muzzle runout Gordy's method

A

alinwa

oft dis'd member
I recently posted about muzzles "commonly running out over 100 thou......"

I did this from memory. So here's some actual numbers.

I set up a really fine custom 32" blank today. Barrel slugs out like a champ with a couple tenths tighter muzzle, lapping bells are short and about 2 tenths taper per inch.

#1-I set muzzle and chamber end to centerline w/indicator, reached in 1.5" on chamber end and found a little wobble, almost a thou. I reached in with a rod and found .0035 wobble at the throat.

#2- I used the rod to center throat, so now I'm zero'd at muzzle and throat. I used the rod to find .004 of wobble from throat back to chamber end of blank. Wobble shows same on indicator probe. So I've got .004 of runout in about 5 inches, this checks with first findings. I marked the top.

#3- I remove probe, clean the setup and reinsert to run from chamber end to about 1" past the throat, I'm now reaching about 6" into the barrel. Numbers all check, almost a thou of runout per inch, almost .005 over the 6" run with a little funkywobble at the 'muzzle' of the lapping bell.

So I've got the "ski jump" marked and the barrel is dialed to zero wobble at muzzle and throat.

#4- Time to "Gordy" the setup........ I start yanking stuff around and end up with ZERO wobble from an inch fore and aft of the throat, DEAD nutz. The rear end of the chamber is running out enough to see, under a tenth.

#5- I run an indicator probe in and manually confirm the tenth of runout, perfect match. So now I've got a 5" section from back of chamber to an inch into the bore DIALED....entire chamber and an inch beyond the throat is wicked tight. I've worked the chuck roundy-roundy and she's all tightened up DEAD STRAIGHT for 5" at the chamber end. About .002+ jump in the end of the lapping bell.

We're dialed.




And the muzzle's running out 82 thou, so about 40-42 thou of "crook" or "banana" in the barrel.

Interestingly the overall crook is about 30 degrees off from the ski-jump at the chamber end. Same side, just slightly twisted.

-4 thou over 4 inches-

-40 thou over 32 inches-

run those numbers, I'ma' go back and drill a hole.

findingsby





al
 
Al,
I am tempted to pull your thread. What do you mean mucking up the forum with hard data? don't you know that it is supposed to be about disagreements as to whose speculation is correct? For shame!
 
Boyd,

Some people are like that. Just when you know what you think, they come along and confuse you with facts!

Jim
 
Al:

I just today dialed in a Broughton 5C 6mm 33" blank to chamber in 6 Dasher, and got similar results to yours. I followed the same process, using a Interapid indicator with the 2.75" stylus to dial in the throat and the muzzle to under 0.0002" TIR in the grooves. I then used a "Gordy" indicator rod, and saw about 0.0025" over 1.5" in front of the throat location. Once the bore was dead true from the throat to about 2" in front of it, the muzzle was running 0.042" TIR, or 0.021" over 33", for a total pointing error of about 2.2 MOA. After making tenon and threading, I shaved the shoulder a few thou so that bore is pointed up when the action is threaded onto the barrel. I can live with 2 MOA extra elevation. I check the throat grooves again before pre-boring with the Interapid to be sure that the grooves are still dead nuts. This is my 5th Broughton 5C in 6 Dasher, and the previous 4 have been excellent, all chambered with the same process. None of them have had more than 0.060" TIR at the muzzle after indicating in.

Cheers,

Chris

www.the-long-family.com
 
As that fellow on "Laugh In" used to say... 'Verrryy Interesting...

Al, any thoughts on how the bore is 'DEAD STRAIGHT for 5" at the chamber end' and then curves the rest of the way? How it became that way? During the drilling of the blank? Or do you think it is in heat treatment?

... and you do need a good camera... :D
 
So what does this all prove other than if a barrel is curved and you use the gordy thing that the muzzle will be way out. Have your muzzle pointing somewhere other than where the rest of the gun is pointed if you want to, I'll keep mine all in line. OK you will index it, now how long is that going to take, another hour, two hours?? Why????
 
Dennis Sorensen said:
As that fellow on "Laugh In" used to say... 'Verrryy Interesting...

Al, any thoughts on how the bore is 'DEAD STRAIGHT for 5" at the chamber end' and then curves the rest of the way? How it became that way? During the drilling of the blank? Or do you think it is in heat treatment?

... and you do need a good camera... :D
Click to expand...

It's not actually "dead straight for 5"" but it's hard to see or find the curvature because I only check for wobble at points on a very gradual curve. My first 'point' is actually twe inches long (the area ahead of and behind the throat) and the other point is the rear of the chamber. I align these two points. The curvature between these two points would be very slight.

I have a good camera.
 
Well....... that was fast. :p I ripped that one out in under 7 hrs.

I owe Gordy an apology :)

Before this turned into 5-barrel project where I had to make up 4 identical chambers without firing a shot....... (I still don't have a sizer die) ............ back when I was still trying to spec this thing, I was in a hurry to get a barrel done. I spoke with Gordy Gritters to see if I could get a barrel chambered on short notice. I remember commenting that "I'll have all the parts and pieces lined out so's if you can just break out a couple hours......??...."

Gordy is a gentleman. I remember the pause....... "I'll fit it in as best I can."

I was WRONG about the "couple hour project."

A barrel done Gordy's way is a full day project....or at least it's gonna' be a long day to do two!

Is it worth it???

I say "PAY THE MAN!!!" It's worth every penny, a true advancement in method.


opinionsby


al
 
Run out in the barrel and results at 1000 yards

I have the highest respect for Gordy. He and I talk on the phone a couple times a year.
I have chambered using his method with good results. I choose to do it a different way not saying it is any better or worse. I center both the tenon bore and the muzzle bore with .0001 indicators until I get no needle tick.

I have one customer who has five barrels that I chambered for his rifle. He told me when he switches from one barrel to another he has less than .5 moa of adjustment to get a zero from one barrel to another.

I think that is pretty darn good. The rest is up to the barrel.

Nat Lambeth
 
Last edited:
Rustystud said:
I have the highest respect for Gordy. He and I talk on the phone a couple times a year.
I have chambered using his method with good results. I choose to do it a different way not saying it is any better or worse. I center both the tenon bore and the muzzle bore with .0001 indicators until I get no needle tick.

I have one customer who has five barrels that I chambered for his rifle. He told me when he switches from one barrel to another he has less than .5 moa of adjustment to get a zero from one barrel to another.

I think that is pretty darn good. The rest is up to the barrel.

Nat Lambethg
Click to expand...
I agree with Nat. It would make me nervous to have each barrel being way off zero every time I swap barrels. It would make me nervous to think my bullet exit was pointing somewhere else other than the gun axis. If the gordy method proved to be the best shooter I'm sure everyone would be doing it that way. As is it seems just a few amatures use it and want everyone to think that method is great.
 
That's the cool thing about this forum :p

I remember when those same words were uttered concerning:
-barrel tuning devices
-weighing powder charges
-18" twist
-the 6MMBR round for anything over 200yds........

time WILL tell...

lol

al
 
I rarely have time to post here, but I read other posts almost daily. I love seeing how different minds work, and looking at things from different perspectives helps me learn things all the time.

I will chime in here with a few things I've observed from my testing and observations over the years that may help some of you see why I look at and do things the way I do. I put an extreme value on what I learn from actual testing and measuring as opposed to what I think or what has been the accepted way of doing things in the past. Testing this way has really opened my eyes to a few things over the years, which I am trying to share with others in my classes and instructional DVD's.

I have dialed in and chambered/crowned well over 1000 barrels since I first found out the bores and chambers weren't aligned very well using the old tried & true methods. These old methods work quite well (still do) but I found occasional problems when using that method, so I set out to find a method that would address those issues.

So I experimented and did a lot of testing with a lot of barrels over several years to develop the chambering method I now use. This method aligns the bore ahead of the chamber to be true to the lathe, then drill and prebore the chamber hole true to that. Now your chamber will be perfectly aligned to the bore ahead of the throat (not just at the throat like the old method gives you) irrespective of how the bore curves as it goes forward beyond the first few inches.

But to do this, the muzzle must be offset to get the bore to align ahead of the chamber the way I want it. In this 1000+ barrels I have observed and learned some interesting things:

1. 90% of good match barrels are within .010" to .040" total indicator reading (TIR) offset at the muzzle (.005"-.020" actual offset from center) to get the bore to align straight at the chamber end. Once in awhile I get one that is better or worse than that but it's rare. I've only ever had 4 or 5 barrels that were over .050" TIR with the heavy match barrels, a little more often with lighter hunting barrels.

2. I have found if I have more than .040" total indicator reading at the muzzle end, it was often because I was bending the barrel with the chuck and spider adjustments trying to make it align where I wanted it. I can't remember if I mention it in the Grizzly video, but I sure stress it to guys in my classes - the importance of relieving the bending stress in the barrel repeatedly while dialing things in. Every time you make an outboard end (muzzle) adjustment you're bending the barrel slightly, so I loosen the jaws holding the chamber end to relax the bend I just put in the barrel with prior said adjustment. Then I rezero the chamber end and indicate forward and back to measure if the bore is running true yet. I keep doing this - making adjustments, loosening and tightening the primary chuck jaws before rezeroing. (It helps to keep the jaws just lightly holding the barrel during the dial-in process - then tighten the jaws very carefully after it's dialed in, measuring to make sure it stays dialed in after they're tight). Now when I get the bore running perfectly straight and true, I know it is doing so without bending. Then you'll find the muzzle end will rarely be over .040" TIR from center, which is an extremely small amount. I like to index or "clock" the muzzle end up for long range guns, and for short range guns I "clock" it either up or down - never to the side for anything.

3. I use the range rod (Grizzly rod or Gordy rod, whatever you want to call it) to get the bore running as straight and true as I can initially. Then with the chamber pre-drilled, I can reach in with my long-reach indicator to the throat and a ways down the bore ahead of the throat to fine tune any remaining runout to zero (or almost zero). This takes care of any clearance you may have between the bushing and the rod and the bore, which is always there to some degree. When doing it this way, I can almost always (most of the guys from my classes and the SHOT show can attest to this) get the indicator readings in the finished chambers to read within .0001"-.0002" all the way through the chamber and then ahead of the chamber for a couple inches, which I can only get when I offset the muzzle slightly to align the bore at the chamber end.

4. One thing I've really learned from helping guys in my classes dial-in barrels is that it really helps to speed things up by "finessing" your dialing-in. I see guys all the time trying to make too big of adjustments and they end up chasing things and getting frustrated. But once they slow down and make small adjustments (finesse it), they get things dialed in very quickly. There's definitely a learning curve just like any new endeavor, but once you've done this a number of times, it won't take you a whole lot longer to dial things in using this method.

Hope this helps shed a little light on things!

Gordy Gritters
www.ExtremeAccuracyInstitute.com
 
Gordy Gritters said:
Hope this helps shed a little light on things!

Gordy Gritters
Click to expand...

So Gordy, as I understand it, the 'old way' lines the cartridge up with the muzzle... and tolerances as they are the bullet is slightly 'off' into the rifling... and this 'new way' the cartridge is lined up with the bore immediately ahead of it and follows the bore where it goes... thus the bullet should be engraved by the rifling a bit more accurately. Would that be a fair analogy?

Dennis
 
Well said Gordy!

Having set up just 7 times using Gordy's method I can attest to the wisdom of "finessing!" I wasted a lot of time over-correcting the first couple times I did it.

The only other "problem" I've had was one of my own creation..... While initially dialing in the barrel I use VERY light hold, like finger tight and loosen/tighten for every adjustment. Then the tightening is done roundy-roundy-roundy. It does take a lot of time. My "problem" occured when I forgot to tighten up after I had it all dialed :)

I'd set one up for my repeatability test in which I set it up/marked it. REMOVED it, set it back up/marked it and then the third time when it came back to zero I went to work.....the first light truing pass had that wavey chattery look, the second one dug in and spun the barrel out.

So I guess technically that makes for 8 setups!

LOL

al
 
This method aligns the bore ahead of the chamber to be true to the lathe, then drill and prebore the chamber hole true to that. Now your chamber will be perfectly aligned to the bore ahead of the throat (not just at the throat like the old method gives you) irrespective of how the bore curves as it goes forward beyond the first few inches.

But to do this, the muzzle must be offset to get the bore to align ahead of the chamber the way I want it.
Click to expand...

I must be missing something. If you pick any two spots, say, (1) barrel just ahead of the end of the throat, and (2) the muzzle, you can get them to run true. I figure you're picking two spots at the chamber end of the barrel, which means the muzzle end will likely run out a bit.

That right?

TIA
 
Thanks Gordy!

I am new at chambering and done only 4 barrels but your method makes the most sense to me and every gun I've chambered has shot 1/2 moa or better.

Your video is always on my TV for review. Thanks for the great lessons....and get us that new video on lapping out soon!

In high regards, Sailhertoo-
 
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