ronlaughlin

I don't know for sure, but from what he has written, i don't think Mike has looked much at an Accura breech plug. If he has he can fix what i say. Otherwise, please allow me to jump in here.

The flash hole of the Accura breech plug is only about 1/8" long. There isn't enough steel there to 'add much more of a concave end to what's already there. This is why i intend to install a vent liner in said breech plug. Installing a vent liner will allow one to make more of a concavity.

Please forgive me, if my intrusion here is unwelcome.

Breechplug

O.K. Mike, but I was just trying to figure out what was best for the use of Loose Powder with the end of the BP. If it was better to have more of a concave end with powder then I was gonna try and give it a little more (concave) As for CVA spending some time on the BP, most of My CVA BP's are the same on the ends, I dont think they tried hard enough or spent enough time.
Thank's for your thought's.
(BP)

sabotloader

Breechplug

I am not really sure whether more or less is the best answer - I believe it is best to have the concave end on the BP. It seems to me it is easier to ignite the tip of the cone of powder and let that burn through the bulk of the powder.

Again the problem that I am trying to help is blow back through the nipple - not ignition. I think if you want to help ignition (if you are having a problem is to install the Lehigh Vent Liner in the bottom of the concave cone of the BP.

Breechplug

Yes Mike Blowback is what were doing here sorry.....I have NO problem with ignition, it was just a passing thought that went with the redoing of the Flashchannel. Im getting the BP drilled out tomorrow and I'll let you know how it goes. I should be able to shoot too as our temps are gonna go up, finally, from below zero to 20.
Thank's Mike
(BP)

sabotloader

Breechplug

When you close your Accura is the primer held in the primer cup tightly against the breech block? If you were to check your Triumph - I think you will find that the primer is held fairly snugly in the primer cup as you pull the trigger guard up to the closed position... This certainly helps reduce blow back also.....

I could show you a prime example of this with my Omega and the 25 acp conversion if you want to drive a few thousand miles...

I think lee has also pointed out that there is no standard length in the world of shotgun primers... Winchesters being the longest - near .030 and Cheddite being one of the shorter @ .286 in length

kb1

i believe you hit the nail on the head here for a blowback free ML.
i have three guns here that are blowback free,the triumph,knight vision and nef sidekick with metrics unlimited BP.
the triumph's toggle lock pulls the barrel assembly tight to the receiver and snugs up the primer tight in the primer pocket sealing the breech.the vision effectively does the same thing as it slightly crushes the primer when you close the action.
the metric's plug uses an o-ring to stop blowback as again it seals the breech.the metrics plug also does not have flash channel.when i had a knight shadow the simple addition of an o-ring turned that gun into a 100 % blowback free gun that shot blackhorn 100 % even in very cold temps.i do believe your on the mark with the larger flash channels helping with the carbon build up and really like the vent liner mods you folks are doing.i am going to try making a brass shim for the NFPJ plug for my disc-xt.this will go in the primer pocket to see if i can get a 100% seal
(it's only about 95% now)this thread has been a very interesting read.good luck to all.........karl

Breechplug

Mike, when the ACCURA is closed it is tight so I cant see what's going on with the Primer and if there's any room inbetween the primer and breechblock. I mostly use T7 Primers, Win W209's my second choice. I have'nt checked to see wich primer leaves the most blowback but I will. I just checked and the Win W209 Primers are a tad bit bigger than the T7's
Ron (BP)

sabotloader

Breechplug

Correct the W209's are slightly thicker in diameter than the Win T7 primers. so they should fit a little better.

Here is a picture of the primer sitting in the pocket on the Triumph. If you lay a straight edge across the primer and the breech plug - the primer is just slightly and I mean slightly taller than the edge of the BP. With the gun closed but not latched you can feel and see the BP touch up against the breech block. When you close the trigger it seems to tighten it just a bit more. This is a Win T7 primer in the cup. I can not actually say that the block presses on the primer but it is very close to that. If the primer expands in length at all during ignition it sure would be.

Breechplug

Sabotloader the Win W209's are also a tad bit longer than the T7's. With some of the longer primers would this cause the primer to be pushed in too tight to the BP and block? I know it's o.k. to be a tad bit loose with the shorter primer but what effect does the longer primer and tighter fit cause if any? I know they cant make the BP and Block to fit just one type of primer so there has to be some kind of clearance to fit all types, but can the longer primers be crushed when the breech is closed damaging the primer?
(BP)

sabotloader

Breechplug

Agreed think I got .305 for the W's and .301 for the T7's

I think the companies have made allowances for the different length primers in tier designs...

It would be my belief that you can compress the primer some and not cause an adverse effect, but if you compress it to much you might cause the primer to become pregnant upon shooting making removal from the primer cup more difficult. Think that is one reason the T7 primers are less in diameter than the normal W209.

I do think you could 'crush' or overcompress a primer...

Interesting experiment for you with the type of BP you have in an Accura. Turn the breech plug out a few threads. To the point that the gun will not close - then back in just enough to get the gun closed. Insert a primer and see if the gun will close. If it does pop the primer - what does the area look like? Keep moving the BP in and testing to see if at some point there is a difference in material you see in the firing pin area.

Busta has installed 'O' rings under the primer to take up the space and get some primer compression.