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10-fp chamber dimensions
has anyone successfully
measured the .308 chamber?
the reason i ask is that
any ammo that is 2.800
is too big to fit in my chamber without being forced into the lands.
i tried cutting a slice into a case and inserting a bullet but the bullet gets stuck in the lands and gets pulled out some when i remove the case.
i found this.
AZRickD
July 17th, 2003, 09:58 PM
I got my Sinclair tools to measure my chamber and my max OAL.
My Speer Reloading manual says that max cartridge length is 2.015" with the Trim-to length being 2.005"
My chamber length appears to be 2.043" (hmmmm).
The Speer manual says that Max Cartridge Length is 2.810".
My max OAL is 2.889" with
What would you advise as a good OAL to start from for my next reloads? Is it *typically* a rule of thumb that the bullet is supposed to jump about 10-thousandths of an inch before engaging the lands for good accuracy and pressures?
Steve Smith
July 17th, 2003, 11:37 PM
You should still trim your cases, and make sure they are all equal lengths.
Regarding your rifling, try dropping .010" off your max OAL and shoot it. You may also want to try .020", and .015". They may need to be single loaded rather than loaded through the magazine.
Remember, you should #1 always keep your measurement bullet so that measurements later in barrel life will be made with the exact same bullet. #2, never transfer OAL data from one bullet style to another.
by making it short enough i am worried about compressing the charge
__________________ "I don't practice what I preach because I'm not the kind of person I'm preaching to."
Last edited by billy; 01-27-2008 at 08:32 AM.
Reason: Automerged Doublepost
I found one load book that gives oal of 2.780" for 180gr bullets.It,s the Lyman 47,th edition.Going by that oal the casing trimmed to 2.015",bullet length-1.280",neck length .343",the bullet would be seated .172" below the neck.I went back in your posts and you stated 40gr,H4895.With new cases that would leave the powder below the neck,I believe.I see no reason to worry about a compressed charge as it would be slight if any.The problem with compressed loads is if they are compressed too much they may push the bullet up a little and if you are running close to the riflings they may put the bullet into them.When using compressed loads you should meisure oal that day and meisure it the next day to see if the charge has pushed the bullet.Charges shouldnt be compressed more than about .010 percent. sam.
Location: a secret lab on the shores of lake titicaca
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somebody gave me copies of load data from the LYMAN 45th and 48th editions.
and i just found em.
i cant remember who because i am an idiot.
i dont have the bullets used in these books .
__________________ "I don't practice what I preach because I'm not the kind of person I'm preaching to."
Dont put yourself in my class,there are enough of us idiots on the loose now.I believe I would seat the bullet .010 deeper or 2.790.I believe the problem is having a thicker jacket on the match type bullets meaning the body of the bullet had to be moved ahead and the ogive shortened to offset the difference in weight between copper and lead.This should work and you arent pushing max so I see no problem. sam.
Yet another way is to push a bullet into the chamber with a stick
and hold it against the lands; run a flat-tipped cleaning rod in
from the muzzle until it hits said bullet, mark the rod at the
muzzle; knock out the bullet and close the bolt; put the rod back
in and make a new mark on it at the muzzle for where it stops when
it hits the breech. The distance between the two marks is the correct
overall cartridge length when using that particular bullet.
Basically, this is not a one-time thing; as the leade advances due to erosion, you
have to follow it by seating further out or you will lose accuracy.
I called a Long range Shooter friend that has been testing for over 10 years and he said that if you seat the bullet at the depth
where the bullet is just touching the lands of the rifling you can expect the best accuracy. He talks with some of the major barrel makers and other Competition shooters that are 1000 yard shooters
and they all claim that the small pressure spike is Normal and Safe, but they all seat to the Lands.
They do NOT use Max Loads, they use accuracy loads and usually just 1 specific bullet , they dont change weight, or Brand of bullet...when they find the one that performs the best in their particular rifle, they stick with it.
Rich
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[I]You know you might be facing your doom,when all you get is a click when you're expecting a BOOM!:( [/I]
My Dad used to shoot long range with some buddies, and I remember he had about a dozen boxes of the same bullet, and a Big stack of the same primers.
He had a second set of dies that were locked down and witness marked to reload only that bullet. I guess to minimize the variables as best as possible.
You could also make a cast of the chamber to measure. I forget what the medium is called. Something like "Cero".
Added: (Found this, may be of some help) When installing barrel that uses the lock nut to what headspace should the barrel be set to?
If your rifle is going to be used for target shooting, you want a minimum headspace chamber. The barrel should be turned against a GO chamber gage and the barrel lock nut tightened. The bolt will probably not even begin to close on a NO-GO chamber gage. This will minimize case stretching and result in long life for your reloaded cases. (Keep those cases trimmed below maximum!)
Hunters who may be hunting under harsh condition, or maybe firing a lot of rounds between cleanings may want a chamber with more room to insure rounds will always chamber, even if the gun is dirty. Then the bolt should be turned tightly against a NO-GO gage and the barrel nut tightened. The barrel should be kept tightly against the gage to insure all the spring is taken up, and the bolt should close with some resistance on the NO-GO gage. You must check to insure that the bolt will not close on a FIELD gage!
For most, the optimum is that the bolt closes easily on a GO gage and will not close on a NO-GO gage. This can be done by putting alternately tightening the barrel against GO and NO-GO gages and keeping the barrel somewhere in between when tightening the barrel nut. This can be aided by the use of a witness mark on the barrel matched with a witness mark on the receiver.
__________________ I keep tellin ya Doc, I'm in pretty good shape considerin the shape I'm in !!
Last edited by SwedeSteve; 01-27-2008 at 06:56 PM.
Location: a secret lab on the shores of lake titicaca
Posts: 23,061
Quote:
Originally Posted by Mooseman684
Yet another way is to push a bullet into the chamber with a stick
and hold it against the lands; run a flat-tipped cleaning rod in
from the muzzle until it hits said bullet, mark the rod at the
muzzle; knock out the bullet and close the bolt; put the rod back
in and make a new mark on it at the muzzle for where it stops when
it hits the breech. The distance between the two marks is the correct
overall cartridge length when using that particular bullet.
Basically, this is not a one-time thing; as the leade advances due to erosion, you
have to follow it by seating further out or you will lose accuracy.
I called a Long range Shooter friend that has been testing for over 10 years and he said that if you seat the bullet at the depth
where the bullet is just touching the lands of the rifling you can expect the best accuracy. He talks with some of the major barrel makers and other Competition shooters that are 1000 yard shooters
and they all claim that the small pressure spike is Normal and Safe, but they all seat to the Lands.
They do NOT use Max Loads, they use accuracy loads and usually just 1 specific bullet , they dont change weight, or Brand of bullet...when they find the one that performs the best in their particular rifle, they stick with it.
Rich
ok i came up with
2.720 with the 165 sierra HPBT bullet jammed into the lands AND I MEAN really jammed in there.
so 2.700?
none of my loadbooks have this weight of bullet.
they only have 168's of this type
the sierra book calls for 2.750 with a 165 sierra HPBT .
that is impossible in this rifle.
they used a savage vs12ss rifle 1-10 twist 26in. bbl.
this shit drives me crazy!
__________________ "I don't practice what I preach because I'm not the kind of person I'm preaching to."
Last edited by billy; 01-27-2008 at 10:32 PM.
Reason: Automerged Doublepost
Location: a secret lab on the shores of lake titicaca
Posts: 23,061
i bought the Stony Point Products O.A.L. Gauge
i got sick of fooling around.
it cost 50 bucks to find out what my chamber dimensions are.
god this pisses me off sometimes.
ok im done venting now........
at least this way i will know beyond a shadow of a doubt.
if anyone needs to borrow this stupid thing after i use it once.
i will need it again in a few years when the chamber has eroded a bit.
__________________ "I don't practice what I preach because I'm not the kind of person I'm preaching to."
Last edited by billy; 03-02-2008 at 01:28 PM.
Reason: Automerged Doublepost
I'm new to this forum, but have been reloading for bolt actions for about the last 35 yrs. Here is my process, that I use for all rifles and all calibers. I have found in the past, that the chamber may be a standard dimension. But, the seating depth of the bullet will allow contact with the lands, prior to the bolt caming into battery.
I have a case (without primer or powder) that I seat a bullet into. Making sure the OAL is above the max. I use a candle to blacken the bullet and place it into the chamber. Lightly close the bolt, do not force the bolt or bullet. Remove the round, look for signs of contact with the lands of the rifling. Place the round back into the seating die and seat the bullet a little deeper. Blacken the bullet and repeat the process.
What I have used for all my reloads is to get the bullet seated to where the bolt will close and the bullet is just touching the lands. Then I try to turn in the seating die and make the OAL .015-.025 shorter. This has worked for me for a long time.
I use a permanent marker and label the cases on the test bullets. I keep them for reference. Now they are only good for that particular rifle/chamber combination. Each time I try a different brand of bullet, I have to make a new one. Luckily, I have been able to keep my inventory of (set-up) rounds to a minimum.
I hope I'm not covering some things that have already been stated, but this thread was the first one that I came across that really interested me.
The Stoney point guage is going to show the max OAL to the rifling engagement for a particular brand, or style of bullet in the chamber it is used in. that establishes a base line for that particular combination in that chamber. reducing OAL from this point allows you to control how much "free run" you are going to allow the bullet to travel. some of my semi autos want .015" of jump for best accuracy (watch magazine length unless you are going to make it a single shot), while some of my bolt guns want it down to .005" (or slightly less even). a chrony is a big help here also. velocity and pressures tend to rise with less free run, so some powder reduction may be in order.
