Is this an excessive lenght chamber?
- Thread starter Davey Boy
- Start date
Davey, the neck diameter of the chamber neck is .3442 At 2.045 the diameter of the neck has decreased to .310; that outs us back to determining the length of the chamber at the end of the neck because the throat diameter drops off in diameter in a hurry as in a short distance. And that is the reason I suggest using modified cases when determining the distance to the end of the neck from the bolt face. The 2.045" is not a case length option.
For those that know their way around the chamber should understand the length of the chamber from the datum to the bolt face. Again and again I have one rifle that has .016" clearance between the shoulder of the case and shoulder of the chamber. When determining the length of the case as in 'when to trim' I have to add the .016" to the length of the case. Meaning: I trim the length of the case for that rifle to 2.494 +.017" from the end of the neck to the bolt face. But the case length for the 308 W is 2.020, the reloaders should understand the diameter of the throat drops off in a short distance at the end of the neck.
There is always the exception, again I suggest using test cases by modifying the diameter and length of the case neck.
F. Guffey
The one thing I do not want is a throat that will crimp the neck to the bullet. I do not want anything slowing my bullets dowm before the bullet gets out of the neck. I am the fan of the bullet jump, I do not like the ideal of the bullet setting at the lands wondering if it is going to be able to get past the lands. I want my bullet past the lands before the bullet knows the lands are there.
F. Guffey
F. Guffey
243winxb provided the SAAMI chamber drawing and in the lower right it has the chamber tolerances.
And the SAAMI dimensions are guidelines and not written in stone.
F. Guffey you keep telling us how smart you are but you can't even read a SAAMI chamber drawing.
You should try providing actual information instead of so much bovine scat and ignorance.
Davey Boy
Todays chambers have to be large enough for the cartridge and also fit the company lawyer in.
Below from the SAAMI chamber drawing (Guidelines)
CHAMBER
UNLESS OTHERWISE NOTED
ALL DIA +.002
LENGTH TOL +.015
So as 243winxb stated your chamber is .005 longer than SAAMI "guidlines".
Last edited:
Vere good info, i agree.
A case trim length that is to long may crimp the bullet in the case. Pressure would go up. This is why a "safety zone" is built into chambers.
But if the reloader has taken measurements, .010" longer then maximum trim length may work well. Trim after every fl sizing, if needed.
There is another thing to consider, shoulder set back from the firing pin strike. This may allow the neck to go deeper into the chamber on firing? More testing is needed. A 223 pin strike has set my shoulder back .006" ** when i had a misfire from a bad primer. The 2nd strike pushed the shoulder back even more. Annealed brass may go even deeper? I dont anneal.
Added ** Set back confirmed by another handloader , same model rifle. Savage Axis 223.
Last edited:
Dusty Stevens
Shiner
It is case neck diameter
Good day gentlemen
New poster master machinist and mechanic
Not to offend but some corrections need making
The datum is 1/2 the distance between the shoulder junctions to the bolt face
Max 308 case length is 2.020
The distance from case mouth to bullet lands is called free bore or jump and is there to transition from the case mouth to lands and grooves, Basically an “acceleration zone” and a sort of pressure buffer. Has anybody seen myth busters with the 3k FPS gunshot film?the smoke you see before the bullet exits the barrel is from this area
New poster master machinist and mechanic
Not to offend but some corrections need making
The datum is 1/2 the distance between the shoulder junctions to the bolt face
Max 308 case length is 2.020
The distance from case mouth to bullet lands is called free bore or jump and is there to transition from the case mouth to lands and grooves, Basically an “acceleration zone” and a sort of pressure buffer. Has anybody seen myth busters with the 3k FPS gunshot film?the smoke you see before the bullet exits the barrel is from this area
If true you have a BIG problem
The 2.068" measurement may be longer then the chamber , because the chamber diameter is larger then the Sinclair plug. (If using SAAMI standards)
If you trust your measurements, its possible to use a longer trim length then standard, for the 1 rifle. But SAAMI shows a "safety zone" of only .010" in a minimum chamber.
I keep my 243 win brass at maximum trim length for 1 target rifle. This required checking trim length after every fl sizing. When brass grows a few thousandth over, i trim it back. Does it make a difference? No idea. I just feel better about it, as it may help throat errosion.
Set back confirmed by another handloader , same model rifle. Savage Axis 223.
As you say the posted max length is 2.015. A safe trim length is 2.010 .
New Nosler Brass when measured average 1.997 they will load and shoot just fine. The main growth of a 308 comes from re sizing with an expander ball on the de capper rod.
Stop doing that IMO you'll save a lot of brass. Trim to 2.010 and go out and shoot.
SPJ
Last edited:
Master machinist and mechanic:
And then you say;
And then I ask: How can that be if the 8mm57m 30/06, 280, 270 and 25/06 use the same datum? The datum/round hole/circle for all of the chambers listed is .375 or 3/8". The length of the shoulder from the case body/shoulder juncture and the shoulder/neck juncture can not be located half way between both junctures for all of the chambers listed.
F. Guffey
I have heard that one before, I have rifles with killer firing pins, I have pulled down 'failed' to fire ammo that has been struck 8 times with 4 different rifles and I have kept up with the length of the case from the datum/shoulder to the case head and found no evidence the firing pin strike shortened the case when the primer is struck,
For those that can keep up: There is .005" clearance between the shoulder of the case and shoulder of the chamber when the firing pin is struck if the firing pin strike shortened the case .004" there would be .009" clearance between the bolt face and case head.
I understand that means absolutely nothing to anyone on this forum but .009" clearance is the difference in length between a go-gage chamber and a minimum length full length sized case. According to you the shoulder of the case starts out at the shoulder of the chamber, in my opinion that is a bad habit because the case will lock onto the chamber with the case head .009" off of the bolt face. When all of that hot, high pressure builds metal cutting gas builds the case will only have one option and that option would be to stretch between the case head and case body.
I am the fan of cutting down on all that case travel.
F. Guffey
How did I foretell this thread would turn to poop as soon as I saw an appearance?
Upgrades & Donations
This Forum's expenses are primarily paid by member contributions. You can upgrade your Forum membership in seconds. Gold and Silver members get unlimited FREE classifieds for one year. Gold members can upload custom avatars.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.
Click Upgrade Membership Button ABOVE to get Gold or Silver Status.
You can also donate any amount, large or small, with the button below. Include your Forum Name in the PayPal Notes field.
To DONATE by CHECK, or make a recurring donation, CLICK HERE to learn how.