Kevin Stenberg
Well-Known Member
Waco are you nose sizing your bullets? I was thinking about what Bama was getting with his cast on CB.
312290 @ 500 yards
- Thread starter waco
- Start date
waco
Springfield, Oregon
No, I am not.
Ian
Notorious member
I meant that through his observations he discovered something important. That's a great thread. I went back and snipped some of the gems that have been posted since I last read it. Waco, you might benefit from a careful read of the following selections and think about working up your velocity to full-on jacketed levels for your 500-yard+ shooting. You can do it with just lube and gas checks, but it's about 100 times more difficult to get good results even though the exact same principles that Bama discovered for himself still apply. It still all boils down to a achieving a balance of powder curve and alloy characteristics, once you get the other details of precision handloading sorted out. Bama figured out what happens when he got powder and alloy just right, there are many combinations at many different velocity levels that achieve this, but the effect we're looking for is the same.
From Bama's thread on CB:
"I started with with bore riders and to date have found them to be more accurate than other designs at higher velocities. With the bore rider it is already past the throat and in the bore almost half its length before primer ignition. Depending on alloy and pressures a portion of the bullet will be deformed. At the higher velocities bullets recovered from the most accurate rounds show swagging or "nose slump" to about 3/16" from the nose. I believe the initial pressure spike actually does the swagging. The portion of the bullet that is already closely fitted in the bore is swagged in one movement to fit the rifling, the portion in the throat is expanded to the throat and then into the rifling. This is why a loose fitting bore rider is seldom accurate because of the axial alignment. I believe it is also what makes a bore rider more accurate at high velocities ( when neck of bullet is swagged into rifling). Powder coating provides the barrier between the alloy and the barrel. This is one reason that the lubed bullets run into problems because on the heavier bullets as much as two thirds of the bullet went down the bore before the first grease groove. These are just my theories trying to explain what I have found so far." [Ian's note: My explanation for why lubed bore riders don't do HV well is not only the tendency to have a crooked launch, but also rifling abrasion and gas cutting much further up the bore as pressure on the bullet base and acceleration against the land edges peaks. Polymer jackets substantially mitigate this problem. Self-aligning bullets can be used together with a slower-burning powder to get a straight launch and peak the pressure later on in the barrel (respectively), and so are less subject to the gas-cutting factor, provided you don't have too brittle of an alloy for the job. Bore-rider's don't seem to like the slower powders as much at HV, probably due to insufficient bump in the throat.]
[snip]
"...in "pre-slumped" if you are referring to the old slug guns in which the bullet was forced into the rifling and driven down the barrel the end result is similar. Sizing the forward portion to the correct size to firmly ride the top of the rifling insures better axial alignment and reduces the chances of a non uniform slump. Since I have been playing with this I have not found any indication of any slipping or trying to strip in rifling. I am still trying to fully define or how to control the alloy to get velocity wanted, slump to fill out full rifling in forward portion of bullet for accuracy, and with enough copper to hold bullet together at the velocity." [Ian's note: Experiment more with powder burn speed at this point, 2600 fps doesn't require 6% antimony and copper additions to prevent bullet dusting, I offer 2700 fps/10" ROT with water-quenched, straight wheel weight alloy in a paper jacket as proof of that concept.]
[snip]
"In addition to the bore rider fitting snugly in rifling, the lead-in portion that is tapered where bullet transitions from .301 to .310 is "jammed" similar to a non bore riding bullet. This is controlled by seating depth. The "bore riding" portion of bullet (.301) seems to become full bore (.308) diameter before the front of bullet actually starts moving. Experience to date shows a significant reduction in group size when occurs." [Ian's note: I found the same thing, with the key being the bullet being straight, either by static or dynamic guidance, before the bump occurs.]
[snip]
"I have found from recovered bullets I am now sizing the bore rider portion of the bullet to .301 in. and the drive bands to .310 in. using a modified Redding bushing. As I go up in velocity and groups will suddenly drop to about half the previous size with the addition of just one grain of powder. Recovered bullets show little if any markings on the larger group bullets but the small group bullets show full engagement all but the last 3/16" of round tip. The overall diameter is in the .308 in. range on both driving bands and bore rider portion. The rifling marks on the bore rider portion are crisp with no scraping or shadowing on either side of each mark which indicates to me that the diameter was expanded before the bullet had a chance to really start moving down the bore. I believe that the accuracy results from having a substantial portion of the bullet already in the bore(rifling not just throat) and accurately aligned with the axis of the bore. The back section (driving bands) serve to over fill the throat to provide the seal to prevent blow-by in throat and and between bottom of groves and top of lands until pressure spike expands expands the bore rider portion."
[snip]
"If you go up into the higher velocities ie. more pressure you will probably find that all but the very tip will be expanded out to the full bore diameter with full rifling engagement. In all test so far groups suddenly get a lot smaller when expansion occurs."
[snip]
"Everything I have tested so far indicates that up to the point that the bore rider expands to full bore diameter the same parameters apply as a conventionally lubed bullet apply. Bullet fit is the main requirement for accuracy. Powder coating allows us to use the pressure to fully form the bullet to the full bore similar to the old black powder slug guns where a hammer was used to form the bullet to rifling. [Ian's note: Powder coating also aids dynamic alignment by creating a strong, slick bullet surface that can help the bullet "funnel" into the bore with less deformation, just prior to or as the bullet is bumping.] Fit is still an issue but from what we have seen alignment with bore also is a strong factor. We have started taking the old C&H sliding sleeve bore seaters with the same shoulder angle and boring out to just over the bore rider diameter and short lead to case diameter. If the necks are slightly chamfered you don't have to flare the necks and get almost no run out."
Then there's this guy, he almost gets it:
"Aha!
What happens when you hit the base hard enough to swage the nose into the barrel?
Concentricity errors are corrected,
.....and groups get smaller!!"
Well.....that's part of it. It won't happen like that if you don't establish the right environment for that to occur in the throat by pre-fitment, alloy choice, overall concentricity, powder choice, etc.
From Bama's thread on CB:
"I started with with bore riders and to date have found them to be more accurate than other designs at higher velocities. With the bore rider it is already past the throat and in the bore almost half its length before primer ignition. Depending on alloy and pressures a portion of the bullet will be deformed. At the higher velocities bullets recovered from the most accurate rounds show swagging or "nose slump" to about 3/16" from the nose. I believe the initial pressure spike actually does the swagging. The portion of the bullet that is already closely fitted in the bore is swagged in one movement to fit the rifling, the portion in the throat is expanded to the throat and then into the rifling. This is why a loose fitting bore rider is seldom accurate because of the axial alignment. I believe it is also what makes a bore rider more accurate at high velocities ( when neck of bullet is swagged into rifling). Powder coating provides the barrier between the alloy and the barrel. This is one reason that the lubed bullets run into problems because on the heavier bullets as much as two thirds of the bullet went down the bore before the first grease groove. These are just my theories trying to explain what I have found so far." [Ian's note: My explanation for why lubed bore riders don't do HV well is not only the tendency to have a crooked launch, but also rifling abrasion and gas cutting much further up the bore as pressure on the bullet base and acceleration against the land edges peaks. Polymer jackets substantially mitigate this problem. Self-aligning bullets can be used together with a slower-burning powder to get a straight launch and peak the pressure later on in the barrel (respectively), and so are less subject to the gas-cutting factor, provided you don't have too brittle of an alloy for the job. Bore-rider's don't seem to like the slower powders as much at HV, probably due to insufficient bump in the throat.]
[snip]
"...in "pre-slumped" if you are referring to the old slug guns in which the bullet was forced into the rifling and driven down the barrel the end result is similar. Sizing the forward portion to the correct size to firmly ride the top of the rifling insures better axial alignment and reduces the chances of a non uniform slump. Since I have been playing with this I have not found any indication of any slipping or trying to strip in rifling. I am still trying to fully define or how to control the alloy to get velocity wanted, slump to fill out full rifling in forward portion of bullet for accuracy, and with enough copper to hold bullet together at the velocity." [Ian's note: Experiment more with powder burn speed at this point, 2600 fps doesn't require 6% antimony and copper additions to prevent bullet dusting, I offer 2700 fps/10" ROT with water-quenched, straight wheel weight alloy in a paper jacket as proof of that concept.]
[snip]
"In addition to the bore rider fitting snugly in rifling, the lead-in portion that is tapered where bullet transitions from .301 to .310 is "jammed" similar to a non bore riding bullet. This is controlled by seating depth. The "bore riding" portion of bullet (.301) seems to become full bore (.308) diameter before the front of bullet actually starts moving. Experience to date shows a significant reduction in group size when occurs." [Ian's note: I found the same thing, with the key being the bullet being straight, either by static or dynamic guidance, before the bump occurs.]
[snip]
"I have found from recovered bullets I am now sizing the bore rider portion of the bullet to .301 in. and the drive bands to .310 in. using a modified Redding bushing. As I go up in velocity and groups will suddenly drop to about half the previous size with the addition of just one grain of powder. Recovered bullets show little if any markings on the larger group bullets but the small group bullets show full engagement all but the last 3/16" of round tip. The overall diameter is in the .308 in. range on both driving bands and bore rider portion. The rifling marks on the bore rider portion are crisp with no scraping or shadowing on either side of each mark which indicates to me that the diameter was expanded before the bullet had a chance to really start moving down the bore. I believe that the accuracy results from having a substantial portion of the bullet already in the bore(rifling not just throat) and accurately aligned with the axis of the bore. The back section (driving bands) serve to over fill the throat to provide the seal to prevent blow-by in throat and and between bottom of groves and top of lands until pressure spike expands expands the bore rider portion."
[snip]
"If you go up into the higher velocities ie. more pressure you will probably find that all but the very tip will be expanded out to the full bore diameter with full rifling engagement. In all test so far groups suddenly get a lot smaller when expansion occurs."
[snip]
"Everything I have tested so far indicates that up to the point that the bore rider expands to full bore diameter the same parameters apply as a conventionally lubed bullet apply. Bullet fit is the main requirement for accuracy. Powder coating allows us to use the pressure to fully form the bullet to the full bore similar to the old black powder slug guns where a hammer was used to form the bullet to rifling. [Ian's note: Powder coating also aids dynamic alignment by creating a strong, slick bullet surface that can help the bullet "funnel" into the bore with less deformation, just prior to or as the bullet is bumping.] Fit is still an issue but from what we have seen alignment with bore also is a strong factor. We have started taking the old C&H sliding sleeve bore seaters with the same shoulder angle and boring out to just over the bore rider diameter and short lead to case diameter. If the necks are slightly chamfered you don't have to flare the necks and get almost no run out."
Then there's this guy, he almost gets it:
"Aha!
What happens when you hit the base hard enough to swage the nose into the barrel?
Concentricity errors are corrected,
.....and groups get smaller!!"
Well.....that's part of it. It won't happen like that if you don't establish the right environment for that to occur in the throat by pre-fitment, alloy choice, overall concentricity, powder choice, etc.
Last edited:
fiver
Well-Known Member
remember what I wrote about the 2 designs you asked about in the PM.
if you look at those while reading the above I think you'll understand why I recommended the 165 over the xcb design.
and what I wrote further in that reply will make sense.
the 165 is allowed to bump from the base and the front band is already pre-slumped [and funnel shaped to flow into the barrel easier] this leaves just the nose to push back.
the flat nose doesn't have a tip to roll to one side or the other.
you'll see a strong resemblance between it's nose shape, it's front band area, and the silhouette bullet Brad mentioned earlier.
if you look at those while reading the above I think you'll understand why I recommended the 165 over the xcb design.
and what I wrote further in that reply will make sense.
the 165 is allowed to bump from the base and the front band is already pre-slumped [and funnel shaped to flow into the barrel easier] this leaves just the nose to push back.
the flat nose doesn't have a tip to roll to one side or the other.
you'll see a strong resemblance between it's nose shape, it's front band area, and the silhouette bullet Brad mentioned earlier.