Sinclair Chamber Length Gage question

[SWThomas]

So I got the Sinclair Chamber Length Gage for my rifles. I followed instructions and measured the chambers for my GAP-10 in 308 and my Rem 700 in 30-06.

The GAP-10 measured 2.041 and the Rem 700 measured 2.529.

My question is, how much should I subtract from these measurements to get my new trim-to length? The instructions say 0.024 but that seems conservative to me.

What say you?

 

[SWThomas]

Ttt

 

[wildfowler]

What is the difference between published load data trim to guidelines and SAAMI chamber specification?

That might be a good a number to shoot for?

I just got my gauge in last week. Haven't used them but was considering that formula.

 

[Victor N TN]

So I got the Sinclair Chamber Length Gage for my rifles. I followed instructions and measured the chambers for my GAP-10 in 308 and my Rem 700 in 30-06.

The GAP-10 measured 2.041 and the Rem 700 measured 2.529.

My question is, how much should I subtract from these measurements to get my new trim-to length? The instructions say 0.024 but that seems conservative to me.

What say you?

I cut mine 0.010" to 0.015" shorter and trim after every firing. (Semi auto is .015", bolt gun is .010")

 

[Victor N TN]

What is the difference between published load data trim to guidelines and SAAMI chamber specification?

That might be a good a number to shoot for?

I just got my gauge in last week. Haven't used them but was considering that formula.

Every gun will have a slightly different chamber. Using published data may have you trimming brass .030" to .040" short. This will cause the gas leaving your brass to act like a cutting torch against your chamber. Yes it's only millionths of a second. But it's VERY hot and under high pressure. After hundreds or thousands of rounds it cuts and deteriorates the general throat area of the chamber. The people saying to cut your case necks way short, don't have to pay to get your chamber re-cut when it's messed up.

 

[wildfowler]

Every gun will have a slightly different chamber. Using published data may have you trimming brass .030" to .040" short. This will cause the gas leaving your brass to act like a cutting torch against your chamber. Yes it's only millionths of a second. But it's VERY hot and under high pressure. After hundreds or thousands of rounds it cuts and deteriorates the general throat area of the chamber. The people saying to cut your case necks way short, don't have to pay to get your chamber re-cut when it's messed up.

Sorry, I probably did a poor job of explaining this and didn't have time earlier to look all this up. I was suggesting that if you look up the SAAMI case dimensions to see how long the chamber is supposed to be and compare that against published "trim to length" to see how much the powder manufacturer suggests to trim for a SAAMI chamber ( big assumption on my part to assume published load data is for SAAMI chamber )

http://www.saami.org/PubResources/CC_Drawings/Rifle/308 Winchester.pdf

308 win for example. Chamber length is supposed to be between 2.015 - 2.020" Hodgdon online reload data for came caliber gives trim length of 2.005" for a difference of .01 - .015"

So for 308 Win my suggestion would also be to trim .01 - .015" shorter than the measurement of the individual chamber. I don't happen to know without checking if other cartridges would have the same comparative measurement.