Mainspring making contact with barrel.

[Jerry V Lape]

I haven't actually reached the point where I have the problem, but it appears it is going to be very close with respect to the mainspring inlet coming through the side of the stock into the barrel channel.  My best measurements indicated I should be okay but it is a lot scarier in person.  I knew I was on dangerous ground before  starting because I am putting a Ditchburn lock on an 1 1/16" swamped barrel.  We had a discussion about this combination of lock and barrel on here sometime ago and I was encouraged to proceed.  Stan also encourage me that this would work.   If the main spring protrudes into the barrel channel, what happens if I grind some main spring metal away (not a lot) carefully without heating up the spring to gain clearance.  This lock, which is very similar in size to a small Siler, has a very hefty main spring which already has an angular surface on it to make clearance with the barrel a little easier.   I have seen some examples of the barrel being relieved to accommodate the spring but I'd rather not cut much on the barrel. 

[Jim Kibler]

You can bevel the mainspring a touch or it's pretty simple to use a round bottom die sinkers chisel to cut a portion of the barrel away for clearance.  Both methods are historically correct.  There is plenty of meat on a swamped barrel at the breech for this.  The spring should be fine if just a touch of material is removed, but removing too much could cause problems.  Filing a spring is not a problem.  No need to grind.

[chuck-ia]

I'm sure someone with more experience than me will will chime in on this. Seems I break into the barrel channel on every gun I do. The last one I took a smidgen off the main spring, allthough I think filing the barrel would have been better. Looking forward to the experts advice on this. chuck

[Dennis Glazener]

I agree with Jim, I've had to do both, just remember to file or grind the main spring long ways not cross ways and polish smooth. No need to ask me how I know! Since then others told me why but I had experience!
Dennis

[Jerry V Lape]

Once again thanks for the advice.  I will report back once the spring is inlet and I can actually determine whether anything is required. 

[Jim Kibler]

You know it's kind of funny.  The modern idea is that springs should be rather finely finished and tool marks should go with the spring, but this is often not the case with original work.  Even on really good grade English or European work of the 17th or 18th centuries springs are finished relatively coarsely and file marks are often at a fairly steel angle relative to the length of the spring.  It's understandable that a heavy tool mark is a stress riser, but I think that we overestimate the impact.

[B Shipman]

I routinely file the spring and rarely run through the inlet. I don't touch the working part of the spring, that's not what causes the problem. The top part  does  and can be filed in width, beveled, without consequence to a point. All it does is hold and support the working part.

[Jim Kibler]

The upper leg of a mainspring does carry load.  Envision the spring pivoting on it's stud when load is applied to the tip.  In some cases you can see the spring drop down at the bend when the lock is cocked.  Now with that said, you can often get away with removing a little material in this region.

[Acer Saccharum]

Using a small lock on a big barrel can cause this to occur on a regular basis. Tipping the lock up at the nose will increase the likelihood of contact.

[T*O*F]

I suppose you know that the touch hole doesn't HAVE to be in the exact center of the barrel.  Dropping it a bit on a large diameter barrel can provide a bit more spring clearance.

[bgf]

I suppose you know that the touch hole doesn't HAVE to be in the exact center of the barrel.  Dropping it a bit on a large diameter barrel can provide a bit more spring clearance.

Exactly what I did with Chambers Late Ketland and 1 1/8" breech.  I also dropped the tail of the lock a little, and I never had a clearance problem -- my impression is that the contact would be near the tumbler on the upper arm of the mainspring, at least that is what it looked like was going to happen. 

[Acer Saccharum]

It's good test to lay the lock on the barrel before any plans are drawn, to see if it will locate where you want it. Put a sharpie mark for the touch hole, see if you can align it without the mainspring hitting the bbl.

[Jerry V Lape]

I did lay the lock on the barrel before ever deciding to use this lock for this rifle.  Moved the lock down about 1/32" - 3/64" below center line and all seemed to be good - and it might still be as I haven't finished inletting the spring yet.  Have one spot on the inlet which looks to be about paper thin and I am hoping that it stays that way. (Had to leave the project yesterday to pick up granddaughter and do my 5th grade homework, won't get back to it today either)  I am really not too worried about the spring going through as the advice received about relieving the barrel a little and/or taking a little off the upper arm of the spring will surely take care of it if necessary.   Decided to check on my options before the potential problem actually occurred. 

Another thought came to mind as I was reading through one of the building books which discussed using a wedge shaped shim with straight barrels to increase the stock width at the rear of the lock.  Could have solved this problem up front by silver soldering a thin flat shim on the backside of the bolster.     

[Jim Kibler]

It is absolutely no problem if the inlet for the spring breaks into the barrel channel.   It's also no problem if a touch of material is removed from the spring.  Finally it's just fine to remove a little material from the barrel.  This is all normal stuff and perfectly acceptable.  Don't sweat it!

[Acer Saccharum]

To reiterate again what Jim said, I repeat, I've seen many originals with a deep groove hogged out of the bbl, and mainsprings filed off to fit the bbl. It was absolutely acceptable for old work.

[Dennis Glazener]

I've seen many originals with a deep groove hogged out of the bbl, and mainsprings filed off to fit the bbl. It was absolutely acceptable for old work.

That's when I really embrace being "period correct"

[Jerry V Lape]

Well I don't like the looks of the inlet, but it is finally done.  I place that lock on the barrel many times before deciding to proceed.  It appeared I had clearance, not much but what should have been enough.  The mainspring and barrel are in conflict with the spring protruding through the wood into the barrel channel.  In hindsight I should have silver soldered a 1/32 thick shim on the bolster which would have given me enough standoff to leave wood between barrel and mainspring but I can't go back on that now.  Guess I will either be filing the mainspring or gouging the barrel.     

[B Shipman]

Jim, as I said , you can remove material from the top -to a point-. But as you said , you can go beyond the point.