why some precision rifle builders do not use bushings

[mikeinco]

precision rifles, not hunting not tactical, benchrest type precision
we have to start with a basic understanding that rifle bores are NOT straight.
they "worm" down the bbl.
we are not talking big numbers worst case .003/.004 some less.
if you put a bbl thru the head stock or on rollers and turn it while looking down the bore,
you can see that the bore really is not straight as a laser( but good enough for a rifle).
this ain't new . trying to get a "straight" hole in a 30" blank aint easy.
the ideal condition in a chamber is to have the bullet engage the rifling straight. as in .0000 straight.most precision rifle makers use a .0001 indicator.
( some use rods with indicators, i do not use that method, but it works)
so the setup is to dial in the bbl in the lathe with the indicator at the intended THROAT.
this is why pre-bore, taper bore and ream without a bushing .
the slight worming of the bore can cause stress on the bushing, the reamer is steel and the back end of the reamer with move out of line causing and over sized chamber at the back plus if the bushing is allowed to follow the bore it can be a couple thou off from center when finished. look at the lands are the all cut uniform in length from start to finish the same start the same finish.
i had a worst case in a remington bdl i bought new.
the land on one side was only partially cut in the throat, on the opposite side the land was cut past the groove and into the bbl!
brand new rifle with the throat cut maybe 2-4 thou off center.

ask away
i will try to answer questions of those that are interested.

[Robinhood]

The tail stock being off center can cause an oversize bore also. How primer pockets expand too quickly.

[mikeinco]

not likely in a percision shop using a free floating reamer holder.


The tail stock being off center can cause an oversize bore also. How primer pockets expand too quickly.

[Robinhood]

not likely in a percision shop using a free floating reamer holder.


What reamer holder do you use?

[mikeinco]

it is unmarked, likely an early JGS well 15 plus years old
i used my own design before that

[Robinhood]

Those seem to handle angular issues but what about offset.

[mikeinco]

please stay in the context of the discussion.
precision rifle building
the lathes are quality machines. we are not talking a harbor freight $599 lathe nor a $1600/2000 imnprts
my lathe had a list price of close to $14000, they are cheaper today. weights 2000 lbs and digital read out to .0000x( the machine is not the good)
and this is close to the bottom end of acceptable.



Those seem to handle angular issues but what about offset.
?

[Robinhood]

Are/Where you a machinist by trade Mike?

Do you understand why I am the only person to post on this thread?

[mikeinco]

i was trained as a machinist and did work in the field for a short time. a very long time ago.
there is a reason i moved the subject here....less noise.



Are/Where you a machinist by trade Mike?

Do you understand why I am the only person to post on this thread?

[charlie b]

So what do you use for an indicator? Seems to me it is the key for the entire setup since all the rest of the operations are based on that.

[mikeinco]

cannot have too many tools.
these are not cheap

for short chambers 6ppc/30br etc interapid 300 series with .0001 dials
as chambers get longer (300 win mag etc) i use a 0.0005 and "read between the lines"
(if you add a longer arm the fial reading decreases by the same factor the length increased)

[gbflyer]

I like to pre-bore also. Makes a painful slow operation go a little faster. I’m not sure my results are any better but I ain’t a pro. Best one I ever had was a Hart that was reamed with a finisher set up between centers. Shot a couple “oughts” in 100 yard BR. Oh yeah, I didn’t do the work. I question if a good quality barrel is going to be out enough in 2 inches to worry about. The barrel is so important and out of our control. Tony Boyer culls several new ones every year. Same smith, same process, same barrel manufacturer.

Fun stuff though. Those fake wood plaques get expensive[emoji1]

[mikeinco]

pre bore AND taper bore.
its it about being out just a little..because the reamer is a chunk of steel it does not flex and if the bushing is going around .0002 then 2 inches back the reamer is probably doing .002 or more.
and if the throat is off then EVERY bullet is forced in to the bore sideways and reforms as it goes down the bore.
tony tosses more than"several" bbls every year. more like chambering 20 and picking only the best of those...he can afford it..
i know guys they shoot $2000 scopes for only ONE YEAR, thell them and buy new ones every year...because the can and do fail.


I like to pre-bore also. Makes a painful slow operation go a little faster. I’m not sure my results are any better but I ain’t a pro. Best one I ever had was a Hart that was reamed with a finisher set up between centers. Shot a couple “oughts” in 100 yard BR. Oh yeah, I didn’t do the work. I question if a good quality barrel is going to be out enough in 2 inches to worry about. The barrel is so important and out of our control. Tony Boyer culls several new ones every year. Same smith, same process, same barrel manufacturer.

Fun stuff though. Those fake wood plaques get expensive[emoji1]

[gbflyer]

Ok so I’ve been wondering about something. We do this extensive setup with our Interapid on our almost perfect Japanese bearing’d many thousand dollar tool room lathe using a barrel we have no way of really measuring bore and groove diameter to perfection on unless we have an air gauge. Axial and radial alignment are as perfect as we can get if we convince ourselves our 2.75” long $400 perfectly solidly mounted test indicator is really measuring half a tenth. We taper bore with our solid carbide boring bar just leaving enough to clean up with the reamer that we have no control of the dimensions of (unless you have an optical comparator, then we can send back and have the toolmaker try again, unless we also make the reamer). So, for all intents and purposes, we’re as perfect as we can get, start the pressurized oil system and go to work with our couple hundred dollar “floating” reamer holder we bought from JGS or Manson or Kiff or made ourself. We turn it around and cut a crown, either single point or with a piloted cutter with the perfectly sized bushing since we have every size there is for our particular bore diameter. Straight, recessed, 11 degree, however we like it, polished but sharp. Then we screw it on our perfect custom action we have no control over in our perfectly bedded perfectly stable stock. We put a scope on it we have no control over tolerances on in perfectly lapped rings. Then we go shoot it. It’s perfect.

Just one question after all that: How many rounds will go down the barrel before erosion takes out all of our careful work getting a perfect handoff from case to rifling and we get to start over? One match’s worth?

[yobuck]

Ok so I’ve been wondering about something. We do this extensive setup with our Interapid on our almost perfect Japanese bearing’d many thousand dollar tool room lathe using a barrel we have no way of really measuring bore and groove diameter to perfection on unless we have an air gauge. Axial and radial alignment are as perfect as we can get if we convince ourselves our 2.75” long $400 perfectly solidly mounted test indicator is really measuring half a tenth. We taper bore with our solid carbide boring bar just leaving enough to clean up with the reamer that we have no control of the dimensions of (unless you have an optical comparator, then we can send back and have the toolmaker try again, unless we also make the reamer). So, for all intents and purposes, we’re as perfect as we can get, start the pressurized oil system and go to work with our couple hundred dollar “floating” reamer holder we bought from JGS or Manson or Kiff or made ourself. We turn it around and cut a crown, either single point or with a piloted cutter with the perfectly sized bushing since we have every size there is for our particular bore diameter. Straight, recessed, 11 degree, however we like it, polished but sharp. Then we screw it on our perfect custom action we have no control over in our perfectly bedded perfectly stable stock. We put a scope on it we have no control over tolerances on in perfectly lapped rings. Then we go shoot it. It’s perfect.

Just one question after all that: How many rounds will go down the barrel before erosion takes out all of our careful work getting a perfect handoff from case to rifling and we get to start over? One match’s worth?
Apparently it isnt about the trip itself, preparing for the journey is what really matters. lol

[mikeinco]

i know a well known BENCHREST SHOOTER that recuts the chamber (less than .250) every 250 rounds on a well shooting rifle. he is a master machinist and an expert benchrest shooter. he is the only one I KNOW that does this. there maybe others.
there are some long range shooters that do the similar at higher count and recrown( hot gasses cutting the crown).
for the "average" competition shooter they redo or rebbl when accuracy drops off.
it aint a cheap game and gets more expensive the closer to the top you get
the average savage shooter will never notice or simply replace with another average bbl.
no one i know uses a piloted cutter to do crowns, all single point.
there are guys that chamber 10 at a time, and test them all, and only keep the best, some guys when they get an excellent shooting bbl will save the bbl for matches only, using another bbl to practice with. i know guys that come to a match with several bbls.
i am on a fixed budget, i shoot till they don't shoot.


Ok so I’ve been wondering about something. We do this extensive setup with our Interapid on our almost perfect Japanese bearing’d many thousand dollar tool room lathe using a barrel we have no way of really measuring bore and groove diameter to perfection on unless we have an air gauge. Axial and radial alignment are as perfect as we can get if we convince ourselves our 2.75” long $400 perfectly solidly mounted test indicator is really measuring half a tenth. We taper bore with our solid carbide boring bar just leaving enough to clean up with the reamer that we have no control of the dimensions of (unless you have an optical comparator, then we can send back and have the toolmaker try again, unless we also make the reamer). So, for all intents and purposes, we’re as perfect as we can get, start the pressurized oil system and go to work with our couple hundred dollar “floating” reamer holder we bought from JGS or Manson or Kiff or made ourself. We turn it around and cut a crown, either single point or with a piloted cutter with the perfectly sized bushing since we have every size there is for our particular bore diameter. Straight, recessed, 11 degree, however we like it, polished but sharp. Then we screw it on our perfect custom action we have no control over in our perfectly bedded perfectly stable stock. We put a scope on it we have no control over tolerances on in perfectly lapped rings. Then we go shoot it. It’s perfect.

Just one question after all that: How many rounds will go down the barrel before erosion takes out all of our careful work getting a perfect handoff from case to rifling and we get to start over? One match’s worth?

[mikeinco]

I know a 2 mile shooter that is a wild cater. for a working wild cat he gets 5 bbls done at a time. they last a couple of hundred rounds and are toast.
think a 400 gr solid, lathe turned bullet in a cnc turned case running 4000 fps.
he has MONEY.


Just one question after all that: How many rounds will go down the barrel before erosion takes out all of our careful work getting a perfect handoff from case to rifling and we get to start over? One match’s worth?

[gbflyer]

I’m with you Mike. Shoot them until they don’t shoot. I only competed in short range NBRSA BR a few times, never enough to get good at it or wear anything out. Now it’s just for fun. One of my “pod” (I’m trying to embrace the vocabulary of times, hahaha), has a 7mm Ultra that has at least 3” of throat erosion. It got there in probably 300 rounds. It’ll still print an honest .625. He’s still deadly with it when we whack steel at 1000, even though the temptation is great to make a goat stake out of it. It got reamed between centers.