markymark Posted January 21, 2018 Report Share Posted January 21, 2018 Hello, Can anyone tell me what is the minimum barrel diameter for a 18x1 thread to be machined? Is it 18mm or is not that simplistic? The reason I ask, I’m might chop down one of the barrels but it obviously thins as it goes back. But I still wanted to retain the 18x1 thread for exsisting mods and compatibility with other rifles. Thank you, Mark Link to comment Share on other sites More sharing options...
Akeld Posted January 21, 2018 Report Share Posted January 21, 2018 Which barrel profile do you have that reduces towards the chamber? Link to comment Share on other sites More sharing options...
markymark Posted January 21, 2018 Author Report Share Posted January 21, 2018 Think it’s a swamped barrel. From the chamber end it goes thick, thinner in the middle, then thicker again at the muzzle end. From memory the thinnest part is 19mm. Link to comment Share on other sites More sharing options...
Big Al Posted January 21, 2018 Report Share Posted January 21, 2018 1 hour ago, markymark said: Hello, Can anyone tell me what is the minimum barrel diameter for a 18x1 thread to be machined? Is it 18mm or is not that simplistic? The reason I ask, I’m might chop down one of the barrels but it obviously thins as it goes back. But I still wanted to retain the 18x1 thread for exsisting mods and compatibility with other rifles. Thank you, Mark I would want 20.00mm to work from, you could get away with a little less but it isn't ideal. A 20mm starting point gives you a 1.00mm (40 thou) shoulder, its rare to see very much less. You can't just thread an 18mm barrel as there would be no shoulder to square up for the moderator to align itself with. I do a 19.00mm muzzle on my heavy porter profiles but I thread either 17mmx1mm or 5/8UNF You could of course make a bush if you understand alignment and how to achieve it or get someone who does to do the job for you. The bush could remain on the barrel or in the moderator, whichever you prefer. Ive done this a few times when the need arose. Link to comment Share on other sites More sharing options...
baldie Posted January 21, 2018 Report Share Posted January 21, 2018 Mark, if the barrel is fatter at the muzzle than it is in the middle, its been profiled incorrectly. Don't think i've ever seen one like that. Simple answer to your problem is to have the muzzle thread cut M18 but with a spigot, which are common on the ASE mods. This aligns on the spigot behind the thread and requires very little shoulder at the rear. Link to comment Share on other sites More sharing options...
Big Al Posted January 21, 2018 Report Share Posted January 21, 2018 2 hours ago, baldie said: Simple answer to your problem is to have the muzzle thread cut M18 but with a spigot, which are common on the ASE mods. This aligns on the spigot behind the thread and requires very little shoulder at the rear. Thats fine if he wants to buy a new moderator. It wont retain the compatibility/interchangability that he asks for in the original post unless of course all the other M18x1 moderators he has are spigot fitting? Link to comment Share on other sites More sharing options...
markymark Posted January 21, 2018 Author Report Share Posted January 21, 2018 Cheers guys, Thank you both for the input. I’ll have to measure the barrel diameter again to see what it is. Found this, suggest that 19.5mm should be the minimum for M18x1. If not will most likely go for 5/8x24 UNEF. Got a thread bridge for one of those too. Fingers crossed it’s 19.5mm The barrel contour isn’t incorrect, it’s a Tikka T3 tactical 24”. I thought it was quite strange when I first got it, but looked at others since and they all have it. The Tac A1 doesn’t, nor does the 20” tactical models..... just the 24”. It was / is up for sale, as a barrelled action but had no takers. So considering chopping it down to 16.5” short barrelled, walkabout / deer rifle (with mod). No point it going for pennies when it can be used for other things unless I have some late stage interest. Link to comment Share on other sites More sharing options...
baldie Posted January 21, 2018 Report Share Posted January 21, 2018 Thats a new one on me Mark. Never seen a heavy barrelled tikka or sako that wouldn't take an 18MM thread...it is , after all, their standard Varmint weight barrel thread. They must have changed the profile. Measure back where you want the thread, and see what you have at that point, diameter-wise. Link to comment Share on other sites More sharing options...
markymark Posted January 21, 2018 Author Report Share Posted January 21, 2018 Looks like I’m good for 18x1. For your info it’s 22mm at the muzzle for around 5” then down to 19.95mm for while before it starts to thicken up for the breach end. It’s barely noticeable, I can only assume they did it for weight saving purposes. Link to comment Share on other sites More sharing options...
baldie Posted January 21, 2018 Report Share Posted January 21, 2018 Very interesting Mark. Not the commonest Tikka profile, which is why I haven't noticed it. Thinking about it, all the shorter barrels are factory threaded, the long ones usually aren't. That means they usually come in for a thread at full length, or are getting pulled off, in favour of a new tube. As you say, it can only be a weight saving exercise. Link to comment Share on other sites More sharing options...
bradders Posted January 21, 2018 Report Share Posted January 21, 2018 26 minutes ago, baldie said: Very interesting Mark. Not the commonest Tikka profile, which is why I haven't noticed it. Thinking about it, all the shorter barrels are factory threaded, the long ones usually aren't. That means they usually come in for a thread at full length, or are getting pulled off, in favour of a new tube. As you say, it can only be a weight saving exercise. You should look at the Colt Hbar and original M4 .750" at the muzzle and .600-650" under the handguards! Link to comment Share on other sites More sharing options...
TattooedGun Posted January 22, 2018 Report Share Posted January 22, 2018 I know it's not exactly the same thing, but my Anschutz target rifle has a profile of barrel that is thicker at the muzzle than the actual barrel, too - very slightly but it is there. Though I wouldn't expect many of these rifles get threaded... Link to comment Share on other sites More sharing options...
Kalahari Posted January 22, 2018 Report Share Posted January 22, 2018 Is the thicker end in a target rifle to alter the barrel harmonics??? David. Link to comment Share on other sites More sharing options...
.jpg.0972b4e2bdf0b5a4109eb96f2b1b62ad.jpg)
(200x135).jpg.0fd0a94f065c6cb243fdff1b40e0819a.jpg)
Recommended Posts
Archived
This topic is now archived and is closed to further replies.