I've read the info at that link and I don't remember it saying anything about why the bullet needs to be in the case when contact is made with the rifling.
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Deliberately throating a match barrel long
- Thread starter Tumbleweed
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I've read the info at that link and I don't remember it saying anything about why the bullet needs to be in the case when contact is made with the rifling.
MontanaRifleman
Well-Known Member
It doesn't. What it does say is that the case is pushed up and centered before the bullet leaves the neck.
J E Custom
Well-Known Member
Everyone is correct in different cases and rifles. Some chambers are loose and some are tight
on purpose.
Ideally, a match grade chamber has no slack because the case fits and the head space is .000
causing the bolt to close with light pressure on the case shoulder or belt. this is also the reason
that we square the lugs and the bolt face. this forces the case to align it,s self even with the neck
size smaller than the neck portion of the chamber. Neck sizing only is used in many cases where
the chamber is not particularly tight after sizing.
On semi autos the case is sized more to make chambering and extraction easy.
On belted cases they were designed that way so they could be Small base size so chambering
would never be a problem but head space was still within safe limits (.002 to .004).
Belted cases that are not used on dangerous game rifle can be fired and then sized to a minimum
so they will actually head space on the shoulder, improving consistency.
If a chamber is true and head space is minimum .000 to .0005 and bolt face and locking lugs
are square , alignment of the case should be true to the bore and therefore forcing the bullet to
engrave true unless it is allowed to move on its own. (Unrestrained).
J E CUSTOM
on purpose.
Ideally, a match grade chamber has no slack because the case fits and the head space is .000
causing the bolt to close with light pressure on the case shoulder or belt. this is also the reason
that we square the lugs and the bolt face. this forces the case to align it,s self even with the neck
size smaller than the neck portion of the chamber. Neck sizing only is used in many cases where
the chamber is not particularly tight after sizing.
On semi autos the case is sized more to make chambering and extraction easy.
On belted cases they were designed that way so they could be Small base size so chambering
would never be a problem but head space was still within safe limits (.002 to .004).
Belted cases that are not used on dangerous game rifle can be fired and then sized to a minimum
so they will actually head space on the shoulder, improving consistency.
If a chamber is true and head space is minimum .000 to .0005 and bolt face and locking lugs
are square , alignment of the case should be true to the bore and therefore forcing the bullet to
engrave true unless it is allowed to move on its own. (Unrestrained).
J E CUSTOM
Tumbleweed
Well-Known Member
I appreciate everyone's responses so far but looks like we're getting off track quick. I understand that case alignment to the center line of the bore is critical for accuracy. The match chamber will have a tighter tolerance to keep the cartridge body centered, I get that. Maybe I complicated my question. I am only talking about the throat here and alignment into the rifling.
If a cartridge is chambered and the bullet enters a .5" long throat area that has the same dimensions as the O.D. of the bullet, is there any reason that the bullet should lose accuracy even when guided precisely into the start of the riflings? Maybe the bullet has to actually move .5" before contact is made with the rifling. Will the .5" jump in and of itself cause inaccuracy?
If a cartridge is chambered and the bullet enters a .5" long throat area that has the same dimensions as the O.D. of the bullet, is there any reason that the bullet should lose accuracy even when guided precisely into the start of the riflings? Maybe the bullet has to actually move .5" before contact is made with the rifling. Will the .5" jump in and of itself cause inaccuracy?
MontanaRifleman
Well-Known Member
I think you missed a little of the exchange. The throat area is not the same diameter as the bullet. Most throat's are .0005 to .001 greater in diameter than cal. I.e., a .308 throat may be .3085 or .309 in diameter. Not to mention that most bullets are actually .0005 to .001 less than cal, so there is going to be space between the bullet bearing surface and the throat wall. How much that affects accuracy vs your throat length is debatable and every chamber, load, bullet combination will have a unique personality. I personally would not throat a RUM more than .300 and would prefer about .200
search alittle about taking some freebore out of those rums. i have a 700sendero 7rum i have .40 freebore and it will not shoot any vld's 4'' groups@ 100 this is because of the saami specs and because it is uncontroled. i am in the process of rechambering it. ill take a little volocity for accuricy anytime . the differnce of a spend round to a reloaded one is .12. the loaeded round is 3.11. and a shot round is 3.23 this means there is .051 space around my bullet when loaded which even after running through a consentricity tool shoot terrible. the only bullet i got to shoot in the rifle is the 160 accubond because it hit the riffleling before it left the brass.this is also why i will never buy a new factory gun again.(boo remington)
I thought I remembered something about this.
http://www.longrangehunting.com/forums/f28/230grn-berger-out-300-rum-134551/
http://www.longrangehunting.com/forums/f28/230grn-berger-out-300-rum-134551/
