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View Full Version : Does anyone undercut their shoulders?



alinwa
07-14-2019, 04:10 AM
Like "hold side pressure on the cross slide and ease off as it comes out" undercut?

Jim Kobe
07-14-2019, 09:07 AM
Explain please

Wayne Shaw
07-14-2019, 11:36 AM
I'm going to assume he means making sure there is no "inside corner/radius" at the tenon/shoulder junction. Then again, I could be entirely wrong.

retired
07-14-2019, 12:40 PM
i do not "under cut" i do ensure the bbl radius corner,
is less than the reciever face.

alinwa
07-14-2019, 02:27 PM
I mean "actually cut the shoulder out of square" so that the outer portion of the shoulder contacts the action face before the inner portion. so that the outer part must deform before the part nearer the tenon/shoulder junction makes contact. So that the shoulder "irons in" like a head gasket.

Mike Bryant
07-14-2019, 04:58 PM
Jim Farley did when he chambered barrels. Set the compound slightly off perpendicular to the lathe bed and cut a very minute amount of taper to where the receiver face contacted the outside edge of the shoulder with the inside not touching.

sdean
07-14-2019, 08:28 PM
Iíd say if everything isnít square at that point, that lil bit at the end ainít going to make a difference. I do plunge a bit in case of an inside radius.

alinwa
07-14-2019, 11:16 PM
Iíd say if everything isnít square at that point, that lil bit at the end ainít going to make a difference. I do plunge a bit in case of an inside radius.

???

Ya' lost me there boss, what's "not square?"

sdean
07-14-2019, 11:44 PM
???

Ya' lost me there boss, what's "not square?"

Just trying to figure out why you would do that. At first glance it seemed a solution looking for a problem. But evidently you think it will improve something. I usually can follow your logic but Iím lost on this one. I mean like square is square. I just donít see if you have no radius at the shoulder how doing another step will help. Plus the fact I donít think I torque the barrel as much as you do.
I reread and see now. I still think if your set up is good and all is right then when you iron in your shoulder as you say I think you will be at the same place as not doing it. I guess this is longer and more confusing than my first post.

alinwa
07-15-2019, 03:55 AM
Barrel joints move. They move because bolt thrust unloads the joint while the barrel's being whipped about wildly.

WILDLY, like bending the barrel.

I build big guns.

I also build small guns...... I've chambered 7 barrels in 6PPC and one in 6BR in the last week. And 5 in 6X47L, just a long BR.

In My Opinion, using the 6PPC you can probably get by with 40-60ftlb torque without fear of the barrel joint unloading.

Even bumping up to the .473 casehead bolt thrust isn't horrendously increased, probably still OK in the 50-70lb range.

BUT, these rounds offer very small bolt-thrust stresses. Also IMO, bigger ones like the 300WSM needs more like 100lb........

And I am currently testing 338-378 VS 338 McCallum (338 Lapua case) VS 338"EDGE" VS necked-back-from-404-Jeffery's.

Actual-Factual repeatable 1/4moa accuracy with these big dawgs ain't a lightly realized endeavor.

jackie schmidt
07-15-2019, 08:58 AM
To answer the question in your original post, ......no.

As for the premis, it is always better to have a barrel a tad too tight than too loose.

But even the magnum cases at 60,000 psi only exert around 13,000 psi force against the bolt face. That is no where near enough force to compromise the holding power of a properly machined and properly tightened 1.062 diameter thread machined from high tensil material, such as 17-4, chrome molly, or even 416.

msalm
07-15-2019, 09:44 AM
I have done it that a time or two but just by undercutting tight to the tenon and leaving a perpendicular ring that bears on the action. It was a theoretical exercise that didnít provide any measure of improvement but didnít hurt either AFAIK. I always thought an action with a chamfer/cone fore and aft of the threads that the barrel would engage would be ideal, and couple that with a square shoulder to minimize any swaging effect. Most likely overthinking but when reading Rifle Accuracy Facts my mind tended to wander.

Dave Tooley
07-15-2019, 01:13 PM
Al

Yes there is a load on the tenon pushing it forward but there is also a load transferred to the threaded joint by chamber expansion. The larger the case diameter the more it expands and the greater the load on the joint. This would at the very least have the same effect as increasing the torque on the threads. Now we get into thread profiles and getting them to match up. lubed joint vs non lubed , what type of lube and it goes on and on.

retired
07-15-2019, 01:59 PM
DAVE,
how much torque did you use on the 338 edge ?
( i am at 150)

Dave Tooley
07-15-2019, 02:56 PM
DAVE,
how much torque did you use on the 338 edge ?
( i am at 150)

I can't get any more rotation after about 85 ft/lbs. I use 100 ft/lbs at the most.

retired
07-15-2019, 03:36 PM
ya want to see some torque specs look at nuc reactor vessels.
i have seen hollow studs with heaters in them, then torqued.
they do not go "bang" but they get some pressure/heat.

alinwa
07-15-2019, 10:00 PM
Al

Yes there is a load on the tenon pushing it forward but there is also a load transferred to the threaded joint by chamber expansion. The larger the case diameter the more it expands and the greater the load on the joint. This would at the very least have the same effect as increasing the torque on the threads. Now we get into thread profiles and getting them to match up. lubed joint vs non lubed , what type of lube and it goes on and on.


I didn't know that "lubed VS non-lubed" was an option :) (Try that on a BAT!!!)

I've been happy with Davey Dohhrrrmannns TruKote barrel lube but I'm nearly out. I've been using lead-based anti-seize and medical lanolin.

How's that for a juxtaposition..... one product is illegal, the other medical grade. hmmmm

Gene DeLoney
07-17-2019, 01:40 AM
This post jogged my memory of a fellow shooter/ experimenter Don Jackson.
If he told you something would or wouldn't work it was because he had tried it.
He at one time cut the face of his Panda action with a 5 degree negative cone and cut the barrel shoulder to the same 5 degree positive trying to achieve a more solid joint. Sort of like old Ford spark plugs....no gasket needed.
Seamed to work as he shot very well with that setup in his " Screendoor Special" light varmint made entirely of aluminum.
He kiddingly said he would like to some how weld the barrel to the action but could not come up with a feasible process.
Gene

alinwa
07-17-2019, 05:47 AM
I haven't done it on a custom action yet..... but I WILL epoxy on one of these days. Probably when I screw up and index one too far for my normal torque.

Al Nyhus
07-17-2019, 07:49 PM
Barrel joints move. They move because bolt thrust unloads the joint while the barrel's being whipped about wildly. WILDLY, like bending the barrel.

Actually, not.

As a matter of fact, I've seen one example of a BR gun that had no threads in the receiver. The barrel shank area of the B.A.T. receiver was bored to remove the threads and a narrow 30 degree taper was machined forward of the locking lug abutments. The shank of the barrel was turned to a gauge fit to the receiver's i.d. with a matching 30 degree taper on the rear that mated to the taper in the receiver. Two pinch bolts clamped the receiver to the barrel shank.

This was done to test for possible gains from 'clocking' the muzzle and the guage fit allowed the barrel to be easily rotated to any position desired. The 'clocking' tests proved inconclusive but the barrel/receiver attachment method was a non issue.

The owner, an engineer that loved to experiment, took the gun apart to show me his work while we were testing prior to the Wisconsin State NBRSA Hunter Championships. His first shot on the sighter when we went back up was a solid '10'. ;)

Good shootin'. -Al

alinwa
07-17-2019, 11:47 PM
Actually, not.

As a matter of fact, I've seen one example of a BR gun that had no threads in the receiver. The barrel shank area of the B.A.T. receiver was bored to remove the threads and a narrow 30 degree taper was machined forward of the locking lug abutments. The shank of the barrel was turned to a gauge fit to the receiver's i.d. with a matching 30 degree taper on the rear that mated to the taper in the receiver. Two pinch bolts clamped the receiver to the barrel shank.

This was done to test for possible gains from 'clocking' the muzzle and the guage fit allowed the barrel to be easily rotated to any position desired. The 'clocking' tests proved inconclusive but the barrel/receiver attachment method was a non issue.

The owner, an engineer that loved to experiment, took the gun apart to show me his work while we were testing prior to the Wisconsin State NBRSA Hunter Championships. His first shot on the sighter when we went back up was a solid '10'. ;)

Good shootin'. -Al

What did the two pinch bolts do?

Shooter71
07-18-2019, 12:35 AM
For what itís worth... I had to rebarrel a 700, when I finally got the barrel off I discovered probably the worst threading job Iíve ever seen. Very very loose and rough. Whoever did it RocSetted (verb) on there, probably figuring it would never be seen. I later asked how that barrel shot, he said really well. Might be worth an experiment.

Al Nyhus
07-18-2019, 08:58 AM
What did the two pinch bolts do?

Tightened the receiver to the barrel shank. -Al

alinwa
07-18-2019, 04:13 PM
Tightened the receiver to the barrel shank. -Al

And this shows that barrels don't whip about wildly?

retired
07-18-2019, 04:42 PM
yep al,
i think they are all wet.


And this shows that barrels don't whip about wildly?

Al Nyhus
07-18-2019, 07:22 PM
And this shows that barrels don't whip about wildly?

Well, it's germane to your statement:


Barrel joints move. They move because bolt thrust unloads the joint while the barrel's being whipped about wildly.

Good shootin'. :) -Al

retired
07-18-2019, 08:48 PM
you have us lost kind sir.
if they do not move,
why the need for pinch bolts ?
a taper fit will hold well on its on...just not in a rifle


Well, it's germane to your statement:



Good shootin'. :) -Al

alinwa
07-18-2019, 10:54 PM
Well, it's germane to your statement:



Good shootin'. :) -Al


OK..... I guess.

I can't see it, but that's what makes thee world go-round :)