1. The Primer Pocket
2. The Fire Channel - that hole between the primer pocket and flash hole.
3. The Transition Area - the area that connects the fire channel to the flash hole.
4. The Flash Hole
5. The Face of the Breech Plug
6. QRBP: the Length - and this is what has been the driving force in causing us to have to pay more attention to the other five features.
So one GOOD feature works with the the next and so on and so on, but one bad one in the mix...refer to the bad apple story we've heard all our lives. But the best way I found for me to understand where the problems were was to break it down and look each feature. At the end of the day, everything is relative.
And one bad apple....
To begin: the Flash Hole
Only two things to look at here:
Diameter seems to be a big topic in the industry. You'll find conversations on blogs and forums all over the internet about this small, but pertinent hole.
Most of us want to make it larger, but others are fine with it the way it is. I'm one of those guys. Many have found that making it larger, especially in the case of the CVA Quick Release Breech Plug, does not necessarily fix an ignition problem. So in some cases, bigger is not better.
Flash Holes seem to run from around .026/.028 all the way (with our intervention) to .035. Why then do some work flawlessly at .026 and others fail at .035? For the answer, it's as simple as going back to the bad apple story. One breakdown / flaw in the fire flow from primer to powder and the bad apples wins.
Just what should the diameter be? From what I've seen in testing, smaller is better if it works. Reason being is because in most cases, a larger Flash Hole opens the door for more blow-back (same as blow by, I call it blow back). There are cases where this is not true, but there are a lot of factors that determine how much un-wanted blow-back a larger Flash Hole can cause, or not.
One manufacturer tells me they're worried about increased pressure levels on the frame at the firing pin / breech face on alloy frames from the larger holes. If they're concerned, I am too.
The next factor with the Flash Hole is it's Length.
In the case of the Thompson Center Speed Breech XT, that hole is .150 +/- and the CVA Quick Release Breech Plug is .138 +/-0. Which one is optimal? Well, again - all things are relevant and everything this hole sets between matters. From what I've seen, the length of this hole is not a huge factor if everything else is right - with no bad apples.
Now comes what I've called "the Face of the Breech Plug", which I'm going to call the Powder Pocket from here on out.
In my opinion, a breech plug that has a Powder Pocket or one that doesn't have one is a big factor. The one that HAS a recess to hold powder will always have my vote.
One of my readers has asked why I haven't mentioned the Omega Breech Plug and so for him, I have now. It is one of the most trouble-free factory breech plugs available, always has been. In large part, I believe because of the nice powder pocket design (and it is shorter).
I like this Omega pocket for two reasons.
1. the powder seems to be exposed to more fire as the fire exits the Flash Hole
2. it moves the powder closer to the primer
This pocket is one factor that allows the Thompson Center Speed Breech XT to out-perform the CVA Quick Release Breech Plug for reliability in ignition.
Whoa there, hold on! Hear me out and look at the photo of the two side by side. At first glance, it looks like the CVA breech plug should have less problems than the Thompson Center, I mean, it is a lot shorter. A closer look shows this:
The difference between the two breech plugs is that the Thompson Center has to deliver it's fire .434 further than the CVA.
So with all that said and keeping in mind that neither have great transition areas, why does a much longer, Thompson Center plug out-perform the much shorter CVA plug?
1. The Thompson Center's Fire Channel is a larger diameter
2. The Thompson Center plug has a much more defined Powder Pocket.
My vote goes to the Powder Pocket being the most important contributing factor here.The reason? I believe the fire is delivered in a much more efficient manner due to the Powder Pocket design. The CVA plug is obviously designer to shoot pellets and it does a great job with those, if that what you choose to shoot (but we wouldn't be talking about this if it were, now would we).
The new plug that Western Powder has designed has a very deep Powder Pocket.
When I write the article on that plug, I'll tell you more about it (dimensions, etc) but the reason it's so deep was to overcome the added length. It puts the powder around the same distance from the primer as the old-style , shorter plugs (namely the good ol' Thompson Center Omega plug!).
Just for the heck of it, I've thrown in some photos showing the above powder pockets full of powder:
For those of you not familiar with the CVA Quick Release Breech Plug, the shoulder you see around the top is not a Powder Pocket. That shoulder is part of the plug design that allows it to seal the plug to the barrel and keeps fowling from getting into the threads. For that purpose, it's an excellent design, as you will never find fowling in these threads and can always get the plug out by hand.
In closing this segment, I believe the Powder Pocket is a bigger deal than the diameter or length of a Flash Hole. Just as long as there's no bad apples in the mix, cause we all know that all it takes is one....
Watch for the last segment in this Breech Plug series: The Primer Pocket coming in a few days.
Till then, An Apple a Day (cleaning, cleaning and more cleaning) Keeps the Breech Plug Doctor Out of a Job!!!