Gunsmithing Cutting barrel to length

[texasleftychef]

Just got my barrel back from the gunsmith and noticed something that seemed kind of counter intuitive. It seems that my barrel was cut to length from the breech end which I found odd. So now the MTU is 1.25 inches just for a bit and tapers down .970 before the threads on the muzzle.

Is this normal? Maybe just how it turned out when you chop a little off both ends?

 

[natdscott]

Depends.

Yes, most smiths will part off at least 0.100-0.250" off the breech before chambering, probably to make sure they are getting into clean rifling before they indicate the reamer. Some blanks are better than others, and a good smith hopefully knows the difference. Bartlein, for example, typically cleans up very quickly.

That being said, it usually is not a matter of INCHES unless it is a stock inletting concern (very real, by-the-by).

It can also have to do with needing contour left at the MUZZLE for thread shoulder. Depends on what the measurements were. Now a 5/8-24" on a 0.970 muzzle is about without reproach...

Measure with calipers and see how long the shank actually is compared to what you sent them.

If I am being very specific on what I need a rifle to be, and I almost always am, I will draft and spec what I need cut, and send the parts I want used. It works really well, and I simply say in my letter enclosure that anything I did NOT spec, to please use their best professional judgement for how it should be done for my needs of the rifle.

Using good smiths, I haven't had the first thing come out opposite what I sent. Same as pointing bullets to the right place, it may not always turn out exactly as I had hoped, but a good smith will deliver what is asked.

ETA: my guess is stock fitment.

-Nate

 

[texasleftychef]

To be fair and transparent here I did ask them to make me a little plug with the extra barrel trimmed off to help with my reloading. They did this for me and didn’t charge but I was surprised they used the breach part of the barrel instead of cutting the muzzle.

A rifle that I got from SAC second hand had one of these but it was cut from the muzzle end of the barrel I think.

None of this probably matters and the barrel Will probably shoot just fine. I was just curious if it’s standard to cut from the breach end.

 

[bohem]

The muzzle end typically has more bellmouth from lapping as almost every barrel maker I know makes sure that the lap is poured from the muzzle end and the strokes are biased from a final push in the direction of bullet travel in order to cut down on copper fouling during breakin process. Using the breech cuts down the bellmouth and it also allows for easier stock fitment. Furthermore, when the barrel is dialed into the breech and setup for the chamber slug to be cut it takes minimal re-dialing (if any at all) to move onto cutting the tenon ring. Doing it from the muzzle is sometimes requried depending on the setback required (or not required) for a stock. There are lots of ways to do things, the way 1 shop does it can be different and accomplish the same thing.

If a barrel does have extra lap runout at the muzzlee and the chamber is cut into that runout area (sometimes this is upwards of 2-3 thousandths on the bore diameter) it can affect the point at which the bullet touches the lands by a substantial amount. If you check the math on a triangle that's a 1.5 degree angle for a opposite leg of only 0.004" then pushing the leg length up to 0.005 or 0.0055" due to extra runout will change that load length substantially. If that's the case then making it from the muzzle end was an exercise in futility and the piece of barrel is best cut from the breech and and the slug of the muzzle belongs in the recycling bucket.

Sometimes this technical benefit aids in the rifle building process.


Typically I cut them from the breech end when the contour can afford it because it allows me to inspect for bellmouth and remove it before the reamer ever enters the bore as opposed to having to gauge the chamber region and make sure that the lapping runout will completely clean up before starting the tenon process. This is one of those things I learned the hard way on a personal barrel that well but never shot "really well"... in speaking with a very well known, well accomplished rifle builder he asked me if I'd ever looked. Until that point in time I had always figured the chamber would clean out the lapping process... on a short little chamber it didn't quite clean up. Lesson learned, I look for it on every barrel. This is part of the reason why I indicate directly on the bore with a long wand instead of using range rods.

 

[natdscott]

Bohem, have you ever considered using plug gauges after your initial parting cut off the breech, or is it something that doesn't really require that level of precision?

-Nate

 

[bohem]

We do use them (deltronic pins) to fit the proper bushing but those just give us a final pass size. They don't tell roundness, if a groove is deeper than the others, or the rate of bellmouth as the bore advances into the final shape.

 

[Rubicon Precision]

I typically remove length from the muzzle end unless the customer specifies otherwise. I have one customer that always wants .5" taken off the breech then finish 27.5" length from there. The chamber is going to remove 2"+ of bore so I'm personally no too concerned about cutting length from the breech.

 

[bohem]

I typically remove length from the muzzle end unless the customer specifies otherwise. I have one customer that always wants .5" taken off the breech then finish 27.5" length from there. The chamber is going to remove 2"+ of bore so I'm personally no too concerned about cutting length from the breech.

6x47's don't are on the hairy edge of that length.
6mm BR only takes about 1.61" off

 

[Edds]

When I have a barrel chambered, I always tell the person that is chambering it how long I want the straight part in front of the action and how long I want the barrel.

 

[Rubicon Precision]

6x47's don't are on the hairy edge of that length.
6mm BR only takes about 1.61" off

It’s actually the dasher guys that request the .5” removed from breech. But for 99% of what I do, more than 2” of bore will be removed.

 

[bohem]

It’s actually the dasher guys that request the .5” removed from breech. But for 99% of what I do, more than 2” of bore will be removed.

That's not surprising as the Dasher is the same length as the BR.