Question about the ID of Muzzle Brakes.

[tobnpr]

I made the thread .700 28tpi.

How do you determine correct pitch diameter for a non-standard thread like this?

 

[gunsandgunsmithing]

How do you determine correct pitch diameter for a non-standard thread like this?

A 28tpi thread is the same depth regardless of major diameter.

 

[DaveTooley]

How do you determine correct pitch diameter for a non-standard thread like this?

UN imperial screw thread calculator

theoreticalmachinist.com

 

[tobnpr]

A 28tpi thread is the same depth regardless of major diameter.

I know that. Doesn't give you a PD, though. I don't feel comfortable relying on whatever the tables say for compound/cross in-feeds to get perfect thread fit- I always measure PD with a thread mike.

UN imperial screw thread calculator

theoreticalmachinist.com

Thanks, Dave.

 

[gunsandgunsmithing]

I know that. Doesn't give you a PD, though. I don't feel comfortable relying on whatever the tables say for compound/cross in-feeds to get perfect thread fit- I always measure PD with a thread mike.

Thanks, Dave.

Just add the difference in od's. Say a 1/2-28 has a pd of .475 and a major of .500. To get the correct pd for a non-standard od like a .700-28, just add .200 to the 1/2-28 pd of .475 and you get .675. There ya go. It's correct and you don't have to overthink it. Of course then, since you have a non-standard female thread, you may or may not have a standard fit, such as a class 2.

I didn't mean to sound condescending. It just really is that simple is all. If you go in .020 for a 1/2-28 you also go .020 for any other 28tpi thread, regardless of the od. Just an example. Machinery's Handbook goes into great detail explainig the geometry, the why's and the how's. But your depth of cut is the same regardless of the major od, for a given pitch.

 

[tobnpr]

Yeah, after I actually thought about it, I realized the PD as relates to major/minor diameters is constant, so all that needs to be done is make that +/- adjustment based on major diameter. I was overthinking it (as I'm wont to do sometimes )

 

[jackieschmidt]

I have always made my brakes with an expansion chamber and bored the front to around .020 to .025 over bullet dia. I have always seated on the shoulder. Typically, for a 30 cal., the chamber is .406 and the front is .328 ID. Four circles of six holes. A variation on this was to drill at .406 all the way through then thread the front to 7/16x32 to accept an insert which was bored to .020" over bullet diameter. I had a reason for doing this but don't recall what it was!
I have always felt, if a 308 won't shoot 1/2 moa or better, with 41 of 4895 and a 168 Sierra, there is something wrong with the rifle. 168 Lapuas are at least as good. WH

I agree with that last sentence 100%.

I know that. Doesn't give you a PD, though. I don't feel comfortable relying on whatever the tables say for compound/cross in-feeds to get perfect thread fit- I always measure PD with a thread mike.

Thanks, Dave.

I bored the brake to .040 under .700, put a .705 counterbore for about 1/8 inch, then established the 28 tpi, just touching the counterbore with the tool for the final few passes.

The barrel is turned to .695. I simply threaded it untill the brake screwed on correctly.

Not really that complicated.

 

[jackieschmidt]

Well, I stopped by the range today home from work to try my 308 again.

What has changed? First, taking Wayne Shaw and Tooley’s advice, I made a new muzzle brake to incorporate a tapered expansion chamber, leaving the last 1/2 inch at .025 over bullet diameter. I then scored some 155 grn Sierra Match Kings And Reloader 15.

To top it off, I bought a complete PTG bolt from Carlsbad, (big shout out), and re-headspace the barrel to fit it.

I worked with it a little, then settled on 48 grns of Reloader 15 behind the 155 Sierra MK, just touching the lands.

Over a three flag set at 100, I shot these two 5-shot groups just before dark. One in the L/R, the other in a R/L condition.

I have definenatly reached my 1/2 inch inch threshold, the rifle is working pretty good. The muzzle brake works great, recoil is about like my 13.5 pound 30BR.

Thanks to member Phil Keil for the loan of the reamer.

All I need now is a good variable scope suited for hunting, some good bullets designed for game, and let someone take a White Tail with it.

 

[INTJ]

Well, I stopped by the range today home from work to try my 308 again.

What has changed? First, taking Wayne Shaw and Tooley’s advice, I made a new muzzle brake to incorporate a tapered expansion chamber, leaving the last 1/2 inch at .025 over bullet diameter. I then scored some 155 grn Sierra Match Kings And Reloader 15.

To top it off, I bought a complete PTG bolt from Carlsbad, (big shout out), and re-headspace the barrel to fit it.

I worked with it a little, then settled on 48 grns of Reloader 15 behind the 155 Sierra MK, just touching the lands.

Over a three flag set at 100, I shot these two 5-shot groups just before dark. One in the L/R, the other in a R/L condition.

I have definenatly reached my 1/2 inch inch threshold, the rifle is working pretty good. The muzzle brake works great, recoil is about like my 13.5 pound 30BR.

Thanks to member Phil Keli for the loan of the reamer.

All I need now is a good variable scope suited for hunting, some good bullets designed for game, and let someone take a View attachment 1286040View attachment 1286042View attachment 1286041White Tail with it.

No all you need to do is find a load for it that shoots almost as well with a hunting bullet........

 

[mac86951]

I'll add that adding mass to the end of the barrel can affect load tuning, similar to adding a tuner albeit a fixed one. Looks like you've got it set already, so enjoy!

 

[PhilKeil]

Glad it came together Jackie. I have good luck with the sierra #2140 game king in my 30-06 and my friend loves them in his 308. My son likes the tipped game kings.

 

[jackieschmidt]

No all you need to do is find a load for it that shoots almost as well with a hunting bullet........

I would like to try the Barns TSX in 150 grn, or maybe some Accubonds.
I would not expect a true hunting bullet to shoot as well as the Match Kings, anything around 3/4 inch would be great.

 

[INTJ]

I would like to try the Barns TSX in 150 grn, or maybe some Accubonds.
I would not expect a true hunting bullet to shoot as well as the Match Kings, anything around 3/4 inch would be great.

I agree. I really like the consistent terminal performance of Accubonds. They hold together at high velocity but still expand well at low velocities. The issue is ABs are often very inconsistent. So inconsistent that I sort them by BTO. I also like TTSXs and LRXs at inside of about 300 yds. They really seem to need 2200 fps to expand well.

That said, I will take a .75 MOA bullet with good terminal performance over a .25 target bullet when it comes to hunting.

 

[AlNyhus]

Well done, Jackie. I know that project fought you for a while...nice to see what happens when a person keeps after it.

In the hunting style .30's I mess with, the Nosler 150 BTip, the Sierra 150 flat base Pro Hunter and the Nosler 150 Accubond are the three that consistently show the best accuracy and performance on white tails and mule deer. In a light weight hunting style rig chambered in 308W, the Sierra 125 gr. Pro Hunter works really, really well with Winchester 748, VVN135 or Accurate 2520.

Are you looking for a 1" or 30mm scope? -Al

 

[jackieschmidt]

Well done, Jackie. I know that project fought you for a while...nice to see what happens when a person keeps after it.

In the hunting style .30's I mess with, the Nosler 150 BTip, the Sierra 150 flat base Pro Hunter and the Nosler 150 Accubond are the three that consistently show the best accuracy and performance on white tails and mule deer. In a light weight hunting style rig chambered in 308W, the Sierra 125 gr. Pro Hunter works really, really well with Winchester 748, VVN135 or Accurate 2520.

Are you looking for a 1" or 30mm scope? -Al

Al, those nice US Optics rings I have on the rifle are 30mm.

As for keeping after it, it sort of became an obsession. Kind of like doing a custom car Project. You keep changing things and spending money untill you have what you set out to have, a $40,000 car that you spent $200,000 building.

This tends to be a downside of being able and having the facility to build your own stuff. It’s too darned easy to tear it all apart and start over.

 

[AlNyhus]

Jackie, if you haven't decided on a variable hunting scope yet, I'd suggest taking a look at the Sightron S-TAC series. I've got a 4-20X50 with the MOA2 reticle. It's right at 23 oz and 14.8" long. They also make a 3-16X42 version with the MOA3 reticle that's about 2" shorter. They show that one as also 23 oz but the one I mounted recently was about 21oz. on my postal scale. Nice optics, solid mechanicals and very reasonably priced. They are both available with a standard DuPlex style reticle, also.

Randy Robinett has been working with these and I know he's impressed, as well. Lance @ Buchanan Accuracy (a sponsor here) offers great pricing and delivery on them.

For what it's worth.... Al

 

[PhilKeil]

+1 on the Sightrons. great buy. Put a s tac on my Grendel and love it. have several s3 and no issues.

 

[jackieschmidt]

I decided to add a tuner to the muzzle brake.

I took a piece of 660 Bronze and machined a tuner with a 1.075 32 tpi, alone with a counterbore to fit tight on two captured O Rings on the barrel. I chucked the barrel back up and did all of the necessary work to fit the tuner.

I gave the O rings sufficient compression so it takes a reasonable effort to turn the tuner.

I think it came out nice.

what I would like to do is find a load with a good ES and SD, then fine tune the grouping capability with the tuner.

Doing stuff like this is fun.

 

[LC Tikka]

I turn the ID 20 thou over bullet dia, then cut rifling and twist as in the barrel, keeps the gas flow more uniflow on exit.
LC