serves as a metering device to slow the building of pressure in the flame channel. This orifice opens up gradually due to flame cutting by the flow of superheated gasses. Fast powders, like n110, imrsr4759 tent to erode it fastest. Hotter loads of slower powder can do the same thing. The breechplug can be modified to accept a carbide bushing, to replace the ventliner, that will likely outlast the gun under normal hunting conditions.
Primer pocket = The space that holds the primer cup and seals the primer cup to the breechplug.
After ignition, pressure builds in the flame channel the entire time the bullet is in the barrel. This is referred to a "barrel time". Like water thru a nozzle, a given amount will flow at a given pressure. The flame channel fills at that rate. a larger or worn vent or a small, carboned up flame channel will build pressure faster and to a higher pressure. A clean flame channel or a tight vent will build pressure slower.
The remainder of this discussion will follow the photo below.
Top breechplug standing on end, New and never used. Notice a small shelf or ring down in the primer area. This is a very narrow shelf that is approx .280" into the primer pocket. It just so happens that a Winchester 209 primer measures right about that length. The primer to the right of that plug is a Winchester 209 primer. Notice the bulge in its diameter, That is what helps seal it to the plug in a Savage plug. The middle plug is an unmodified plug. I pushed the primer into it by hand. It is not seated on that little shelf. It is just tight in fit. The bottom plug has a shim installed in the primer pocket that makes the pocket .180" deep. This allows the primer to seal on its face AND not be allowed to be driven further into the plug by the firing pin. So, a properly set up Savage plug has a shelf for the primer to seal against and the inside diameter sized for the primer you intend to use. (Federals are hotter but are straight, not always round, and do not seal as well as Winchesters).
So, to recap, All Savages seal on the sides of the primer cup and have a tendancy to be driven in by the firing pin. Primer cup tension fit in the plug is very ticky, making one rifle stick where another does not. So, when the firing pin strikes the primer, it is driven deeper into the plug, leaving a void between the primer cup and the bolt face. Then when pressure builds in the flame channel, the gold part of the primer inside the cup is driven out of the cup into the bolt face. This causes the primer to stick in the bolt face. By properly supporting the primer, proper headspace is achieved and the gold part of the primer cannot be blown out of its cup because the cup is sandwiched between the bolt face and the primer shelf in the plug giving the gold part nowhere to go.
Yes, my LRMP modules are slip fit in the bolt face.
And the picture below is of a slip fit savage rifle action bolt face with a savage plug and a winchester 209 primer inbetween. It is set up for maximum primer insertion into the plug for added support to stop primer cup swelling with higher pressure loads.
Below is a single shot 45-70 converted to sml with a Savage plug. It also has the primer nose supported. The typical rifle firing pin is set to .055". Proper headspace is a must for proper firing pin strikes.
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Great explanation! I see now why Savage told me to only use winchester primers too. Btw my primer slot in the boltface is much larger than yours. Only problem I ever had was when I used CCI primers. Tons of misfires, winchester primers have been perfect for 20 yrs in my gun.
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- Jun 4, 2020
- Messages
- 4,076
I replaced an old one like that on a gun I eventually traded. It worked fine.
It is amazing how far smokeless has evolved now.
