Breech Gap

[DHouse]

When I tighten the tang-bolt, it pushes the barrel forward a few thousandths and creates a roughly .008"-.012" gap between the breech and stock.

What might I try to close this gap? How can one drill a tang-bolt hole with a hand-drill inside a +-.001" tolerance? Surely there's a little trick here that I don't know about. I hope 

Or if there's a thread already on this topic I would greatly appreciate any help finding it. Thanks for reading and any help guys!

-DHouse

P.S. I respect the freedom to bed a gun and the potential benefits of it, etc., but am looking for a more mechanical approach if one exists.

[Majorjoel]

You could open up the tang bolt hole just a tad (with the trigger and plate removed) and should stop the barrel movement.

[smylee grouch]

What is forcing the barrel forward? The countersink portion of the tang bolt hole or the actual hole for the screw shaft? Hope I asked that correctly.

[DHouse]

The countersink. As I tighten the tang-bolt into countersink, it pushes forward.

I drilled the hole through the trigger plate into the stock like my book said. Once contact was made with the underside of the tang I removed the barrel, transferred the mark, replaced the barrel, and drilled down through tang-mark into the trigger-plate and tapped it.

In the future maybe I can scoot that transferred mark rearward about .010"-.015" so that when I tighten the tang-bolt, it sucks tight to the stock.(?) I wish I'd thought of that. Still open to suggestions or any advice.

[akroguy]

The very same issue hit me as well on my Lancaster build.  Countersink isn't 100% concentric with the bolt hole.  Wallowing out metal or wood to make it work not an option to me.  I just epoxy bedded the breech and it sits in there nice and tight now. 

Yeah, it's cheating but it takes a lot of skill to inlet swamped barrels with exacting tolerances. I just don't have that ability now...but I'm working on it.

I think my mistake was not using a piloted countersink.  Won't do that again.

[Bob Roller]

On the few I built I used a milling machine and counterbored them and then made screws to fit.
Bob Roller

[Steeltrap]

I dunno how off center your countersink is, but you might look at obtaining a piloted countersink, make the countersink concentric. This may require a new screw with a larger diameter screw head.

You will have to measure all of this before making the countersink "again". You don't want to end up with using a bigger screw head and still have the countersink not concentric....thus a gap....and making the issue worse than when you started.

[flehto]

When using a ctsk, the work piece should be able to move so the ctsk can center the hole. Was a tool and diemaker for many years and never had any problems centering the actual ctsk w/ the hole. Did 1000s  of holes w/ a ctsk and never had any problems w/ off center ctsks and the ctsking  tools were nothing special.....Fred

[RAT]

It depends on where the slope of the screw head is hitting in the counter sink. If the counter sink and screw head are different angles it may only be hitting at the top or at the bottom. I'd start by drilling a slightly larger hole in the tang. If that doesn't work, you can adjust the counter sink in the tang. Maybe by canting your countersink forward or back... again depending on where it's hitting. It might not take much.

[jm190]

I had the same problem with one of my first builds. After making sure the tang bolt hole in the stock wasn't the problem I blackened the tang bolt hole then started the tang bolt in till it just made contact so I could see exactly where the bolt was contacting in the countersink. I then ground away the "high" spot.

John

[Dan Fruth]

The countersink in the tang needs to move toward the barrel. Use a multi flute countersink and turn it slow rpm. You will need to use a drill press to do it. Otherwise, you will need to stake the countersink over by hand. Ive done this before.

[archer829]

I did exactly what JM190 described.

[Eric Krewson]

I have this happen several times, it was particularly bad on my first build. One way I corrected the problem was to drill my initial tang hole through the tang and wrist, without removing the gun from this position I would countersink the hole in the tang at the same time at the exact same angle as the drill.

I locked the gun in the exact position with sandbags. I am drilling through the trigger plate with a tap drill in the picture but use the same set-up for the tang bolt hole.

[P.W.Berkuta]

My solution to the OP issue is to plug the threaded hole in the trigger plate and plug the hole in the stock then set up the assembly in a drill press like Eric has shown and re-drill the stock/trigger plate using the tang countersink as the guiding factor

[Mike Brooks]

Pin the barrel in first and you won't have this problem.

[Birddog6]

Mark where it is hitting on the countersink. 

1st option: Clamp the barrel in a drillpress vice, clamp it down off just a tad & cheat the hole over a tad. You end up with a oblong hole.
2nd option:  Drill for a larger head bolt & again, cheat the hole over. This may erase the oblong hole. If you were using a #8 & a #10 will go, go with the #10.
3rd:  Weld up the hole & redrill, using mild wire in a wire welder.
4th: Replace the breechplug/tang & drlll it correctly
5th: Accraglas the breech/tang area, clamp well into place & forget it. Fill holes & voids in barrel/breechplug/tang with modelers clay.

Note: 1:  Always have the barrel in, pinned, & secure before drilling the tang bolt.

 2: Always have angled Pilot holes prior to drilling tang bolt hole or the hole for the same bolt in the triggerguard.  You may get the tang hole OK, but drilling that triggerplate hole, the drill bit will try to walk away without a pilot hole.

[DHouse]

Thanks everyone for weighing in and helping me figure this out!

Dan, thank you for the tip, that is what I did, I favored the countersink toward the barrel a little bit and it helped the barrel sit back where I wanted it to. It didn't take much.

A sheet of paper .002-.003" thick is mostly unable to fit in-between the breech and where it touches the stock(the end-grain). This may be within tolerance(?), but I am a new builder, so my tendency is to second guess myself. I'm wondering if I ought to bed the breech area anyway, given the overwhelming online recommendations to do so. My next build I think I can get it much closer to perfect, and hopefully have no use for bedding.

The barrel was pinned when drilled, but the tenons/underlugs I slotted, as I've heard many builders talk about stock-expansion and given that I will take this gun from very hot/humid environments to very dry/cold ones, I felt almost obligated to do this. Is it not necessary?

[Birddog6]

I always slot them.  If it is a solid underlug I drill/pin it & come back later & make the hole oblong or a slot.
If I am using a slotted underlug, I clamp the barrel at the muzzle & the breech when I drill it, so it can't move.

I hope you have the lock in Before the barrel was put in, if it is a precarve. Because normally the lock goes where they cut the inlet & no way of moving it. You position the barrel to the lock in other words. Otherwise you may have more issues unknown at this time.

[Mike Brooks]

The barrel was pinned when drilled, but the tenons/underlugs I slotted, as I've heard many builders talk about stock-expansion and given that I will take this gun from very hot/humid environments to very dry/cold ones, I felt almost obligated to do this. Is it not necessary?

Slot the lugs after the tang screw is in. In fact, slotting is one of the last things I do.

[Waksupi]

Try chucking the tang bolt in a drill press, and use a file to remove metal from the bottom of the screw head. It may work. That is also how you index screws and bolts.