Breech Plugs

[denphillips2]

Hi,
I am new to the board. Thank you for a great forum!

I just received my new Brux 20 twist 45 cal barrel. I plan on putting it on a 700SA CF with a Std boltface. It is going to be smokeless for non saboted bullets with the option for BP subs.

I am trying to decide which style of breech plug I want to go with.

I am a gunsmith, and have no problems making my own plug also.

I have done a lot of research out there and come up with a lot of ideas.

So, the question is... What is the best breech plug design and why? Cost, strength, accuracy, reliability, longevity. Also if you have dimensions, that would be greatly appreciated (thread size and length).

Thank you very much for your time!
Denny

[edge]

Can I assume that this is a standard shouldered Rem barrel?

edge.

[denphillips2]

Yes, it is a light palms contour. Finish length is 30". Might not stay that long but I can't add length...

Thank you for any input you have!
Denny

[edge]

Tough decision!

You need to decide if you want to use 209 primers or Large rifle primers. They each have their own drawbacks.
On a shouldered barrel I prefer the 209 since it is very forgiving on the headspace.
With a Savage barrel the headspace can easily be adjusted to fit your priming system and an ACP case or some other rifle case can be cut down to make a convenient primer.

I think that with a lugged rifle you would want to go with smaller diameter threads than the Savage BP and RB used a 5/8 thread which is a good compromise between size and strength.

Being a gunsmith you have the advantage of being able to adjust components so pick your priming method and work from there.

The easiest BP I made was using a 5/8 set screw for my Marlin conversion, but I have only fired it enough to get on paper.
When it warms up a bit I will put it through its paces

edge.

[denphillips2]

Well, I am an accuracy nut

So, I am thinking that the LR primers will give me the most consistent ignition. I have no problems headspacing the cases. I was thinking of using either 45ACP or cut down rifle cases.

So a 5/8-18 would be a good size to go with? How long? I am guessing just past the shoulder would be good, or doesn't it need to go that far. Minimum flame channel is what we need with LR primers. What would ideal flame channel diameter and length be before it gets to powder? Can I counter bore the front of the plug so powder falls down in it?

Is there any factory (T/C, CVA, Traditions) that would fir the bill with some modifying, or would it be better to start with a grade 8 screw?

Sorry for all the questions. I want to do this once the right way.

Thanks!
Denny

[dave d.]

:)denny just past the shoulder will be fine and as far as flame path stay with in 1.2 and you will be fine with lrms. I have used t/c plugs with cut down cases but they are to short (work great in a break gun ). Imo the plug edge just did for his marlin is a nice easy design. I'm not sure how long it wound up but if is longer then 1.2 you can just recess it back. Maybe edge could show a pic of his latest plug.

[edge]

I used a 5/8 - 18 x 2" set screw. If you are going to tap it for a vent liner you will want to anneal it as they are through hardened in the 50+ Rc range.

here is a sketch for the 40 caliber plug. I made the plug with a slight taper that slightly flares the open end of the case to keep any blowby from escaping the case and it ensures perfect alignment of case to BP.



Plug with 45 ACP:



Plug:



The flame channel is 0.950 to the end of the bushing.

edge.

[denphillips2]

Thanks Dave! Wasn't thinking about a factory plug being too short.

I like the way yours is though out Edge. If I remember right you had the carbide bushing laying around. Any idea where to get one? I am assuming that using carbide will just make it last so much longer.

Looking at the picture, looks like about an inch of threads. Do you think it would be better to have a shorter case and a longer thread section? Guess it might get harder getting the case on the plug when loading and you would loose some of the hex for the socket to bite on.

Where it shoulders in the barrel. You have it undercut, I am guessing just under bore dia. Key is to have a flat mating surface between pug and barrel to prevent any gas leakage, right?

Thanks for your help!
Denny

[edge]

There is about 0.650 of threads.
While there are not a lot of threads, this is a centerfire action and the case needs exact headspacing. This is a lugged action unlike the Savage ML.

This is a 40 caliber plug and the last lip is 0.398 in diameter to just slip into the bore.

The OAL was determined by the existing barrel threads that came with this particular barrel.
Had I started from scratch I may or may not have designed it this way but since they were already in there there was nothing for me to do.

On your Remington I would just go past the recoil lug.

edge.

[guppy]

I got a quote for some carbide bushings if anyone is interested. $40.00 right now each but if we order enough there could be a price reduction. Let me know if your interesteed and and we can put an order together. Kevin

[Jon]

Guppy. Sounds interesting. Who would either make or modify the plug. Preferably new and better design. If so put me down for a couple I have one more build I would like to do. I've never try-ed a bushing I modified a plug to except one but as soon as I fired a primer it blew the bushing out. I'm sure it wasn't a tight enough fit even with lock tight. I got into experimenting with different vents and never got back to it.
Jon
Jon

[jims]

I am with Jon. I have one carbide bushing BP by RB. I also have his recessed that uses vent liners. It is just easier for me to change vent liners than to find someone to put in a new bushing when it goes bad and the cost etc.

[denphillips2]

Let me know the dimensions of the plug. I may be interested.

I am still pondering exactly how I want to do it, but it will be along the lines of the one Edge did.

Edge, if you were to do it any way you want. IE Breech plug first. Would you go with the 5/8-18 threads?

Thanks!
Denny

[dave d.]

:)denny go 5/8 just for the fact that you can grap a set screw and machine away. I tried finding 11/16" with no luck.

[edge]

Using a standard size thread makes things easy if you are not making it from bar stock as I normally do.

If I were not using a lugged action I would want more threads than I have on mine.

edge.