Poor barrel threading

Austin

Well-Known Member
Anybody else experience this? you can see from the picture that the moderator doesn't go flush and their is a small gap. It doesn't affect accuracy or poi just a something that is annoying to look at.

mod.jpg
 

takbok

Well-Known Member
It looks like either the undercut on the barrel isn't adequate or there's a slight possibility that the threaded length is too long and it's bottoming out inside the moderator (moderator construction dependant. Post a close picture of the thread and it might be clearer what the problem is. A washer that's slightly thicker than the gap would temporarily solve the problem.
 

Miki

Well-Known Member
Is the crown up against something or is there a shoulder at the base of the thread (not undercut as @Ronin said) ?
Can you take the mod apart and look inside ?
Not effecting the accuracy is good ....
 

Edinburgh Rifles

Well-Known Member
Factory or man with lathe?

lets see the rest of the thread
had several mods where the length of thread internally is less than the length of the thread on the rifle
especially when 1/2" UNF is cut with about 15mm of thread length!

the crown bottoms out inside the mod

or as pointed out the undercut is not present
or worse ...as is the case with many rifle designed for a muzzle brake...cut with a step in excess of the OD of the thread itself!
 

Andy-shooter

Well-Known Member
Looks too big a gap to be a lack of undercut between the thread and shoulder. Most cutting tips have 0.25-0.5mm radius.

I’m guessing the threaded portion is too long for the mod or it’s a spigoted barrel and a normal mod.

Personally I wouldn’t be comfortable shooting that, the interface between shoulder and mod is what radially aligns the mod to the bore (unless it’s a spigoted barrel & mod) the threads are not necessary cut to a sufficient tolerance to ensure good alignment on their own.
 

Austin

Well-Known Member
Thanks for the replies.

just to add more details.

Its a factory remington 700 barrel.

The threaded bridge is what comes with these aim sport mod's so you can swap them between rifles.

I don't believe the thread length to be too long as when the mod is remove and looking into it their is a long way in till it could contact anything.

i have shot a few hundred rounds through this set up with no issues but possibly i haven't had issues because im shooting a 6.5mm through a 7.7mm mod.

Hear is some more photos with the mod off looks like the threading hasn't been finished (note im a sparky so have not machining knowledge)
 

Attachments

kennyc

Well-Known Member
Thanks for the replies.

just to add more details.

Its a factory remington 700 barrel.

The threaded bridge is what comes with these aim sport mod's so you can swap them between rifles.

I don't believe the thread length to be too long as when the mod is remove and looking into it their is a long way in till it could contact anything.

i have shot a few hundred rounds through this set up with no issues but possibly i haven't had issues because im shooting a 6.5mm through a 7.7mm mod.

Hear is some more photos with the mod off looks like the threading hasn't been finished (note im a sparky so have not machining knowledge)
looks like there is no undercut between the thread and the shoulder (see pic below), that would stop the mod engaging the shoulder (unless the mod had a recess to accomodate the non threaded area )
 

Attachments

Miki

Well-Known Member
Yup, no undercut at all, if that's a factory cut it's not right (surely ?). If it was done by a man with a lathe, it needs finishing. Either way. it's not right.
 

ejg

Well-Known Member
In my apprenticeship we learned to bore out the female threaded part to outside thread diameter 1 or two threads (overcut?). Stronger solution than undercutting the male threaded part. That is why some mil barrels do not have the undercut I presume. Hausken mods I have fit on my CTR barrels that have no undercut.
edi
 

Andy-shooter

Well-Known Member
Yep, thread isn’t cut right back to the shoulder and an undercut should have been used to eliminate the uncut part of the major diameter.

it’s a very easy fix.
 

Austin

Well-Known Member
Brilliant thanks for the help.
Looks like ill be getting a smith to sort it out once i can get it too them. ( toying with the idear of having it shortened as its a varment 24" barrel and its for stalking/foxing with no range use)
 

kennyc

Well-Known Member
In my apprenticeship we learned to bore out the female threaded part to outside thread diameter 1 or two threads (overcut?). Stronger solution than undercutting the male threaded part. That is why some mil barrels do not have the undercut I presume. Hausken mods I have fit on my CTR barrels that have no undercut.
edi
thats all well and good, but if general practise is to undercut the thread and moderator manufacturers build to that, then you are going to get this problem.
 

ejg

Well-Known Member
thats all well and good, but if general practise is to undercut the thread and moderator manufacturers build to that, then you are going to get this problem.
That is what you think, as I said in my apprenticeship in 1980 it was already general practice to choose the stronger option in situations where it is of advantage. Yes we also used undercut but we learned and calculated that it would weaken the connection substantially. Why choose the worse solution if a good solution is so easy?
edi
 

kennyc

Well-Known Member
That is what you think, as I said in my apprenticeship in 1980 it was already general practice to choose the stronger option in situations where it is of advantage. Yes we also used undercut but we learned and calculated that it would weaken the connection substantially. Why choose the worse solution if a good solution is so easy?
edi
It's not what I think it's common industry practise, they will have calculated the stresses involved and decided that this is the best way forward, or have you heard of multiple barrel separations at the muzzle thread ?
Im not disagreeing with your premise just stating reality
 

ejg

Well-Known Member
If the tgread relief is machined to root depth of thread (what I do) there is no loss of strength or integrity

A relief also works on female thread
Mostly to be sure it works the relief cut is done X deeper than the root, there probably is a DIN standard for that. Anyway it is exactly where the connection has the weakest point. Meaning one weakens even further. Every one can do the maths themselves, take an extreme example such as M14 and 308 bore which is standard on hunting rifles. Stick a long mod on the front... trip and fall on the rifle. Calculate the stress.
Solution just buy a mod that fits, like a Hausken.

One has two options. Choose the weaker solution or the stronger solution.
edi
 

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