I'm planning to hang a new bartlein barrel in 6cm on my AI-AT. For those familiar with the job, would you be able to suggest where I could obtain a chamber print. If I take the specs off my existing barrels, any thing I should be especially concerned to note?
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Gunsmithing Chambering for Accuracy International
- Thread starter f>b25
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http://shop.otmtactical.com/6MM-CREEDMOOR-AI-AXMC-LONG-ACTION-REPLACEMENT-BARREL-_p_721.html
If you don't really want the headache of figuring it all out your self.
If you don't really want the headache of figuring it all out your self.
Not very likely to find a print. Measuring your existing barrel is OK. If you measure to the bolt nose with a depth micrometer you may be tempted to cut your tenon longer than the 1.499-1.500" that you are likely to measure on your existing barrel. However at a length of 1.500" there is usually only .002-.003" clearance between the breech face and the locking ring where your lug abatements are. You'll likely wind up with .015"+ bolt nose clearance. You might also cut yourself a collar to slip over the tenon to measure headspace because you wont be able to screw the action on while the barrel is in the lathe for obvious reasons.
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There's no black magic to it. M-27x2.0 thread with 0.125 relief on each end. Measure pitch diameter over wires (25.701 PD). Measure headspace from existing action face to the bolt face with a depth mic, subtract tenon length (or measure to shoulder), and use that for your go-gauge protrusion when chambering.
You'll also want a generous chamfer (80-90 thou) to act as a feed ramp, but if you're using the original as a guide, you already know this.
Thanks Gene, I am working from an original AI 308 barrel. Do you have a video to go with the pic?
Sorry, no video for that. What part of the process would be helped by a video? There's not much I can think of besides the metric threads that's any different from any other barrel job.
Like Gene has mentioned, it isn't any kind of black magic voodoo spinning up an AI barrel. The first few barrels I've ever spun up we're all for my AX.
I did make a sleeve with the ID cut to the max major diameter of the threads and ends squared up so that I could measure headspace off of the shoulder with a depth mic and go gauge. I am by no means a seasoned gunsmith but it is a pretty straightforward process.
I did make a sleeve with the ID cut to the max major diameter of the threads and ends squared up so that I could measure headspace off of the shoulder with a depth mic and go gauge. I am by no means a seasoned gunsmith but it is a pretty straightforward process.
Dave, I'm familiar with your work. A few techniques have been mentioned regarding headspace. Would you mind sharing your preferred method? It is the one part of the job I still want to study.
As I mentioned to Dave Tooley, getting the headspace correct is the part of the job I'm giving my attention to. Backspace and Diamar1492 offered their thoughts which I have found helpful.
It's just a measurement. With the bolt installed and in battery, measure from the action shoulder to the bolt face with a depth mic. Should be about 1.632 if I remember correctly. While chambering, when getting close, measure from the end of the go-gauge to the shoulder. Zero head space will be the same (1.632 in my example above). I'd shoot for a thou or two more (1.630 in my example above).
These pictures are for a Panda, but illustrate the process. I gave that one about a thou over zero headspace:
It is easy. However, I have found it easier to get consistent measurements when measuring from the collar that I made. It was annoying to try to keep the depth micrometer from running at an angle along the threads or pivoting itself when making contact with the back of the go-gauge. Sounds like my sleeve is similar to the one Backspace described, 1.063" ID so not much clearance over the threads.
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Well AI provided drawings for all their barrels. It's just numbers like I would use from any other action. I trued up two 700's this morning. Here's what's in my log book.
HS .8800" Stub .8700" Counterbore .145" +.010" (for thread pitch diameter)
I don't need anything else.
I despise using a depth mic when chambering a barrel. I have collars for different diameter tenons and different length tenons. Each has a micrometer thimble in one end. All are calibrated either on a surface plate for 1" and under or I use gage blocks for those longer than a inch. It's very easy to measure chamber depths to a few tenths.
Making those is a good exercise for any new guy. A boring bar A chunk of steel and a $50 micrometer thimble off EBay or from MSC is all that's needed.
You can splurge which is what I have and use large diameter thimbles that read directly to a tenth. The carbide face of the micrometer thimble squares up the gage and you get accurate repeatable measurements. I'd also recommend getting a cheap set of thread mics and learn a few things about thread nomenclature. You can get the needed numbers from the internet for any thread pitch. Learn to use your brain and measuring instruments instead of doing trial and error.
Remember when it comes to chambers, Measure small cut small
HS .8800" Stub .8700" Counterbore .145" +.010" (for thread pitch diameter)
I don't need anything else.
I despise using a depth mic when chambering a barrel. I have collars for different diameter tenons and different length tenons. Each has a micrometer thimble in one end. All are calibrated either on a surface plate for 1" and under or I use gage blocks for those longer than a inch. It's very easy to measure chamber depths to a few tenths.
Making those is a good exercise for any new guy. A boring bar A chunk of steel and a $50 micrometer thimble off EBay or from MSC is all that's needed.
You can splurge which is what I have and use large diameter thimbles that read directly to a tenth. The carbide face of the micrometer thimble squares up the gage and you get accurate repeatable measurements. I'd also recommend getting a cheap set of thread mics and learn a few things about thread nomenclature. You can get the needed numbers from the internet for any thread pitch. Learn to use your brain and measuring instruments instead of doing trial and error.
Remember when it comes to chambers, Measure small cut small
I would like to thank everyone who offered their expertise. I finished this and couldn't wait to test it. It shoots the Hornady factory Match to just under 1MOA. Hand loads have been 1/2 MOA at 750yrds. These are better results than I could have anticipated for my first effort. I pulled the barrel and engraved, polished and cut the tool flats and the return to zero was exact. Your input on the collar was especially helpful. Picked up a blank for a 22CM. Cutting a barrel is as enjoyable as burning one out.
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Along the lines of what dave and the others have said, making a gauge for AI barrels simplifies things. I threaded mine so I could index flutes or time the muzzle exit. I have one for each tenon size. If you make one, don’t polish it like I did. Looks pretty, but slippery as hell.
I measured a prefit barrel. Use 1.500" as your tenon length and cut threads to M27x2.0. Leave a healthy chamfer into your chamber to act as a feed ramp. Look at some pics to get an idea of what that should look like. I also made a collar to fit snug over the threads and measured my headspace with a depth mic from that. Its impossible to get a bonded AT or AX chassis with the action on it into a lathe to check headspace, unless you're using a monstrosity of a lathe. Measure a prefit barrel threads with thread wires and cut yours to match if you are okay with the fitment.
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