Mike Rock Ballels

[mikekelly]

I bought a Mike Rock barrel blank with 5R rifling. I put it on a Rem 700 L.A. Now I want to turn it down to about the dimensions of the Rem. varmint barrels. It is only slightly smaller than the diameter of the original blank. My Gunsmith says I shouldn't do that. He says he will not guarantee the accuracy if I cut much steel off the diameter. Has anybody on this site ever lightened a Mike Rock Barrel? Was it detrimental to accuracy? Does it cause an increase in the inside diameter of the bore?

Generally you dont want to machine on a heat treated and stress releived barrel.

However, I have gotten barrels from Shilen and Lilja and have turned them down to the taper I wanted. The accuracy has not been affected. It depends greatly though on how much you take off and the imparted stress levels machined into the material when machined.
I took on the average .025 per pass.
If you have any doubts send it off to have it cryo treated and this should remove some of the surface stresses but not as good as heat treating would.
Be sure to use as small a radius (carbie inserted cutters) to avoid part felxing and chattering, if your using HSS make sure to hone your cutting edges and once again a small radius on the cutting tip would lessen part flex.
As always correct speeds and feeds will result in less stresses imparted.
IMO if you take light cuts but enough for correct tool pressure (when using carbide inserts) and correct speeds and feeds the stresses imparted will not affect the accuracy.
The Shilen barrel I turned produced groups of 3 inches at 400 yards with a 10 shot group and the Lilja barrel produced 1.7 groups at 400 yards 10 shot groups.
My personal Lothar Waltherd barreled 300 wsm Win 70 produced extremely tight goups .2's and lower @ 100 yards, .2's @ 200 yards and .5 @ 300 yards consecutivly shot, all groups were 3 shots (didnt do enough loads up for 10 shot groups)
10 shot groups will show you if the barrel wants to walk or not.
Dave

[meichele]

One problem with machining the outside diameter of a barrel after the bore has been cut is that the bore will get bigger as the outside gets smaller. I wouldnt have the barrel turned down even a little.

Umm I am gonna have to claim BS on that. As a machinist of 15 years I have never seen a dimensional change to a bore of any kind after turning the outside dia (once it has cooled if not using coolant). Thermal expansion will happen when machining if you allow the barrel to get warm. Steel moves proprotionately to the level of heat, keep it cool it doesnt move much, it will however return to original size unless you get it so hot that it enters the transitional range where you begin heat treating. I have bored a heck of a lot of holes making bushings for landing gear on aircraft and other items. In either case of turning the outside first or last the stability of the material never changed dimensionaly.
If the barrel has been properly heat treated and stress relieved the molecular structure should not change.
Furthermore heat treated and stress releived material exhibit more stability dimensionally as the molecular grain structure is more closley connected and "lined" up.
Material in the annealed condition will exhibit dimensional change as the grain structure is unstable and thus this is why you leave "grind" stock if you plan to heat treat because it will change shape.
During the turning process if you do not use coolant and allow the barrel to warm you will get dimensional change but it will not reach a certain size and stay there the heat will dissapate and the material will return to original dimensions.
If it were true every shot you take would make your bore bigger and bigger.
I believe the reason why barrel manufacutures wont warrenty it or suggest it is because they cannot control the circumstance at which a barrel is machined at other than in their shop. If you machine the barrel incorrectly you will or may ruin a barrel. All three of mine shoot extremely well and never have run into a probelm with them.
Or what about cutting the threads for a muzzle break at the most imporantant part of the barrel, the muzzle exit, no stress releiving here.
I've managed to turn three barrels and nothing has affected them yet, I will not say that this wont happen to everyone it just happens to be the case with my barrels.
Just food for thought, if the bore will expand when the outside has been machined will the chamber contract when chambered?

[chris matthews]

Daveosok,
I'll back you up on what you said.....but a barrel's inside dimensions can and will open up a little when turned down for a muzzle brake or fluted- seen it happen too many times...especially when it's a light weight barrel to begin with and the thread OD is running small to get a brake that matchs the barrel countour or when flutes run deep.
Not always but I have seen it happen enough to say that it would be easier to sell that barrel and buy one of the desired contour.

FWIW- Rock buys stressed relieved steel but then does not do any further stress relieving after the barrel making process.

[1doug]

a little long winded daveosok,you must have been in the glass bottles when you typed that. LOL [img]/ubbthreads/images/graemlins/grin.gif[/img]

[meichele]

[ QUOTE ]

but a barrel's inside dimensions can and will open up a little when turned down for a muzzle brake or fluted- seen it happen too many times...especially when it's a light weight barrel to begin with and the thread OD is running small to get a brake that matchs the barrel countour or when flutes run deep.


[/ QUOTE ]

This is from an actual gun smith and not just a machinist.