Author Topic: COL - isn't it about how much bullet is in the case?  (Read 450 times)

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Offline sirgilligan

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COL - isn't it about how much bullet is in the case?
« on: March 04, 2018, 01:55:49 PM »
I have been reading the posts about finding the COL for my CZ pistols. You know, put a bullet in a case and put that in the barrel and press it into the barrel and then pull it out carefully and measure and then take that number and maybe round down a little and then find a load published for that weight bullet, your powder, and the COL that you measured.

That seems a bit wrong to me. Isn't it about how much of the bullet is in the case (how much of the ice berg is below the water line)? That is what decides case capacity.

Or is there some standard that says all 124 grain .355 bullets are the same length?
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Offline painter

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Re: COL - isn't it about how much bullet is in the case?
« Reply #1 on: March 04, 2018, 02:09:11 PM »
The point of the push test exercise is to find a length that will fit the shorter CZ leade, it isn't about seating depth.

Seating depth, of course, comes in to play when you're trying to decide if a particular published load works with your possibly shorter OAL.

If you religiously start at the starting load you'll most likely be safe whatever constraints your required OAL put on your choices.

For example, if you have to load .010 shorter than a load you want to try, starting load will be safe. Maximum load 'might' be a little hot, but there's a formula to decide.
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Offline Wobbly

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Re: COL - isn't it about how much bullet is in the case?
« Reply #2 on: March 04, 2018, 02:16:56 PM »
The barrel of every gun always determines the Max OAL with any bullet/ barrel combination. The issue is that many very popular hand guns have such a gracious freebore that they'll allow any OAL to be used.... so for people who start loading pistols, like Glock, it's a moot point and they sometimes forget about this rule. BUT the rule is still there, and still is in effect.

What you may have forgotten is that not all chambers are the same. They all have to meet SAAMI specs, but SAAMI doesn't cover freebore dimensions, just like they don't discuss how much support the head of the case should have. This is how one brand ended up generating "Glocked brass".

You have the Max OAL and the Min OAL, and the reloader is free to pursue other personal standards AFTER they meet those requirements.

So you are merely confusing the requirements with the desirable traits.


Hope this helps.
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Offline IDescribe

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Re: COL - isn't it about how much bullet is in the case?
« Reply #3 on: March 04, 2018, 06:21:26 PM »
Isn't it about how much of the bullet is in the case (how much of the ice berg is below the water line)? That is what decides case capacity.

Or is there some standard that says all 124 grain .355 bullets are the same length?

Yes and no.  How deep the bullet is seated into the case has a definite ballistic effect.   BUT it's negotiable.  You can account for it.  How long you can load the bullet without engaging the rifling lands is non-negotiable.  It is what it is.   So you determine that first, and negotiate everything else subsequently.

Offline Wobbly

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Re: COL - isn't it about how much bullet is in the case?
« Reply #4 on: March 04, 2018, 07:26:10 PM »
Yes and no.  How deep the bullet is seated into the case has a definite ballistic effect.   BUT it's negotiable.  You can account for it.  How long you can load the bullet without engaging the rifling lands is non-negotiable.  It is what it is.   So you determine that first, and negotiate everything else subsequently.


Nice and succinct.
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Immature reloaders ask: What's wrong with this gun?
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Offline painter

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Re: COL - isn't it about how much bullet is in the case?
« Reply #5 on: March 04, 2018, 08:03:51 PM »


Nice and succinct.
Silver tongued devil, he is. ;D
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but not the ability.

Offline ReloaderFred

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Re: COL - isn't it about how much bullet is in the case?
« Reply #6 on: March 05, 2018, 11:45:57 AM »
The other consideration is the length of round the magazine will accommodate.  This isn't as big an issue in CZ pistols, due to their generally short leade, but in other pistols, and most pistol caliber carbines, this is an issue.  Some chambers will accept a round that the magazine won't accept.

Bullet design also comes into play.  A short blunt bullet will allow the ogive to contact the rifling sooner than say a NATO design bullet, with it's long slender ogive, which is designed to feed through any chamber in that caliber that NATO nations may employ.  For instance, a 9mm caliber bullet that is designed for the 357 Sig, which requires a short ogive, and long bearing surface, due to the short neck of the case, will have to be seated deeper in a 9x19 case to feed through the chambers of a lot of pistols chambered in 9x19.  Conversely, a NATO designed bullet won't work in the 357 Sig cartridge due to the long taper and short bearing surface, which ends up below the short neck of the 357 Sig case.  And they're both normally .355"/.356" diameter bullets of the same weight.

Hope this helps.

Fred
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Offline Moken

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Re: COL - isn't it about how much bullet is in the case?
« Reply #7 on: March 05, 2018, 12:27:15 PM »
Regardless of firearm it's a balacing act. Seat deep and pressures elevate. So powder must be adjusted. Length can effect feeding and accuracy.
All that to me is part of the fun of reloading, tuning the round for your piece and working for better results.jmho

Offline newageroman

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Re: COL - isn't it about how much bullet is in the case?
« Reply #8 on: March 05, 2018, 01:55:09 PM »
Also keep in mind that hollow points will naturally be longer than the same weight of a roundnose, all else being equal. Still having to keep them under the mas COL, this would put more of the bullet in the case, another reason to always start low and work up a to a load when changing ANYTHING in a load.

I had just recently purchased some hollowpoints by accident. It was the only box they had left, I was in a bit of a hurry and was the same weight as the round nosed that I had used previously. Differences in packaging were minimal, but it really was my fault in the end. I was concerned about compressed loads, but - New component, another round of load development (starting low). Can't wait to shoot these up and move back to the round nose.

Offline IDescribe

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Re: COL - isn't it about how much bullet is in the case?
« Reply #9 on: March 05, 2018, 03:57:21 PM »
Also keep in mind that hollow points will naturally be longer than the same weight of a roundnose, all else being equal.

Quick correction -- you have that backwards.  Jacketed hollowpoints are shorter than their RN counterparts.  That's all the major manufacturers.  If you look at an FMJ-RN and JHP of the same weight from the same manufacturer, the FMJ-RN is going to be the longer of the two bullets.   ;)




Offline sirgilligan

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Re: COL - isn't it about how much bullet is in the case?
« Reply #10 on: March 06, 2018, 08:15:45 AM »
Thanks to all for the information.

SirGilligan
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Offline Wobbly

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Re: COL - isn't it about how much bullet is in the case?
« Reply #11 on: March 07, 2018, 11:36:31 AM »
To visually sum up this information we have a cartoon....



...with the understanding that the limitations set by the barrel are fixed, whereas the limitations set by the recipe can be modified by more advanced reloading techniques and those calculations and assumptions then verified by a chrono.

Hope this helps.
In God we trust; On 'starting load' we rely.

Immature reloaders ask: What's wrong with this gun?
Mature reloaders ask: What did I do wrong ?

Offline sirgilligan

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Re: COL - isn't it about how much bullet is in the case?
« Reply #12 on: March 11, 2018, 10:54:44 AM »
I cartoon is worth a thousand words.
SirGilligan
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