I have a barrel that I would like to rebore but I have been getting varying numbers on the minimum wall thickness (outside diameter - groove diameter divided by 2) after the rebore. There is agreement for .140 at the muzzle, .050 at the front sight holes and .100 at rear sight holes. However, I am interested in the minimum wall thickness for the first 12 inches of the barrel from the breech. I have been quoted .200 or .100 over groove diameter. The max SAAMI pressure is 62,000 psi and the bores I am considering are 375, 411 and 416. Thanks for the help.
Talk to the person who will be doing the reboring. They will tell you what they are willing to do, based on caliber, barrel type, etc. Whether it is safe or not, it does not matter what anyone else says, because they are not doing the work.
One morning I shot an elephant in my pajamas. How he got into my pajamas I'll never know. - Groucho Marx
Posts: 3821 | Location: Eastern Slope, Colorado, USA | Registered: 01 March 2001
Concho: No can do. The barrel is for a T/C Dimension and it has a barrel extension milled for the bolt to lock up in like an AR-15 or Benelli. Machining time is cost prohibitive and T/C's largest caliber is 300 Win Mag.
MGM make barrels for Contender and Encore, The Dimension is a bolt gun, I do not think they make barrels for it due to the extension. How thick the barrel needs to be depends on the cartridge. As said before talk to the smith doing the bore.
Mark
Posts: 1234 | Location: Arizona | Registered: 09 January 2005
In your original post, did you really mean 0,100 to 0.002", or did you really mean 0.100 to 0.200 inches over the grove diameter.
If it is any help, when I had a chrome-moly barrel rebored from .277 to .308, Danny Peterson told me that he would only do an absolute minimum of .100 wall thickness over the grove diameter. I was told the same thing by Cliff LaBounty when he did another barrel for me, and was still in business. I have seen drillings and double rifles with thinner barrels, but the cartridges operated at a lower pressure. I believe that for a new stainless steel barrel, Kreiger wants about 0.200 over grove diameter. If it were mine, I would consider the reputation of the reborer. If the 0.100 came from a reputable person, I would trust it.
Dave
One morning I shot an elephant in my pajamas. How he got into my pajamas I'll never know. - Groucho Marx
Posts: 3821 | Location: Eastern Slope, Colorado, USA | Registered: 01 March 2001
I have not seen seen the 'Notebook' reference myself, but recall reading that Julian Hatcher turned down a Springfield barrel to find out. The story I recall was that he got down to 1/16th inch over the chamber and it still held until, sick of the experiment, he blew the side out with a proof round.
The informant thought Hatcher only got that far because of the excellence of the ordnance steel and was not recommending the practice for any sporting-rifle purpose.
One downside to reboring I have heard is that you might have to shorten the barrel afterwards because the drill lacks support at the muzzle and may take an inch or two to begin running true.
Posts: 5008 | Location: Melbourne, Australia | Registered: 31 March 2009
I have rebores that were done by Cliff LaBounty, possibly THE person that defined reboring. His rule was .100" a side at the muzzle and I have rebores where he did just that. I also have a factory Ruger M77 RS 35 Whelen that goes .100" a side at the muzzle. Further I had a Zastava 9.3x62 that went .090" a side. This one below.
Posts: 1575 | Location: Either far north Idaho or Hill Country Texas depending upon the weather | Registered: 26 March 2005
I would think that if you rebored from .300 Win Mag to .411 or .416 there would be issues with feeding reliably from the magazine and feed ramp. I know that some rifles use one magazine for .243, .308, and .358 or for .270, .30-06, and .35 Whelen but .40 caliber is a big increase over .35 caliber and a HUGE increase over .30 caliber. Then there is the problem of smoothly feeding those big cartridges up the feed ramp and into the chamber as they move alternately from the left side and right side of the magazine.
In the M16/AR15 the barrel is screwed into a barrel extension. Using a barrel extension facilitates manufacturing a system in which the bolt lugs can lock into the barrel. In reality, the bolt on AR rifles doesn't really lock into the barrel. It locks into the barrel extension screwed onto the barrel. Trying to machine the locking surfaces into a one piece barrel would be a difficult task whereas the barrel extension can be machined from both sides.
AR15 barrel, bolt and barrel extension
T/C bolt, reciever, and barrel parts
Does T/C use a barrel extension? It looks that way to me. If so, rebarreling would seem the best way to go, though you might still need to deal with some feeding issues. If not, then reboring to .338 Win Mag or .358 Norma may be a more practicable alternative.
I am not a gunsmith but maybe one of the qualified gunsmiths here will weigh in on the feeding situation I discussed to confirm or deny my assumptions.
.
Posts: 10900 | Location: North of the Columbia | Registered: 28 April 2008
Gren: There are no feed rails, magazine box, etc. The feeding mechanism is a straight line single column detachable magazine. I have all ready checked for feeding issues and the cases feed perfectly due to the simplicity of the straight line feeding. I want a 416 but will accept a 375. All I am trying to get is a definite answer on the minimum wall thickness. The information is more allusive than I thought. We have not even broached the subject of barrel taper and the relation to chamber pressure in relation to distance from the breech end of the barrel. I sincerely appreciate everyone's input on this subject.
Box: Plenty of "meat" at the muzzle. The problem area is from 4" from the breech (where the barrel tapers down from the chamber area) to about 12" from the breech.
Sambar: Thanks for the lead on Hatcher's work. I looked it up on on page 201 of "Hatcher's Notebook". He turned the barrel down to 1/8" wall thickness and fired 70,000 pounds (I assume this was pounds per square inch) loads with no visible effect. He then turned the barrel to 1/16" thick over the chamber and fired 3 regular service rounds with no effect. A 75,000 pound shot blew a piece out of the barrel.
Originally posted by bobmn: I have a barrel that I would like to rebore but I have been getting varying numbers on the minimum wall thickness (outside diameter - groove diameter divided by 2) after the rebore. There is agreement for .140 at the muzzle, .050 at the front sight holes and .100 at rear sight holes. However, I am interested in the minimum wall thickness for the first 12 inches of the barrel from the breech. I have been quoted .200 or .100 over groove diameter. The max SAAMI pressure is 62,000 psi and the bores I am considering are 375, 411 and 416. Thanks for the help.
I think you need to listen to the fellow that rebores and rifles your barrel.
Butch: Which fellow should I listen to? The reborer that says .200 is the minimum wall thickness or another roborer that says .100 wall thickness is adequate? Or maybe the third reborer that I actually sent the barrel to after giving him all the information and who returned it to me after 2 months with a note that said "too thin"?
Originally posted by bobmn: ...... Or maybe the third reborer that I actually sent the barrel to after giving him all the information and who returned it to me after 2 months with a note that said "too thin"?
That says it all right there. I would put more stock in a gunsmith who had the barrel in-hand to examine and measure than in any general statements about wall thickness.
.
Posts: 10900 | Location: North of the Columbia | Registered: 28 April 2008
quote:Originally posted by bobmn:...... Or maybe the third reborer that I actually sent the barrel to after giving him all the information and who returned it to me after 2 months with a note that said "too thin"? That says it all right there. I would put more stock in a gunsmith who had the barrel in-hand to examine and measure than in any general statements about wall thickness.
+1
As usual just my $.02 Paul K
Posts: 12881 | Location: Mexico, MO | Registered: 02 April 2001
Originally posted by jpl: Depends on the bore and the pressure. Just a back of the envelope calc (hoop stress) on a .500 bore:
60ksi * 0.5 = 30,000lbs of force
If you assume barrel steel of 150ksi yield strength, you'd need 0.2 inches of steel, or a .100 wall.
So with 60ksi in a .500 bore with a .100 wall, you basically have no safety factor.
Assuming you are correct, you need to realize that the only place (on a bolt action) that the barrel wall will only be .100" is at the muzzle, where pressures will not be any where near as high as at the chamber.
Aut vincere aut mori
Posts: 4861 | Location: Lakewood, CO | Registered: 07 February 2002
My Verona O/U in 30-06 was .060 per wall (bottom of grove to OD) per side. Cliff LaBounty told me he had several pre-war double rifles through his shop in the .080 range. That doesn't mean I recommend .060; if nothing else you run a greater risk of dinging the muzzle out of round. But hoop stress isn't an issue at muzzle pressures of 1800-3000 psi. Can't opine on the breach end but Winchester Featherweights had tiny, skinny straight tapered barrels without much meat at the breech.
"Experience" is the only class you take where the exam comes before the lesson.
Posts: 11137 | Location: Texas, USA | Registered: 22 September 2003
Tigger: I have a model 70 featherweight barrel and measured it. From the breech there is a 1 1/4" cylinder at 1.2" diameter, an abrupt taper to .960" diameter and then it tapers to .635 at 11" from the breech. I believe the largest bore the featherweight comes in is 30 caliber. So .635 - .308 = .327 divided by 2 = .1635 minimum wall thickness. Thanks for your comparison to the featherweight barrel.
Working with Mr. Ackley on a rebore just before he retired, he said I needed "2" calibers, eg. .22 to .24, to have enough cleaning up of the old bore. That is on the inside.
In his books he wrote that the important thing was to have enough "meat" in the barrel to resist bending. I didn't recall the Hatcher info although I read the book many decades ago, but Mr. Ackley wrote of turning down military barrels until he could crush them with his fingers but still, before crushing, he could fire military ammo safely. So his idea, left with me, the young punk, you want enough barrel that it doesn't get bent. Makes sighting a pain. Luck. Happy Trails.
A standard re-bore uses a reamer to clean the old rifling plus enough meat to prevent chattering. If I remember his description correctly, Cliff LaBounty would re-bore double rifles intact (without separating the barrels) by literally cutting the lands out with a tool similar to the rifling cutter, cut the bore the same way and then rifle the barrel. In all, many, many, and many more passes than a simple re-bore. The cutting head was flexible and would follow the arc of the barrels as soldered together. He did a trial job for Holland's on the recommendation of a mutual friend and charged them $900. By comparison a standard re-bore less chambering usually runs under $200. He told me that Holland's called him after receiving that first trial set and were happy with the quality but he needed to understand that no one in their market would give him professional credibility for that low price. So he bumped his price to $1300 and became the premier (as in only) double rifle re-borer in the US. And did much of the work for Europeans wanting to give old shot-out doubles new life. I don't know the gentleman that bought LaBounty's business and whether he wanted the double rifle work; a large percentage of the guns were that were candidates had been done by that time but I'm sure they crop up from time to time. But I always thought that was a fun story.
So if you want to re-bore a single barrel to a close caliber I suppose for $650 (half of a double barrel set) you could have gotten it done around 1990. Today, maybe $1200 or more.
"Experience" is the only class you take where the exam comes before the lesson.
Posts: 11137 | Location: Texas, USA | Registered: 22 September 2003
Originally posted by iiranger: Working with Mr. Ackley on a rebore just before he retired, he said I needed "2" calibers, eg. .22 to .24, to have enough cleaning up of the old bore. That is on the inside.
In his books he wrote that the important thing was to have enough "meat" in the barrel to resist bending. I didn't recall the Hatcher info although I read the book many decades ago, but Mr. Ackley wrote of turning down military barrels until he could crush them with his fingers but still, before crushing, he could fire military ammo safely. So his idea, left with me, the young punk, you want enough barrel that it doesn't get bent. Makes sighting a pain. Luck. Happy Trails.
That all makes sense to me. Put another way, long before you have dangers of a blow-up, your grouping will go to hell and the impacts will walk as the barrel heats up.
Posts: 5008 | Location: Melbourne, Australia | Registered: 31 March 2009
I just had a back and forth with Jim Dubbell of delta/Clearwater and he says .100 on each side min. I specifically asked about a .600 muzzle to .366 bore. Said he has done lots of model 70s (my gun) to 9.3. There is obviously a range of acceptable thicknesses based on the one doing the work. Jim's name comes up a lot and is the reason I contacted him in the first place. Good luck.
Originally posted by BaxterB: I just had a back and forth with Jim Dubbell of delta/Clearwater and he says .100 on each side min. I specifically asked about a .600 muzzle to .366 bore. Said he has done lots of model 70s (my gun) to 9.3. There is obviously a range of acceptable thicknesses based on the one doing the work. Jim's name comes up a lot and is the reason I contacted him in the first place. Good luck.
Imagine that.
Posts: 1575 | Location: Either far north Idaho or Hill Country Texas depending upon the weather | Registered: 26 March 2005
