hey guys, i used the sinclair chamber length gage to find out the max length. (for trimming my brass) my 260 rem was 2.055 so at what length do i need to trim and how far under this do i need to trim. thanks for any help.
chamber length with sinclair gage
- Thread starter ttfreestyle
- Start date
ttfreestyle said:
Here's a good guide:
Chamber Length Safety Zone
Q: How many thousandths shy of actual chamber length does one establish as a safety zone, before assigning a trim "from" length, once measurements have established a rifle's true chamber length?
Mike Bryant
A: I use .010" for each increment. For instance, if the chamber length is 1.570" from the base to the end of the neck on the chamber, then the maximum case length would be 1.560" with a trim length of 1.550". Don't let the cases get over 1.560" and you'll be in good shape.
Jackie Schmidt
A: I use a .010" window. 6mmPPC chambers have been shortened to 1.510". Since shooters fire cases to expand them, the cases come out close to 1.500". I trim them back to 1.490."
Agree 100% with Mike & Jackie. I also use .010" shorter as my standard, but with the ppc's and BR's I use .005", but they are watched closely and measured for over all lengths after every run thru the Redding FL bushing die. Keeping these close tolerences has prevented any formation of a ring of carbon at the chamber mouth. With some of my factory chambers that do have really long chamber lengths, ( all as verified with the Sinclair gauges) carbon buildup is a problem. Yet another big plus for what I'm able to see with my borescope. 
There is a balance to reach based on your cartridge design and load. Ideally you want to seal the neck consistently,, so near instantly. But it isn't always practical or easy to do.
I think the 10thou is based on alot of FL sizing tiny cases and running extreme pressure fast powder loads.
But if your using hunting size cartridges with rational loads of slower powder, anything over 5thou creates more sooting and increases ES.
With well designed hunting size cartridges and moderate loads, body sizing requirements are minimal(few trimmings), and it's easy to stay within 5thou. These necks seal fast, with little sooting, and less carbon buildup.
Sometimes careful strategies are needed to reach this trim length(with improved wildcats) given that FL sizing probably will not lengthen these cases, for further trimming.
I rarely trim beyond initial(don't need to), so I need to get my length right with fireforming, which often shortens my cases.
And as mentioned there is carbon buildup forward of fired case mouths. If you don't watch this, your clearance will eventually fall to zero there. The greater your trim length clearance, the faster this becomes an issue(just opposite of what you might think). If you look at the case mouths after firing, they show shiny where carbon contact is occuring. In the extreme this could spike pressures, or inconsistently allow gas by the case mouths, combining to raise ES.
I clean the chamber neck and check trim lengths, needed or not.
I think the 10thou is based on alot of FL sizing tiny cases and running extreme pressure fast powder loads.
But if your using hunting size cartridges with rational loads of slower powder, anything over 5thou creates more sooting and increases ES.
With well designed hunting size cartridges and moderate loads, body sizing requirements are minimal(few trimmings), and it's easy to stay within 5thou. These necks seal fast, with little sooting, and less carbon buildup.
Sometimes careful strategies are needed to reach this trim length(with improved wildcats) given that FL sizing probably will not lengthen these cases, for further trimming.
I rarely trim beyond initial(don't need to), so I need to get my length right with fireforming, which often shortens my cases.
And as mentioned there is carbon buildup forward of fired case mouths. If you don't watch this, your clearance will eventually fall to zero there. The greater your trim length clearance, the faster this becomes an issue(just opposite of what you might think). If you look at the case mouths after firing, they show shiny where carbon contact is occuring. In the extreme this could spike pressures, or inconsistently allow gas by the case mouths, combining to raise ES.
I clean the chamber neck and check trim lengths, needed or not.
thanks for the info guys, as always very helpful to a novice.
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.