Chambering a 338 Lapua Magnum?

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pinzmann

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I'm getting ready to chamber a barrel in 338LM. I'm fairly new at this as I've only done about 8 chamber jobs and all have been short to medium calibers. I usually indicate at the area where the lands meet the bullet and the bore at the muzzle. With the length of this caliber my indicator can't reach that far only to about where the neck/shoulder junction. Is this good enough or is there a better method?
 
That's about as far as I can reach with an Interapid indicator with 2 5/8" long stem. I've done several .338 Lapua's indicating in as far as I can reach with the Interapid indicator with the long point. It is a .0005" indicator between hash marks, so I just work with the indication until I can get the same reading from one groove to the next all around the bore. I indicate as far as a I can reach with the indicator, drill out most of the chamber and open it up to .010" under shoulder diameter with a boring bar for the full length minus .050" of what I drilled to keep from running the boring bar into the bevel at the drill end. Then open up the front edge of the bored hole to reamer shoulder diameter push the reamer in with a dead center for most of the length of the chamber and then towards the end of the chamber switch over to a floating pusher. The dead center gives support until the pilot gets into the bore. For most of the chamber the pilot is unsupported. If you try to push the reamer with a floating pusher with the pilot unsupported then you risk having chatter. Better to push it with the dead center as long as your dead center is centered and then switch over to the pusher when the pilot gets into the lands.

As to good enough or is there a better method, on this forum that's opening up a can of worms. There are a few people here who use different methods and will swear up and down that their method is the best. I'm unconvinced that other methods are better and I've tried everything that comes down the pike. It all comes down to how it shoots when you're done. If it shoots well, you've done a good job.
 
pinzmann said:
I'm getting ready to chamber a barrel in 338LM. I'm fairly new at this as I've only done about 8 chamber jobs and all have been short to medium calibers. I usually indicate at the area where the lands meet the bullet and the bore at the muzzle. With the length of this caliber my indicator can't reach that far only to about where the neck/shoulder junction. Is this good enough or is there a better method?
Click to expand...

Indicate as far in as possible before the last reamer cuts, .100" before final reamer cut borescope the throat cut band area looking for a concentric equal band length, if band length is not equal distant then readjust barrel and re-ream in .020" increments until throat band is equal length 360 degrees.

When throat band length is equal distant and perfect then chamber is absolutely concentric to bore at its furthest most length...................Don
 
Over the last three years I've chambered hundreds of LM barrels. I have a 200 more to do this year. Mike does it the same way I do. Long stem Interapid and then go to work. The advantage I have is I use a three flute caliber specific roughing drill to start with. With the finish reamer I make two passes. One to clean up the roughed in hole. Clean everything up, take a measurement then the final pass. It's even more fun doing 50 cal. chambers but I set the barrels up the same way. Chambering three 50's right now.

Mike

Is the chatter issue caused by misalignment using the floating holder or rigidity? I see it more on cases with 40 degree shoulders. If I can't use a roughing drill, caliber specific or at least the parent case for a wildcat, I start the chamber with the finish reamer until I have about .100" of the body cut. Then rough it out with a drill and then back to the finish reamer. That has eliminated chatter problems for me on sharp shouldered cases.


Dave
 
Dave, I think the chatter issue is when the pilot isn't in the bore using a floating pusher that the only place the reamer is supported is where the shoulder is running in the bore. The dead center gives the reamer support in two locations, the shoulder and the rear of the reamer. With my current lathe, I thought I was getting reamer sized chambers pushing all the way with a dead center. I couldn't feel any sideways movement in the reamer when it was full depth. I cut two PPC chambers for me, one pushing the reamer with the dead center and the other with the pusher. The pusher cut the smaller chamber as I couldn't use brass from the other barrel in it. It had no effect on accuracy, just brass size. After that I at least finish the chamber with the pusher if I don't ream the whole chamber with it. If the pilot is in the bore, I use the pusher. If it's not then I push with the dead center until the pilot gets into the bore, then switch to the pusher. Probably could switch over sooner as after the reamer is cutting on the taper it's supported. Seems like chatter is usually a reamer problem as I've had very few reamers that would do it and you're right they were usually Ackley's. Finishing up a .423 on a Jeffry's case today for a customer's wife in Alaska.
 
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