Bullet Comparator Question

[Zeneffect]

I dont understand the tool as it is presented. Why would you measure the outsides of the collars then + bullet length? The resultant OAL would he extra long wouldn't it?

2:00 in the video.

[Velocity]

Lets forget the tool!

I am trying to find the seating depth (CBTO) of this barrel for a 90gr. TNT bullet.
How do I do it? Just like everyone else does.

1) I take a fire case from my chamber
2) Put a bullet in to the case neck (snag fit)
3) Push cartridge in chamber until it's seated
4) Remove cartridge and measure

CBTO measurements reads as follows:
1.7420" for a 90gr. TNT bullet
1.7689" for a 120gr, Gold Dot
1.7210" for a 123gr. SST
1.7220" for a 129gr. SST
1.7320" for a 120gr. Lapua Scenar-L

COAL measurements reads as follows:
2.3180" for a 90gr. TNT bullet
2.3950" for a 120gr, Gold Dot
2.3790" for a 123gr. SST
2.3860" for a 129gr. SST
2.3050" for a 120gr. Lapua Scenar-L

The barrel is new and I shot it 4 times for case measurements.
The only question I'm going to ask is;
Do the above numbers indicate the barrel is for an AR-15 or a Bolt rifle?

Thank you, I am sorry for all the previous confusion.

[Dt219]

My chamber measures with hornady tool
90 tnt. CBTO 1.730. COAL. 2.240

123sst. CBTO 1.690. COAL 2.280

If you are doing it right. Your throat is long I’d say. Close to .100 longer than my throat is

[Dt219]

Also I have had it happen numerous times. If the case doesn’t grip the bullet the lands WILL PULL THE BULLET OUT OF THE CASE SOME AFFECTING MEASUREMENTS.

[Zeneffect]

2.30 - 2.39 swing in measurement is pretty huge.
I measure mine like yours (hornady style tool) except

Once bullet and case are seated fully, release tension from the pusher rod and lock it down ensuring you don't have preload in the rod which will make your measurement long once you remove the case.
Pull case and bullet
Push bullet back until it touches pusher rod
Measure.

Repeat a few times then take an average. If the measurement swing is that large, reevaluate and see what I'm doing wrong. When I do the max coal measurements, usually the repeatability within is .003" of each other unless I'm messing up the methodology.

[Velocity]

Dt219
That is exactly what I was trying to find out. I you go back to post #6 I said using 90 gr. TNT bullet and getting CBTO of I only had .079" of bullet in the case. And with your measurement CBTO 1.730. COAL. 2.240CBTO 1.730. COAL. 2.240 it shows I'm .100" longer. BINGO!

Adding that .100" to my .079" the bullet should be .179" deep which is better than .079" I would think. I'm just trying to find out if my barrel is BAD. I mean the seating depth is longer than my magazine.

[Dt219]

I gotcha. Like I mentioned yesterday I believe a lot of people can’t load in magazine if bullets are seated to reach their lands. I might be wrong

[SCJim]

here is a thought, try seating the bullets to the COAL the manufacturer recommends. I am a newbie at AR reloading but so far managed to get .5 MOA just by seating at manufacturer suggested COAL. These are not single shot benchrest rifles we are dealing with here. If you really want to play with it start at magazine length and works your way in to the manufacturer suggested length. I have a target grade .223 bolt gun that likes the 80.5 Bergers at .135 jump which some find unbelievable

[Dt219]

I agree with Jim your not going to single feed them I wouldn’t think

[Velocity]

So all the time I was watching videos and reading about seating depth goes up in smoke?
I spent $400 for a barrel and all I need to do is make sure they fit the magazine and when I do that I'm already .100" plus off the lands.
What happen to, find your CBTO then back off .020", well I can see that's out of the picture. No fine tuning needed on this barrel, it's preset for 100 yards.

[Dt219]

Bolt guns yea you can. Far as I know a lot of ar15 guys can’t. It’s not up in smoke unless it doesn’t shoot worth a crap. $400 is a good bit. What barrel was it ? How new is it ?

[Velocity]

It's new and like I said before only shot it four times in the dirt just to get the fired cases for measurements.

[Dt219]

Brand ? And at least you didn’t buy a lilja with a big possibility of an out of spec chamber like I’m about to have sent off

[SCJim]

So all the time I was watching videos and reading about seating depth goes up in smoke?
I spent $400 for a barrel and all I need to do is make sure they fit the magazine and when I do that I'm already .100" plus off the lands.
What happen to, find your CBTO then back off .020", well I can see that's out of the picture. No fine tuning needed on this barrel, it's preset for 100 yards.

spend your time however you want

I spend mine shooting

magazine length at 830 yards with a off the shelf upper[ATTACH=CONFIG]18680[/ATTACH]

magazine length with a Wilson barrel while doing load workup, I have not had a chance to stretch it out yet

[ATTACH=CONFIG]18681[/ATTACH]

[Velocity]

I did a lot of research "persa" and read about all the good, bad and ugly and decided on that barrel maker. This is my 3rd AR-15, the 1st was a CMMG 300 Blackout the 2nd is a 5.56 I made myself it has a 20" Green Mountain barrel and the 3rd is a 24" Atheris barrel. There maybe noting wrong with it, it's probably just my screwed up thinking when the numbers looked to long. I was in Tool & Die back in the 80's and I retired as a software programmer.

I built this Grendel with hopes of doing some long range shooting, here are some ingredients;
24" barrel
BCM Upper - I had to Thermo-Fit the barrel
17 Design lower receiver
Ballistic Advantage - bolt carrier group
LaRue - 2 stag trigger
Seekins Precision - adjustable gas block ect...

[Velocity]

SCJim

Nice

[StoneHendge]

Make a dummy and seat it at your desired depth according to your calculations. Just size a case (or use a virgin piece) and seat a bullet (no primer or powder). Put it in a mag, slam the bolt home, pull the trigger and see if it breaks, then see if you can extract it. If you can, measure the COAL and see if it shrank and inspect the bullet to see if it engaged the lands. This will tell you if it is indeed your barrel or if it's however your measuring. This is the only real way to confirm depth - I use the Hornady comparator but I find it to be prone to measurement error.

[SCJim]

the reason I posted those three targets is to show two things

1. that you can get decent groups with mfg suggested seating depths
2. the first stage in load development is not seating depth but is finding a powder and charge that gets you a decent ES/SD

once you have that then you can start adjusting the bullet in or out in .003 increments to tweak the harmonics. Groups will be either horizontal, vertical, or round. Adjust seating depth in .003 increments until the groups go round.

Precision reloading is simple. Don't over complicate it. I have no idea where the bullets in those targets are in relationship to the throat. I don't care becasue all I care about is how they print on target.

[Velocity]

Got up today made my coffee and went to my reloading room, deleted the spreadsheet I used for the last two days, put the Sinclair and Whidden gauges away. Only using the Hornady Gauges today, using so many gauges got me all screwed up and I kept fighting it.
All you guys that came to help, I really appreciate you jumping into that tornado of confusion I created. What a 2 day ride.

Starting over today, I made 5 separate measurements to get the case base to lands measurement, my CBTO and a COAL for a 90 gr. TNT bullet. Those numbers are; CBTO 1.813" and COAL 2.313".

Then I loaded a dummy round and using Speers data sheet for a 90 gr. TNT with an OAL 2.260" which gave me a ogive number of 1.749".

Subtracting both CBTO's
1.813"
1.749"
.064" jump using a 90 gr. TNT bullet

Is this correct or am I starting another TORNATO?

[Oso Polaris]

Got up today made my coffee and went to my reloading room, deleted the spreadsheet I used for the last two days, put the Sinclair and Whidden gauges away. Only using the Hornady Gauges today, using so many gauges got me all screwed up and I kept fighting it.
All you guys that came to help, I really appreciate you jumping into that tornado of confusion I created. What a 2 day ride.

Starting over today, I made 5 separate measurements to get the case base to lands measurement, my CBTO and a COAL for a 90 gr. TNT bullet. Those numbers are; CBTO 1.813" and COAL 2.313".

Then I loaded a dummy round and using Speers data sheet for a 90 gr. TNT with an OAL 2.260" which gave me a ogive number of 1.749".

Subtracting both CBTO's
1.813"
1.749"
.064" jump using a 90 gr. TNT bullet

Is this correct or am I starting another TORNATO?

You are over-thinking it. You have One Definitive Limitation/Constant: Magazine Length (2.26" COAL), which is the universal limitation for reloading AR15s. Load the 90gr TNT to magazine length and see how it shoots. You only have one solution to your "Jump" concerns and that is to increase the amount of jump.... no way to shorten it without a custom throated barrel.