5R Chamber Runout

C

Curious

New member
Im happy with my chambering method now after some experimentation over the last 12 months or so and after reading a lot of the good material here.

I work between 4 point spiders front and back, I taper bore then ream using my back centre to push. Ive used the floating pusher method as well but I find Im getting as good if not better results using the dead centre as my tailstock is very close over the distance Im working, Ive checked and measured in many places.

Anyway, to the point.

Im just not getting as good a results with 5R barrels as I do with 3, 4 or 6 groove barrels. Typically Im getting figures in the 0.0003" TIR or very often less with all other barrels but with 5Rs its always a little more, generally 0.0005" but rarely is it much less. Now I know these are good numbers but I just dont like these 5Rs as I get vibration through the reamer as the unsupported flute is cutting and Im convinced this is what leads to the higher runout. Ive tried reaming at speeds between 70-190rpm with oil flushing between 40-80psi and Ive tried a tight pilot and leaving different amounts of cut for the reamer to take but the results are the same.

I know that 0.0005" is still good and again Im maybe getting too anal about this but is that just the way of the 5Rs and have I got to live with it? Im always much happier when chambering any other barrel as the experience and results are nicer.
 
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First, your taper boring is time consuming, unnecessary, and is probably the cause of your chatter. If you are chambering a PPC, you are only boring an 0;010" total taper. If this almost, total contact is exactly total, i.e. exactly like the reamer you will get some chatter, just like you would with a large forming tool. Too much surface contact, especially for most lathes.

With a snug fit reamer bushing you should get no more chatter on ratchet rifling than any other rifling configuration.

You say you are getting the same results with a fixed (dead center) reamer support as you are with a floating reamer pusher. Amazing. That means your tailstock is exactly in alignment with the rotating headstock. Never seen that before. We've aligned lathe tailstock/headstocks, perfectly, with very expensive laser alignment equipment. That alignment will hold for a few days or sometimes a few weeks, nut eventually the lathe will move. And, these are on floating foundations that contain several yards of reinforced concrete.

If you can give more detail as to your equipment perhaps someone can give you more help.

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5R chambering

Hey remember 5R the lands are canted the side of the lands are not square to the bottom of the lands has a tendency to cause some issues as the reamer slides up the land instead of cutting through at 90 degrees so to speak. Ask Gordy Gritters as he has a solution to chambering a 5R he is on here from time to time.
 
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JerrySharrett said:
First, your taper boring is time consuming, unnecessary, and is probably the cause of your chatter. If you are chambering a PPC, you are only boring an 0;010" total taper. If this almost, total contact is exactly total, i.e. exactly like the reamer you will get some chatter, just like you would with a large forming tool. Too much surface contact, especially for most lathes.

With a snug fit reamer bushing you should get no more chatter on ratchet rifling than any other rifling configuration.

You say you are getting the same results with a fixed (dead center) reamer support as you are with a floating reamer pusher. Amazing. That means your tailstock is exactly in alignment with the rotating headstock. Never seen that before. We've aligned lathe tailstock/headstocks, perfectly, with very expensive laser alignment equipment. That alignment will hold for a few days or sometimes a few weeks, nut eventually the lathe will move. And, these are on floating foundations that contain several yards of reinforced concrete.

If you can give more detail as to your equipment perhaps someone can give you more help.

.

.
Click to expand...

Its not a PPC Jerry. Most recently they have been cases like .223, .243, 6BR and 6.5x47s so quite a variation in case length and taper.

I have been taper boring to around 0.0060" short of full depth, my compound is set to within a thousandth or less of the correct taper over the case length, I didn't think matching the taper to within a few tenths was necessary? I taper bore until the chamber mouth will accept the first 0.250" or so of the reamer or enough so that about half the bushing length is engaged.

I have a floating pusher which I have used, I used to start by pushing with a dead centre for maybe 30% of the overall depth then change to the pusher for the rest. I found with my first 5R that the vibration was so bad I wasn't confident using the pusher as it seemed to be moving around too much in my hand so I went back to the dead centre which seemed to stabilise things better. TIR was 0.0005" so all was not lost.

As for my results using the dead centre, I have no reason to lie. I was a little surprised myself to see that I was getting very accurate chambers using the dead centre but that is the way it is. I align my tailstock using the less sophisticated methods of turning between enters and measuring diameters over 18". I appreciate this only corrects fore and aft but having checked my tailstock height and quill travel with both locks torqued Im happy.

The reason I have asked about 5Rs is because it seems to me that my chambering method is generally sound when doing non 5 groove barrel types, runout is less and this vibration (I dont want to call it chatter because its doesn't leave chatter marks on the chamber walls) isn't there.

Why do you feel taper boring isn't worthwhile?

If I didn't taper bore then on cases longer than PPC I can't get the bush to make contact before the reamer starts to cut.
 
f21sh said:
Hey remember 5R the lands are canted the side of the lands are not square to the bottom of the lands has a tendency to cause some issues as the reamer slides up the land instead of cutting through at 90 degrees so to speak. Ask Gordy Gritters as he has a solution to chambering a 5R he is on here from time to time.
Click to expand...

OK, this is interesting...... I searched Gordy Gritters and found this which may shed some light on the subject.

Thanks f21sh!


Gordy Gritters07-22-2011, 07:05 PM

MIT, I seriously doubt the reamer is the problem here. Measure the OD on the freebore section on the reamer, and if that measures OK the reamer won't be the problem. It may be something else, but you very well might be experiencing something I frequently see to one degree or another, especially in canted land barrels. Go in with your long-reach indicator and see if the free-bore section of the throat is smooth. My guess is it's not, which means you have experienced reamer chatter.

It's amazing how much reamer flex can happen in these chambers, and it's especially prone to do this in canted land barrels (it can do it in conventional land barrels also, but not nearly as readily). It will do it no matter how true you have the bore dialed in, how well-fitted the reamer bushing is in the bore, how carefully you feed the reamer in, or how big and expensive your lathe is. Carbide reamers are much stiffer and won't do it as bad, but most reamers are HSS and they will definitely do it!

I started seeing this unexplained reamer chatter phenomenon as soon as I started using canted land barrels quite a few years ago. I called the barrel maker on it a number of times, but he told me I was the only guy in the country he knew of who had seen this. I told him maybe I was the only guy who consistently measures for this all the way through the chambering process, but I see it to this day on about every canted land barrel I chamber. I still use and like canted land barrels, but I just know to be extra careful when chambering them.

I often demonstrate this in my classes (and will be showing this in-depth in an upcoming "Advanced Chambering" DVD) - I'll tell the students exactly when the chatter will start. I will be chambering along and the indicator shows absolutely no chatter whatsoever anywhere in the chamber. When the reamer is far enough in to start cutting the throat, we will then instantly be able to measure chatter through the whole length of the chamber. In every single case, when I can feel the reamer start to cut the throat, I'll tell them we'll now put the indicator in and see what happens - sure enough, we can now measure chatter beginning, not only in the throat area, but in the entire chamber. Usually its very minor and if you didn’t measure for it you’d never know anything was going on, but it’s there and can get worse if you don’t catch it in time.

Then I show them the method I now use to prevent this as much as possible - simply prebore the lands away clear to the end of the neck while you are pre-drilling and boring the body of the chamber. This allows the reamer to be completely seated (and now fully supported) before it finally gets to the throat area as it comes to full depth. When the reamer is fully supported and cutting completely before it finally picks up the throat way at the end, this really minimizes chatter problems.

Now if you have to cut a longer throat with a separate throating reamer after you've done using the main chambering reamer, you really have to be careful the chatter doesn't get away from you, since the body of the throater is completely unsupported. Both the throater and the chamber reamer will benefit by using the wax-paper wrap trick since this dampens the flex somewhat and will help keep you out of trouble.

I've tried quite a few things over the years trying to figure out what causes this and how to prevent it. In my opinion, what happens is the conventional land barrels have straight vertical sides on the lands, so when the straight vertical flutes on the reamer cuts into them, they meet square and there is no side pressure on the reamer flutes so they cut very nicely. But in canted land barrels, the lands are sloped at a pretty good angle, so the flutes of the reamer want to ride up the lands instead of cutting straight into them. Most of the canted land barrels are an odd number like 5 land/groove, so each time a reamer flute tries to ride up a land, it pushes away from that land making the opposing flutes dig into the grooves between the opposite lands (you can usually see this in a borescope if you know what to look for). Measure it and you'll see that the freebore is now 5-sided and not round!

This can happen severely enough that the effective diameter of the freebore section in the throat (the tops of the chatter) is smaller than the reamer itself. The reamer just flexes up and down in these grooves and flexes sideways just enough to form "lands" which is what you're measuring with your indicator. I've often seen it (and measured it) where the reamer chatter in the throat made the effective freebore smaller than the bullet diameter like you've seen here.

Check it out and see if maybe this is what you're experiencing. Hope this helps!
 
Thought I had seen/heard in the past that using wax paper with your reamer when cutting would dampen chatter caused by the reamer running up on the canted lands?
 
I just chambered 2 6.5 Creedmoors one was an Obermeyer 5R the other a Krieger 5R and the Obermeyer had problems no matter what I tried. No matter what anybody says the reamer will flex enough in the throat area even with a tight fitting pilot to chatter (if that is what you want to call it) personally I think it is more a function of the reamer pushing off from being temporarily unsupported. The Krieger cut beautifully with no problems what so ever. I ended up having to make a lap and lap the throat on the Obermeyer, what was left of the land would touch the bullet on factory chambered Hornady ammo
 
Take A Cut!

Curious said:
Im happy with my chambering method now after some experimentation over the last 12 months or so and after reading a lot of the good material here.

I work between 4 point spiders front and back, I taper bore then ream using my back centre to push. Ive used the floating pusher method as well but I find Im getting as good if not better results using the dead centre as my tailstock is very close over the distance Im working, Ive checked and measured in many places.

Anyway, to the point.

Im just not getting as good a results with 5R barrels as I do with 3, 4 or 6 groove barrels. Typically Im getting figures in the 0.0003" TIR or very often less with all other barrels but with 5Rs its always a little more, generally 0.0005" but rarely is it much less. Now I know these are good numbers but I just dont like these 5Rs as I get vibration through the reamer as the unsupported flute is cutting and Im convinced this is what leads to the higher runout. Ive tried reaming at speeds between 70-190rpm with oil flushing between 40-80psi and Ive tried a tight pilot and leaving different amounts of cut for the reamer to take but the results are the same.

I know that 0.0005" is still good and again Im maybe getting too anal about this but is that just the way of the 5Rs and have I got to live with it? Im always much happier when chambering any other barrel as the experience and results are nicer.
Click to expand...

There is no need to taper bore. Dial in your barrel bore and predrill. Get one of the long carbide-shanked boring bars (they sometimes come as a kit in 1/4” and 3/16” size that take the CDCD-505-CG6 inserts with a 0.007” or smaller radius. Bore the rifling away about 0.010 to 0.015” under the neck diameter and approximately 0.030” short of the total chamber length, and straight-bore the chamber and leave approximately 0.030” of material under the final chamber dimension. It is important that you leave enough material for a finish ream so the tool can “take a cut”. You must bore away the canted rifling section away so the reamer flutes take a symmetrical cut on both sides of the reamer. There is a chance your reamer isn’t ground properly with the proper stagger between the flutes, but if you don’t get chatter on standard profile rifling barrels, then it should be fine. Bore about 0.050” short of the chamber length. Again…you want to leave enough material behind so the reamer takes a cut (that is part of your problem). Ditch the floating reamer holder or pusher or whatever you have (another problem) and keep using the dead center and make sure it’s lined up within 0.001 of your center of rotation. Load the flutes up with pure lard. Your reamer should have a pilot 0.0003-0.0005” under the bore diameter. Depending on how rigid your lathe is, you should be able to ream at 160-200 RPM and a feed of 3/8 IPM or so.
 
greg and company have built a ton of rifles.
having said that i will stick with jackie's taper process.

Greg Walley said:
There is no need to taper bore. Dial in your barrel bore and predrill. Get one of the long carbide-shanked boring bars (they sometimes come as a kit in 1/4” and 3/16” size that take the CDCD-505-CG6 inserts with a 0.007” or smaller radius. Bore the rifling away about 0.010 to 0.015” under the neck diameter and approximately 0.030” short of the total chamber length, and straight-bore the chamber and leave approximately 0.030” of material under the final chamber dimension. It is important that you leave enough material for a finish ream so the tool can “take a cut”. You must bore away the canted rifling section away so the reamer flutes take a symmetrical cut on both sides of the reamer. There is a chance your reamer isn’t ground properly with the proper stagger between the flutes, but if you don’t get chatter on standard profile rifling barrels, then it should be fine. Bore about 0.050” short of the chamber length. Again…you want to leave enough material behind so the reamer takes a cut (that is part of your problem). Ditch the floating reamer holder or pusher or whatever you have (another problem) and keep using the dead center and make sure it’s lined up within 0.001 of your center of rotation. Load the flutes up with pure lard. Your reamer should have a pilot 0.0003-0.0005” under the bore diameter. Depending on how rigid your lathe is, you should be able to ream at 160-200 RPM and a feed of 3/8 IPM or so.
Click to expand...
 
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