Bore Rider Design

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  • Last Post 13 January 2022
Wm Cook posted this 08 January 2022

Disclaimer; I've been shooting cast for 30 years but it's only been in the past two years that I focused on cast accuracy. In short I'm not smart enough to eat at the big people table when it comes to cast accuracy.  But to a degree I'm smart enough to listen to what they say and I do catch the occasional cuss word.

Two years ago I would have flunked the test for the definition of bore rider vs bearing surface.  Even today there may be a dispute about where bore riders design ends and bearing surface begins. But I hope we can start out with the expectation that bore riders must make contact with the lands.  between 20/1 and Linotype are a couple of variables that makes this a pointless to argue over.

Borerider accuracy: Pieces of the puzzle started to fall together when Covid hit and I started to spend a lot of time at the bench.  After a through weeding out of my gun safe I wound up with a new Savage 10F in .308.  That led to a second 10F in .308.  That was the start of the rabbit hole that had me hooked on the number of variables that must be controlled for accuracy. Not many will argue that cast accuracy is significantly tougher to achieve than jacketed accuracy.  And although I'm talking about bore riders I believe the majority of folks will agree that a properly fitted tapered design will be more accurate then a borerider. 

From Ken

i have always thought that bore riders are a good way to get down to about 1 moa, but full groove diameters necessary to get much under that

But I hope to have this thread focus on boreriders because it is user friendly for a number of shooters.  I think tapered design is better but there's a steep learning curve to understanding bullet to throat fit. 

A couple years ago the only competitive mold I had was a Lyman 311299.  This is a borerider design.  I may be way off base but it strikes me that the freebore design is a good middle of the road choice for a production rifle.  As long as the freebore can take .310 sized shanks you can get the gas check at the bottom of the neck and you should be reasonably accurate.  I believe the freebore design started with the Springfield four groove barrel way back when but I'm not a historian, ballistics expert or a machinist so others know a lot more than me. 

Unique to the .308 rig I'm working with is that the bore is oversized.  As best I can tell the bore on this barrel is ~ .3014.  I've tried to measure bore (tip to tip lands) every way come Sunday and its hard as heck for me to get an actual measurement on the bore.  I've tried measuring, using a small bore gauge, pound cast, chamber side bullet tap and even  reverse engineering guesstimate to see where the lands contact the nose (non bore riding bullet) but everything boiled down to an estimated ~ .3014 bore.

My two cavity Lyman 311299 drops similar bullets with a ~ .2985 to ~ .3004 nose.  The dimensions differ through the length of the nose but you get the picture.  With some support from someone on the forum I was hand fed the how to beagle a mold.  I haven't received my certification yet on Beagling but I've come far enough that I can compare nose to lands tolerance as an independent variable to cast accuracy.  

Results: Four five shot groups with a proven load were shot side by side. Lyman 311299 weighted to the .1 grain, #2 Lyman, 23.0g H4198 ~ 1760fps, Fed 210 primers, Can Bl lube, .335 bushing, sized .311.

  • ~ .2985 to .3004 nose diameter aggregate 2.285" MOA
  • ~ .3010 to .3014 nose diameter / aggregate of 1.453" MOA

I may be the last person on this forum to figure this out but I believe that bore rider tolerance is as critical to accuracy as olgive to lands is with jacketed bullets.  Where jacketed accuracy is found by starting on jam (.001 to .002 of sticking on a new barrel) and then backing off in increments of .002/,003; optimum bore rider accuracy may be found with nose to land tolerance of +/- .00025.  And although alloy (#2 Lyman vs Linotype) gives us a variable to work with, the alloy source is critical.  

OU812's design for sizing the nose seems like a big step towards to finding that sweet spot.  Beagling is another choice.  There is always the alloy and of course you have Tom who can cut anything you need for bore dimensions.  A custom mold and playing with the alloy can give you +/- .00025 to work with. Maybe the tolerance isn't as tight as I think.  Maybe .0005 impression of the lands on the nose is good enough.  Maybe .00075" is right.  Then on top of that throw in the typical BS / SS (Barrel Specific / Shooter Specific) factor and you have an interesting puzzle. 

Unique to my situation is that I have a tight freebore.  Instead of the SAAMI .310 I had ~ .3085 on each barrel.  My guess is that this bullet will never be competitive in the barrel I'm putting it through. That's why the bullets are seated down to the shoulder.  Thanks, Bill. 

Here is the difference between the .~.300 vs the ~.3014 nose on the bore of my rifle.

 

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Squid Boy posted this 13 January 2022

I have a couple using custom bullets that measure a half thousandth clearance per side. I also had one that needed a bullet that was .470" on the base to do it and going into a .462" groove diameter. It shot very well with a bore riding style bullet. I seem to have better luck getting them to shoot if I match the chamber neck and bullet base to the minimum. At least for now anyway. Thanks, Squid Boy

"Squid Pro Quo"

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MP1886 posted this 13 January 2022

I guess I see this different then most.  First I have to ask about straight wall cases. They have a neck such as a bottleneck.  LOL just being silly guys.  Okay, neck expansion: simple reason is that the whole case swells from the gas pressure inside. Think obturation.  The gas also gets up to the neck. I don't think "they" back in the early days of cartridge cases really planned for necks to expand and seal, it just happened. Y'all making too much out of it.

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Ken Campbell Iowa posted this 13 January 2022

Ric .. probably the biggest reason for neck expansion is ::  to seal the front of the chamber ...  

next is perhaps that tolerances would eventually cause a dangerous tight pinch if the goal was zero clearance in the chamber neck ...

but i wouldn't worry much if loaded with lead and to our usual medium pressures worked up. 

ken

 

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RicinYakima posted this 13 January 2022

Question. Not being funny, but why does the neck have to expand? We put the bullet in there when the neck ID is less the the OD of the bullet. So why doesn't it just slide out when the round is fired?

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Tom Acheson posted this 12 January 2022

This might be off base but....about the tightest ckearance between the OD of a loaded round and the ID of the chaber's neck area is often expressed as 1/2 thou per side. There must always be some room for the brass to expand during ignition. You need to mic (not caliper) the OD of the loaded round and know for certain the ID of the chamber neck. When that clearance is reduced, you start to get into neck turning, etc. 

This sees the advantage of necks that are too thick. You get to customize the bras to fit the chamber. But...if you change the OD of the sized cast bullet, all dimensions need to be re-evaluated. Sizing smaller isn't a bad thing but be real careful if you increase the size of the cast bullet.

Tom

 

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Squid Boy posted this 12 January 2022

The bullet/case neck clearance on this set-up is about two thousandths. Squid Boy

"Squid Pro Quo"

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OU812 posted this 12 January 2022

Seated bullet case neck clearance in chamber should be tight also.

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Ken Campbell Iowa posted this 12 January 2022

my 2 cents on freebore ... it should be less than 1/2 thou bigger than groove diameter ... and very little longer than the protruding groove dia of your bullet seated out as far as you retain the bullet.

this for a match chamber.  heh, another $300 for PTG ...

ken

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John Alexander posted this 12 January 2022

If by legal you mean eligible for CBA competition the answer is it is in all classes except Hunting Rifle Class.  Can't do anything to rifles in HR except adjust the factory trigger and rebed. This is to keep cost of equipment to compete in HR to a bare minimum.

John

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OU812 posted this 12 January 2022

This next question may require a topic on its on. What is the perfect free bore length and diameter when using 30 caliber bore ride style cast bullets. A freebore that will also shoot jacketed well also.

I think a .310 diameter by .200 length would be perfect for most. Much like the 308 NATO. Isn't it legal to cut freebore longer if need be?

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OU812 posted this 12 January 2022

I've also had real good results using the softer 20/1 alloy in 233 Remington at lower velocities (Tite Group powder) . Also had good results using linotype at higher velocities (4198 powder, Reloader 7) Lots of testing and lots of rounds fired.

Reloader 7 works good in 308. Never tried Tite Group in 308, but I am sure it will work at lower velocities. Please try it with 20/1 alloy.

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Squid Boy posted this 11 January 2022

I am still pretty new at this but figured that more nose ride the better and the bullet I designed could have been a bit longer but the throat is short in my Stevens 44 in 32-40 and almost all of the nose is the barrel when it is loaded. The engraving is only half a thousandth per side so it goes in pretty easy. This is the second (string 2) target I shot with it at 100 yards after getting it on the bull. 20-1 alloy and the load data is on the target. I need to get back and shoot this more. Squid Boy

 

Accurate 32-172D

 

 

Target String 2 - 10 shots - 100 yards

"Squid Pro Quo"

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Tom Acheson posted this 11 January 2022

John,

I’ve been all over the map on alloy hardness. On the soft end for a Remington Rolling Block in .38-55 with 27:1. The other end was a 30 PPC using 50/50 Lino /Mono @ about 32 bhn (I think). For my Sharps .40-70 SS (40 cal. 2 1/2) 15-16:1 seems to be working (today).

For this new project I need to start somewhere. I have quite a bit of pure lead, wheel weights and tin.

Tom

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Tom Acheson posted this 11 January 2022

OU8,

The cartridge will be a 22 BR. Cases are re-formed 6.5 BR. The starting mold will be an NOE 227-79-SP-B5

Lilja barrel, 1:8 twist 3-groove.

Tom

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John Alexander posted this 11 January 2022

Tom: My experience is that with linotype any engraving but the lightest may cause trouble chambering the bullet and run the risk of pushing some of them back somewhat in the case.  But some engraving shot better than none. With soft (25:1) bullets anything from light to 0.002" may shoot. But mine seem to like more engraving rather then less. This with a beagled bullet that is no longer round and usually shows only 4 of six land marks.  This is a bullet with a nose 66% of length and a uniform diameter bore ride section that is of 40% of of total length --if that makes any difference.

This is a guess but I wouldn't be suprised if a very hard bullet might shoot well with the bullet almost big enough to engrave. 

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Ken Campbell Iowa posted this 11 January 2022

paul pollard ..  " loose nose shot best " 

*******

are you saying cast bullets can't read ? ...

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Paul Pollard posted this 11 January 2022

Tom Acheson asked, "Is there anyone involved with this thread that can offer any advice as to what is the desired relationship between the measured bore (land ID) and OD of the bore riding portion of the bullet nose?"

I did a test of nose sizes in 2017 for my 6mm. The Mountain Molds bullet was a copy of the Eagan design, except the nose came to a point. The Eagan was a truncated cone. The other dimensions were the same.

I made bump dies with 11 different nose reamers. The noses ranged from .2355 and ended at .2395. The rear portion of the die sized the base band at .245. The front band was tapered at 3 degree included angle to fit the throat tapered section. The rifle had a well-worn throat, so I thought a larger nose was needed. It turned out that the nose of .2367 was the best grouping. It felt loose in the bore at the muzzle. There was not really any engraving.

 

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Wm Cook posted this 11 January 2022

John A should ... upon wearing out his magic 223  ...  or being outlawed at the CBA Nats ...  rechamber that same barrel to  22-250.

Ken, I heard rumors that at this years annual board meeting the CBA has an agenda item to discuss the creation of of a "Youth Hunter Class" for all .22's to shoot in. Heard that their doing that because the .223 Rem is kinda known for being so-so on accuracy.  Some felt it wasn't fair to have .223's compete against real actual manly bona fide accurate cartridges.  Just kidding.  Really I am kidding.  I meant no disrespect.   Again, kidding.  Really and truly kidding. Not picking a fight here MP.

The real questions is how much insurance he has on that D Mos mold?

.22-250?  Maybe.  Since he would be shooting out of class I would see if there's enough life in the barrel to have it re-chambered for .222 Rem.  I always had a soft spot in my heart for the .222.  But since some rifles fall into that "old home week" classification he'd probably scrounge up a new factory .223 barrel and just keep going.  Thanks, Bill.

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Ken Campbell Iowa posted this 11 January 2022

on a lighter note...  kinda relevent to fresh throats .. weakly relevant ...

John A should ... upon wearing out his magic 223  ...  or being outlawed at the CBA Nats ...  rechamber that same barrel to  22-250.

reason being that JoeB spent many hours and bullets ... an excellent shooter with excellent technique and excellent equipment ...  showing that 22-250 chambers are more accurate than 223 chambers.  yep, grit your teeth but hard to ignore ...

just think how good that prize winner Tikka would be in an accurate cartridge !! ...

enough for now, i had my fun.  ken

 

 

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OU812 posted this 11 January 2022

Although I have used the NOE bore ride sizer to reduce size before bumping.

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