? Sinclair Seating Depth Gage

[DHC]

Just bought the Sinclair Seating Depth Gage and my first time using it I've arrived at some measurements that seem incorrect. If someone who has experience with this might guide me as to what I am doing wrong, I'd appreciate it.

I've read the instructions carefully and am confident I've followed them correctly. Here are the specifics and measurements gathered:

* Bighorn Arms Tactical action - .308 Winchester
* Measurement from Base of Case to Base of Bullet (with bullet resting gently in the barrel and then using a once-fired case - as per instructions): 1.505 inches
* OAL length of the bullet (SMK 175gr): 1.238 inches
* Combined COAL: 2.743 inches

Presumably, this would be the maximum COAL for the bullet to be resting on the lands (assuming I understand this process correctly). Yet, the 'book' specification for .308 Winchester shows a COAL of 2.800 and the M118LR ammo I've been using measures a bit longer than 2.810 overall.

If the Sinclair measurements are correct, that would mean the M118LR ammo is being jammed up into the lands - I *think*. However, the M118LR ammo is not showing any signs of difficulty when chambering, hence, I feel I must me doing something wrong with my measurements. The only other thing to note is that my chrono readings for the M118LR do tend to run a bit hotter than I expected - the average being about 2738 fps, but no other anomalies to indicate over-pressure or anything.

Any help?

 

[Rhyno]

You'll need to measure base to ogive to see if they're jammed. Coal isn't a good indication because the front of the bullet won't touch the lands.

 

[DHC]

You'll need to measure base to ogive to see if they're jammed. Coal isn't a good indication because the front of the bullet won't touch the lands.

Base to ogive per Hornady Comparator is 0.664 inches.

ETA: Measurement is for bullet base to ogive. Sorry, I am still working to figure this stuff out. Did you mean from the base of the case, or ??

 

[Rhyno]

Okay, I'm a bit confused. Here is what I've done in the past.

Seat a bullet long into a case that has been resized. (I usually loosen the case a bit by seating a bullet and pulling it a few times) then I chamber the round. I extract the round, sometimes the bullet stays in the rifling, most of them time it stays in the case.

I then measure base to ogive, I do this 5 times to get a better reading. And then average the results.

That gives me the base to ogive reading to touch the lands.

 

[Rhyno]

Base to ogive per Hornady Comparator is 0.664 inches.

ETA: Measurement is for bullet base to ogive. Sorry, I am still working to figure this stuff out. Did you mean from the base of the case, or ??

Yea base of case to ogive. With the bullet seated.

 

[Starbuck]

You should take the bolt face (base of case head)>base of bullet measurement 3 or 4 times until you are sure you've got it right - there is some slop caused by the way the rod can wiggle around in the bore guide, causing variations in the measurements.