Home Forums Reloading Big Game Rifles OACL Question

OK I'm new to reloading and hope this isn't a stupid question. But in my Nosler #7 manual on a 243 maximum oval is 2.710 but you look and tested oacl is 2.680. At what length should I seat mine? Also when you seat the bullet farther it can cause more pressure right? Do I always want to seat at max oacl? Someone care to explain?

Given constraints or latitude of the magazine, the measurement in determining seating depth that is most is important is the length of the chamber to the ogive (where different bullets contact the rifling) in your rifle. There are several tools available to help you determine the OAL of your chamber or you can make up a dummy round using once fired brass from your rifle. Once you have determined your rifles max OAL you can adjust from there.

There ain't no such thing a MAX OAL. As stated, it depends on throat/magazine constraints.

Try making a dummy round that just fits your mag box and see if it chambers. If it doesn't, seat the bullet in deeper a little at a time until it does comfortably. Use that as a guide for now for that particular bullet.

What are you working with specifically?

What CLB said however, not to add to confusion, you ideally should measure to the ogive and NOT the OAL.
I'd recommend that you get the Stoney Point (now Hornady- I think) "thingy" to measure to the ogive.
Using a dummy cartridge, seat a bullet out to a length that you know is too long to chamber and then try to chamber it. Gradually
seat the bullet deeper and keep trying to chamber it. At some point, the cartridge will just fit. Measure this length to the ogive.
This is your max. seating depth. Then, for starters, I'd seat the bullet about 0.025" deeper than your max. depth reading.
Once you find a load giving good accuracy at a decent velocity, you can play with adjusting the seating depth to slightly
improve your accuracy. Make sure to keep good notes on your results to include seating depth changes. I put mine in an Excel routine.
Hope I didn't complicate things too much and good luck.
Bear in Fairbanks

Well what about putting the bullet in the case then chambering the round will it not seat it and then I would have a decent idea?

That wont work if you have fully sized the neck. Too much pressure and you will only jam the bullet into the lands and frustrate yourself.

If you want to try that idea, set up your die so you size only about 1/4 of the neck. Just enough to hold the bullet. If it works out well for you, you will have the distance to the lands.

Put that dummy in your seater die for initial set up, then remove that round and spin the die in about 1/8 of a turn and seat a bullet. Try it in your chamber and if all is good then load up a few at that length.

Do some searching and get some tools: bullet comparator, headspace gauge, etc...

So would you guys recommend the hornady tool although you half to buy separate cases it seems like it works good.

The 2.710 is a SAAMI spec, Sporting Arms and Ammunition Manufacturers' Institute. SAAMI is a voluntary guideline that all commercial gun manufacturers, ammo makers, and reloading die builders choose to follow. It is what allows Remington ammo to fit in the magazine and chamber in Winchester rifles. If you also build your ammo to those standards your ammo will work well in any mass produced rifle. So this isn�t a bad place for a beginner to �start� just to get some confidence and get some rounds down the barrel.

Beyond that, I always start with a new rifle by measuring the inside length of the magazine. This will be one factor in determining the max oal of a cartridge. I take the mag length and subtract .020� as an absolute max cartridge length based on the magazine size. In some guns this will be the only defining factor because at this length you are still well off the lands, so no way to get closer to the lands unless you want to go single shot. If you find the -.020 is a problem then alter it accordingly, but that works on all my guns from 22 hornet to 375HH.

Example: On my 243 the mag length is 2.910, so based on mag length alone I know I can load any bullet to a max oal of 2.890 for functioning. Using 95gr ballistic tips they hit the lands at an oal of 2.789. So with this gun and this bullet the magazine is not a limiting factor, but on some guns it will be. In my case I choose to come back an additional .010 off the lands for an oal of 2.779.

I use the Hornady Lock n Load gauges to get these measurements off the ogive. Get them if finances are not an issue. But I�ll also say you don�t need to have these to �start� reloading. I reloaded very successfully for decades before these became available and probably 100s of thousands reload without them. As your knowledge and confidence grows you can decide if you want to vary from SAAMI and the reloading book suggestions.

This is how I did it prior to the gauges. Measure the mag and subtract .020. Take a sized case with no powder or primer, seat a bullet to the mag length minus .020. Take a lit match and hold it under the bullet ogive area, rotate the bullet and it will completely blacken the bullet with soot. You can also use a marker, a black erasable whiteboard marker works very well. Gently try to chamber the round. If it chambers with no land contact marks you are done. That means even at max mag length you can�t hit the lands with that bullet, the magazine length is the determining factor.

If it chambers but you see land marks then you want to seat it deeper. All my seating die stems are 28 thread or .036� per revolution. So if you turn the seating stem � turn you�ll get about .009 deeper seating. Do that until you don�t get land marks anymore. Wipe and re-mark or re-soot with each try. Doing this you will find close enough for hunting purposes without extra tools where the land contact point is. Then you can measure the COAL.

And no, seating the bullet deeper will not increase pressure. Seating it longer will. A bullet that has a long running start at the lands will not pressure spike as much as a bullet that is resting against the lands. Resting against the lands is like a barrel obstruction and the pressure will ramp quicker trying to get it obturated into the barrel.

Don�t know if any of this makes sense in writing.

SAAMI 243 drawing. You can see length range is 2.540 to 2.710. You need to be sure if you are using short lightweight bullets that you have enough neck bearing surface/depth to provide good neck tension.

I have the Hornady tool and use it periodically but prefer to use a once fired case from the rifle in question and either slightly size the neck or press the side of the mouth in just enough to grasp the bullet so it doesn't slip. It doesn't take much.
The idea is that the bullet will make contact with the rifling and slide back into the case and stay put without jamming into the lands .003 to .005 thousandths or more and throwing your measurement off or becoming stuck in the rifling.
It sometimes takes a little fussing but once you done it a few times it will become pretty easy.
I would suggest repeating the process a few times and check your measurements to verify a consistent measurement.
IME, a Hornady or Sinclair tool with the correct comparator parts to measure dummy cartridges to the ogive of a seated bullet is an indispensable piece of reloading kit and will give you additional info to produce accurate and safe ammo.
BD

Any good with tools? Make your own out of fired brass in your rifle.
5/16 x 36 tap
19/64 drill bit.
Drill out primer pocket and case head, tap said hole.
inside ream case neck after neck sizing so bullet moves freely.
Waaalahhhh modified case.

Have fun, its easy.

^^^^ This ^^^^^
I've found that fired cases out of your chamber provide more accurate OAL's after the shoulders have filled out and moved forward after firing opposed to the modified cases sold by Hornady.
Swiftly nailed it, and they are very easy to make.

BD

Good info thanks

Ok i got a question if i use a once fired brass shouldnt the brass be trimmed to the correct length before doin the bullet test or no. Please explain

This is a hunting rifle using a full length sizing die. If you shoot and make a reference measurement on an expanded case and then go and RESIZE it to seat the bullet, by very definition you are changing the dimensions you just set as a reference. The bullet is always seated into a resized case so that should also be your reference for measurements. Hornady cases are shoulder sized to unfired dimensions same as the sizing die that will be used.

If you're going to build your own then it should be under the same conditions as the bullet that will actually be seated. But really! it's $6! VERY widely used for decades.

Trimming it is irrelevant unless it is over length, it is the shoulder dimension that is important.

Take a quick measure with your calipers and compare to the specs. Once fired may or may not need to be trimmed.

Here is a good treatment of the subject from Berger. Goes thru the SAAMI discussion, magazine length considerations, pressure vs distance, and use of the Hornady equipment.

http://www.bergerbullets.com/wp-content/uploads/2013/03/COAL.pdf

So other than buying cartridges for the hornady tool it is your best bet?

Read the thread I have in the link. Many ways to go about it and you don't necessarily need the Hornady tool and a bunch of cartridges to get it done. Once you figure out the distance to your lands and have a dummy round made up with the bullet you want to shoot you are golden.

Read Here

pseshooter:
Here's what I was referring to. No custom cases involved. Follow the link.

http://www.midsouthshooterssupply.com/item.asp?sku=00005B234

Good luck.
B.I.F.