Pre fit barrels question

RTH1800 · 2024-11-14T13:50:05-0500

I’ve been on this site since ‘09 iirc. Shooting since too long ago.

Lot of changes taking place. One that I notice is pre fit barrels. Seems no action is acceptable unless it accepts pre fits.
Has anyone compared accuracy of pre fits vs top notch custom work?
Are they equal or just “good enough”?
Would Tony Boyer compete with a pre fit or would @Terry Cross build a rifle that way? Would @Frank Green prefer a custom barreled rifle to one built as a pre fit?

Not looking for one off one group antidotes but real scientific testing.

Secant · 2024-11-14T14:01:17-0500

You might want to define what the difference is between a prefit and a "top notch custom work" barrel. In a lot of cases, whether you send an action into a smith or not, the barrelwork is exactly the same.

Mauser48 · 2024-11-14T14:05:20-0500

The same precision machining applies. The actions are held to a tight enough tolerance to where the gunsmith doesn't need to measure each one. The only real difference I'm aware of is they can time the natural curvature of the bore to the action if they have it in hand. Don't think that matters too much.

Secant · 2024-11-14T14:31:11-0500

Mauser48 said:
The same precision machining applies. The actions are held to a tight enough tolerance to where the gunsmith doesn't need to measure each one. The only real difference I'm aware of is they can time the natural curvature of the bore to the action if they have it in hand. Don't think that matters too much.

And to dovetail onto that, prefits can have the bore curvature timed as well.

oldrifleman · 2024-11-14T14:33:33-0500

As has been said before prefit does not mean sitting on a shelf at some mom and pop barrel shop. It only means the tolerances on the action are tight enough that they do not need the action to fit the barrels. In reality top shooters have been using prefits for years. Years ago I shot Centerfire Bench Rest and we would call up our friendly Barrel smith and they had had our tenon specs in their files and we would order a bunch of barrels (between 3 and 12 depending on activity and bank account). These were prefit, cut by spectacular smiths, and we installed them ourselves. I am sure other disciplines did the same. Nothing really new, it is just that the action makers just hold the actions to tighter specs so that the barrel smith don't need the action to deliver a great pre-head spaced barrel.

ma smith · 2024-11-14T14:34:12-0500

RTH1800 said:
Seems no action is acceptable unless it accepts pre fits.

This is simply because with modern CNC, the factory specs do this by default.

diggler1833 · 2024-11-14T14:45:58-0500

RTH1800 said:
I’ve been on this site since ‘09 iirc. Shooting since too long ago.

Lot of changes taking place. One that I notice is pre fit barrels. Seems no action is acceptable unless it accepts pre fits.
Has anyone compared accuracy of pre fits vs top notch custom work?
Are they equal or just “good enough”?
Would Tony Boyer compete with a pre fit or would @Terry Cross build a rifle that way? Would @Frank Green prefer a custom barreled rifle to one built as a pre fit?

Not looking for one off one group antidotes but real scientific testing.

So I have both pre-fits and custom screwed-on barrels from the same gunsmith. Two pre-fit rifles and three screwed-on to be exact.

I notice no difference in accuracy. All of the rifles are capable of accuracy that is beyond what I'm capable of.

A lot of benchrest or F-Class guys will get multiple barrels done up at once and then change them themselves...so I would say that the level of precision is more determined by the gunsmith than whether or not the barrel is screwed on by the individual or not.

reelserious · 2024-11-14T14:49:41-0500

I have 2 prefits from PVA and they are both 1/4 moa shooters.

spife7980 · 2024-11-14T14:59:10-0500

Secant said:
You might want to define what the difference is between a prefit and a "top notch custom work" barrel. In a lot of cases, whether you send an action into a smith or not, the barrelwork is exactly the same.

This.
The consistency of actions these days means a cut to spec part and a cut to fit part should be the same thing.

RTH1800 · 2024-11-14T15:06:46-0500

RTH1800 said:
Not looking for one off one group antidotes but real scientific testing.

Anyone have data?

ma smith · 2024-11-14T15:26:36-0500

RTH1800 said:
Anyone have data?

You keep asking if you need a TacOps to shoot PRS, and the answer is...NO

Howver, top shooters in every serious discipline from PRS centerfire, 22LR rimfire, and Fclass, ELR etc all use gunsmiths.
In pro-level PRS is approx 70/30 custom /pro fitment barrels vs pure DIY lego builds, with about 30% of the guys have pro-fittment (bedding) done on their chassis.

Secant · 2024-11-14T15:28:30-0500

RTH1800 said:
Anyone have data?

Don't take this the wrong way, but data about what? What do you see as the difference?

If I send a smith my action, smith measures said action, cuts a barrel, then sends me the action & barrel separately, is that a prefit or a "custom" barrel?
If the action mfg sends tenon print, smith cuts barrel based on tenon print, and then smith torques the barrel to the action, is that a prefit or a "custom"?
If smith has action in hand, measures action, and the measurements match the mfg print, is the barrel that gets subsequently cut a prefit or a "custom"?

Is the difference whether or not bore curvature is timed? Is the difference whether or not the smith torques the action to the barrel themselves? Does the engraving need to be timed? Is there something else that you are thinking of that differentiates the two?

Shanerbanner10 · 2024-11-14T21:40:13-0500

I have “data”. I’ve done barrels for a custom action with it in hand. I recorded the specs in a notebook so I no longer needed the action in hand. From that point on I span the customer “prefits”. The prefits shot just as well as the “custom fit barrel”. There is no difference.
Actions that accept Prefits are simply actions which should have better QC/QA than actions which don’t accept Prefits from a production standpoint.

JR1200W3 · 2024-11-14T23:04:36-0500

Shanerbanner10 said:
I have “data”. I’ve done barrels for a custom action with it in hand. I recorded the specs in a notebook so I no longer needed the action in hand. From that point on I span the customer “prefits”. The prefits shot just as well as the “custom fit barrel”. There is no difference.
Actions that accept Prefits are simply actions which should have better QC/QA than actions which don’t accept Prefits from a production standpoint.

@Shanerbanner, correct me if I'm wrong. The difference when your threading to fit a barrel on an action or cutting a prefit is you take several passes on the tenon threads and as you get close to the thread spec you test with the action by screwing it on. On a Prefit you just cut the threads to a predetermined spec. So on a thread to fit barrel vs a prefit you may get a slightly tighter thread fit. That is the only difference, ya?

My own interpretation: Barrel torque erases the difference.

Shanerbanner10 · 2024-11-14T23:20:38-0500

JR1200W3 said:
@Shanerbanner, correct me if I'm wrong. The difference when your threading to fit a barrel on an action or cutting a prefit is you take several passes on the tenon threads and as you get close to the thread spec you test with the action by screwing it on. On a Prefit you just cut the threads to a predetermined spec. So on a thread to fit barrel vs a prefit you may get a slightly tighter thread fit. That is the only difference, ya?

My own interpretation: Barrel torque erases the difference.

Rem 700 threads are still the standard 1.0625” x 16 tpi. The thread tolerance or “class” determines how “tight” a thread fits. Most smiths will cut class 3 threads for prefits unless the print says otherwise (Bighorn origin which if memory serves calls out for a class 2 thread).

In the case above, I would determine if a standard class 3 thread fits as it should and make a note of it. I would use the thread mic to note the pitch diameter. If it was a trued action the threads specs would likely be different than standard. You are kind of correct that a smith would typically cut the thread to fit, but that does not dictate accuracy of a rifle. The squareness of the shoulder/receiver surfaces are a major factor there along with how the barrel is indicated.

JR1200W3 · 2024-11-14T23:22:14-0500

Shanerbanner10 said:
Rem 700 threads are still the standard 1.0625” x 16 tpi. The thread tolerance or “class” determines how “tight” a thread fits. Most smiths will cut class 3 threads for prefits unless the print says otherwise (Bighorn origin which if memory serves calls out for a class 2 thread).

In the case above, I would determine if a standard class 3 thread fits as it should and make a note of it. I would use the thread mic to note the pitch diameter. If it was a trued action the threads specs would likely be different than standard. You are kind of correct that a smith would typically cut the thread to fit, but that does not dictate accuracy of a rifle. The squareness of the shoulder/receiver surfaces are a major factor there along with how the barrel is indicated.

So the difference in how you would chamber the two different types of jobs are minorly irrelevant to accuracy?

Shanerbanner10 · 2024-11-14T23:30:34-0500

Threads, for the most part, just align an action and barrel. They do not determine how square and concentric things are (unless they are horrible threads). Accuracy is more reliant on how straight the bullet starts in the rifling which is determined by indicating the barrel at setup and how square the shoulder is to the receiver.

JR1200W3 · 2024-11-14T23:35:14-0500

There's you're answer @RTH1800. There's nothing done to a thread to fit barrel vs a prefit that is significantly different in the accuracy department.

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