Co-Axial Muzzle Alignment

[Greg Walley]

I might know someone. I know everything else affects the bullet behavior at exit, twist rate, land configuration, muzzle pressure etc.
Are going to Shot and are you available for dinner one evening? If you are I can see my wife's eyes already glazing over.

I won't be at the Shot Show this year - too much to do at the shop. I'll be at the SW Nationals for two weeks, so I'll be getting as much shop time in between now and then. I hope to see you at the FISS this year...WITH A RIFLE!

 

[Greg Walley]

Wouldn’t a boat tail bullet with a trued 90° crown have the same effect as a flat base bullet with a trued chamfered crown? I guess the length and angle of the chamfered crown would make a difference but then that would also be true of the boat tail bullet base length and angle.
I have no idea but just seems that the gases would start to exit before the base of the bullet either way chamfered or boat tail.
P.S. just me thinking out loud.

Chet

I don't know if that is the case. You might have a point, although the final results on the target are about all we typically have to go by. I took flat base bullets and put a small (~0.001") score mark on the corner of the heel with a triangular file, and those bullets did not shoot very well. The release point on a boat tail is the major diameter in front of the boat tail, so it would be interesting to see how much of an effect it would have if this section were deformed.

Incidentally, with a sharp 90° crown, I saw no effect on the target when I machined the crown with the bore running out as much as 0.010" TIR. I didn't try it, but it would be interesting to see how poorly an angled crown would shoot if it were cut eccentric.

Another can of worms...an angled crown theoretically can't be cut evenly with a single-point tool feeding with the compound slide, because it will form a helix of the same angle the compound is moved from perpendicular. I suppose if the feed rate were super slow at high RPM, the imperfection doesn't amount to much. After all, I shot good groups with angled crowns too.

 

[JerrySharrett]

Another can of worms...an angled crown theoretically can't be cut evenly with a single-point tool feeding with the compound slide, because it will form a helix of the same angle the compound is moved from perpendicular. I suppose if the feed rate were super slow at high RPM, the imperfection doesn't amount to much. After all, I shot good groups with angled crowns too.

Those micro-bevels can be cut as a forming operation by taking a sharp HSS tool set on 45 degrees and just feed out. The micro-bevels can run as small as just cutting to the root of the grooves. This does make a more durable crown but the bore needs to be indicated to dead-nuts zero.

I did offer Tooley a rifle at the 2016 Super Shoot, but with his old age and arthritis he couldn't pull the Kelbly trigger set on 1/8 ounce. When my camper motor blew in West By Gawd, I offloaded 4 rifles into the van I rented to get to North Lawrence so there was no shortage of firepower!!

We'll get Dave to shoot next year.

.

 

[coyotechet]

Single point chamfered

Those micro-bevels can be cut as a forming operation by taking a sharp HSS tool set on 45 degrees and just feed out. The micro-bevels can run as small as just cutting to the root of the grooves. This does make a more durable crown but the bore needs to be indicated to dead-nuts zero.

Here is what my crowns look like with a super sharp HSS cutting tool unpolished 740 RPM/.0008 feed.

I just really enjoy indicating to .0001 at two points, or at least to what the indicators show .0001. and a bevel just a few thousands larger than the lands.
Chet

 

[Pete Wass]

This is the type crown

Those micro-bevels can be cut as a forming operation by taking a sharp HSS tool set on 45 degrees and just feed out. The micro-bevels can run as small as just cutting to the root of the grooves. This does make a more durable crown but the bore needs to be indicated to dead-nuts zero.

Here is what my crowns look like with a super sharp HSS cutting tool unpolished 740 RPM/.0008 feed.

I just really enjoy indicating to .0001 at two points, or at least to what the indicators show .0001. and a bevel just a few thousands larger than the lands.
Chet

View attachment 18747

I prefer and strive for.

Pete

 

[Pete Wass]

I have not

Pete maybe one groove was slightly deeper then the rest. Has anyone ever indicated the lands and then checked the grooves to find out that they aren't exactly concentric? If they were, there would never be a debate as to indicate on the lands or the grooves. Which brings up another point....when a barrel maker says the barrel is lapped within .0002 from end to end, is that the bore or groove diameter?

but will when I get back to my lathe. I indicated the barrel in using pins on both ends but did not check the grooves. Off the cuff, it appear to me that the barrel had not been indicated in OR who knows? There isn't a lot of metal coming out of a rim fire chamber. Weird looking chamber though.

Regarding barrel dimensions; how many among us can really tell what we get anyway?

At worst, I'll cut the tenon off and re-do it. The barrel shoots OK but just OK. I didn't pay a lot for it.

Pete

 

[HiWall]

Those micro-bevels can be cut as a forming operation by taking a sharp HSS tool set on 45 degrees and just feed out. The micro-bevels can run as small as just cutting to the root of the grooves. This does make a more durable crown but the bore needs to be indicated to dead-nuts zero.

Here is what my crowns look like with a super sharp HSS cutting tool unpolished 740 RPM/.0008 feed.

I just really enjoy indicating to .0001 at two points, or at least to what the indicators show .0001. and a bevel just a few thousands larger than the lands.
Chet

View attachment 18747

Hi Chet- Could you please show a picture of the tool that you used to cut the chamfer?

Thanks!

 

[Pete Wass]

Good looking jaw inserts

Can you show us some pictures of one, perhaps? Pretty please with sugar on it .

Thanks,

Pete

 

[coyotechet]

HSS bits

The tools or cutting bits are from McMaster Carr they are a HSS left hand tool bit but I use them as a right hand tool the 5/16 is for cutting the bore chamfer only never use it for anything else. The 3/8 tool is used for only facing both the recess and the rest of the muzzle and then use the same tool to put the outer chamfer on the barrel. The bore chamfer is only a .005 to .006 cut. The recess and facing is done in three passes with the last two cuts being only about .001 or less at 740 speed/.0003 feed.
I put a small radius on the point of each tool with a diamond lap and then stone each surface until I get a super sharp cutting tool with a burr free cut using a 10x glass to check the work.
I probably over do the crowning but I want it totally burr free and pretty. I tried some custom ground carbide bits and the where very sharp but could not always get a burr free bore chamfer.
Below is picture of the HSS bits and the carbide.
Chet

Mcmaster Carr # 3364A37 (5/16) # 3364A48 (3/8)