Gunsmithing Barrel-Reciever Threaded Joint

[mdesign]

In Harold Vaughn's book, <span style="font-style: italic">Rifle Accuracy Facts</span>, he talks about using a SpiralLock(TM) Ramp Thread for the barrel thread so that the forces were more evenly applied across the length of the joint. Data inticated that this was better than the standard V style thread.

Anyone have any experience with this?

I have seen custom actions with a longer length tenion for a "better", more stable joint and Savage has proven that the nut design works as well. I have seen the pictures posted here by smiths that go to great precision when working on action and barrel threads and am curious as to the correlation between threads and accuracy.

If the goal is to stabilize the joint and reduce vibration, might it also be possible to epoxy the threads so as to fill in the voids?

 

[Hunt]

Re: Barrel-Reciever Threaded Joint

When using spirallocak threads, my understanding is that one of the joints become sacrificial in that there is some crush fit involved. With that said, it is usually the receiver threads. I had asked about this on benchrestcentral.com and the general consensus is to use a good firm fitting convential V thread and all would work out in the end.

Not about to crush threads on a custom action.

 

[FNuser]

Re: Barrel-Reciever Threaded Joint

I've barreled less then 20 actions on my own lathe so I'm far from an expert, It seems to me that the perfect headspace made possible by their nut system may have more real world effect on accuracy then a opposing force that bears on the receiver front. However in theory anything that increases rigidity must influence accuracy, so if you can't cut threads that fill the female perfectly maybe a compound would take up some slack, I've had the joy of cutting such threads 6 times and when I get it just right it requires a wrench to put the barrel on. thats why its critical to leave a minor diameter area so you don't pop out the last thread also that puts the flex further in the joint and act as a lock. I would think that filling the receiver with barrel would be preferable when possible though. A related question that I've never satisfied though is in this case we are saying stress actually improves the accuracy when we are trying to remove it everywhere else, this seems elementary but I've got to admit it still seems counter-intuitive.

 

[wnroscoe]

Re: Barrel-Reciever Threaded Joint

spiralock


There have been numerous discussions concerning spiralock vs the standard V or UNF threads on BR Central by Machinist and Tool & Die Makers. The argument for spiralock is the thread load is more evenly distributed across the threaded portion of the tendon with roughly 40% to 45% of the load on the first few threads and the balance being evenly distributed through out the rest of the threads. The standard V thread would have 80% to 85% of the load on the first four or so threads and decreasing for each thread from there. Harold Broughton of Broughton Barrel fame once made the statement that two threads is all you need to hold a barrel on. While I'll be using more than two threads, I have to agree. The V threads are self centering and the barrel shoulder against the receiver face is providing the lock up.

As I understand it, the Spiralock thread was primarily designed for high vibration applications where the V thread would work itself loose over a period of time. I believe the aircraft industry is the largest consumer of spiral lock threads as of now. I've never priced or used the spiral lock inserts but, I've heard figures as high as $200.00 per insert. At one time I considered using them but, if the inserts are $200.00 each, I'm passing.

 

[mdesign]

Re: Barrel-Reciever Threaded Joint

Thanks. Knowing BR shooters, someone has probably tested this and would be using it if there was a real advantage. If a person really only needed 2 threads to hold the barrel on, then why the sales pitch for the longer tenion on some of the custom actions.

On V threads, when threading a barrel, does one have to be careful to check the thread angle in the action as compared to your cutting tool to get the best fit you can?

 

[wnroscoe]

Re: Barrel-Reciever Threaded Joint

For internal and external threads I check tool alignment with a fishtail prior to cutting and adjust my threading tool cutting tip to be just at or below center. Regardless of the existing thread angle in the receiver, I cut until I get 100% cleanup after my initial tooling setup.

I went back and researched the threads concerning the spiralock inserts and threads. Mike Bryant is the one that told me about the Harold Broughton statement. There were those that tried the spiralock threads and saw no difference in accuracy in their rifles, BR Rifles at that. I doubt very seriously that any gain would be noticed in a Tactical / Comp / Hunting / Field type rifle. The cost was described as over $200.00 per insert. I'm out.

 

[300sniper]

Re: Barrel-Reciever Threaded Joint

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mdesign</div><div class="ubbcode-body"> If a person really only needed 2 threads to hold the barrel on, then why the sales pitch for the longer tenion on some of the custom actions.</div></div>

because it's a sales pitch.

i am thinking the two threads was an exaggeration. unless i saw some hard evidence that a longer than standard tennon actually improved something, i won't believe it does. i think as long as there is enough thread to keep them from pulling out, the diameter of the barrel shoulder has far more to do with the rigidity of the joint than the length of the tennon. i personally think a integrated recoil lug is more of a selling point than the longer tennon length.

these are just my thoughts. i have not done any experimenting with it.

 

[mdesign]

Re: Barrel-Reciever Threaded Joint

I've also wondered about barrel shoulder dia. Logic would seem that there would be some improvement to the stability of the joint by having the barrel shoulder be the same diameter as the action and sandwiching a precision ground lug between them.

Just from an engineering perspective, the free-body diagram would indicate that such a joint would be more stable to but weither it translates into better accuracy probably depends on other things as well.

 

[wnroscoe]

Re: Barrel-Reciever Threaded Joint

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mdesign</div><div class="ubbcode-body">On V threads, when threading a barrel, does one have to be careful to check the thread angle in the action as compared to your cutting tool to get the best fit you can? </div></div>

Remember, these are usually class 2 threads. The crest of the barrel thread never touch’s the root of the receiver thread and the crest of the receiver thread never touches the root of the barrel thread. Regardless of the receiver thread dimensions, V threads are self centering and the barrel threads should be cut to just fit the receiver threads. When all is finished, there’s clearance in the receiver / barrel thread joint. The contact faces at the barrel shoulder, recoil lug (both faces) and receiver face dictate lock up. I feel it is these contact surfaces that is the most crucial for extreme accuracy. With the receiver diameter being 1.355”ish, I’d hate to have a barrel on a field rifle with a breech diameter in the 1.350” range. I doubt it would make much if any stability difference when compared to a 1.250” or 1.200” breech. JMHO

 

[19Scout77]

Re: Barrel-Reciever Threaded Joint

Reading that book made me feel really really stupid...

Thank god for people like Mr. Vaughn!

 

[wnroscoe]

Re: Barrel-Reciever Threaded Joint

We'd probably be very surpeised to know how many rifles that set records didnt utilize the spiralock threads. My quess would be in the high 99.something % range.

 

[bigmac125]

Re: Barrel-Reciever Threaded Joint

I think that I've seen more problems from over torquing than from threads that are not perfect. I've actually loosened barrels and retorqued to 65-75 ftlbs and the things started to shoot. I guess I'm trying to say be careful with to much interferance.

 

[FNuser]

Re: Barrel-Reciever Threaded Joint

wnroscoe, O.k. but the nuts on a savage do run 1.3"ish so if a guy put a 1.35 section on a barrel say an inch in length it would look a whole lot like that. (A savage nut)I'll let you know I just got word back from hart they're doing it in a #5 1-8 .284 for me.

 

[wnroscoe]

Re: Barrel-Reciever Threaded Joint

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greengo</div><div class="ubbcode-body">wnroscoe, O.k. but the nuts on a savage do run 1.3"ish so if a guy put a 1.35 section on a barrel say an inch in length it would look a whole lot like that. (A savage nut)I'll let you know I just got word back from hart they're doing it in a #5 1-8 .284 for me. </div></div>

Numerous receivers run barrels with no lugs or nuts. 1.200" up to 1.350" and up to 31" in length.

 

[FNuser]

Re: Barrel-Reciever Threaded Joint

I'm not sure I got the point of your last post It's probably my fault, maybe my point wasn't to clear either I was merely pointing out that there were in fact several thousand "field rifles" out there like that. Something that may or may not contribute to their reputation as as "accurate" rifles besides contributing to ease of perfecting headspace expediently may be the increased smear surface the nuts give the primary torque shoulder in this case the face of the receiver as you had pointed out earlier.