Timing a receiver to the barrel question
- Thread starter kawsam62s
- Start date
Yes I do index them at 12 o'clock, and sometimes you do need to work on the shoulder to make it work, but it's never that much. So to answer your question, I don't try to calulate it or over think it, just get it close and adjust. I'm sure there are plenty of real operators out there that can come up with the proper method. Mine works for me.
Jesswil61
Gold $$ Contributor
Example, If you are turning 16 threads per inch that would mean that each revolution would equal .0625", so it you needed a 1/4 turn to get to the top .0625/4=.0156" should get you pretty close. I typically take half the number check the result then adjust for the final cut as necessary.
I don’t do it - our scopes have a huge amount of adjustment. But to calculate it (assuming you have the spot you want clocked up marked) you can take your thread TPI and convert it to degrees of revolution per thou taken off the shoulder.
Example:
1/18TPI = .0555 inches per revolution, so .0055/360 degrees = .000154 inches per degree of revolulution.
so if you want barrel to rotate 45 degrees to center it, 45*.000154 is .0067 you need to take off the shoulder.
Example:
1/18TPI = .0555 inches per revolution, so .0055/360 degrees = .000154 inches per degree of revolulution.
so if you want barrel to rotate 45 degrees to center it, 45*.000154 is .0067 you need to take off the shoulder.
This gets back to another recent thread about how much people assume headspace will decrease when torquing beyond snapped hand tight to 45-85lb/ft (normalish range).
If you look at the measurements above in my example and consider there were people saying they assume .002-.003 of crush when torquing, that moving 20+ degrees. I'd argue that if you can snap it hand tight and then move it that much more when torqing, something about your shoulder isn't square to the reciever or the shoulder isn't flat and you're galling down a high spot/ridge.
10 degrees is .0015 of shoulder depth (and thus headspace crush). If you've done your best job on the barrel I would guess you never see even 5 degrees of movement from hand to fully torqued.
I don't align vertically, but I do like the barrel markings to be on plane with the action markings or sitting nicely spaced above the chassis line. I snap that hand tight and mark the line i want them on, spin it off and mark the barrel and do the lasering. When I final torque it on, the text definitely isn't sitting 20 degrees higher than where I wanted it to align or I'd be pissed!
If you're trying to align the barrel curve to the top, if you're off 10 degrees to either side of dead nuts thats also going to be barely noticable on paper, its tough to indicate a barrel to less than 10 degrees with the grooves and lands all getting in the way =p
If you look at the measurements above in my example and consider there were people saying they assume .002-.003 of crush when torquing, that moving 20+ degrees. I'd argue that if you can snap it hand tight and then move it that much more when torqing, something about your shoulder isn't square to the reciever or the shoulder isn't flat and you're galling down a high spot/ridge.
10 degrees is .0015 of shoulder depth (and thus headspace crush). If you've done your best job on the barrel I would guess you never see even 5 degrees of movement from hand to fully torqued.
I don't align vertically, but I do like the barrel markings to be on plane with the action markings or sitting nicely spaced above the chassis line. I snap that hand tight and mark the line i want them on, spin it off and mark the barrel and do the lasering. When I final torque it on, the text definitely isn't sitting 20 degrees higher than where I wanted it to align or I'd be pissed!
If you're trying to align the barrel curve to the top, if you're off 10 degrees to either side of dead nuts thats also going to be barely noticable on paper, its tough to indicate a barrel to less than 10 degrees with the grooves and lands all getting in the way =p
.002" of crush would be an excessive amount of torque, if it's even possible. When I get the machining right, the barrel hard stops when hand tight and torquing it doesn't change headspace hardly at all----maybe .001" if even that.
I try to get the barrel indexed up, or down, but I don't obsess over it.
I try to get the barrel indexed up, or down, but I don't obsess over it.
Geez.....you guys are way too talented......I know alittle about what you all just discussed, but man I am impressed.
Buy a lathe - you'll figure out the rest in short order!
jackieschmidt
Gold $$ Contributor
As a Short Range Group and Score Shooter, I have never thought much about barrel indexing. The way I chamber, there is no high or low side to the muzzle end. Typically, all of my barrels for the same rifle will hit within 2 to 3 inches of each other at 100 yards.
From a machinist point of view, I suppose the whole concept of indexing finds it’s roots in the way people chamber, or to be exact, the way they set barrels up. When indicating the first several inches of a barrel on the chamber end, the result is usually muzzle runout. Often this runout is quite small, but at times can be very noticeable.
I guess the object is to get that runout pointed upwards in relation to the action.
The way I set barrels up, and chamber, the muzzle end, throat, and chamber all run in line with each other. Any thing in between those points is ignored since you can’t do anything about it anyway.
When I torque my barrels, I make it up firm with a light pressure, then with a sharpie pen, make a mark between the action ring and barre. I then torque the action untill the two markers are 3/32 apart. That usually takes around 80 pound feet. That results in a lose of headspace by less than .001 from the actual measurements.
For a threaded joint to remain stable under the loads it is subjected to under use, the joint has to be put in tension. This means sufficient torque to actually “stretch” the metal parts.
there are many of us who have played through the years with torque levels. The important thing to remember is you must make sure that the barrel actually advances. Proper thread finish, proper lubrication on the joint all come into play. Suffice to say, it is better to have a barrel a little too tight than too loose.
From a machinist point of view, I suppose the whole concept of indexing finds it’s roots in the way people chamber, or to be exact, the way they set barrels up. When indicating the first several inches of a barrel on the chamber end, the result is usually muzzle runout. Often this runout is quite small, but at times can be very noticeable.
I guess the object is to get that runout pointed upwards in relation to the action.
The way I set barrels up, and chamber, the muzzle end, throat, and chamber all run in line with each other. Any thing in between those points is ignored since you can’t do anything about it anyway.
When I torque my barrels, I make it up firm with a light pressure, then with a sharpie pen, make a mark between the action ring and barre. I then torque the action untill the two markers are 3/32 apart. That usually takes around 80 pound feet. That results in a lose of headspace by less than .001 from the actual measurements.
For a threaded joint to remain stable under the loads it is subjected to under use, the joint has to be put in tension. This means sufficient torque to actually “stretch” the metal parts.
there are many of us who have played through the years with torque levels. The important thing to remember is you must make sure that the barrel actually advances. Proper thread finish, proper lubrication on the joint all come into play. Suffice to say, it is better to have a barrel a little too tight than too loose.
AlNyhus
Silver $$ Contributor
Jackie, I took the liberty of highlighting a sentence in your reply that most don't consider.
This is a Krieger that 'Humble' Henry Rivers did for my new 30BR. I do the install as you point out with one variation. After the initial torque up, I crack the barrel loose, re-torque it and then make the witness marks. In the whole rifle pic, you can see the marks. Your thoughts on that?
Have to add a shout out to 'Humble' for his work. With Stan Ware's retirement and recent passing, 'Humble' has been doing my barrel work for several years. He's a true professional machinist and his threading, finish and chambering are absolutely top notch.
There's 10-12 barrels here for the Panda/Kodiak/Atlas 1.115 headspace actions split evenly between Stan's and Henry's work. If you blindfolded me and handed me a barrel to install, I couldn't tell you whose it was. 
Good shootin'
-Al
I had a gentleman in here a couple of days ago from the firearms industry. He worked for several large manufactures setting up production lines and making barrels. But he's not a gun guy and wanted to see how I chambered barrels. One of the first things he picked up was my HS measuring device. Nothing more than a micrometer thimble with a collar that slips over the tenon. I can measure HS to within a few tenths. If you can't measure small you can't cut small. A depth mic on a rocking HS gage is not what I would consider measuring small. I have never gotten much of a change in HS after installing the barrel.
If you look at the threads of your action it will give you an indication of where to start cutting threads on your barrel.From the start of the thread go up about 1/2 to 5/8 of an inch this is where the action will start to engage .Set the threading cutter to the exact back of the barrel "or best as you can guess" with every thing engaged.Once I get the barrel dialed in ,I like to undo the spider to indicate the high side . The copper wire in the 4 jaw is plenty to hold the barrel. This is the way the barrel will hang off of your action. Once you determine where the threads start practically turn your barrel accordingly ,I give it another 1/4 turn just in case. I like missing on the fat side rather than going all the way around to catch the top of the barrel.
jackieschmidt
Gold $$ Contributor
^^^^^^^
Same here.
jackieschmidt
Gold $$ Contributor
Al, that is about what I do. I generally snug the barrel a few times to make sure everything feels right, snug it, put the marks on, then torque it so I can see the marks have indeed moved, proving the threadEd joint actually advanced.Jackie, I took the liberty of highlighting a sentence in your reply that most don't consider.
This is a Krieger that 'Humble' Henry Rivers did for my new 30BR. I do the install as you point out with one variation. After the initial torque up, I crack the barrel loose, re-torque it and then make the witness marks. In the whole rifle pic, you can see the marks. Your thoughts on that?
Have to add a shout out to 'Humble' for his work. With Stan Ware's retirement and recent passing, 'Humble' has been doing my barrel work for several years. He's a true professional machinist and his threading, finish and chambering are absolutely top notch.
Good shootin'
Dave - I'd be interested in seeing your thimble setup. Some of the go guages I've got are a good fit with no rock, some rock like a see saw, and others (for reasons that I can't explain) have the center cut out of them so you can't even try and use the center which makes the "rocking" issue substantial. I'd wager that 90% of any amount I miss from my target is due to variability in measurement on exactly what you describe.
I use a collar and depth mic to the back of the go, but the go can still easly rock and provide .002 varience between measurements which is annoying so you end up measuring 10 times and crossing your fingers.
I'll get a pic up. Take your collar, extend it but with a closed top. Drill and reamer to fit a micrometer thimble, secure with a set screw. Calibrate on a surface plate or other flat stock. A ground HS lathe bit works fine. It combines the collar and mic into one unit. I used direct reading tenth thimbles. My one inch X 1.0625" D I screwed further out and scribed lines on out to 1.200". Large surface area on the face of the thimble squares up the gage. I have two with different ID's for HS from 1"-2"
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