Breech testing continues - Cupped breech inferior

[Larry Pletcher]

Today Steve Chapman and I finished the flat breech testing and did most of the testing on the cupped breech.  We have one more test we want to run with the Chambers WH liner, but we expect we know what the result will be.

To start here is a chart showing the comparison between flat and cupped breeches with different liners:


liner (clean/dirty)--------------------------flat-----------------------cupped

Pharris (.055 - .101)(clean)---------------.0398----------------------.044
(counterbored)
Pharris (same as above - dirty)-----------.0474----------------------.054

Pharris (3/32" hole)
(large hole w ext. cone-- clean)---------.0309---------------------.0378

Pharris (same as above-dirty)-----------.0377---------------------.0449

Chambers WL .064  (clean)--------------.0370---------------------.043

Chambers WL .064  (dirty)-------------.040----------------(next session)

With this session behind us we conclude that the cupped (dished) breech is inferior to a plain flat breech.  Every test done showed the flat breech was faster.  Whether the vent was carefully cleaned or left dirty, the cupped breech was slower.

Fouling continues to be the priority with all liners, with small straight holes to be the most likely to be affected.  Even the large (3/32) diameter holes suffered.  The following photos show fouling that is normally seen, but also some unusual areas.

You expect to see fouling on the surface of the liner.


Here is what we found below the liner.


And here is a shot of a "tube" of fouling being pushed out of the liner with a drill bit.  This formed in the Pharris large diameter vent.  The tube-shaped fouling has a funnel shape on one end where the external cone was located.  (Dan wondered about this.)


Here is another shot of the fouling tube next to the liner.


And here looking through the fouling tube.  There is no doubt that the liner diameter was reduced by this fouling.


So far we have not looked behind a WL liner to see if a layed of fouling is found.  We expect not.  We concluded that small diameter vents work well but must be kept clean.  We saw and heard slow times that the shooter would have been unaware of while firing his gun.  We also concluded that large vents and vents with large interior cavities are more forgiving when it comes to fouling. 

After what I saw today, I will continue to use a "cavity" liner with a large enough hole to use a pipe cleaner if necessary.  And I like the flat breech as opposed to a dished one. 

I hope Steve adds to this.  By now he may know what level of fouling he found behind the WL liner.
Regards,
Pletch

[chapmans]

Larry,
  I will do it in the morning, if I find anything significant I will post. As for the tests I was surprised that the cupped breech was slower in every test we performed, as for the reason,well I'm not sure but there is considerable more powder behind the liner, more powder means more fouling, also with the touch hole close to the breech face (in the flat breech) maybe there is more pressure at the vent. I do know what kind of liner I will be using from now on and where I am going to put the prime in the pan. I also would like to do some testing at the range with prb to see if the fouling is the same.
   I also wonder what the inside of a TC breechplug looks like, is it anything like the cupped breech we are testing?? I guess Larry will have to post a pic of the cupped breech.
   Steve

[Daryl]

The TC breeches I've seen were quite cupped, as were most Hawken cast bolsters.  Could the slowing ofignition of the cupped breeches have been caused by the charge powder being fully contained by the hollowed breech and not being right besdie the vert hole?

[Larry Pletcher]

The TC breeches I've seen were quite cupped, as were most Hawken cast bolsters.  Could the slowing ofignition of the cupped breeches have been caused by the charge powder being fully contained by the hollowed breech and not being right besdie the vert hole?

That is a good thought, but in this case the cup is shallow enough that most of the charge is forward of the edge of the cup. I'd guess that less than 1/4 of the charge would be needed to fill the cup - the rest being out in front.   I think Steve took the cup breech plug with him or I'd measure it.  i'll look for a pic.
Regards,
Pletch 

[LynnC]

Speaking of photos, I'd like to see a line up photo of the different breeches for comparison.  Thanks............................Lynn

[Larry Pletcher]

Speaking of photos, I'd like to see a line up photo of the different breeches for comparison.  Thanks............................Lynn

Hi Lynn,
Page 5 of Gun BUilding has a topic called "Breech timing Begins Tomorrow".  It has a number of pictures, but mostly of the setup for thetests.  I'll get a couple of the actual plugs and post them too. 

Regards,
Pletch

[Scott Bumpus]

I wonder if some of the fouling problem seen could be because of there being no projectile to build pressure.  It would seem that a barrell would build more pressure when there is a ball being shot.  This  pressure would help to blow the liner clear.  I know that when I have fired blank loads in muzzleloaders that the barrell will foul much worse than when shooting normal loads.  What's yalls thoughts on these ideas? 

[Larry Pletcher]

I wonder if some of the fouling problem seen could be because of there being no projectile to build pressure.  It would seem that a barrell would build more pressure when there is a ball being shot.  This  pressure would help to blow the liner clear.  I know that when I have fired blank loads in muzzleloaders that the barrell will foul much worse than when shooting normal loads.  What's yalls thoughts on these ideas? 

We gave that some thought and decided to use a sabot for that purpose.  In the trials where we did not clean, the sound of the report and the velocity of the sabot was increased - at least based on the human ear - in which I have little or no faith.

I should add that we found the fouling in the series where we did no cleaning at all.  In the "clean" trials we cleaned VERY carefully:
1. wet patch both sides
2. dry patch both sides
3. brushed the pan
4. vent pick or pip cleaner
5. compressed air thro vent
In those trials we can state that fouling did NOT enter into the results.  We did the "dirty" trials because in the real world fouling happens.

The difference between using a sabot in a 2" barrel and a ball in a 42" barrel we didn't address.  We are limited to inside work because our photo cells trip in normal day light.  We are working on a solution to this and hope to do outside testing thsi summer. (We are confident in the flat vs cupped breech result because we did trials with both in the same way.)

Regards,
Pletch

[Daryl]

Maplebutcher - I agree about vents staying cleaner - but your blank loads foul more as there is no cloth or paper patched ball to clean betwen shots.  These would leave only 1 shot's fouling or with really, rattly loose loads, a slowly building fouling, instead of a rapid build with no such pressure or scraping.

 The pressure spewing out the vent would indeed help to keep things cleaner down there, but it still builds, especially in long channel cap-locks. It will actually build until there's barely a hole through to the nipple's base.  I've pulled Hawken breeches, properly cast and designed as well as production 'Hawkens' with lock-plate slotted bolsters and found tiny foul-lined holes from the front ends of the 'cup' back to the nipple seat. Some, with upwards of 100 shots or more fired, will be full of fouling from the bottom of the 'cup' out to the end of the threads.  Flat-faced plugs stay much cleaner.

[Daryl]

Larry- some chronographs use a 'diffuser' above the photo cells to allow them to 'see' the bullet or ball more clearly.  These diffusers are opaque or frosted plastic sheet. I wonder if a frosted finish sheet of lexan above the pan, in the same 'light' would provide a means of shooting outdoors?

[Scott Bumpus]

I agree with larry,  for comparring differences this testing is accurate.  From what he has shown it seems the flat breech will be faster ball or no ball.  Daryl is right on, the worst cleaning job is after firing 20 blank loads.  I have a 50cal rice barrel that is waiting to be breeched according the these test results.  I eagerly await the nock breech testing.  THANKS AGAIN TO LARRY FOR THIS GREAT INFO!!

[Larry Pletcher]

Larry- some chronographs use a 'diffuser' above the photo cells to allow them to 'see' the bullet or ball more clearly.  These diffusers are opaque or frosted plastic sheet. I wonder if a frosted finish sheet of lexan above the pan, in the same 'light' would provide a means of shooting outdoors?

Ya, I use diffusers on my chrony.  It may work; however in teh garage the issue seems to be how sensitive the cells are.  I can leave flourescent lights on, but have to cover the windows.  The photo cells have a rubber spark plug boot with a piece of cardboard glued on teh front end. A small hole is drilled through teh cardboard.  The cells trigger immediately if teh boot is removed.  This evening I'll take a pic of teh photo cell and the boot.  I'm sure a pic is better than what I just writ.
Regards,
Pletch

[Larry Pletcher]

Daryl,
Here are the pics of the photo cells.  The first shows the cell with the boot as it is used in the fixture.  If we remove the boot the room light triggers the cell immediately.



Here is naked photo cell with the boot next to it.  In some ways needing to use the boot protects the cell from fouling and smoke.  It's barely 2 " away.


This last photo cell may be the answer.  We're testing it as a possible replacement.  If the new interface and photo cells work, we'll change over before the Apple IIe dies.


Regards,
Pletch

[roundball]

Today Steve Chapman and I finished the flat breech testing and did most of the testing on the cupped breech. 

What is a 'cupped breech'...do you have a sketch of one?

[Larry Pletcher]

What we tested were simply bolts that that were threaded into the breech plug threads.  The first one was flat - just like an ordinary bolt end.  The cupped or dished (don't know what to call it) was mildly hollowed out instead of flat.  It was maybe 1/8" deeper in the center - nice hemisphere shape.   Dan Pharris did the machine work on it.  Steve Chapman has it right now or I'd get a photo of it.  If Steve doesn't see this and snap a pic, I'll do it when I get it back.  BTW this next phase is where we'll do the TC vent  you sent.

Regards,
Pletch

[roundball]

Thanks...that probably explains the rounded tip shape of breech face scrapers I've seen in catalogs.

The powder chamber in TC's patent breech plug come down into a 1/4" diameter horizontal channel that comes in from the vent liner

[northmn]

I find some of the comments interesting.  I have had a gut level feeling that flintlocks seemed to perform best with a certain minimum pressure.  It seemed that too light of loads caused ignition problems and that a little heavier load seemed to blow thing clear.  For instance I felt I had ignition problems with loads below about 40 grains of 3f in a 45 due to fouling.  As I have used cuped breeches I still cannot see why one would be slower if clean.

DP

[Daryl]

When I switched to the warm weather accuracy load of 55gr. 2F, I had the odd misfire (flash in the pan) due to fouling blockage in the vent.  Pricking the vent always cleared the problem 'piece' of fouling and allowed it to go normally next fall of the cock.  When using 65gr. of 3F, this never happens - or when using 75gr. of 2F - same deal - never happens - they both develop much higher pressure.  With the light charge, 'it' happens and often enough to make me think about pricking the vent every shot just so it won't occur.

This could be related to the minimum pressure you spoke of, DP.

With cap guns and light charges, the hammer's pressure on the nipple keeps all the pressure inside and 100% of it's force is used to expell the ball. Not so with a flinter.  At some point, I get blockage with very light loads, and not with heavier ones.

[northmn]

When I cup a breech it is very near the bore diameter, just enough less so as not to have a ridge in the fit on the breech side.  I cannot see why there would be a difference in a clean barrel.  I have seen percussion patent breeches foul so badly that they need to be literally pumped out to work again.  I had heard of tests run that showed that the best English flintlocks were actually as fast or faster than some of the percussion guns with patent where the flame had to go through their longer channels.  Good to know someone else had the same experiences with misfires and light loads in flinters.

DP

[Larry Pletcher]

We recognize that there may be a difference in fouling with light and heavy loads.  It is one of a number of reasons that we ran one set of trials cleaning religiously.  If fouling was totally eliminated, we felt we could learn something about the breech.  I cannot speculate as to why the cupped breech tested slower in the clean trials.  It wasn't a fouling issue.  We wiped with two patches, used a pipe cleaner and blew compressed air between each trial. 

As far as testing with full power loads, that won't happen in my garage.  If our current photo cells would not trip in normal light, we probably would have tried outside as the weather improves.  The newer interface and photo cells that are undergoing tests may allow us to do that.  It's also possible that under a covered firing line we may find that we'll do better than we think.

Until we have either the weather or functioning photo cells, I'd stand behind our careful cleaning to eliminate fouling as a cause in our light loads.

Regards,
Pletch

[Daryl]

My post in no way was related to you're Pletch.  It was addressing the low pressure, vent misfires noted by DP.

 Another observation dealing with that very phenominum is that with very low pressure, or high spring weight in cap guns, is the 'disk' of fouling or paper oft left at the top of the 'tube'.(nipple) This will, at times assist in producing misfires in cap guns, unless cleared prior to recapping the tube.

[Larry Pletcher]

My post in no way was related to you're Pletch.  It was addressing the low pressure, vent misfires noted by DP.

 Another observation dealing with that very phenominum is that with very low pressure, or high spring weight in cap guns, is the 'disk' of fouling or paper oft left at the top of the 'tube'.(nipple) This will, at times assist in producing misfires in cap guns, unless cleared prior to recapping the tube.

I took no offense at your post.  If I gave that impression, it was my fault.  I was surprised to find the disk of fouling behind the cylinder-hole liner but shouldn't have.  When Steve took the test barrel apart, he did NOT find that disk of fouling in the open cavity WL liner.  That is to be expected too, I think.

It will be cool if the photo cells would work under our covered firing line.  The data we're trying to collect could be verified with a normal load.  BTW we appreciate the ideas from the list.   It really helps to run theory past you fellows.  My overwhelming concern is controlling variables, and your thoughts help to comfirm our methods.

Regards,
Pletch

[Dphariss]

Some of the powders we have today are not really that great in some breech designs.
My Nock breech needs a pretty good powder to be usable. I have an old can of FFG Schuetzen that fouls the Nock so bad it becomes non-functional in 3 shots or less.
If produces the large flakes of fouling and if one falls over the passage to the "antechamber" their is nothing at the vent.
With Swiss it can be shot as long as I want.
Since Goex also produces flakes I wonder if it will work in this breech.
I think newer Schuetzen is better from reports of cartridge shooters.
Knowing this I assume that by 1780s-90s the English had some pretty good powder.
Dan

[Dphariss]

Very interesting, again.
My take...
The fouling "tube" in the vent is *probably* pressure related. Higher pressure will tend to clean the vent.
But I don't think this is that critical to the testing though the vent obviously is going to form a better barrier to heat transfer when fouled.
If I can get out, snowing pretty hard right now ( naturally I told Daryl's wife we live in a Banana Belt here but weather does not show it right now..).
Was 40ish yesterday....
Anyway when I can I will shoot the 16 bore and take some photos of the outside of the vent clean, clean loaded and fouled/fouled loaded. It has a shop made "White Lightning" that is a little nicer than that sent to Pletch. The fact that the very close shop made "WL" is slower than the real "WL" shows that minor differences DO matter.
If I can do so I will take some photos through the cleanout and show the internal fouling.
I don't know why the cupped breech should be slow but there has to be some reason.

Doing *meaningful* tests at full pressure would require near full length barrels probably 24" to 30" and etc etc etc.
Due to the variables it is possible that a breech that tests slow with a squib load might be faster with even a 10-12" barrel. I would not be surprised if the Nock is "slow" in the current tests.
This does not mean the tests are invalid since the current tests are basically for testing pure speed of the vent and breech in lighting the main charge.
The Nock was meant to get the charge out the muzzle faster and by the technology of the time, how far a projectile would be cast by a given charge of powder, the Nock was either first or second. The tester in this case, W. Greener, claimed his design was better but....
But this was not scientific by modern  standards.
I expect as many questions as answers since this generally occurs when doing such things.
We really need to give our testers a round of applause.

Dan

[northmn]

I used a sort of nock design in the breech of a shotgun I built using a modern barrel so that I would not have to shorten it too much.  It is understandable that that design would foul out fairly quickly.  In a clean barrel it appears to work well.  It also needs a minimum charge of about 50-60 grains of 2f to avoid a gap between the powder and the shot charge.  Shooting it I feel the design is a usable one. 
I do not have even a vague idea why a cupped breech would have slower ignition.  While it might change pressures of equal loads to promote fouling, in a clean barrel I understand it.  The results are there, but I wonder if there isn't some outside factor.  Kind of like comparing velocities between smooth bores and rifles of equal caliber.  It would take quite a few different barrels from each to form a conclusion.  Or if you wanted to compare differences in vent liners, it might take a few of each.  Two different WL may give different results?  Just speculating.  I am even admitting the results might be valid.  I do not have any way to dispute them.

DP