Squaring and crowning muzzle

[Lucky Shooter]

Seems that one of the fundamental aspects of cutting muzzle/crown is that the muzzle face
is square to the bore centerline and there is a certain amount of indicated "straight" centerline
behind the muzzle face.

What is the least allowable amount of "straight" at the muzzle ?

One of the most slow parts of this step is "steering" the muzzle with the outboard spider. I've done this by indicating the inside of a pilot, the outside of a pin gage and indicating the lands/grooves with a long stem indicator.

Any comments about doing this task ?

A. Weldy

 

[LVLAaron]

I use a 1.5" stem.

I stick the barrel out 1.5 inches from the chuck. Direct read at the chuck. dial that. move the indicator to the muzzle end. Dial that with the outboard spider. back and forth a few times until the last 1.5 inches is dead straight.

 

[SKWERLZ]

It not that bad to indicate in with spiders unless you occasionally spike your progress with a backwards move (DOH!) if your looking for really fast get a piloted muzzle cutter.

 

[linebaugh]

Typically I use a range rod/grizzly rod here to get very close and then I go to direct indication off the bore at the muzzle and again back about 1.5-2". I also do not cut anything other than square/flat crowns. This is mostly superstition on my part but in my head i think flat crowns leave less room for error. I do cut them recessed but I do not cut the 11 degree crowns anymore. Again this is not technically necessary, it's in my head but I also see ne gain in 11 degrees.

I am not a gunsmith nor a machinist. Im just a self taught guy who does work for myself and I put some very accurate guns together.

 

[dnellans]

I use a 1.5" stem.

I stick the barrel out 1.5 inches from the chuck. Direct read at the chuck. dial that. move the indicator to the muzzle end. Dial that with the outboard spider. back and forth a few times until the last 1.5 inches is dead straight.

The bearing surface of the bullet is much shorter than 1.5 inches - food for thought.

 

[GenePoole]

I could probably look it up, but my guess is that 11° is just to get some distance from the end in case it is dropped. A dished crown does the same thing. I do a dish and an 11° just because it looks cool.

Why 11°? My guess is that it is supposed to be 11.25° which is π/16 radians or 1/32 of a full circle. Old machinists like to work with halves (1/2, 1/4, 1/8, 1/16, etc). Half of 90° = 45°, half of 45° = 22.5°, half of 22.5° = 11.25°. New machinists work with 10ths.

 

[SKWERLZ]

The bearing surface of the bullet is much shorter than 1.5 inches - food for thought.

I think more separation between measurements points than bullets bearing length is possibly more representational of a straight path for bullet like a longer sight radius.

 

[gunsandgunsmithing]

I guess minimum would be the bearing surface length of the bullet, fwiw.

 

[LVLAaron]

The bearing surface of the bullet is much shorter than 1.5 inches - food for thought.

True. You're going to chase your tail if your two indication points are less than half an inch apart.

 

[kendog]

Had a Win 70 varmint come through several years ago in 22-250 that shot 1/2 moa consistently. UNTIL the owner had a brake put on it. Then the bullets were blowing up at 50 feet from the muzzle. I checked the work on the brake and it was as flawless as it gets. Beautiful threads, .020" bullet clearance, etc. Chucked it up in the lathe and then saw the factory muzzle was actually cut at an angle to the bore! Must have been made on a Friday...
Anyhow, it shot like a million bux with a "crooked" crown.

 

[LVLAaron]

Had a Win 70 varmint come through several years ago in 22-250 that shot 1/2 moa consistently. UNTIL the owner had a brake put on it. Then the bullets were blowing up at 50 feet from the muzzle. I checked the work on the brake and it was as flawless as it gets. Beautiful threads, .020" bullet clearance, etc. Chucked it up in the lathe and then saw the factory muzzle was actually cut at an angle to the bore! Must have been made on a Friday...
Anyhow, it shot like a million bux with a "crooked" crown.

Factory AR barrels are the same way. Many way out of square and unsafe to use with a suppressor. Usually just chasing the threads a bit and fixing the shoulder works... but it's an important detail to get right.

 

[gunsandgunsmithing]

Had a Win 70 varmint come through several years ago in 22-250 that shot 1/2 moa consistently. UNTIL the owner had a brake put on it. Then the bullets were blowing up at 50 feet from the muzzle. I checked the work on the brake and it was as flawless as it gets. Beautiful threads, .020" bullet clearance, etc. Chucked it up in the lathe and then saw the factory muzzle was actually cut at an angle to the bore! Must have been made on a Friday...
Anyhow, it shot like a million bux with a "crooked" crown.

Ive got a Savage 17hmr that way. The crown is cut so far out of square to the bore that it's as plain to see as the nose on your face, even with the naked eye...but the dang thing shoots great.

 

[762plinker]

I could probably look it up, but my guess is that 11° is just to get some distance from the end in case it is dropped. A dished crown does the same thing. I do a dish and an 11° just because it looks cool.

Why 11°? My guess is that it is supposed to be 11.25° which is π/16 radians or 1/32 of a full circle. Old machinists like to work with halves (1/2, 1/4, 1/8, 1/16, etc). Half of 90° = 45°, half of 45° = 22.5°, half of 22.5° = 11.25°. New machinists work with 10ths.

i "think" 11 degrees is stolen from nozzle design...a real pc of science in rockets. not so sure it applies to bbls and bullets. i use a FLAT MUZZLE and the end of the rifling to the muzzles gets cut at 45 degrees, inside to out at high speed to a depth of about 5-8 thou

 

[boltfluter]

Typically I use a range rod/grizzly rod here to get very close and then I go to direct indication off the bore at the muzzle and again back about 1.5-2". I also do not cut anything other than square/flat crowns. This is mostly superstition on my part but in my head i think flat crowns leave less room for error. I do cut them recessed but I do not cut the 11 degree crowns anymore. Again this is not technically necessary, it's in my head but I also see ne gain in 11 degrees.

I am not a gunsmith nor a machinist. Im just a self taught guy who does work for myself and I put some very accurate guns together.

I think the same way. A flat crown seems to be more tolerant as far as perpendicularity with the bore goes. 11 degree crowns just look cool! I just do what the customer wants, dialed in correctly of course.
Paul

 

[Judd]

I do a lot more 11 degree stuff because I’m just doing my personal rifles and they are easier to clean the suppressor back pressure carbon off of than a recessed target crown. I’m to the point where I rarely have a rifle that isn’t suppressed any longer. Seems I’ve given up match shooting for building rifles

 

[762plinker]

I do a lot more 11 degree stuff because I’m just doing my personal rifles and they are easier to clean the suppressor back pressure carbon off of than a recessed target crown. I’m to the point where I rarely have a rifle that isn’t suppressed any longer. Seems I’ve given up match shooting for building rifles

so make the muzzle flat...and much less carbon if the suppressor fits flush to the face of the muzzle..

 

[Bogusname]

I do 90* and the thread protector .100 longer. No threads, recessed 90* unless specified otherwise.

 

[Lucky Shooter]

I've read some discussions on indicating the muzzle where
there were some who recommended indicating the grooves and some
who preferred the land tops.

I have a gut feeling---at least for cut rifling---to use the land tops because
that is the primary reamed hole.

How about other, more knowledgeable, opinions ? Does it even matter ?

A. Weldy

 

[SKWERLZ]

I've read some discussions on indicating the muzzle where
there were some who recommended indicating the grooves and some
who preferred the land tops.

I have a gut feeling---at least for cut rifling---to use the land tops because
that is the primary reamed hole.

How about other, more knowledgeable, opinions ? Does it even matter ?

A. Weldy

I indicate off of the original hole diameter for cut or button but am looking forward to and answer from the professionals.

 

[Steel Mover]

I build my own ARs, my own cans with a Form 1, and shoot cast powder coated bullets. I only do recessed crowns anymore, have no idea why you have residue that you can not clean up, if you built anything.