Original Blunderbuss - Reworking the Trigger Guard

[Pukka Bundook]

Dave,
When a couple of us back home made a 4 bore barrel, the proof load we used had for  second proof less powder as shown in your chart, but a heavier charge of shot than first proof.
In the above, I can not see any increase in projectile weight for second proof.

I'd have to look up the specifics, as there should be more projectile weight for second proof, but less powder.

[Hudnut]

That chart is for rifled barrels - which would normally operate at a higher pressure than smoothbores.
What would a load of buckshot weigh?  Two or three ounces?  Service load of powder might be 100gr?
How about 150gr Fg powder with 2oz buckshot, followed by 4oz buckshot over 100gr Fg powder?
Unless someone were really pushing things, those loads are unlikely to be exceeded.

 

[Daryl]

I would suggest that a 7 bore would use 4 to 5 drams of powder for a "service" charge
considering today, 4 and 4 1/2 drams of powder is a "service" charge equivalence for a 10 bore shotgun.

[davec2]

Thank you guys for the comments.....I found an old chart in a 1972 Dixie Gun Works catalog that had some Belgian service and proof charges.  The service charge was 158 grains behind a 7 gage round ball but the proof charge was over 500 grains !!!  I like the idea of perhaps 180 to 200 grains as the proof charge behind 3 oz of shot for the first proof.  Less powder and a little more shot for the second.  The barrel is only 12 inches long, so I really don't want to fill it half way with powder and then a load of shot  ....I could be inadvertently testing that old black powder BS about "oh you can fill the whole barrel with powder and it would still be fine !"
Thanks again

[Daryl]

5 drams is 135gr.

[Dphariss]

Nice historical piece, David. The lock is nicely done.

Would you machine the barrel from a simple brass bar?  Going to be a lot of brass chips on the floor after machining that cannon muzzle.  And do you have the means of drilling the bore?  Is it possible to cast that barrel?

Love the shortness of the piece - just over 2' in length; right tidy for crowd-control work.

Going to be an interesting follow-along.  Walnut stock or maple.  And will you tackle the barrel first, or the lock?

I would be astounded if the original barrel was brass. The British knew better and its surely the same bronze, naval bronze is the common name, used in cannon. Brass is NOT suitable.

[Dphariss]

My 1896 edition of WW Greener’s “The Gun and Its Development” . But the British had a more energetic prood than Belgium did in most cases or so I have read. Not do I believe that barrel length for long arms made much difference. And in a bore this large 500-600 gr is not going to take up a lot of space. Track sells .760 RBs which weighs 661 gr which is not far off from some of the loads in this table for a 7 bore. And should work if properly wadded or add a .54 ball on top. The British, if I have read correctly, used a faster BP for proof than would be typical in a service load.

[davec2]

Dan,

Thanks so much for the information.  I am quite sure the barrel on the original is brass and not bronze just from the color of the metal and the color of the verdigris on the underside.  What particular alloy of brass I am not sure.... but I may have a contact that has a hand held XRF (X-ray fluorescence) analyzer that can non destructively tell me exactly what the alloy is.  We will see how the proof testing goes with the 485 Naval brass alloy I selected for the barrel.  I also know that the 4 bore barrels I have used from Ed Rayl are brass and not bronze, but I do not know what alloy he used.  I will say that the breaches on these barrels are fairly stout. 

Here are some comparisons between 485 Naval brass, 464 Naval bronze, and 4130 steel........







I guess the proof test will determine if I wasted my time making the barrel out of 485 or not 

I do have a question about the table you sent.  What is the difference between a "definative" and a "provisional" proof?  And what does First class, second class and third class mean?  Are they just proofing the barrel three times ?

Thanks for the help on this.

[davec2]

Just for fun I put 600 grains of FFg in the bore.  It filled the 7 bore (0.875 in this case) between the two blue tape marks....i.e. the brass showing between the two pieces of tape is the length of the bore filled with 600 grains of powder.  Looks a little excessive to me.....but what do I know 

[Justin Urbantas]

Are you putting in 2 balls? You have a temporary breech plug on it?

[davec2]

Temporary breach plug made of the same steel I will use for the actual plug.  Haven't decided about the projectile.  Might just use a charge of lead shot that weighs what the proof tables prescribe.  However, looking at the amount of powder that the tables call for is still giving me pause.....although a fair amount of a powder charge that heavy may get blown out of that short  barrel and just burn in the air.  Not sure.

[JTR]

When you get around to it, I'd sure like to see a video of that test! 
Hopefully, John 

[davec2]

John…. Rest assured I will video the proof test!!

[davec2]

On my way to Seattle but had a chance to start on modifying the butt plate I had to match the original more closely. Just needed some bending and trimming to make it narrower and shorter.

[davec2]

I had a little time between business trips to look at the barrel again and make some decisions about proof testing.  The first thing I realized is that I didn't really like the profile of the new barrel.  I had taken the easy way out and, in cutting the outside taper, I had just used the compound on the lathe.  The travel is only about 4 inches on my compound so I had to cut the full length taper in three sections.  Then I cleaned up the surface with a lathe file and then various grits of abrasive paper.  The result was OK but after closer inspection is was a little...well....lumpy.  You can't really see it with the naked eye, but I could feel it running my fingers over the surface.  It bothered me so much that I decided to recut the taper.  And if I was going to take off more metal, I should do that first before I did the proof firing.  So I re-cut the taper properly.  I took the time to calculate the offset required on the tail stock, off set it, and then ran the taper cut in one pass with the cross slide in auto feed.  Came out great and feels right now...   (The hard part here is getting the tail stock back on center....not really hard, just time consuming.)  As soon as I get back from my next short trip I will build a test fixture and take the barrel out to my test site to run the proof firings.

[Hudnut]

That looks really good.

[Pukka Bundook]

You have done a grand job Dave, but a shade more  would be wonderful!

[JTR]

You have done a grand job Dave, but a shade more  would be wonderful!

Mmm, Maybe just the difference in color between the two barrels, but the original barrel appears to have more taper than your new one?
John

[davec2]

JTR,

Both barrels measure 1.390" at the breach.  The original barrel measures 1.178 just behind the decorative collar.  The new barrel measures 1.195 at the same location.  So the taper is different by 0.017 on the diameter and 0.0085 on a radius.  So you are correct....the original barrel has more taper by eight and a half thousanths of an inch.  Close enough I think.   

[davec2]

I'm going out to my Mojave Desert test site for some work related stuff tomorrow.  It presented a good opportunity to proof test the barrel since I cannot really do the test in my backyard here in town.  So I quickly make up a wooden fixture to hold the barrel while it is being fired.  I will use the British Gun Barrel Proof Act (1868) table for the first and second charges.....473 grains of powder for the first and 315 for the second.  Both will push 2,100 grains (~5 oz) of lead shot.  I will set it off electrically.  A service charge for a 7 bore is 158 grains of powder behind a ball half that weight.  I think this is sufficient for a proof test.....

Here is the fixture.  The cross piece over the barrel with be bolted in place tomorrow.

[JTR]

Well that's certainly close enough!

Even now, knowing the small difference, the original (darker) one looks to have more taper. It must be the old shinny vs. dark illusion trick!

John

[davec2]

Ran the proof test today. First proof was 473 grains of 1F powder, 315 grains for the second test. Both pushed 2,100 grains (~5 oz) of lead shot. I set it off electrically each time. Just to give you a feel for how large the charge and shot column were, on the first test they took up 7 inches of a 12 inch barrel. The second proof charge took up 6 inches. Here is the set up .....I have a video but do not know how to post it here....Fairly dramatic !!  If anyone can tell me how to do it I would appreciate it.  In the last picture here, I remeasured the barrel after the two tests.  All the original barrel diameters at 1 inch intervals were the same both before and after all the testing.  I'm calling it good.

[snapper]

You ever wonder how many cracks you are creating by doing the proofing? 

A few years ago, I had some research money at Iowa State University for acoustic emission testing of anhydrous ammonia nurse tanks that were undergoing hydrostatic pressure testing.  The research showed that some existing cracks were caused to grow, and others were formed as the result of higher test pressures.

Not saying you should not have done this, but I always wonder on proof testing if perhaps we are simply creating cracks for another day.

Your barrel did not go beyond yield, that is good.

Fleener

[davec2]

Snapper,

I understand.  In my aerospace experience we usually design with only a 25% factor of safety on yield and then do a five cycle hydrostatic pressure test to just below that point.  It is always a question if a sixth cycle would have caused a failure....or a seventh...etc., etc.  But at least in the rocket engine world, the statistical analysis says if it can pass a five cycle proof test, it's good.  I'm happy with the two I just did on this barrel.

[JTR]

I hope someone knows how to post the video!