Bullet seating depth

[sr250]

Trying to determine distance to lands using a Stony pt tool for a 22-250 rem. Following the instructions for the tool it says to stop when resistance is felt with bullet and to use a wooden dowel inserted into the barrel and sandwich the two. If I push the bullet in with a little more force the bullet goes in a little further and it feels like it has bottomed out. The measurement for when resistance is felt with the bullet is anywhere from 2.004"-2.077". While pushing the bullet further in it is around 2.133".

With these different measurements tried the splitcase method. Wanted to make sure it is being done correctly. Take a FL resized case cut two slits in the neck down to shoulder, insert the bullet, insert the case in the action close the bolt, remove the case with the bullet still in the case and take reading. The readings averaged 2.138". Used a stony pt comparator for all the readings.

Why is the stony pt oal gauge getting different readings? And which reading from above is the right one to use? Any advice is appreciated. Thank you.

 

[cmillard]

hmmm, never had that problem. i use a hornady Lock-n-load OAL gage. i would assume that you are using the same bullet each time? you could load up a round at varying OALs and either smoke the bullet or take a magic marker to mark the bullet, then put it in the chamber (point in safe direction) and close the bolt. eject the round and see if there are any marks on the bullet.

 

[fdshuster]

sr250: I've been using the Stoney Point/Hornady oal gauge since it first became available, and have the same experiences as you are. The different readings will depend on how "hard" you push on the center rod. I'll concentrate on using the same amount of "push", and take several readings, average them, and that's the dimension recorded for that bullet & chamber. Even with these small "differences" I still believe it's the most accurate method of determining throat depth.

 

[25AI260]

Sr250.. another way,
with your action closed run a dowel down the barrel against the bolt mark the stick at the muzzle
then jam a the bullet in the barrel against the lands run the dowel back in to touch the bullet mark the stick at the muzzle again..
measure those two mark points... that being your AOL... make a dummy round using the measurement..
then you can measure the ogive of the dummy, it should be really close
...remember that is for that bullet another brand or size will differ

 

[bsekf]

I gave up on trying to push the bullet into the lands and then getting a measurement. I use the split neck system. You do have to be careful because the bullet will sometimes stick in the rifling and give you a false reading. I use the Lock and Load gauge and get several measurement until I am convinced I have it right. Keep in mind that you are only getting the "jam" measurement so you have a place to start when you tweak seating depth.

 

[jo191145]

You can fix those inconsistent readings by opening up the case mouth of your Stoney Pt cartridge case. I usually spin a little sandpaper in there to get a little extra room. Shade Tree Mechanics but it works most of the time
Those cases usually require a little fine tuneing when new.

The cause? Could be run out in your SP case or you could be seeing a non concentric chamber.

If its a brand new gun you might be getting caught on a burr in the throat.

And of course make sure the bore is clean before using. At least until you have the bugs worked out. My SP once warned me of a massive carbon ring build up when I found my throat had shrunk .040 after jumping short bullets with a dirty powder.

If your getting wildly inconsistent readings like that something is not right. I've seen readings like that in a factory tube once using a SP case proven to work in other barrels. Without a borescope its impossible for me to say exactly what was going on. The problem disappeared after shooting about 100rds.
Only three things I can think of to cause it. Non concentric chamber, Burr in the throat or last and not likely, an abnormally tight free bore. Or a combo of any of the above.

Don't force the SP quage. The little plastic rod is very weak and using too much pressure will weaken it further causing erroneous readings. Sand out the case mouth and see if it improves.

You will find with time the correct reading is in the 2.133 range. You should'nt need to force it to get there tho.

These OAL guages work very well once you get the bugs out of the cases.

 

[sr250]

Thanks to all who replied. Rechecked all measurements. The split case method and using the Stony pt oal gauge with some more force are roughly the same measurements. I have used the Stony pt gauge before and one could tell when it is was touching the lands.

When I use the gauge and resistance is first felt it just takes a little more force and one can feel the bullet slide and then bottom out. The plastic plunger is not bending while doing this.

 

[sr250]

Where did you get the measurement of 2.133 as quoted below?

(quote)You will find with time the correct reading is in the 2.133 range. You should'nt need to force it to get there tho.

This is near the exact measurement I keep getting with the Stony pt OAL gauge and pretty close to the split case. Also, the plunger isnt really being forced a great deal that it is bending. A little more pressure and the bullet slides in further and then bottoms out. Thanks for your help.

 

[jo191145]

Where did you get the measurement of 2.133 as quoted below?

(quote)You will find with time the correct reading is in the 2.133 range. You should'nt need to force it to get there tho.

This is near the exact measurement I keep getting with the Stony pt OAL gauge and pretty close to the split case. Also, the plunger isnt really being forced a great deal that it is bending. A little more pressure and the bullet slides in further and then bottoms out. Thanks for your help.

I got that measurement from your original post. 2.133

Its good you do not need to exert a lot of pressure to get there. Open up the case neck interior diameter a little and hopefully your troubles will go away.

Another tip: Using the same bullet many times over, especially if its been forced even slightly can give you "slight" inconsistent readings.

Open the id of the neck, get rid of the stickyness, grab a fresh pill and you should have your DTL with one try. For that particular lot of particular bullet anyway.

 

[RDavies]

I have found the very same thing a few times. It is most likely the freebore being fairly tight. When it has a bit of carbon fouling in the freebore, the bullet starts to just contact the parrelal section. I found this with a few different factory barrels as well as long seated target chambers if fouling built up.