OAL Questions

[mgsutton336]

New reloader with some possibly typical new reloader questions. I'm loading 168 grain A-Max for a .308 and questions have arose about the over all length. Everything I have read says 2.810" is max length, so nothing I have reloaded thus far has exceeded that (about 150 rounds with once fired brass). My question starts with the tolerances of that. Everything I have loaded has been between 2.806-2.810", but I measured a box of Hornaday Black 168 grain A-Max (the round I'm basing my reloads off of) and they measure between 2.798-2.804". Am I seating mine too long? They seem to be shooting fine. Also I know that .004" is about the diameter of a human hair but it still seems like a lot. Should that tolerance be tighter? Should I be crimping? Using a Lee press with Lee dies and shooting out of a 20" Remington factory barrel. I know someone is gonna mention something about measuring headspace, but hold that thought I'm just trying to not break anything and creep up on that 1000 yard mark. There's still time to get super technical later.

 

[308pirate]

I know someone is gonna mention something about measuring headspace, but hold that thought I'm just trying to not break anything and creep up on that 1000 yard mark. There's still time to get super technical later.

Well, OK, so you come here not knowing what you're doing (mostly) but then tell us what you think you need to know and what you don't think you need to know?

Good luck with that.

PS, why are you trying to copy factory ammo instead of following a reloading manual recipe (what you should be doing)?

PPS, headspace has nothing to do with what you're asking here. Distance from bullet ogive to lands (aka bullet jump) has everything to do with what you're asking. So the time to get "super technical" is now.

PPPS, Stop worrying about tolerances for everything and instead focus on reducing process variation.

 

[Dirty8404]

Yup, need to be ‘super technical’ now. Get a reloading manual ASAP. First off, you need a comparator for your micrometer. Bullets vary a bit in length around the tip so a few thousandths of variation is normal.

As 308pirate said, you need to know distance to lands. Look up how to find it and go from there. SAMMI max OAL is not super useful aside from a rule of thumb, the key issues are distance to the lands with the bullet used and what you can fit in a mag.

Don’t crimp. I don’t consider .004 oal variation a big deal. My 190gr NCC 308 load is 2.855 for reference. Get a reloading manual.

 

[spife7980]

A forum member, @elfster1234, made this 10 video playlist. You dont need to do everything in it such as annealing but it is very comprehensive and a good watch. Youll learn a bunch. (I would rather learn a bunch when youre firing those rounds off 6" in front of your face than wade into it with ignorance)
https://www.youtube.com/playlist?list=PLCyPEnjRX7ebb28MKusD6VfMZlnsNkpK0

But for starters, measuring Over All Lengths will never get you consistent numbers. The only thing you need to worry about OAL for it to make sure it fits in your magazine.
What you want is a measurement down the nose of the bullet right in front of the bearing surface, thats the cylinder portion of the bullet that actually touches the barrel. We care about the interface of the bullet to the barrel, the tip is just floating in space and not that useful. The term for what we are looking for is CBTO, Case Base To Ogive.

The ogive is the entire curvature of the nose of the bullet but what we care about is that part right at .300 for a 308 where the lands will first contact the bullet. When we reloaders say to the ogive that is just slang to that specific point. The bullet first contacts the smaller diameter, the lands, and then is forced into the barrel through pressure engraving itself into them when fired.

You can see here in this image that if you seated these different bullets to the same OAL that the ogive of each particular bullet is in a completely different location. That could lead to you inadvertently jamming your bullets into the lands. That can cause pressure spikes and be bad juju.

So to measure where the bullet is actually touching you are going to want to get a bullet comparator to put on your calipers. This will allow you to measure on a consistent part of the bullet repeatedly. https://www.midwayusa.com/product/1...ad-bullet-comparator-basic-set-with-6-inserts

And some nice images to look at and study the relationships with

So thats what youre looking at with bullet seating depth. Now, how to actually find that depth. You can use a cleaning rod down the barrel to measure the difference in distance from an empty chamber to a bullet placed in the lands. That will be based off of the over all length of the bullet so there will be some error but its a crude approximations that is much more elegant that just trying to guess at it from a book. At least youll have an actual number instead of an arbitrary one.

You can do much better with a hornady loack and load oal gauge. You seat the bullet deep into a modified case and then push it into the chamber, and then use the internal rod to push the bullet forward to the lands. Extract it when you feel contact and take your measurement.

Finally you can measure it with your actual chamber

 

[JimLee]

Your rounds are safe. Factory ammo will always err on the side of caution. I tried to do what you are doing once, I thought I could get a good shooting reload at SAAMI spec and worry about seating length later. I ended up shooting way more rounds than I needed to through a good barrel during the process. If you plan on jumping into the deep end its just best to get it over with as the others here have stated.

 

[918v]

First, find the oal where the bullet touches the rifling. On my rifle it was about 2.865”. Making sure that you are not jammed in the rifling, you should try 2.800”, 2.805”, 2.810”, etc to see which one shoots the best. In my rifle it was 2.830”. I had .035” clearance.

The variance in oal is normal. Bullets are not perfect. You might wanna get a seater die with micrometer adjustment capability to make your oal adjustment easier.

Headspace is important. I know you said you don’t wanna break anything, but if you move the shoulder back too far on the case you’ll break the case. Get a .40 case and invert it over the neck. Compare your sized case to your fired case. Make sure it’s no more than .004” shorter.

 

[NineHotel]

Dragging the bullet tip on the front of a mag box is a sure fire (pun intended) way to cause a malfunction. As there are mfging differences/variances in magazines, the factory ammo maker is giving himself some margin and loading to an OAL under SAAMI max for that chambering, plain and simple. You might consider doing the same.

 

[mgsutton336]

Thanks everyone. That is some really good information. Maybe I should have specified if I was working loads for a particular gun or a general purpose rounds to work in whichever gun. Also I do have a manual just not a very good one. Any suggestions? Hornady? Lyman? Sierra? All of them?

 

[spife7980]

I have heard that the lyman manual is one of the more comprehensive introductions. Ive also heard that Metallic Cartridge Reloading by McPherson is great as well.

I will go on record and say that you should keep brass with the rifle it was fired from and develop specifically if you want to get the best performance.

 

[NineHotel]

Not much has changed in them over the years - a used book store should provide all you need for cheap. A bud just gave away 15 reloading manuals/guides. If you are in Denver I can get you the used book dealer info that has them. I have used the RCBS manual for 20+ years.

 

[mgsutton336]

Not much has changed in them over the years - a used book store should provide all you need for cheap. A bud just gave away 15 reloading manuals/guides. If you are in Denver I can get you the used book dealer info that has them. I have used the RCBS manual for 20+ years.

I’m in Longmont so I could make that trip to Denver

 

[yakstone]

Check your local library and online sources too.

 

[bax]

SAAMI max is interesting but, unless you are an novice reloader, it is not particularly important or useful. If you are a novice, stick with SAAMI max until you understand what you are doing. It is almost certainly not the best setting for long-range accuracy.

One caution. One might develop a load that shoots pretty well then be tempted to experiment with COL. For the sake of argument, say that the load showed marginal pressure signs and you were inspired to change from a .050 jump to a zero jump or, to put it another way, from a COL of 2.800 to 2.850 (I made up those numbers but they are fairly decent for a 308).

THAT would be risky. The zero jump usually generates the highest pressure. As part of the argument, I said that the round was already marginal on pressure. Changing from a .050 jump to no jump will increase pressure. Modern rifles are really strong but that is a recipe for rapid unscheduled disassembly. Be safe out there. Decrease the jump carefully while watching for pressure.

FWIW, I saw a fellow blow up a rifle once. He had brass and steel peppered all over his face and chest and the ex-weapon was in three large pieces. He experienced a number of small leaks. Medical attention was required to address the leaks and remove the extra metal. And he was highly excited. Don't be that guy.

Most of us develop a good load based on experience, talking to other people, and on the brass, bullets, and powder we like. Then we tinker with COL. There are really good articles on this web site about that process.

 

[elfster1234]

Very good info buddy !

A forum member, @elfster1234, made this 10 video playlist. You dont need to do everything in it such as annealing but it is very comprehensive and a good watch. Youll learn a bunch. (I would rather learn a bunch when youre firing those rounds off 6" in front of your face than wade into it with ignorance)
https://www.youtube.com/playlist?list=PLCyPEnjRX7ebb28MKusD6VfMZlnsNkpK0

But for starters, measuring Over All Lengths will never get you consistent numbers. The only thing you need to worry about OAL for it to make sure it fits in your magazine.
What you want is a measurement down the nose of the bullet right in front of the bearing surface, thats the cylinder portion of the bullet that actually touches the barrel. We care about the interface of the bullet to the barrel, the tip is just floating in space and not that useful. The term for what we are looking for is CBTO, Case Base To Ogive.
View attachment 6981010

The ogive is the entire curvature of the nose of the bullet but what we care about is that part right at .300 for a 308 where the lands will first contact the bullet. When we reloaders say to the ogive that is just slang to that specific point. The bullet first contacts the smaller diameter, the lands, and then is forced into the barrel through pressure engraving itself into them when fired.
View attachment 6981019




You can see here in this image that if you seated these different bullets to the same OAL that the ogive of each particular bullet is in a completely different location. That could lead to you inadvertently jamming your bullets into the lands. That can cause pressure spikes and be bad juju.
View attachment 6981016


So to measure where the bullet is actually touching you are going to want to get a bullet comparator to put on your calipers. This will allow you to measure on a consistent part of the bullet repeatedly. https://www.midwayusa.com/product/1...ad-bullet-comparator-basic-set-with-6-inserts
View attachment 6981022


And some nice images to look at and study the relationships with

View attachment 6981023


View attachment 6981024






So thats what youre looking at with bullet seating depth. Now, how to actually find that depth. You can use a cleaning rod down the barrel to measure the difference in distance from an empty chamber to a bullet placed in the lands. That will be based off of the over all length of the bullet so there will be some error but its a crude approximations that is much more elegant that just trying to guess at it from a book. At least youll have an actual number instead of an arbitrary one.
View attachment 6981029



You can do much better with a hornady loack and load oal gauge. You seat the bullet deep into a modified case and then push it into the chamber, and then use the internal rod to push the bullet forward to the lands. Extract it when you feel contact and take your measurement.
View attachment 6981030




Finally you can measure it with your actual chamber