Co-Axial Muzzle Alignment
- Thread starter Curious
- Start date
C
CMaier
Guest
i certainly hope that was humor.
anyone running an indicator hard enough to "score"
the material, is in the wrong business.
anyone running an indicator hard enough to "score"
the material, is in the wrong business.
Butch Lambert
Active member
Dave Tooley
Active member
Of course I was poking Al. He makes it easy. Just pointing out how ridiculous we sound sometimes.
If a gage pin can be a problem what chance do we have with a reamer bushings going in and out of a dirty bore? It really doesn't matter.
Dave,
It's funny you say that. I indicate off of the grooves when dialing in the barrel for crowning, and every time I've done it, I've noticed a little "Ring Around the Bore" caused by the indicator stylus. As I indicate right where I want my crown, this gets faced off, and a 45 degree chamfer is cut on the bore.
I got to thinking about this the other day and ended up on the Long Island Indicator website. They sell stylus' for Interapids with a phenolic ball on the end that I imagine would take care of "Ring Around the Bore"...if one decided to tackle the issue.
No...I didn't buy one.
Justin
Dave Tooley
Active member
I'll bet you could put some bore paste on a patch and in just a few passes that would disappear.
NezRongero
Member
Thanks, Dave.
Well, I clean it up some.....what happens is, since I screwed one up a while back and left a turned ring on the outside, it's become a 'feature' and now I just turn a matching ring on the inside to get rid of that scored section..... and most often they line up perty good
JerrySharrett
Senile Member
Coupla' other things;
Use a stylus with a large diameter ball. A large ball will climb out of the groove to the land much better than a small one.
On odd numbered grooves (3, 5, etc) if you are using a 4 point adjustment (4-jaw chuck or spider) place a reamer pilot bushing in the bore then indicate the bore of bushing. I know, I know, with this method you are indicating the lands but the lands are the pilot hole of the bore, it was there first.
.
Use a stylus with a large diameter ball. A large ball will climb out of the groove to the land much better than a small one.
On odd numbered grooves (3, 5, etc) if you are using a 4 point adjustment (4-jaw chuck or spider) place a reamer pilot bushing in the bore then indicate the bore of bushing. I know, I know, with this method you are indicating the lands but the lands are the pilot hole of the bore, it was there first.
.
Jerry,
Good stuff right there.
I try and use 4 groove barrels whenever I can and index the grooves with the chuck's adjustments. Makes life a whole lot simpler. Plus, if you use a 4 groove and slug your barrels prior to chambering, you can measure the slugs with a regular set of mics, if that blows your skirt up.
Having said that, I've chambered up a couple of Lilja 3 groove barrels (both were outstanding, by the way) using a reamer pilot bushing in the bore to indicate off of, just as Jerry suggests. Worked like a charm. I've never been able to figger' out why one would need a pile of gage pins to indicate bores when more than likely one has a pile of reamer bushings that they could use for the same purpose. Am I missing something?
As far as indicating off the lands, I've always thought that made more sense than using the grooves as the lands had a better chance of being dead-nuts round as compared to the grooves, my logic being that the lands were put there by a reamer...which can be made quite round...as opposed to the grooves which were either (in our case) cut or buttoned. I know, and am familiar with the "use the grooves" chain of thought, but I still think your "rounder hole" will be the lands.
Having said that, I indicate off of the grooves as there are a whole lot of more experienced people on this forum, who have chambered a metric ass-ton of barrels, and they recommend dialing-in on the grooves.
In the end though, as Dave Tooley has pointed out, it probably doesn't matter.
Justin
Pete Wass
Well-known member
On crowns:
I bought a finished, new, Rimfire barrel this summer from a lad I know and trust. The barrel was finished off by a fellow with a good reputation. A preliminary inspection with my borescope suggested it had been test fired only or fired very few shots at most.
When I got around to testing it it seemed to shoot OK. When I looked in it again with my borescope, I noticed the chamber showed reminents of one of the grooves present. I removed the barrel, chucked it up and indicated it in.
It took .015" of cut to square the muzzle off. After re-installing the barrel, I saw no difference in the way the barrel shot. I am still wondering how the reminence of a groove is present in the chamber though.
Pete
I bought a finished, new, Rimfire barrel this summer from a lad I know and trust. The barrel was finished off by a fellow with a good reputation. A preliminary inspection with my borescope suggested it had been test fired only or fired very few shots at most.
When I got around to testing it it seemed to shoot OK. When I looked in it again with my borescope, I noticed the chamber showed reminents of one of the grooves present. I removed the barrel, chucked it up and indicated it in.
It took .015" of cut to square the muzzle off. After re-installing the barrel, I saw no difference in the way the barrel shot. I am still wondering how the reminence of a groove is present in the chamber though.
Pete
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bill larson
Member
Great point!
I'll still always center the crown on the grooves, but for chamber work that gives a somewhat overriding importance to the bore.....
Greg Walley
Member
Crown Experiments
In my experience (BR gunsmithing fifteen years), I have found that rifles shoot more precisely with the standard 90° sharp target crown. If one expects gilt-edged accuracy (<0.2 minute for a full twenty-five shot aggregate), not only does the 90° crown produce the best results, but the barrels should probably be recrowned every 500 rounds or so. I’ve resurrected a lot of mediocre shooting barrels with a simple recrown job. Sometimes the results were dramatic…even with crowns that looked fine under inspection with a loupe. Recrowning benefits typically depend on how aggressive one is with their cleaning rod. Although I expect that even with careful cleaning, recrowning is good insurance for optimum precision because the muzzle becomes flared out like a blunderbuss around 0.010” from the edge, and the wear is uneven. This is apparently from the hot gases eroding the sharp transition edge of the muzzle. This wear pattern is present even on barrels cleaned only with patches (no brushing). Interestingly enough, this erosion is also present on the chamfered crowns that are reamed with a tool.
I think the chamfered crowns may be preferable for general purpose field rifles since they are more durable. If they are done properly they work very well. It is often times difficult to get the chamfered crown to cut evenly in the land-groove junction even with a perfect fitting pilot. I’ve found that if a little pressure is exerted on one side of the tool so it cuts on one flute (like Dave Tooley mentions above), it results in a more perfect transition between the lands and grooves. The far edge of the pilot will score the rifling with this method, but it can be minimized with a little EP bearing grease smeared on the pilot. Holding the tool in a collet holder (rigid or floating) even with a perfectly dialed in bore AND chamfer tool, the tool will often times cut unevenly.
As far as my experiments with chamfered crowns vs. sharp vs. lapped vs. 11° crowns, it seems to me that lapped and chamfered crowns provide excellent accuracy, but the groups don’t seem to be quite as small – almost as if the bullets are more sensitive to wind changes. Incidentally, I wasted thousands of really good bullets, an exceptionally good lot of gunpowder, and wore out a couple of very good rail-gun barrels testing the above over a three year period. In retrospect, I should have just left well enough alone and settled on the sharp 90° crown like the old timers said was the best.
An interesting tidbit about 11° crowns: Wally Siebert told me years ago that lab technician, Dan Pawlak (Hodgdon Pyrodex fame) claimed that under high-speed photography, the gases exiting around the bullet at the muzzle were perfectly cone shaped with an 11° crown. Many different angles were tried, but none of them exhibited this characteristic.
Nevertheless, I shot better aggregates and smaller groups with a sharp 90° crown than with a sharp or lapped 11°
Greg Walley
Kelbly's Inc.
In my experience (BR gunsmithing fifteen years), I have found that rifles shoot more precisely with the standard 90° sharp target crown. If one expects gilt-edged accuracy (<0.2 minute for a full twenty-five shot aggregate), not only does the 90° crown produce the best results, but the barrels should probably be recrowned every 500 rounds or so. I’ve resurrected a lot of mediocre shooting barrels with a simple recrown job. Sometimes the results were dramatic…even with crowns that looked fine under inspection with a loupe. Recrowning benefits typically depend on how aggressive one is with their cleaning rod. Although I expect that even with careful cleaning, recrowning is good insurance for optimum precision because the muzzle becomes flared out like a blunderbuss around 0.010” from the edge, and the wear is uneven. This is apparently from the hot gases eroding the sharp transition edge of the muzzle. This wear pattern is present even on barrels cleaned only with patches (no brushing). Interestingly enough, this erosion is also present on the chamfered crowns that are reamed with a tool.
I think the chamfered crowns may be preferable for general purpose field rifles since they are more durable. If they are done properly they work very well. It is often times difficult to get the chamfered crown to cut evenly in the land-groove junction even with a perfect fitting pilot. I’ve found that if a little pressure is exerted on one side of the tool so it cuts on one flute (like Dave Tooley mentions above), it results in a more perfect transition between the lands and grooves. The far edge of the pilot will score the rifling with this method, but it can be minimized with a little EP bearing grease smeared on the pilot. Holding the tool in a collet holder (rigid or floating) even with a perfectly dialed in bore AND chamfer tool, the tool will often times cut unevenly.
As far as my experiments with chamfered crowns vs. sharp vs. lapped vs. 11° crowns, it seems to me that lapped and chamfered crowns provide excellent accuracy, but the groups don’t seem to be quite as small – almost as if the bullets are more sensitive to wind changes. Incidentally, I wasted thousands of really good bullets, an exceptionally good lot of gunpowder, and wore out a couple of very good rail-gun barrels testing the above over a three year period. In retrospect, I should have just left well enough alone and settled on the sharp 90° crown like the old timers said was the best.
An interesting tidbit about 11° crowns: Wally Siebert told me years ago that lab technician, Dan Pawlak (Hodgdon Pyrodex fame) claimed that under high-speed photography, the gases exiting around the bullet at the muzzle were perfectly cone shaped with an 11° crown. Many different angles were tried, but none of them exhibited this characteristic.
Nevertheless, I shot better aggregates and smaller groups with a sharp 90° crown than with a sharp or lapped 11°
Greg Walley
Kelbly's Inc.
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?
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Darren White
New member
Dave Tooley
Active member
Greg
Did you see any differences between FB and BT bullets?
Did you see any differences between FB and BT bullets?
Greg Walley
Member
I shot zero groups with both the flat base and the boat tail bullets with all of the crown configurations. I honestly couldn't tell if there was a difference between the two bullets with the 11° or 90° sharp crowns. But both styles of bullets were seemingly more sensitive to wind changes with lapped or chamfered crowns. Admittedly, I probably only shot 300 or so boat tails, so it probably wasn't a fair test. I think I know where you are going with this...and if you're thinking what I'm thinking, in that a longer bullet with a longer boat tail would benefit from the 11° crown, I don't know. These were 22 caliber 52g bullets with a very short boat tail.
It would be interesting if someone could get Lapua or some testing facility with modern instruments to see the phenomena of gas exit and its effect on bullet behavior with different crown configurations.
Dave Tooley
Active member
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.
coyotechet
Chet
Chamfered or boat tail
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
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