Bullet seating depth

[Carson5]

Just starting to reload.... having problem measuring how far to seat bullet in case...

Using once fired .308 Fed GMM brass, in Mod 12FV, using 168g Sierra Match bullets.

Tried to measure throat length by making up dummy round using once fired brass and slightly ovaling neck so it will hold .308 round lightly.

Placed dummy round in breech and chambered round, slowly eject round without releasing firing pin.

Measuring OAL varies from 2.815" - 2.887"! OAL of Factory loads of GMM meas 2.800"-2.805".

What could be causing variance in measurements? Does floating bolthead have anything to do with this?

[Texas10]

I'm certainly no expert, but a couple of questions come to my mind.

Is the chamber new, never shot?

Is there carbon build up in the throat?


Are you measuring base to OGIVE or OAL?

What tools are you measuring with?

Did you use a cleaning rod to tap the bullet loose?

Did you remove extractor to prevent pulling bullet out of the case as you opened bolt?

You can partially size the neck to get a tighter fit to the bullet. Or you can neck size, seat the bullet long, paint it with marker and chamber. Look for scratches indicating contact with lands or tight throat.

Use a Hornaday or similar OAL gage. Takes practice to use it and get consistent results. Chamber has to be CLEAN, no carbon build up.

[Zero333]

The lands are grabbing the bullet when you do that, hence the different measurements.

Watch these videos

https://www.youtube.com/watch?v=GmDi7v530Og&t=569s

https://www.youtube.com/watch?v=TWmIwPwLyyg

You can also get the Hornady OAL tool.

I also recommend getting the proper bullet comparators for more repeatable measurements.

Open tip match bullets vary in length because their tips are not all the same. The Bullet Comparator will measure each bullet at the ogive where the measurement is more uniform.

[adammiddagh]

I use this tool and love it.

http://www.brownells.com/reloading/m...prod35491.aspx

Under brownells learn tab, they have the directions.

[bearcatrp]

I use a cheap dowel run down the barrel, measure to bolt, then measure to a bullet seated tight to the lands. Do three readings. Done. Do this for each different bullet.

[Wide Glide]

I don't know how I managed without the hornady setup. I use the only gauge with both the headspace comparator and bullet comparator. I was never confident with the MacGyver methods.

[jpx2rk]

I use the Hornady tool as well, usually starting at the 7/8AM position, (using the thumbscrew as the indicator) and rotate it around the clock face taking 4-5 measurments. I do get some variances, but occasionally I get a consistent large variance in one position.

Would this be caused by the lands, or what??

[Wide Glide]

I always assumed it was me varying the amount of pressure while inserting or being too rough with the dowel when removing. I usually take 10 measurements with a different bullet each time, disqualify the most extreme long and short. Then average the other 8. Probably overkill but it helps me sleep easier at night lol

[jpx2rk]

I've read about being consistent with the pressure on the tool when bumping the lands and try to be careful, I have lots of "do overs". I usually ignore the big variances as well, it's still something I wonder about. I've got a Lyman's borescope and used it once for trying to determine what the issue was/is but being inexperienced with the scope, did not find anything that stood out.

[Carson5]

Tex10:

Chamber has about 450-500 rounds thru it.

Can't see or tell if there is any carbon buildup. I do clean chamber with chamber brush after each range session.

Measuring OAL using digital calipers.

Used cleaning rod to tap bullet loose, I am now using wooden 1/4" dowel.

Did not remove extractor.

Since I posted original message I have sized case and seated bullet @ 2.945" OAL , placed it in chamber and using the wooden dowel method, as suggested in a later post I have measured chamber to be 2.790- 2.810. First measurement using only 169g bullet dropped into chamber, second with dummy 2.945" round.

Can factory cut chamber in 12FV be cut that tite or do you think it could be carbon buildup? If carbon buildup is cause how is it removed?

I am using RCBS neck sizing die which is sizing neck ID to .304, after seating and removing test round ID of case measures .306 ID. Is this too much neck tension?

Thanks for input!

[bigedp51]

When I got out of the military in 1973 I bought my Rockchucker press, two reloading manuals and a plastic Lyman vernier caliper.

I debated bullets and seating depth and decided to cheat, I bought Hornady bullets and seated them to the midpoint of the channeler.

My Remington 760 Gamemaster pump in .270 Winchester with a cheap Bushnell scope didn't mind my seating depth simplicity.

Life was so simple before gauges, then came more reloading books, and even more gauges and then finding .020 off the lands...................

Long range load development at 100 yards.
Erik Cortina
Team Lapua-Brux Captain
http://forum.accurateshooter.com/thr...yards.3814361/

Some of you have asked for more detailed instructions on how I do this. Here they are:
1. Find Jam by seating a bullet long on a dummy piece of brass (no primer nor powder) and apply die wax to the bullet ogive and record it's base to ogive length.
2. Chamber the round and close the bolt.
3. Snap the bolt open and measure the base to ogive measurement. If it is shorter than previous measurement, this is your jam. Do it a few times with different cases to make sure.
4. Load a known powder/primer/bullet combination. I load 4 of each powder charge in 0.5 gr. increments and seat bullets at jam - .020". I use one shot of each to get barrel fouled up and also keep an eye for max pressure at the same time. You can also use these rounds to break in a barrel if you are inclined to. If I encounter pressure on the hotter rounds, I will not shoot groups with the other loaded rounds and will pull bullets when I get back home. Do not shoot in round robin style because position and natural point of aim will be compromised.
5. Shoot 3 shot groups starting from lowest to highest. All groups are shot over a chronograph.
6. Examine target and find the place where consecutive groups line up vertically and ES is the lowest and speed increases the least from one group to the next.
7. Load to the middle of the powder node and do a seating depth test.
8. Load 3 shot groups starting from Jam - 0.005" all the way out to Jam - .040" in .003" increments.
9. When you find the seating depth test that shoots the best, load towards the longest side of the node to allow more room for throat erosion.
10. Final step is to load the new seating depth and load 5 shot groups in 0.1 gr. increments 0.5 gr. on each side of node (if pressure limits are not reached). This will cover an entire grain of powder and you will be able to pinpoint where the powder node starts and ends. In the summer, load towards the low end of the node, and do the opposite in the winter.

HAPPY SHOOTING!

[Texas10]

Some barrels do seem to have an unusually tight throat, I am battling a 20 something year old 243 right now that I cannot get a consistent base to ogive measurement because of a tight throat. I use foaming bore cleaner, chamber brush and still get OAL measurements varying 100 thou. Very frustrating, but carbon in the throat is the issue because the owner of this gun did not use good cleaning chemicals until just recently. And a little bit of carbon in an unusually tight throat is a real PITA.

Digital calipers to measure OAL is nice, but it's a waste of time because bullets tips/lengths are just not consistent. Measuring to ogive is really the only way to get a consistent base line of distance to lands, IMOP, and even then any measurement you come up with is not relevant to another shooter/reloader because there is no industry standard for OAL gauges. That's why manuals quote base to tip OAL and is mostly relating to magazine fed ammo.

Your line about measuring ID has me confused. If you mean OD, then yes, .002 neck tension is about right. Measure the case neck OD before seating a bullet, and then again with the bullet in the case. If it measures about .002 larger, you have .002 neck tension.

[LongRange]

if you have carbon build up foam is not going to touch it if you want the carbon out your going to have to scrub it out with brass/bronze brushes and a good carbon remover or JB bore paste and patches.

with that said everyone is way to concerned about an exact measurement here...if your getting a big difference in measurements with the hornady tools then its most likely you...or maybe in T10s case carbon or a shot out throat.
take your mod case screw it onto your tool and put it into the chamber and wiggle it around and note how loose fitting it is...if your moving the case all around in the chamber thats going to cause issues and keep in mind your never going to get an exact measurement consistently with it...insert the mod case and let the case rest in the bottom of the chamber holding the tool snug so that it stays there...slide the rod forward with firm even pressure(as if trying to jam the bullet .002 or so into the lands)now take your measurements.

now if you want to start load development with your bullet touching or slightly into the lands start with the measurement you just took and work from there...every bullet ive shot shoots better anywhere from .015 to .035 OFF the lands NOT touching or jammed.
when i measure for seating depth my numbers are ALWAY pretty close...i only take 3-5 measurements and go with the middle number unless i get 2-3 that are the same...i always start .025 off the lands and work from there.....you guys are putting WAY to much into trying to find a perfect number...as i said take a few measurements pick one and work from there.

[FW Conch]

^ Best advise I've heard so far ;-)) ^

[m12lrs]

I use the Hornady tool. Takes a bit of practice to get the feel. Once you get three or 4 measurements that are pretty consistent I call it good. Realize over time that measurement will change. Realize also you have to measure with each bullet you use. They will all be different.

I always start my seating depth test with a ten to fifteen thousands jam. I have found that most of the time that will be the most accurate. Of course I mostly use berger bullets and they like a jam. If that is a target rifle and I get what I want then I am done. If it is a hunter or pinker and I want a mag length load then I use the berger seating depth test. If it's there that will find it.

[Carson5]

Your line about measuring ID has me confused. If you mean OD, then yes, .002 neck tension is about right. Measure the case neck OD before seating a bullet, and then again with the bullet in the case. If it measures about .002 larger, you have .002 neck tension.[/QUOTE]

What I mean to say is after neck sizing I've measured the inside diameter of case with calipers. Measures .304". After seating and removing bullet inside diameter of neck then measures .306". This means I am inserting a .308 bullet into a .304 neck. Is this .004 difference too much neck tension? Should I back off the neck sizing die a bit until measured ID is .306 after sizing?

[m12lrs]

Most common way to establish neck tension is to measure outside diameter of several loaded rounds and subtract 3 thousands. If you are using a bushing die you want to get a range and try different ones till you find the sweet spot.. Remember when you size the neck depending on the work hardness of the brass you will get about a thousandth of spring back.

Personally I feel consistent neck tension is more important that dialing in 2 thousandths of.neck tension. Annealing helps keep neck consistent.