CVA .50 Hawken nipple blow out.

[bpd303]

A friend was shooting his .50 CVA Hawken and had the nipple blow out on him shooting 90 gr Goex FFG with a 325 gr maxi-ball. The CVA manual lists 100 gr as the maximum load. He thought the nipple may have been cross threaded at one time.

I picked up an oversize nipple from TOW which is 7.1mm listed for the CVA with bad threads in the drum. I taped the drum out to 7.1mm and installed the nipple. The threads were good and the nipple went in and tightened up fine.

I proofed the barrel with the 325gr maxi-ball over a starting load of 70gr FFG, and checked the nipple which was still tight, then increased the charge to 80gr and 90gr checking after each charge and the nipple was fine. Then I fired 100gr and the nipple blew out again.

Any ideas as to why?

 

[slumlord44]

My educated guess would be that it had loosened up over time. I make a habit of checking everything when I clean the gun after use. Always pull the nipple when I clean it and make sure the nipple is tight when I reassemble it. Also use never seize to make sure it does not stick. Any other ideas?

 

[19 16 6]

For the nipple to blow out there must be a weakness in the threads.
Which thread striped, male on nipple or female in drum ?
O.

 

[bpd303]

I couldn't inspect the nipple because it flew off into the nether-land. Looking at the drum it looks like the threads there failed, although some are still visible only flattened some.

On a side note I decided to replace the drum with one I have from a barrel that is plugged. After soaking it with Kroil overnight, when I tried to loosen it the drum sheared off flush with the barrel. That also surprised me because I didn't use that much torque on it to have it break. When I tried to use an easy out to remove the remainder of the plug in the barrel it just acted like a drill bit removing material like it had been annealed very soft.

The barrels serial number starts with 86 xxxxxx so I think it was made in 1986 and wonder if near max loads all those years weakened the metal. Another thought is improper cleaning of the patent breech system may have corroded the interior of the drum weakening it. The bore is perfect but I don't know if the breech was flushed well enough.

I plan to get a new barrel from Deer Creek and make this barrel into a flintlock by drilling out the remaning drum & installing a vent liner.

 

[Rifleman1776]

As others have suggested, that blow-out could have been from any one of several causes. My guess is inferior nipple of soft steel. Or loose fit.

I plan to get a new barrel from Deer Creek and make this barrel into a flintlock by drilling out the remaning drum & installing a vent liner.

Genius. :applause:

 

[bpd303]

I don't think it was a loose fit because I had to use the nipple wrench to run the nipple down and it tightened up fine. I wish I could find the nipple to inspect it. I'll take my big magnet and sweep the area today.

 

[Shifty]

Those drums are very long and screw into the breech plugg on this gun( there was a picture of this system on the site at one time) and almost inpossible to get out best bet is have a machinist drill the rest of the drum out and make new one then start over, OR have the barrel cut and rebreeched to a regular breeech plug and drum arrangement. I have done the latter myself on a couple and had no problems.

 

[hawkeye2]

Though not often discussed overtightning of a nipple can cause major problems. Overtightning will distort the threads seriously weakening them. It can also actually start the process of shearing the threads off or to put it another way actually start the stripping process which will lead to the threads failing far below their rated working load. Using a lube or never seize makes it even easier to pull them down too tight. A combination of frequent nipple removal and overtightning leads to thread wear and possible failure. I do advocate the use of a lube to prevent the nipple rusting in and to make it easier to remove at a match. Good lubes: Breach plug lube, Choke tube lube, Never Seize, chassis grease and there are others.

A 7mm bolt has a maximum torque rating of 156 inch-pounds (13 ft-lbs) dry and 116 in-lbs (9.67 ft-lbs) lubed. 8mm: 18 ft-lbs dry, 14 lubed. 6mm: 8 ft-lbs dry, 6 lubed. 1/4"-28 grade 5: 10 & 7. A nipple needs only be tight enough to eliminate any axial play (slop) in the threads and snug enough to insure it doesn't work loose. As one can see from the figures above the force required to properly tighten a nipple isn't very high and can easily be exceeded specially if you have strong fingers. I regularly watch shooters tighten the nipple like they were tightening the lug nuts on a F350 and it does worry me. If nothing else it puts a lot of wear on the threads weakening them. BTW, the same applies to breech plugs.

bpd303 I hope you understand I'm not accusing you of overtightning but I did feel this was a good time to bring up this subject.

 

[crockett]

I don't think it should have happened. Some folks never take out the nipple when cleaning a firearm after a day of shooting. This can cause rust in the area and that may have weakened things. The other issue is the conical. A lot of folks are unaware that when you switch from a patched round ball to the much heavier conical that the internal pressures go up through the roof. There is some argument that with a PRB you cannot over charge the rifle- the excess powder just gets blown out the muzzle. I don't entirely agree but generally you are dealing with much less internal pressure with the PRB.
When you say blew out- I am assuming you mean the nipple went flying off the drum. Sounds pretty darn dangerous.
The fix- not sure- I think changing the drum is best.

 

[nkbj]

Any possibility of well lighted close up photos?

 

[19 16 6]

Seems like the drum is soft & there is your weak link.
Made that way, I would say & not softened or annealed over time through use.
All steels aint all good steels Sal.
I would be making up a new drum of the correct steel & hardened properly. Match those threads correctly so as to have max engagement & as another shooter mentioned "don't over tighten" the nipple. Go chimpanzee with the spanner, not gorilla.
O.

 

[hawkeye2]

"Go chimpanzee with the spanner, not gorilla." :haha: Well put, I'll have to remember that though I might substitute wrench for spanner.

 

[bpd303]

Well never could find the nipple and it did blow out of the drum. I was proofing it by securing the rifle in my workmate with plenty of padding, then firing it from a distance with a string and my Jeep between me and it.

Thanks for posting the problems that over tightening the nipple can cause. I've been working on muzzleloaders & firearms in general for 50+ years and forget that there may be some reading the thread who are novices.

I have removed several CVA patented drums & breeches over the years and am aware how they are constructed and know that removing them cancels any warranty from CVA.

When I tapped the drum the threads were good, snug enough that I had to use the nipple wrench by rolling it between my fingers to install the nipple with no slop and not overtightened. The nipple did not shoot loose on the lower charges.

The rifle is now fixed with a .54 cal barrel. I'll post later with the fix and pictures.

 

[Zonie]

Although the Lyman BLACK POWDER HANDBOOK & LOADING MANUAL doesn't show a 325 grain Maxi-ball, it does show a 350 grain Buffalo HP Conical in a .50 caliber barrel.

Using 100 grains of GOEX 2Fg under the Buffalo slug the breech pressure reached 12,100 psi.

The effective area of the 7.1mm thread is .0614 square inches so there was essentially 743 pounds of force trying to blow out the nipple.

A good 7mm thread should be able to take a force of over 1330 pounds.

This suggests that although you retapped the hole for the larger size, the parent material had already been damaged and had begun to shear (fail).

This could easily been caused by someone overtightening a nipple in the gun sometime in its past.

Even if the overtightening by itself did not cause the threads to fail, if heavy slugs and large powder loads were shot in the gun the combined forces of overtightening the nipple plus the powder gas pressures could have exceeded the threads strength.

How much overtightening would this take?
If the thread was good for 1350 pounds and the 100 grain powder charge created a force of 743 pounds force, that would leave 607 pounds in reserve.

If the nipple was torqued over a force of 25.45 inch pounds (2.121 ft/lbs) it would create over 607 pounds of load.
That plus the load from firing the gun could exceed the strength of the threads.

When the threads strength is exceeded, small cracks occur but to the naked eye they are invisible.
It takes a process like Penetrant inspection where a special fluid is applied and allowed to sink into the cracks to make them visible.

This all boils down to not overtightening the nipple on a percussion gun.
2.12 pounds of torque feels like almost nothing when twisting a nipple wrench so when installing a nipple, just tighten it down so it gives a little resistance and call it good.

 

[azmntman]

My pop had a fox river 50 blow the nipple. Came home with his glass blackened on one lens (thank God he was wearing em) and the nipple knocked his cowboy hat off as it went through (straw hat). I had the nipple switched and re-threaded and have not had a problem? Have not shot conicals though.

 

[hawkeye2]

Zonie, thanks for taking this to the next step. You have made an excellent point about the combination of the explosive force plus the preload over and above that created by torquing to the correct spec. It shows that a dangerous situation could be created even if the threads themselves hadn't suffered any damage (unlikely) from overtightning. It really scares me when I watch somebody tighten a 1/4 or 5/16 thread for all they are worth and then look directly at me and say "Gotta get em tight, don't want it to blow out".

 

[bpd303]

After inspecting the drum, I think the problem was found. Someone had drilled out the original clean out screw, which was 5mm and tapped it for a 7mm screw. This worked ok until I tapped the 6mm nipple hole to 7mm which did not leave enough material for adequate threads. The rifle probably would have shot all day without any problems with a patched round ball and less than maximum loads. The combination of the heavy conical + 100 grains of powder caused a breech pressure greater than the compromised drum could withstand. I also think that is why the drum sheared off when I tried to remove it.

The pictures are of the drum and a plug I removed from my .54 caliber barrel that Deer Creek said was done at the factory and couldn’t be removed.

It was fairly easy to get the plug out by clamping the barrel in my padded vice & removing the breech plug. Then taking a drift with a heavy hammer and driving the plug from the open breech about an quarter inch towards the muzzle then with a bore size steel rod and tapping it from the muzzle it popped out of the open breech.

I then installed the drum into the blank breech plug and bored it out into the drums flash channel. After reassembling the rifle I tested it with a .530 patched ball and powder charges up to the 120 grains of FFG
Powder that CVA says is the maximum load. First remotely, then offhand. I can tell ya 120 gr with a .530 ball will womp ya. I didn’t have any .54 maxi-balls but the barrel is a slow twist 1:54 and my friend said he could live with that.

Not sure if anyone remembers the thread about the CVA with a plugged breech.
http://www.muzzleloadingforum.com/fusionbb/showtopic.php?tid/290886/post/1427756/hl//fromsearch/1/

 

[bpd303]

BTW I decided to remove the plug and use the barrel after I removed the breech plug and got to looking at it. I blew down the barrel and air passed by the plug so I knew that it wasn't solid and the air was going by the groves in the refiling. I inspected the bore and it was perfect and had all the proof marks. Still don't know why CVA would have plugged it other than to have it as non firing as a display, maybe a salesman sample. The old drum looks like someone tried or did remove it using vice grips instead of a crescent adjustable wrench against the nipple.

 

[Rifleman1776]

Any possibility of well lighted close up photos?

I don't think he knows any photographers. :shocked2: :wink: :rotf:

 

[Billnpatti]

Well, I've never seen nor heard of such a thing as a plugged barrel such as you have. It's a mystery to me. :idunno: But, it sounds as if you did a craftsman-like job of restoring it to shooting condition. Good job!! :thumbsup: