Home Forums Hunting & Shooting Ask The Gunwriters How do you determine COL?

How do you go about determining the max COL and what COL you actually use for a given bullet and rifle? Thanks.

Load to fit/function with the magazine length. After that see if it jams the lands when it just fits the magazine.

If it jams the lands, seat just deep enough to just touch the lands and work backwards from there to see what shoots best.

If it just fits the magazine and doesn't hit the lands, start from there and see what shoots best.

How do you know when it hits the lands? What measuring method do you use? There is plenty of room in the magazine.

I use the hornady oal gauge

You can smoke the bullet and see the contact points, you can also feel it when closing the bolt.

As I posted in the gunsmith section, I take a fired case, neck size about 2-3mm of the case neck, take a boattail bullet and place in the case mouth and then chamber the "round". The act of closing the bolt will seat the bullet into the case pushing against the lands, that is the max coal that the chamber and throat will take for that bullet. BUT unless you are going to use it as a single shot make sure the cartridges will extract w/o the bullet hitting the receiver ring and/or that they will fit the magazine. DON'T do this w/a loaded round and fire as the bullet against the lands may well push pressures above a safe level. Muddy

I have been doing something similar - I cut a slot in a sized case so the bullet can slide in and out easier and I can use that case with different bullets. I was just wondering if there was a better method. And once the max COL is determined, how far off the lands to seat the bullets. Thanks.

My method is a little simpler and cruder, but it works for me -I take a sized case and load a dummy long, then try to load it in the chamber. Bolt won't close? Don't try to force it, use a coated cleaning rod or a wooden dowell to gently tap the dummy out of the rifling (it's probably stuck there). Remove cartridge, adjust seating die to seat 5-10 thousandths deeper, repeat.

Eventually you will be able to close the bolt with some effort. Extract dummy, adjust seating die to reduce COAL in about 3-5 thousandths, should chamber easily now. Make a second dummy with a new bullet/case, leave seating die at previous setting. If you've done it correctly you can NOT feel the bullet engage the rifling (bolt closes easily), when you extract the case you will see the light "witness marks" from the rifling on the bullet - this is a light kiss and the place to start load development.

I like to make at least 3 dummies to check magazine function for any load I develop, so this is just part of the process. If you later realize that a slightly shorter COAL shoots better, its no big deal to run your dummies back through your seater to adjust to the new length.

Picture shows witness marks from the rifling on the bullets - look at the area where the pencil is pointing. Note these rounds have been run through the magazine many times for function checks, so there are a bunch of rifling marks - would only be ~4 or 5 after the first check with a previously unchambered dummy.



Now go back and check COAL on the dummies you just made - don't be surprised if COAL varies by 3-5 thousandths between dummies. The bullet length can (and will) vary. The seater seets based on the ogive, not on length and as such seating depth will be consistent w/ regards to ogive/rifling regardless of variations in bullet and/or COAL.

HTH

David

That's generally how I do it..I also use a sharpie marker to colour the bullet so I can see exactly where and how much its contacting the lands..

I then measure to the ogive using a Hornady bullet comparator and use the info to set up a dummy round just kissing the lands..Again I use sharpie to blacken the bullet so I can see whats going on..

That is with normal jacketed bullets, but be aware that for Barnes X and some other copper bullets, its recommend you load the bullet something like 60thou off the lands as a starting point..

In both cases, once you have a starting point, you then alter the bullet seating depth to see what works best for accuracy..

When checking for rifling contact, it is best to remove the striker assembly from the bolt. Then you only feel resistance if the bullet actually contacts the rifling. If you leave the striker in, you're trying to feel through all the resistance and friction caused by the spring-loaded striker. Not good.

What rifle? None of my rifles have the firing pin exposed and contacting the primer when the bolt is closed.

David

That aint what he's talking about.

Help me out then, what's he talking about?

David

Not that its an issue (to me), but the cocking piece creating resistance. Strip a bolt and run it.it'll be more clear.

As in the resistance with the cocking piece prevents you from feeling a light kiss?

I guess that's another way to do it - the witness marks are gonna be on the bullet from the rifling regardless.

Thanks for the clarification.

David

David,

Many people like to make handloading more complicated. I do it the way you do, looking for rifling marks on the bullet, rather than "feeling" for resistance when closing the bolt.

Thanks for the response. Lots of different ways of doing stuff, just trying to understand what someone else is doing.

David

Thats how i do it as well,using a sharpie. Was just tryin to explain what I "think" BRH was saying.

I use a "modified case" and a Stoney Point tool. I do it three times to make sure I get a consistent COAL with that particular bullet. A new rifle gets this performed right from the start and the data goes into the "book". I usually measure 4-7 bullets depending what I am going to load with. Can't be simpler or more accurate.

My method is pretty easy. I take a resized case with no primer in it, run the neck of the case over the expanded plug a half dozen times. Then partially seat a bullet. Then I chamber that round. BY running the neck over the expanded plug several times, the bullet is a snuff fir in the neck, but loose enough so that when it is chambered, the rifling will push the bullet back down into the case instead of the bullet becoming lodged in the lands. Then, check to see if that cartridge length will function through the action. If it will function, that is your COAL touching lands, and you can measure it, and then adjust to what ever distance you want to be off the lands. Of course, if it doesn't function through the magazine and/or eject properly, you COAL will have to be adjusted to that consideration.