Threading a 300 win mag barrel with a .63 diameter

[Conrad101st]

So I want to thread my Sako 75 finnlight in 300 win mag. Obviously, I don't need a can on a mountain rifle but since it holds 3/4 MOA, I figured a can might make it even better when I was shooting long distance off a ridge against elk in meadows or clear cuts. Yes I know it's not what the rifle was intended to be used originally for, but I ain't humping my sendero with a night force scope up these hills either. I suspect the change in point of impact should not be too extreme with the 7.62 omega hanging off the end of a 24 & 3/8 fluted barrel.

It would appear that 5/8 x 24 (.625), nor 1/2 x 28 threads are not good options as the barrel is a 0.63 diameter contour at the muzzle.

I assume 5/8 thread won't leave enough thread in the first case to grip nor leave enough shoulder to index off of.

1/2 thread wont leave enough barrel meat around the bore (.5 - .308 = 0.192) as most suppressor makers recommend at least .200 of remaining meat - especially on magnums from what I gather.

Now 9/16 (.5625) gives at least a 0.0625 shoulder, especially as the barrel shortens toward the chamber. Also leaves about 0.2545 (+) of remaining meat outside the bore.

My thought is to do 9/16 LH thread pitch and put an 7.62 ASR flash hider on there (which they indeed make), which would serve as a quick detach for my SilencerCo Omega can. Then I can easily attach the can and the can shoulders and indexes off the ASR mount. Not looking to put the muzzle brake as the blast would be obnoxious without the can.

I assume that the .0625 shoulder allows enough meat for the ASR flash hider to hook up firmly or does it (tge ASR FH) even need a shoulder like you would with a can??? This would seem to be a better option than trying to do a direct thread on this barrel contour.

Thoughts? Appreciate your input.

[SC-Texas]

Peter Piper in Hempstead Texas uses the 9/16 for barrels as you have described. 9/16 solution is what I would recommend for my clients in your shoes

Sent from my SM-N920V using Tapatalk

[abso]

I was going to do 9/16 on a tikka t3 308, but I ended up rebarreling the rifle. Thunder beast also clearly states that you need a large enough shoulder. Going 9/16 is viable and most likely your best option. You can also chop the barrel shorter as you mentioned.

[tmwtrfwler]

I went down this road this summer with a nosler m48 300 win mag. We ultimately did a 9/16 thread with a break suppressor attachment despite what is written below....... The break is installed and waiting on the can which is in NFA jail.

Here is the info I posted on the nosler forum from my research
________________________
Here is my update from today. I'll post a separate thread as an FYI to the forum regarding the topic. I learned a lot today regarding the relationship b/w threading and barrel contours. Pretty good stuff.

First, I can't say what a pleasure it has been dealing with Shawn with Nosler, the folks at Thunderbeast, and Crux. All three have been engaged, helpful, and provided an education on the subject. Great customer service.

Now, here's an interesting update after todays discusison with Crux / Nosler / and Thunderbeast

1st Step - confirm the OD of the Pac Nor Magnum Contour barrel that Nosler puts on the gun. That is confirmed by Nosler to be .65

2nd Step - see what Nosler offers for their threaded barrel option (typically for a break). That is confirmed by Nosler at 1/2x28

3rd Step - per the diagram provided in my previous post; call Thunderbeast and see if the Ultra 7 would work with a 9/16x24 thread with a .65 OD barrel.....that would mean the gun would have less shoulder than desired by Thunderbeast specs but, in my mind, the break would more than make up for it. Thunderbeast confirmed that 9/16x24 on a .65 barrel would be too small for their product (their diagram wants .662).

4th Step - see what Crux says about the same situation. They confirmed that a .65 barrel will work with their calculations regarding shoulder size. They want .002 on each end. They can in fact do a 9/16x24 threaded adapter for the .30 cal can. Specifically they recommended the ARK30 over the Saxon or Archangel for my gun setup, situation, and goals of the can. In fact, through the discussion they confirmed they have a 1/2x28 brake for a .30 cal.

So, problem solved. Ark30 it is with a 1/2x28 brake.

[Conrad101st]

Here is what they said (cobbled together over a few emails) regarding using a device to attach my Omega can on my .63 diameter barrel:

We would recommend the 9/16x24 thread pitch. However, we would recommend going with the RH thread and using the muzzle brake. All of our tests have shown that the muzzle brake has better accuracy than the flash hider. If you are worried about the side concussion then you can use the ASR Blast shield to direct the blast forward. The 9/16x24 will give you enough shoulder for proper shouldering of a flash hider or muzzle brake.

[Todd.K]

I'll take the opposing position here if possible.

Some mounts can stop on the muzzle, that with 5/8 thread would be my first choice.

[Conrad101st]

I'm curious as to that thought.

5/8 = 0.625
My barrel is 0.63

That means at the muzzle, the variance will be 0.005 at best.
Now obviously the barrel widens as it moves towards breech, but will 0.005 be enough depth for the threads to have sufficient purchase in order that the muzzle device doesn't just get blasted right off with a 300 Win Mag?

[Todd.K]

Thread size is the outside diameter of the male thread. So 5/8 male thread is .625 OD (actually a few thou under because they are not cut to a perfectly sharp top)