Gunsmithing Barrel torque and flute timing help needed.

[csdilligaf]

I just chambered a Remy 700. When I set the headspace I used just hand tightening for the action while in the lathe. I marked the action and barrel with a line. When it came time to torque the barrel to 90 ftlbs the two lines grew apart by about .210" measured with calipers. So from this I guess when I do a fluted barrel, I should set the tenon length and threads so that the flute is .210" shy of lined up so they will line up at 90 ftlbs. Does this sound about right? Is this how you guys do it? The go-no go guages worked out fine but I want to make sure that with a fluted barrel I get it right.

thanks,

 

[Rthur]

I would mark it torqued to spec and use that as tdc(top dead center). Then decide if you want a flute at 12 or to straddle tdc. It shouldn't burnish the threads much as to change tdc.

R

 

[Sonic Crack]

would be easy to chamber up your barrel, torque it, mark it then have it fluted.

 

[ugsly]

When I do barrels for myself, Im not to worried about flutes lining up. TDC is more important to me then looks. .210 seems like quite a bit for the barrel to index past. How tight were your threads when you cut them?

Kc

 

[csdilligaf]

Threads were a very nice tight fit. Within .001" Pitch dia of being interferance fit. Its just so easy to buy a barrel fluted allready before chambering. For the extra $125 I dont want to get all set up to do it after chambering. I will check the next barrel I do and see if the rotation is consistant before I try a fluted one. I've got a shilen begging to be installed on something. I'm having so much fun doing my own guns that I'm running out of things that need barrels.

 

[LRI]

There's a lot of variables here.

Cylinder diameter
Barrel torque
Thread fit
Lug hardness
Pitch
Thread OD
Type of action wrench used

All of this has to be considered, so it makes challenges when coming up with a hard formula.

This is what I do:

Thread the barrel and snap the receiver on. Note the clock position relative to a flute. Now bust it loose and rotate back to the closest flute and index. Using gauge pins/feeler gauge measure the gap between receiver face/lug or lug/barrel cylinder.

Divide the pitch by the # of flutes. This gives you the distance from flute/flute the action will move when tightening. Now bounce that off your measurement. Expect a .002" "smoosh smoosh" when you snug it up for good.

Threads yield a bit the first few times you pull them up. Its a function of surface finish and the materials plastisizing a teeny bit. Lubricants on the threads also influence how far it turns when squishing up to the shoulder.

You'll find that the math lies to you when your trying to split hairs and get it spot on. When I get close I stop with the lathe. A granite tile makes for a great lapping table to peel a few .001's off of a recoil lug for that last little bit.

Its not an exact science, so its better to creep up on it rather than go too far. I get this out of the way before chambering.

Good luck.

C.

 

[csdilligaf]

Thanks, Chad. I real like the idea of lapping the recoil lug to fine tune it. You mention all the variables, they all make sense for sure. One I did not think of was any lubricant on the threads. With the threads such a close fit I did use a little way oil to help. I may have to rethink what I use and if it is compatalbe. Would anti-sieze be a bad idea or good idea?

 

[2156SMK]

Thanks, Chad. I real like the idea of lapping the recoil lug to fine tune it. You mention all the variables, they all make sense for sure. One I did not think of was any lubricant on the threads. With the threads such a close fit I did use a little way oil to help. I may have to rethink what I use and if it is compatalbe. Would anti-sieze be a bad idea or good idea?

With tight thread fits, keep some lube in there to fight galling.
I routinely cut threads to an interference fit and then finish lap the barrel and receiver together.
With such a thread fit, I never leave them dry because they will gall on you the first chance they get!