Muzzle Brake on 7 mag sporter....couple questions..

[ridgeway]

I plan on installing a muzzle brake on my 7mm mag hunting gun. This is my 1st time doing anything gun wise on a lathe. I ordered a Harrell's 1/2-28 x .750 brake. It comes with a .250 bored hole.

My questions are as follows:

My first operation I plan on opening the hole for proper clearance for 7mm. .020" oversize OK? Should I open up with a drill or use a boring bar? I don't have a set of reamers.

When setting up the brake in the lathe to open the hole, should I set up in a 4 jaw and indicate off the the bored factory hole or on the brake OD?

I don't plan on removing the barrel from the action, so would it be OK to indicate the barrel OD at the chamber end using my outboard spider? And then use my test indicator to dial inside of bore on muzzle end?

Once fitted, I want to turn the OD down to flush with barrel. How should I go about achieving this? Or should I leave it a little larger and radius/taper the fit? Wouldn't a larger diameter brake be more effective on a sporter?

How much clearance do I need between the crown and counter bore in the brake?

Last question, lol. My factory barrel appears to be bead blasted. Is there a way to match the finish without a bead blaster?

 

[Preacher]

.020 over bullet diameter is exactly where it needs to be...
Seeing you do not have a reamer, a boring bar advanced super slowly, and high speeds RPM's will do OK.
Indicate off the brake hole, then indicate off the barrel to cut it to the same diameter
once it's installed...
I personally like the brake larger than the muzzle.. I like the larger opening on the inside of the brake done that way..
Indicating off the chamber end in the spider will work... but indicate the actual bore.....
If you have a buffer, you can run it in reverse to get close to the barrel finish...

 

[Ggmac]

Preacher is correct . All I would add is that a decent book exists all about brakes , design ,and application . Its not expensive . I also like my brake larger than sptr barrel dia. ,I like having more dia. At threated joint .
Harrells brakes are GREAT , the internal bore dimensions are very important as to how well your brake will perform . Internal dia. Diff . Are called chambers .
On harrells brakes , I can machine 3 internal chambers ,the first largest , etc . Leaving just the muzzle ( last 060 to .080 ) .020 over bore diam .
REMEMBER ! USING SABOTS ARE GENERALLY NOT A GOOG IDEA! (dangerous )
Good luck , stay safe

 

[ridgeway]

Thanks for the tips! Got ya on the brake chambers...did not know that.

Preacher...I'll give the buffer in reverse a try...not sure if I can do that with what I have. Would reverse the wiring at the switch reverse it? I just have a 1/2 HP bench grinder with a buffing wheel on one side.

 

[ridgeway]

I went to break the barrel and low and behold, my M700 wrench will not fit in the long mag action. There is a groove in the action that mates to the right lug in the bolt. Why in the world is that there?

If I get the proper action wrench(one that clamps on outside), do you think my Davison barrel vise will hold the barrel enough to break a factory SS barrel? Is it common to use any type of heat?

 

[Ggmac]

Some factory rem barrels are easier. To remove if you cut just in front of rec. Ring .this cut is to relieve the pressure ( compression ) of factory installed barrels . If done ,and you wish to use the barrel again a thicker recoil lug would be needed.

 

[Gundoktr]

I have never had a problem removing a factory barrel on a Remington. Some are definitely tighter than others. You need a good barrel vise with a bushing bored to the same taper as the barrel and a good external action wrench. The action/barrel joint needs heat to melt that "loctite" stuff Remington uses on the barrels.

The reason your internal wrench don't work is caused by the anti-bind part in the action; you probably have an older action without it.

 

[Preacher]

If the buffer won't reverse, just turn the wheel around and run it that way with very, very light pressure, the slapping effect will put a light bead blast finish on the part..

 

[ridgeway]

Sounds good....thanks for the help. Once I get it done, I'll make sure I report back with some pics.

 

[Preacher]

I forgot to mention that it's best to run the part in a counter clock wise direction when your on the buffer.
Usually you would buff with the part going clockwise against the wheel with your right hand, you'll need to go the other way, turning it towards you to get that beaded effect....
Good luck....

 

[ridgeway]

I bored out the hole and miscalculated and wound up with .016" clearance. This OK? Otherwise, I will have to dial back in and bore .004" more. I ended up using a decimal measurement for 7mm, not .284"!

 

[Preacher]

.020 over is your best bet, redial it and cut it to .304............

 

[ridgeway]

Sounds good...that's what I will do.

 

[ridgeway]

I have a couple more questions and I'm sure they can be answered through experience.

Has anyone had trouble with threads on Harrell's brakes?

I got my tenon threaded, but the brake gets extremely tight halfway down. I figured it was my threads, so I take a couple more tiny passes to clean things up. Now, I know its not my threads since the brake fits loosly on the first half of the tenon. I stop threading and tighten the brake on. I used vise grips with aluminum on the jaws to tighten the brake. It threaded all the way on and has a pretty good thread fit. I swear the brake threads are tapered a tiny bit? Anyhow, I can turn on and off by hand and fits square against the shoulder.

Now, I set up to dial the OD of the bore and I can only get to .0005" at best. I swear the OD is egg shaped or something. This common on factory barrels?

 

[ridgeway]

On the tight threads...I think its my fault. When I set the brake up for the first time in the 4 jaw, I think I tightened a jaw or two too tight when dialing. This in turn made two jaw marks right around where the brake gets tight. I'm guessing the force distorted the OD just enough to make it tight? Live and learn I guess...each time I turn the machine on I learn something new!

 

[Preacher]

The brakes are all made on a CNC machine and of the 100's I've installed, none of them have been a problem for me..
We all learn a little each and every day till we stop living.....

 

[ridgeway]

It must have been my over clamping in the 4 jaw then. I'm learning! I'm half tempted to cut off the tenon and start over, but hate to loose barrel length and start all over. Anyow, it fits fine and tightens up square against the shoulder. Just have the OD to turn down now. The next one I do will definitely be better thread fit, that's for sure! Thanks again for the tips!

 

[TRECustom]

Ridgeway, I had the same thing happen to me on a brake. When I called about the tightening thread, it turned out that they were using a tap in the CNC machine instead of single pointing or using a thread mill. It caused the back half of the threads to tighten. Probably because of wear on the front end of the tap.
I fed about "001" on the compound, cut halfway up the tenon, then pulled the crossfeed out and unlatched the halfnut. When I tried the brake, it went home with a surprisingly good fit.

I tried this because I had enough barrel to start over, and because I'm not good at picking up a fine thread and single-pointing it, particularly an internal thread.

Terry Bradshaw said it best..."if I have a choice between being real good or real lucky, I'll take real lucky every time".

Don't know anything about the Harrel brake, but they might be using a tap.

Tom

 

[ridgeway]

Yeah, could be. I may give them a call and ask. I thought about running the compound in to clean up, but was afraid of messing something up. I should have finished threading once the brake started on and turned it on by by hand using a drill blank through the brake holes. Sure enough, there was a tight spot in the brake, but I could have caused it when I clamped it too tight in the 4 jaw for my initial hole boring operation. Its been quite a learning experience. Next on the list is a chamber job, lol.

 

[eww1350]

Chuck,...I recommenf that you leave your brake "hole thru" diameter alone until you get the brake fitted onto the barrel..Then with the brake threaded on to the barrel that you indicated true to the bore..you can use your boring bar to open it up to .020" over the bullet diameter...that way you don't run the risk of distorting the brake...after the brake is bored "true to the bore" you can go back and indicate the O.D. of the barrel then procede to turn the brake down to match the barrel O.D....




Eddie in Texas