Knight KP1 ML question

[ClintM]

Howdy folks, I am in Missouri, near KC, and am new to this forum but have been a member of the traditional ML sister forum since 2008. I have an original, and as yet unmodified, Remington M700 ML in .50 cal. and a couple of stainless steel KP1's and a few ss barrels for them. I think these KP1's are terrific rifles! Just this week I got a gently used ss .50 cal. ML barrel and forearm for the KP1 that I have not shot yet. The breech plug it came with uses 209 shot shell primers. It arrived with the breech plug area being pretty dirty from blowback fowling and the seller made no effort to clean it up before shipping it. The KP1 barrels all have an extractor system under the breech end of the barrel, all the parts of which were pretty fowled and dirty too. I spent about 2 hrs getting it all disassembled and cleaned up. I have read here about a few of the aftermarket products that are available to help reduce/eliminate the blowback in-lines experience, some of which use a special breech plug or a modified plug in conjunction with primer adapters and a small o-ring seal. From what I gather, the KP1 breech plug evidently is not modifiable to use something like the Variflame primer adapter.
My question is, has anyone out there modified any breech plug using a 209 primer by drilling the primer seat just enough deeper to allow a small o-ring to fit under the primer to better seal the breech end against blowback fowling? I imagine drilling the primer seat only deep enough to allow the primer to slip in almost flush, just sticking up a little so that when the barrel is closed, the KP1 action's breech face gently pushes the front of the 209 against the compressed o-ring. Does this sound feasible, or am I barking up the wrong tree? Thanks for your comments in advance!

 

[MrTom]

Welcome to the Modern Muzzleloader forums.

Lots of people use these small rubber o-rings and have very decent success.

https://oringsusa.com/catalog/product_info.php/cPath/26_118/products_id/118000698

 

[iablackpowder]

Welcome. I too like the KP1. I haven't shot the ml barrel yet, I will be interested to see how it works for you.

 

[whelenman]

Welcome. I too like the KP1. I haven't shot the ml barrel yet, I will be interested to see how it works for you.

I have a KP1 , have multiple barrels for it, I also have a muzzle loader barrel, I purchased it in 09 at that time they had a new breach plug that you could order, that would eliminate the problem you describe. I don’t know if you can order it or not.

 

[ShawnT]

My question is, has anyone out there modified any breech plug using a 209 primer by drilling the primer seat just enough deeper to allow a small o-ring to fit under the primer to better seal the breech end against blowback fowling? I imagine drilling the primer seat only deep enough to allow the primer to slip in almost flush, just sticking up a little so that when the barrel is closed, the KP1 action's breech face gently pushes the front of the 209 against the compressed o-ring. Does this sound feasible, or am I barking up the wrong tree? Thanks for your comments in advance!

I did this very thing at first for a Knight KRB7. If you do it just don't use a standard drill bit. The bottom of the primer pocket is flat so if you use a standard drill bit the bottom will then be tapered so that might cause an issue with the o-ring seating or staying in place as it wears. I took a drill bit and ground the end flat, then re-ground the cutting edges with only a Very slight taper. This will give you a more flat bottom for the o-ring to sit on. If you can find one the size you need an end mill bit would be best. I could not find one then. You'll want to go slow drilling as you may only need to remove .010 to .015 of material to allow for the o-ring. Just depends on your breech plug. I used a small bench top drill press so I had a bit more control than with a hand held drill motor. I looked but can't find a pic of the bit i made.

 

[ClintM]

Many thanks for the replies to my question fellas. MrTom, I will give the o-rings a try! iablackpowder, once I get a chance to shoot the barrel, I'll post again with my results. whelenman, I can't find any such plug available now, but will keep looking. ShawnT, I'll do a little more measuring and if no end mill is available, I'll try the drill bit grinding route.
Yesterday, I took a 209 primer and stuck it into the end of the breech plug. I was expecting it to seat all the way to the rim of the primer, but to my surprise it stopped short. This was a good thing because I was concerned as to what I would use to get the fired primer pried back out. I will order some 6mm diameter o-rings from Amazon and measure their thickness. If I deepen the hole for the primer by half to 2/3s of the o-ring thickness, then I expect closing the breech on the primer will squash the o-ring just a little and seal the primer seat pretty well. It least this sounds good on paper!

 

[MrTom]

If I deepen the hole for the primer by half to 2/3s of the o-ring thickness, then I expect closing the breech on the primer will squash the o-ring just a little and seal the primer seat pretty well. It least this sounds good on paper!

You do not need to do anything with the primer pocket. Leave it alone. Just slip one of the o-rings in and have at it. One ring will last maybe 20 shots, then replace it with a new one.

 

[ShawnT]

A 6mm diameter O-ring sounds awful large to me. are you sure the diameter of your primer pocket is that large? O-Rings I have used only run for 3.5mm 4mm and 4.5mm in diameter.

Like MR Tom. If you have not shot the rifle with this barrel on it, try popping just the primers with no powder charge, remove the primer and look at it for soot on the sides of the primer and in the action area. You can also take the ramrod and send a clean dry patch down the bore till it stops and leave it there. Then put a primer in the breech plug and close the action. Point it in a SAFE direction and pull the trigger. The Rod should only move a few inches and not leave the Bore. Once you pop the primer then pull that rod and patch out and look at the patch. This will tell you just how much heat and pressure from the primer is getting to the powder charge area.

This is what a clean sealed breech plug will do for you with a standard shot gun primer. This is from my KRB7.

 

[ClintM]

Wow, thanks for the added info, MrTom. I just assumed that trying to close the barrel without drilling the pocket deeper would make it too hard to close. I'd sure rather not have to drill the primer pocket any deeper if I don't have too!
Thanks too ,ShawnT, for the pic of the primers and patches and test suggestion with the ram rood. Very telling, and I'll re-measure both some primers and the pocket again more carefully. The 6mm diameter was an initial measurement taken quickly as a for instance. Good info, thanks again to all!