!!! I think I got a ruined action !!!

[James Jones]

I bought a Rem 700 LA , barreld action from a local guy for a great deal , the barrel is shot out and he stated that (3000+ round 6mm Ackley) but the gun was supposedly built by a highly reputable builder , fully blue printed rear of the bolt hase been sleeved the works , I pulled it appart and looked it over checked everything and it all mics out great , threads are cut .015" over spec. I measured the barrel shank and recodered everything so I would have record when I rebarrel. Well last night I decided to rebarrel it with an old SS douglas #4 barrel I had , checked everthing again dialed in the barrel and started cutting , I always fit check my threads so they are nice and tight. I tried to thread the action onto the barrel and woulden't get a full turn , so I made another .002" cut , still woulden't turn on. I stopped knowing I was at the same measurement as the old barrel and miced both and the new barrel was .001" smaller , *** !! So I take a closer look atthe threads on the old barrel and see that they are not strait , the look almost like a buttress thread but backwards , obvously when the barrel was threaded the guy diden't have this tool square to the part , not a probelm as long as your cut the action and barel at the same setting but now I have this action whose threads are dicked up and crooked and I don't see how I can straiten them out without seriously messing up the thread pitch or cutting the action VERY thin.
I have heard of some guys cutting their threads half with the compound and half with the cross slide or adjusting their compound at 32 deg rather than 29.5 and claiming that the use a "special thread pattern" so that they would get tha repeat business for the rebarrel and when the next poor bastard has to deal with it their screwed .

I'm not sure what I can do to fix this , I'm still a bit upset and haven't realy thought the trouble out clearly , so I fugured I'd ask you guys your oppinion.

 

[royinidaho]

Yo! James,

I have no idea of what you're talking about........

Cut the crap out of it, make the action as thin as is needed. Then rebarrel with a 22 Hornet of something similar.

Next time you get one of those good deals, get your hugs and kisses up front.

 

[edge]

IMO, if you want to continue, then put the old barrel in your lathe and set a tool so that it will match those threads..whatever they are. Then put your new barrel in and cut the threads. They may be Ba$tards, but they should fit fine.

edge.

 

[James Jones]

I Set up the old barrel in a lathe and adjusted the tool post to fit the threads correctly and they are 60 deg threads its just that they are cut crooked. I have talked to asveral other guys that have a good idea about what can be done to the action as I'd rather fix the problem that just adapt to the screw up , I think that I can straiten out the bad threads now that I know what the actual thread angle is. Its just gnna be hard to find the actual bottom of the thread as a 60 deg insert won't fit into the current threads , I think if I set up enough dial indicators I can either fix it or ruin it. The current thickness of the actiuon walls from the peak of the threads to the out side of the action is .178" , I think that I can probably go safely to .150" being that this is a cromemoly action.

I might get hold to some egg head parts orders at work (engineers) and have them run some numers for me to see what kind of stress that thick of action can take.

Hell If all else fails I can make a shrink fit sleeve for it out of 17-4 , make it .003" smaller than the action , bake the sleeve and freeze the action then press them together and hope for the best.

Who knows whats gonna happen , the worst case is that I wreck the action and I'm out a few hundred buck with a very expensive lesson , at least its my action.

I just hope that this was a simple mistake of the first builders part and not a stupid attempt to make their work specific so that it has to come back to them.

 

[edge]

OK, let me see if I understand the situation correctly.

You have threads that are of a 60 degree included angle, but not perpendicular to the action centerline.

If this is the case, then make the threads wider, but don't go deeper. A thread only holds along the flank anyway. What is important is that the matching thread on the barrel and action are the same angle and pitch. The NON-mating flanks are not part of the action-locking equation.

The fit will be very loose on assembly, but they will lock up tight and your barrel threads will still be standard. Just a thought.

edge.

 

[royinidaho]

Hell If all else fails I can make a shrink fit sleeve for it out of 17-4 , make it .003" smaller than the action , bake the sleeve and freeze the action then press them together and hope for the best.

Now you're talkin'

I envy you guys that know what you're talkin' about and can do that kind of stuff. Very interesting!

 

[WSmitty01]

The last set of dinked up threads I had to fix was on a small block chevy moter mounts, I just filled them in with steel JB Weld and retapped them, but than again I'm not a machinest, and they only let me work on computers where you can't use any high end tools,,anyway good-luck on your endeavor. This is an interesting thread to follow for all of us non-machinest types. By the way, that motor mount is still holding 30 years later!

 

[specweldtom]

James; no matter what you end up doing, you're still going to have a non-standard threaded tenon. Either a tilted thread or a considerably oversized thread. Obviously the turd cut the receiver thread tilted to mate with the barrel thread. To me that would be more acceptable for you to do than thinning the receiver ring at the thread root by cutting a true thread to a considerably larger diameter. From an engineering standpoint, a cylinder under internal pressure will split lengthwise at only half the pressure required to cause it to fail around its girth. Logically, the material lost by enlarging the thread diameter would be replaced by the corresponding increase in the tenon diameter, but my instinct is not to thin the receiver wall. Also, V form threads will exert a lot of radial force when made up hard, so the thicker the receiver wall, the better to resist circumferential stretching from the pitch faces pushing outward, and if it's a sort-of backwards buttress thread, it's going to exert more radial force than a correct 60 degree thread. On the other hand, if the mating pitch faces are on the more vertical side of the thread, that actually isn't bad.

Either way, I would match the thread form, chamber for a case no larger than a std magnum, make up at around 50 - 75 ft/lbs instead of 100 - 125 ft/lbs., and come up with a way to identify the non-standard thread by stamping or with an engraving pen, (maybe on the bottom of the barrel where a 'smith would see it before breaking it out. Then I would tie it down, use a long string, test fire it with several max pressure loads and check extraction and case expansion to be sure it is O.K.

On edit: added long string.

I think you can save it. Let us know what you decide, Tom