LRMP in the Rem700ML or MLII still has a similar flash channel length as 209 primer plug. You dont really gain the same things as you do by using a CF action with locking lugs. They wont ignite powder any better than a 209 can. You need locking lugs to handle the high pressures created with a shorter distance between powder and the primer.
I have built High Pressure 45 caliber muzzleloaders on both the Remington 700 Single Shot action (has locking lugs), and on the Remington 700ML action (no lugs).
The majority of the pressure is handled by the threads on the breech plug in both cases.
The only advantage for the centerfire rifles is a shorter flame path. Both of the breech plugs use a carbide bushing for the vent. The pressure coming through the small diameter hole in the carbide bushing in both breech plugs is not very different. Therefore, the pressure into the primer modules of both rifles is about the same.
I have not seen a real difference in reliability, or accuracy in either rifle.
I use the same load data in both rifles.
Others may have had a different experience than mine.
However, I do know a 209 primer contains much more priming compound than a Large Rifle Magnum primer. You can check this yourself, by weighing them before firing, and then after firing. If I remember correctly, the 209 had almost five times more weight change. Therefore, you are getting a lot more "bang" from the 209 primer.
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