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Touch hole behind Nipple too large?

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If the threads are completely gone, what size does the hole measure? That will determine what size thread you can step up to.

How accurately can you measure the hole size? Based on your earlier posts guess you are using fractional drill bits to measure. Will need a bit more precision than that (.015”). Ideally you could measure with gauge pins, but guessing you don’t have them. Next best bet is numbered and letter size drill bits. A 1/4-28 threaded hole for example requires a #3 drill (.213”).

Once you know the diameter, TOW sells 1/4-28 taps in +.005 increments up to +.025. For a reference example, to tap to the plus +.025 1/4-28 (.275x1/4-28) you would need a hole of .238” drilled with a letter B drill before tapping. You would then order the appropriate oversized nipple from TOW and be on your way. It is not recommended to just use the oversized nipple and ‘hope’ there are no issues (stuck or blowing out nipple for example).

If the above seems overly complicated and/or you do not easily understand it, suggest you find a competent gunsmith or machinist to make the repair. If this gets messed up much more you will have to replace the breech plug, View attachment 16168 an even more challenging task.

I would not recommend a Helicoil repair for a nipple tread, although others may disagree. One major barrel manufacturer has had one or two barrel recalls for doing that exact thing.

Hey thanks.

The hole is an original for a 5/16 nipple. Wich should be 0.312" In millimeters 7.935, on my measurement it says exactly 8millimeters wich would be 0.315"

However when i look at the 8mm 5/16 nipples on ToW it says their base diameter is 0.370" ?

I was actually going to buy a tap that is 10mm or 0.390" and get a nipple accordingly but it seems the 8-1.25 or 5/16 nipples actually are the biggest ones? :-D

Like you say if i mess it up i don't get a second chance but i think i'll be fine. Question is what size would be most likely to succeed in tapping it larger, if it's too small it might not work.
 
Whether a oversize nipple thread can be used or not depends on how badly the existing threads in the gun are damaged.

The oversize nipples for a 1/4" thread come in sizes that are .005 to .025 larger than standard. That is they go from .255 to .275 in diameter with a standard 28 threads per inch pitch.

These are made to replace nipples that have become loose in the hole. They are not made to fix cases where the old threads are completely stripped out.
In other words, if a normal nipple kinda rattles as it is screwed in, these oversize nipples are fine. If there isn't much if any of the old thread left in the hole, these oversized nipples should not be used. There won't be enough of the thread in the gun to engage the nipple with enough strength to be safe.

Put another way, a standard 1/4-28 thread has threads that are .016 tall. (.250 major diameter - .219 minor diameter = .031. .031/2 = .016 thread height).

If most of a 1/4-28 thread is gone so there are only traces of the old thread left, the hole, for all intensive purposes will be .250 in diameter.
If .275-28 threads are cut in that hole and a .275-28 nipple is screwed into it, the amount of thread engagement will be .0125. (275 major diameter -.250 minor diameter = .025. .025/2 = .0125 ). Basically, the new threads will have lost 20 percent of their engagement.

IMO, loosing 20% of the engagement might be OK for normal thread applications but when it comes to the high pressures and explosive speed of the pressure rise when the powder fires, it is not a good way to go.

That gets me back to the 1/4-28 Heli-coil as being perhaps the best option.
Any good gunsmith can install one of these but before he starts, if he is not familiar with black powder guns, point out that the new screw thread insert cannot cover up the flame channel and the 1/4" length of the shortest Heli-coil in that thread size might need to be trimmed slightly to keep the flame channel hole open.

Thank you very much :) If i decide to take it to a smith, wich i guess would be the smartest thing to do, this helps alot! Thank you.
 
What brand is the rifle? That will tell us the size of the nipple threads.

As a mechanic I've used lots of Heli-Coils. I've long had all the expensive Heli-Coil tools but still don't like the things. About 50 years ago i discovered Keensert thread inserts. Simply drill the hole to a standard oversize, thread and install the Keensert.

i've repaired a few muzzleloaders this way using a 3/8X16 Keensert which has 1/4X28 internal threads.

https://www.carrlane.com/en-us/prod...all/key-inserts-thinwall-stainless-steel-inch

Hey it's an enfield with the 5/16-18 nipple. Keensert thanks i haven't heard about that i will do some research thanks :)
 
Hey thanks.

The hole is an original for a 5/16 nipple. Wich should be 0.312" In millimeters 7.935, on my measurement it says exactly 8millimeters wich would be 0.315"

However when i look at the 8mm 5/16 nipples on ToW it says their base diameter is 0.370" ?

I was actually going to buy a tap that is 10mm or 0.390" and get a nipple accordingly but it seems the 8-1.25 or 5/16 nipples actually are the biggest ones? :-D

Like you say if i mess it up i don't get a second chance but i think i'll be fine. Question is what size would be most likely to succeed in tapping it larger, if it's too small it might not work.
Could please tell us who made your gun? It may help someone identify what the nipple thread should be.

Very confusing the way you are presenting the numbers.
  • If originally a 5/15 nipple it probably had a 5/15-24 thread, with the hole for the tap of .272” made with a letter I drill.
  • I have no idea what a 8mm 5/16 nipple is.
  • A 10mm x 1.5 requires a 8.50mm or .3346” drill.
 
Could please tell us who made your gun? It may help someone identify what the nipple thread should be.

Very confusing the way you are presenting the numbers.
  • If originally a 5/15 nipple it probably had a 5/15-24 thread, with the hole for the tap of .272” made with a letter I drill.
  • I have no idea what a 8mm 5/16 nipple is.
  • A 10mm x 1.5 requires a 8.50mm or .3346” drill.

The original nipple is a;

5/16-18 thread, for English mfg. Parker Hale Enfield musket
  • Cone length: 0.475"
  • Thread journal length: 0.275"
  • Overall length: 0.750"
  • Diameter of base: 0.370"

A 8mm 5/16 nipple is;

8-1.25mm metric thread, for Euroarms Italian replica Enfield muskets,
  • Cone length: 0.475"
  • Thread journal length: 0.275"
  • Overall length: 0.750"
  • Diameter of base: 0.370"

Thanks, what nipple would fit into a .3346" drill then?
 
Since the hole is 5/16 in diameter could i just tap it with a 3/8 without drilling it you think?

And what nipple would fit in a 3/8 ? Are there even that large nipples or would i need to coil it?
 
Seems i need a 0,3281(21/64) hole to put in a 0.3125" (5/16-18) helicoil and the hole is currently 0.3150" diameter.

So i would need to drill it up abit then i guess. Damn really thought there were nipples larger guess i've got no choice but to use a helicoil.
 
Hmm looked around abit some people suggested to TIG weld the hole and retap it to 5/16.

I'll see what i choose to do, anyway thanks guys for helping me out i seem to have all the information i need now.

:)
 
As far as the channel going from the nipple to the actual bore it can't be too large (unless it's bigger than the bore :)). The nipple will not be subject to any more pressure (or any less) than exists in the barrel at any time regardless of whether the flash channel is large or too small. I shoot an original '61 Springfield and the passage from the bolster into the barrel is as large as the largest drill bit that will fit through the "clean-out" screw hole, no problems.

Welding the nipple hole should only be considered as a last resort.
 
What brand is the rifle? That will tell us the size of the nipple threads.

As a mechanic I've used lots of Heli-Coils. I've long had all the expensive Heli-Coil tools but still don't like the things. About 50 years ago i discovered Keensert thread inserts. Simply drill the hole to a standard oversize, thread and install the Keensert.

i've repaired a few muzzleloaders this way using a 3/8X16 Keensert which has 1/4X28 internal threads.

https://www.carrlane.com/en-us/prod...all/key-inserts-thinwall-stainless-steel-inch
These things Keensert inserts look very handy, but I am skeptical about using them for a muzzleloader nipple thread. I understand you are a mechanic, but here is my observation from an engineering perspective.
  • Per the instructions the inserts threads require a ‘slightly’ larger tap drill than standard to install.
  • The 1/4-28 to 3/8-16 Keensert instructions says to use a letter Q drill (.332”). This results in a 53% theoretical thread. Generally not desirable, and possibly dangerous in a high pressure situation. The normal tap drill for a 3/8-16 tap is 5/15 or .3125”, about .030” smaller (a big deal in my opinion), resulting in a 77% theoretical thread, much stronger than the 53% thread recommended by insert manufacturer.
  • The change from 1/4-28 to 3/8-16 also increases the area exposed to chamber pressure almost 150% (.332 diameter tap drill has an area of .087sq”, the .213” tap drill has an area of .035sq”), putting even more stress on the threads.
  • Would not attempt on my gun or suggest to any else. For giggles and kicks, 10,000 psi (not an unreasonable chamber pressure with black powder muzzleloaders) results in an increase of force on the threads from 350 pounds on the 1/4-28 thread, to 870 pounds on the 3/8-16 threads. The compromised 53% threads. Don’t want my face right behind that nipple.
 
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The original nipple is a;

5/16-18 thread, for English mfg. Parker Hale Enfield musket
  • Cone length: 0.475"
  • Thread journal length: 0.275"
  • Overall length: 0.750"
  • Diameter of base: 0.370"

A 8mm 5/16 nipple is;

8-1.25mm metric thread, for Euroarms Italian replica Enfield muskets,
  • Cone length: 0.475"
  • Thread journal length: 0.275"
  • Overall length: 0.750"
  • Diameter of base: 0.370"

Thanks, what nipple would fit into a .3346" drill then?
A M8x1.25 tap requires a 6.70mm or .2638” tap drill.

After the dribs and drabs of information, I would suggest this is not something for you to tackle by yourself. Find a gunsmith, machinist or toolmaker and ask them to correct the problem. My approach, again, based on what you have posted, no pictures nor having the gun in hand, would be to set up the barrel in a Bridgeport type milling machine, find the center of the thread hole and then have at it. I would open the hole up to the appropriate size for the smallest insert that would work and allow a 5/16-24 thread bored in it after installing it in your bolster (drill, tap, make sure it doesn’t block powder channel as Zonie recommended, Loctited and staked into place). Result would allow you to use a ‘standard’ 5/26-24 nipple. Believe this is one project you have to hire out.
 
As far as the channel going from the nipple to the actual bore it can't be too large (unless it's bigger than the bore :)). The nipple will not be subject to any more pressure (or any less) than exists in the barrel at any time regardless of whether the flash channel is large or too small. I shoot an original '61 Springfield and the passage from the bolster into the barrel is as large as the largest drill bit that will fit through the "clean-out" screw hole, no problems.

Welding the nipple hole should only be considered as a last resort.

Thank you, yes, the weld will be if all else fails :D thanks for your reply apiritated!
 
A M8x1.25 tap requires a 6.70mm or .2638” tap drill.

After the dribs and drabs of information, I would suggest this is not something for you to tackle by yourself. Find a gunsmith, machinist or toolmaker and ask them to correct the problem. My approach, again, based on what you have posted, no pictures nor having the gun in hand, would be to set up the barrel in a Bridgeport type milling machine, find the center of the thread hole and then have at it. I would open the hole up to the appropriate size for the smallest insert that would work and allow a 5/16-24 thread bored in it after installing it in your bolster (drill, tap, make sure it doesn’t block powder channel as Zonie recommended, Loctited and staked into place). Result would allow you to use a ‘standard’ 5/26-24 nipple. Believe this is one project you have to hire out.

Hey, well i've worked as a welder and i'm pretty handy, after looking at some youtube videos i wouldn't say this is something that requires any skill to be honest.

It could be that we are using different measurements that confuses everything. I've never tapped before so i was unknowing about the difference in thread diameter and actual drill diameter.

I can't tap it to 5/16 since the diameter of the actual hole is the size for tapping it to 3/8.

That means i'm going to have to tap it even larger and there are no nipples large enough.

So the only resort left is drilling it up to a 5/16 or 8,3mm (currently at 8.0mm) and then tapping it to a 3/8 or m10x1,25 mm tap.

That will fit a 5/16-18 helicoil in the new tap and i will be able to place the original nipple. (I've found some nice tapping kits with the right helicoils, drill and tap as a package so i won't fail there :D)


It's not really that hard but took a while to understand :D However, if it fails since i don't own a TIG i'll go to a gunsmith and ask him to weld it together and retap it to a 5/16.




But thanks for your input apritaited :)
 
Another option would be a thread insert, but you would need to set it up in a mill to keep it aligned.

AntiqueSledMan.
 
Per the instructions the inserts threads require a ‘slightly’ larger tap drill than standard to install.

The larger size drill is recommended because of ease in seating the locking pins. i used a larger drill, ground the pins off and used Lock Tite.

Yep, the pressure is being applied through a flame channel about 1/8" in diameter.
 
What brand is the rifle? That will tell us the size of the nipple threads.

As a mechanic I've used lots of Heli-Coils. I've long had all the expensive Heli-Coil tools but still don't like the things. About 50 years ago i discovered Keensert thread inserts. Simply drill the hole to a standard oversize, thread and install the Keensert.

i've repaired a few muzzleloaders this way using a 3/8X16 Keensert which has 1/4X28 internal threads.

https://www.carrlane.com/en-us/prod...all/key-inserts-thinwall-stainless-steel-inch
IMO, the problem with using Keensert's and ring locked screw thread inserts is their external thread size is usually a much larger standard thread.
For example, a Keensert Thinwall insert with a 1/4-28 UNF internal thread has a 3/8-16 UNC external thread (.375-16 UNC). This external thread is much too large for most of the applications found in most muzzleloaders.
For a 1/4-28 UNF helicoil, the external thread is a .300-28 thread.

EDIT:

For a 5/16 internal thread a Keensert insert needs to have a 7/16-14 UNC thread (.437-14 UNC). A 5/16 internal thread Heli-coil has a .388 major diameter external thread.
 
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What we used to do if clearance was an issue, take the next size smaller, drill & tap to what you want. Then you have a smaller insert with your threads in it. Sometimes we just used a bolt & put desired threads in it.

AntiqueSledMan.
 
For example, a Keensert Thinwall insert with a 1/4-28 UNF internal thread has a 3/8-16 UNC external thread (.375-16 UNC). This external thread is much too large for most of the applications found in most muzzleloaders.


Yep, it often can't be used.

i used an O or P drill, forget which. Made a great installation on the guns i repaired.

Heli-Coils are OK for applications where the threaded component is seldom removed. But regular use often results in a buggered coil.
 

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