Barrel thread strength

AlexN

Well-Known Member
Hi there folks,

As the title suggests, how must stick can the barrel take without being damaged when using a moderator.

On a recent shooting trip the heavy window of a European style high seat slammed shut after I'd fired. The wooden window/flap landed on my sound mod with quite a whack that it's left a shiny line/scratch horizontally across it. The mod isn't dented at all but I am concerned about having bent the tip of the barrel, could this happen?

Cheers

Alex
 
Very unlikely in the situation you describe, the barrel is stronger than your moderator as it is in effect a thick walled tube, to bend that short section of thread would take enormous forces.
 
I've been told that a whack on the mod can distort the screw threading, so could result in future shots clipping the inside of the mod.
No first hand experience of this though.
 
I can understand your concern it all depends 1) what is bore/ calibre of the barrel eg: 308win cal = 7.62mm
2)the thread size of the moderator/barrel eg 1/2"unf =12.7mm-7.62=5.08Divide by 2+=2.54 wall thickness each sidewall so no not a lot of metal left and a hard blow could "bend" or fracture the end of the barrel especially if there is no radius at the barrel shoulder /thread start.
 
As per Roebuck9 I think your concern is wholly understandable.

I've always thought the length of 1/2" UNF thread given to 22 rimfires is far too short and is why I have mine cut to 30mm.

At the risk of stating the obvious it is the significant additional leverage a moderator may impart to a barrel if dropped or fallen upon that can ensure more than a temporary change in zero.

K
 
Thanks for the replies folks! The gun is a Sako A7 s, in 308 and the thread is 14x1. I'll be so annoyed if it is damaged because the gun is only 3 months old!!
 
308 is very tolerant of barrel length so having the end lopped off and rethreaded is not then end of the world. Try it first though.
 
if it has just slammed on the mod I can't see a huge lever involved so the mod should have taken the brunt

if however the barrel was positioned so the fulcrum was much closer to you and the force was applied to the end of the mod I can see how it may damage the barrel

just pull the bolt and look through with and without the mod
depending on bore size the tolerance is quite tight and you can easily see potential interference

inspect the thread for damage otherwise
 
The biggest danger is if the thread is bent, the bore may no longer be in concentric alignment with the moderator. Don't shoot it till it has been checked.
Look up the bore to see if you can see the moderator offset. You certainly don't want bullets hitting the inside of the moderator.
You can easily see if a moderator is out of line by laying a long (longer is better)ruler along the outside & back along the barrel, Measure the gap down to the barrel from the ruler. Do this at multiple positions around the moderator - errors will soon become evident. This method does rely on the moderator being concentric of course.
Another way to check is to put a close fitting rod in the barrel bore with the moderator in place. Again any excentricity will show itself.

Ian
 
The weakest point on your thread will be the undercut, this would also have to be your fulcrum point in order to cause any bending of the thread, the force involved to cause any bending would have to be considerable, several tonnes in fact.
To set your mind at ease just insert a cleaning rod down the bore with the mod attached and check the clearence around the exit hole.

Ian.
 
the moderator is more likely to have been damaged than the barrel, next time on the range check the moderator for scoring inside the last baffle, it should be clear but you will see a line if it is no longer consentric
 
Thanks for all your replies! So I managed to get out of work early this afternoon and get onto the range. I put a target up at 100 yards the size of a two pound coin and let a couple of rounds off. Afterwards I unscrewed the moderator and checked for scoring, which thankfully there wasn't any. Apart from one or two clicks to the right I think it's not too bad for factory ammo and I shot straight after walking to the firing point.

AlexImageUploadedByTapatalk1445881063.962067.jpg
 
I fell off a gate onto a granite boulder with my 243 1/2UNF and Jet Z. Put a dent on the moderator which takes some doing on a JetZ and all was fine alignment (and zero wise)
 
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