need tap for rifle barrel

[wdoyle1980]

I've not normally had too many problems finding a tap to match the threads on a rifle barrel. I came to you for some assistance.

The rub is that these are Square form threads. They appear to be square form, not modified square form.

OD/MajDia : .775

MinDia : .715 (aprox)

Threaded length ~.500" (measuring 6 threads in that span; ~12 threads per 1.000")


drill_hole = OD-pitch = .775"-(1/12) = .775 -.0833 = = 0.6917" diameter drill bit (aprox 22/32 or 23/32)

This is kinda what we did last time, and it stuck with me but I'm confused about the square-form threads. It looks like if I use a standard tap, I won't get squat for engagement.

I really couldn't find squat regarding these threads and how to calculate what type of tap I'd need (or where the heck to get it). Any assistance would be super helpful.

Thank you

[David Einhorn]

Have you tried: McMaster-Carr ?

[wdoyle1980]

I haven't tried them yet. I'm more-or-less trying to figure out WHAT size tap i'll need to use on the receiver so that it will accept this barrel and have good thread engagement. Basically - "how to identify what tap size to use when all you know is the above info?" I can run the equation and get a fractional size, but what if that's not a standard sized tap? What would be the next-closest standard tap I could use. I would hate to just have to lathe off the threads and do new ones. will then the wall of that barrel's chamber a bit more than I'm comfortable with.

[Steve McCarthy]

What kind of reciever are you trying to rebarrel? Brownells has the largest selection I know of.

[wdoyle1980]

The barrel is from a Marlin 1895s. The barrel appears to be a modern reproduction. I haven't heard back from Numrich regarding the threading/size for tap needed. I'll check Brownells, too. Thank you :)

[Dragons lair]

Try pressing a piece of clay into the thread then measure the pitch.
Ken

[jimmy seale]

i believe that you are describing buttress threads....but i don't know.jimmy

[wdoyle1980]

well, i measured from the barrel itself; it's in the first post. Pitch (1.00 / tpi ) == (1.00 / 12tpi) == 0.0833

I can't determine what tap size to get from the minor-diam @ 0.715" and where to find Square-form threads. These do not appear to be Acme threads or buttress (square on one side, angled on the other). I've only really had experience with the National Standard Coarse/Fine threads. I assume that I could use a tap from NSF/NSC but that it would need to be a bit bigger to allow for the square threads to engage as much as possible. I would need to do this if i couldn't locate a square-form tap or if I can't get anyone to lathe those threads for me. :(

[Dragons lair]

How about checking with marlin. Probably better answers than numrich.
Ken

[wdoyle1980]

Yes. Good call. That thought came across to me this morning when I woke up I think I got your message via dream Thanks. I'll let you know how it turns out.

[wdoyle1980]

They don't have a posted email address on their 'contact us' page. I took down their ph # and maybe will give them a call during my lunch/breaks.

[Bentiron1946]

It was most likely a proprietary tap size that only they had.

[BIGGUNDOCTOR]

A lot of those threads were done before SAE was around. They were just what the original designer felt would work. There are a lot of odd non-standardized threads on guns.

What kind of receiver are you using? What caliber barrel?

What we did was match the barrel to the receiver threads. Turned them on the lathe to fit, then ran a chamber reamer into it to set headspace. Barrels with sights on them have to be registered to the receiver so they line up properly. This rarely happens where the headspace is correct, and it has to be adjusted. Too tight is better than too loose. Too loose, and you have to trim the barrel one thread rotation to set it back enough so the reamer can recut the chamber. I would recut the barrel threads long before I cut the receiver threads. A lot easier to do, and you don't take a chance of destroying, or damaging the receiver. Get the receiver too thin, and that will also lead to an unsafe condition.

[wdoyle1980]

This is a 'new' repro barrel from numrich gun parts co. This is not an *original* 189X barrel - so i'm pretty sure this is a 'standard' threading (of SOME kind). I checked close with magnifying glass and they do not appear trapezoidal or angular (like in buttress). They appear pretty straight-wall Square Form. This is a new-production barrel labeled with Marlin script and model/caliber (45-70). There are no date stamps, but this barrel is in 'amazing' conditions and has no scratches in bore (it's new) and was like $40 on e-gunparts ;-) It's the weekend and I'm a bit lazy to try to call Marlin on the phone (they'll just tell me to call a 'smith, i'm sure ) . Maybe I'll try to bother them first thing Monday morning If I can't find the tap, and can't get the toolbit to do it on a lathe, I'll probably just lathe off the threads, drill a hole in my home-made receiver and press-fit and try to silver-solder it in place (or just rethread with an available die for barrel, tap for receiver

[BIGGUNDOCTOR]

My first question now is, is the receiver that you made heat treated?

How are you going to set the headspace?

Do you have the go / no-go headspace gages?

Do you have a chambering reamer?

A lot of replacement barrels are short chambered in order to set the headspace correctly with a reamer.

If the headspace is off (loose) you can cause a lot of damage to yourself , or kill yourself, due to a ruptured casing.

Yes, there are a lot of rifles that used square form threads, they are not uncommon at all. Taps for them on the other hand are, and if you do find a set they will be very expensive. Even though it may be a "new" barrel the threads may still be of the 1895 form, so that a new barrel can be put onto an original gun. Square threads are usually done with two taps; one roughing, and one finishing. The receiver can be threaded on a lathe to match the barrel. It can also be done at a shop that can do thread milling. As for the tool bit on the lathe, you grind your own to size, easy to do.

If you are not prepared to do the job correctly, do not do it at all.

[Bentiron1946]

Many years ago I knew an old gunsmith, Gabby Gabert, he had an old Remington rolling block action that had the thread all dinged up something terrible, His solution was to turn a section of tool steel to matching threads and make a tap out it to clean up the inside thread of the Remington action. Worked good too. Couldn't you do something like that?

[wdoyle1980]

The receiver material I'm using (or planning to use) has been pre-treated. I'm not very good at heat treating, so I'd rather spend more time cutting (slowly) than to cut fast and have to be more certain of my heat-treating abilities. I'm pretty sure (and looking at the barrel+empty brass for .45-70) that the round headspaces on the rim, much like a 357mag. I don't have the go/no gos, but they're easy to get from Midway and might just pick them up in a bit to 'be certain'. I do not have the chamber reamer, no and shouldn't need it unless I need to change the whole rear of the barrel (cut-off then re-chamber the whole barrel).

I'm not familiar with creating a tool bit for threading. I've only used taps/dies to create threads. I've used a lathe once (with my instructor) to bore a sleeve for another barrel for use in another single-shot build (.223 remington).

[BIGGUNDOCTOR]

What type of action are you making, or is it your own design?

Are you going with blackpowder 45/70 pressures, or modern day 45/70 loads?

I didn't figure that you would do the heat treating, but send it out to have it done.

What is the material that you are looking to use for the receiver?

You do realize that headspace is figured in just a few thousands of an inch. Gages are pretty mandatory when setting.

Not sure how you are going to set headspace correctly the way you are going.

Do you have a gunsmith in the area that you could talk with about your build?


Not to sound crass, or rude, but from your line of questions I would say that you are a little over your head with this project. Brownells has a lot of good gunsmithing information available. I would say a good plan here would be to put the build on hold, and do some major research on building a rifle. You may want to consider starting with a commercial, or surplus action for your first build, then progress to a DIY receiver. With the pressures involved, and having them inches from your face, you need to make sure that you are building a safe firearm. I have seen what can happen when things go wrong, and it isn't pretty. I am not trying to stop you from ever building a rifle, I just want you to live through the experience.

[wdoyle1980]

I have welded kits before, that's not too biggy since it used commercial barrels and bolts/breeches. My last homebuilt project for weaponeer.net was a 22wmr/22wrf. All of my builds utilize commercial barrels. The 22wrm used commercial barrel+ bolt from armscor. This time, I am looking to do a homebuilt break-open or falling-block design, or a re-take on a Springfield trapdoor modeled from an original Trapdoor receiver and breechblock that I want to recreate in 4130/4140. I have ordered some 3" round 4140 Chromoly Steel from onlinemetals. I use 4130 or 4140 for all of my builds. They're saying about 35 Rockwell C hardness for their heat treating. that should be more than enough tensile and yield strength to hold the barrel in place during firing. The barrel is new-production, so it can handle both the blackpowder and smokeless power loads. The barrel is already chambered for the .45-70 and the resized cartridge seats its rim right up against the barrel-notch for it. There shouldn't bee a need to headspace that, but I don't have an aversion to picking up a $30 set of gauges. I should be able to design my bolt/breech to hold that cartridge in this position, up against the face of the barrel. I like rim headspaced cartridges for that reason Unlike 30-06 or 308s that headspace off of the shoulder. My line of questions stems from the fact that all of the barrels (new/old) I have worked with have National Fine or National Fine or National Coarse threading and typically of a standard tap size. I have limited lathe experience and limited to mostly contouring and squaring; threaded once, but with a tap locked in the tailstock. I don't think you're being crass/rude - this is a blacksmith forum, not a gunsmithing forum. You just see a person <30yrs old talking about making home-built rifles. I think you had a good reason for concern. My peeps over at weaponeer.net haven't been to helpful in getting me info regarding square-form threading assistance.

[Bentiron1946]

I don't know, square threads were the way to go a long time ago. I rebarelled a Spanish Rolling block and it had square threads, my 03-A3 has them, Model 1917 Enfield, well I guess you get the idea that a lot of old guns were not mad with National Standard threads. So I maybe committing sacrilege here by suggesting that if there is enough meat left is to turn the square threads off and then put some nice National Standard threads on the barrel. If there isn't I guess you may have to look at another alternative to cutting your threads or buy a new barrel.

[BIGGUNDOCTOR]

I have done a bit of posting on Weaponeer.net in the past, and currently have over 200 parts kits laying around.

The Trapdoor receiver is only good for low pressure loads, check some reloading manuals for the different 45/70 loads, and cautions on using in older firearms designs.

Threading in the lathe is actually pretty easy, and the fit can be tailored to the barrel. At the gunsmith shop I worked at we cut all of the threads on the lathe.

I am not that far ahead of you at 44.

Even though it headspaces of of the rim, it has to be held close, or the cartridge can slip back when fired. That can lock up an action, or rupture the case. Gages are worth the money.

I believe the M1 rifle receiver is around a 45 Rockwell C. Tough, not hard.

[wdoyle1980]

I'm meeting with my metal-casting instructor tonight and will ask him about putting some time in on his lathe and see if we can cut the threads to match that barrel.

[Pault17]

Having been interested in gun-smithingfor a while now, do you have any pictures?

[wdoyle1980]

Here is a link to my post on weaponeer.net (sorry for the cross-post):

Weaponeer Forums

It's a 22wmr bolt-action build. Used the barrel and bolt from an Armscor 22wmr, the trigger and sear from the MN9130, and a homemade walnut stock from 3x3" table leg blanks doweled, shaped, stained, and sealed. I have a few other projects going simultaneously over there, but not many pictures posted yet.

[Bentiron1946]

I'm sorry but that kind of hash just wouldn't cut when I was a kid and if that is what you are doing with a .45-70 you are going to end up with it all over your face. You are down right dangerous. It is one thing to play at being a gunsmith with a .22 rim-fire magnum but a .45-70 isn't even in the same ballpark. I have seen "gun nuts" get their face rearranged by doing stupid stuff by not knowing what they were really doing and have the action blow up. Think hard and long before proceeding.