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How to find the right length? COL

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 13:43
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Gentlemen.
 
What method do you use to find the right COL (Cartridge overall lenght) for your rifle?  Any good tricks for optimum length?
 
Thanks
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 13:55
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cheaptricks method works well, but you have to remember one thing, just because you oal is one length doesnt mean it will work. the amount of space you have in your rifle's magazine limits the amount of oal you can have.

cheaptricks methos is to take a spent round out of your rifle and put a bullet( marked with a colored marker) in the end of the case. lightly crimp the bullet so it wont fall out. then chamber this bullet and case slowly and gently close the bolt all the way then slowly open it up again. the bullet should have been pushed into the case some and you will be able to see how much ink was scraped as the bullet was pushed into the case.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 14:00
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Well, you are going to be restricted by magazine length ultimately so even if you have a long throat it won't do much good if the mag box doesn't allow for the length. What I do is take a fired case, then do a partial resize to just get enough of the neck resized to hold a bullet firmly. Take a bullet and seat it leaving it very long and run the dummy round into the chamber (assuming we are talking a bolt rifle here). From there, I just see if the dummy round will fit down into the magazine with about an 1/8 clearance front to back. If it doesn't you will be restricted by magazine length for determining your COAL.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 14:09
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Originally posted by Roy Finn Roy Finn wrote:

Well, you are going to be restricted by magazine length ultimately so even if you have a long throat it won't do much good if the mag box doesn't allow for the length. What I do is take a fired case, then do a partial resize to just get enough of the neck resized to hold a bullet firmly. Take a bullet and seat it leaving it very long and run the dummy round into the chamber (assuming we are talking a bolt rifle here). From there, I just see if the dummy round will fit down into the magazine with about an 1/8 clearance front to back. If it doesn't you will be restricted by magazine length for determining your COAL.
 
+1 this is what I did to get mine
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 14:14
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Originally posted by pyro6999 pyro6999 wrote:


cheaptricks methos is to take a spent round out of your rifle and put a bullet( marked with a colored marker) in the end of the case. lightly crimp the bullet so it wont fall out. then chamber this bullet and case slowly and gently close the bolt all the way then slowly open it up again. the bullet should have been pushed into the case some and you will be able to see how much ink was scraped as the bullet was pushed into the case.
 
Basically correct. I don't mark the the bullet with a marker though.
 
Roy's way of partially resizing the spent case is good also and doesn't destroy the case like my method.
(I'm just always in a hurry and prone to just start grabbing pliers!) Wink  
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 15:40
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Originally posted by pyro6999 pyro6999 wrote:

cheaptricks method works well, but you have to remember one thing, just because you oal is one length doesnt mean it will work. the amount of space you have in your rifle's magazine limits the amount of oal you can have.

cheaptricks methos is to take a spent round out of your rifle and put a bullet( marked with a colored marker) in the end of the case. lightly crimp the bullet so it wont fall out. then chamber this bullet and case slowly and gently close the bolt all the way then slowly open it up again. the bullet should have been pushed into the case some and you will be able to see how much ink was scraped as the bullet was pushed into the case.
I guess a lot of rifles have limited magazine length and that is a determining factor in how long the rounds can be.  I've only got 4 rifles, but only one of them has a magazine length short enough that I have to seat the bullets just short enough so that the rounds will fit in the magazine.  The other 3 reach the lands way before getting too long to fit in the magazine.
edit to add. I meant to quote Roy and not Pyro.Big Smile


Edited by ckk1106 - December/18/2009 at 15:42
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 16:45
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I've used a similar method to determine OAL but all it really told me in my case was that the throat in that rifle was so doggone long I'd never be able to seat bullets into the lands. That and the magazine length issue has led me to just always load my .308 rounds to 2.8" (the nominal length) and to focus on other aspects of reloading to get good loads. Remember, some rifles shoot well with a jump. Mine does. So it's not always worthwhile to attempt to seat way out.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 16:56
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some times you can cheat and buy a donor rifle, i know people buy long action rifles in stuff like 30-06 and turn them into a .308 so they can really seat the bullets out there. im not sure what stuff like that costs to do though.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 18:48
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Do they turn them into single shots?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 21:13
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My A-Bolts, a 300 Win and a 338 Win, had the short magazine vs. long throat issue. With the correct factory detachable magazines I could not get either to really shoot as good as I like, especially the 300. It shot "patterns" with factory ammo and handloads that just fit the mag were not much better. I bought a couple of 375 H&H A-Bolt mags on Gunbroker.com, and the longer mag length allowed me to seat out close to the lands in both rifles. Voila! I now have both rigs shooting one ragged hole groups at 100 yards with Accubombs. Didn't really have to vary length much, I started at 0.015" of the lands and both rifles like that COL very much!
 
I use the Stoney Point/Hornady Overall Length Seating Gage setup to determine where the lands start in all my bolt rifles. Different bullets like different length jumps to the rifling, though. Noslers seem to like very little jump (i.e., seat out very close to the lands). Barnes TSX and variants like about 0.030" to 0.050" jump in my rifles. You just got to see where the rifling starts, load some up and go shoot them. I usually try to find the optimum powder charge first, then tune COL to peak accuracy.
 
Hope that helps!
 
Tom
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: December/18/2009 at 21:41
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Well I guess I have been lucky with mag lengths.  I have 6 personal guns and in all of them I can load to the lands if I want and still fit the mag.  Must confess that if I procure a rifle where that is not possible then I will get rid of it or custom rebarrel it to make it happen.
 
Originally posted by shooter4 shooter4 wrote:

Gentlemen.
 
What method do you use to find the right COL (Cartridge overall lenght) for your rifle?  Any good tricks for optimum length?
 
Thanks
 
To me this is a 2 part question.  The first is the mechanics of actually finding the COL.  There are several tools to do this.  The most common is the Hornady OAL Gauge
 
 
 
and you will need a modified case in your caliber
 
 
The tool I use is an R-P Products tool 318-424-7867 r_reeves61@bellsouth.net shown here with the Hornady
 
 
It is simple and foolproof (which helps me out) and you don't need to worry about the headspace difference between your modified case and your brass like you do with the Hornady.  You just insert your bolt in your gun and make sure it is cocked (firing pin retracted), insert the rod into the muzzle to the bolt face and lock the rear collet
 
 
retract the rod, insert the bullet to the lands (hold in place with a dowel or use the Hornady tool if you have one), insert the rod to the bullet tip and lock the front collet
 
 
measure between the collets
 
 
I have tried the slightly tight neck and bullet method and the cleaning rod method and got inconsistant results either because of the bullet being pushed into the lands with different force or the lands grabbing the bullet and pulling it partway back out.
 
The 2nd part of the question is how to find the best length to seat the bullet that will give you the best accuracy in your rifle.  That is pretty much trial and error but in my experience I just seat a bullet I am going to try out at .025" and vary the powder type and weights and usually find a good load before I have to worry about seating depth.  However in my experience if you try to seat too close then you will have problems with more flyers when your COL varies.  It is hard to seat a set of bullets without some variance, commonly .005" or so.  So if you are seating .005" off the lands then some will be touching and some will be .010" off and accuracy will suffer.  Bullets themselves are not always consistant in bearing surfaces, ogive curves and length (not to mention weight).  If you back off then the seating depth variances will not have as great an effect as they have when seating close.
 
So if your magazine is restrictive, seat to fit the mag and vary the bullets, powders, primers and cases.  If you can hit the lands, back off .025" for common bullets or .050" for monolithics like Barnes TSX, and vary the other factors.
 
JMHO
 
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