Author Topic: COL woes  (Read 2068 times)

Offline fmiller

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COL woes
« on: January 05, 2015, 01:21:12 PM »
Hi


I'm loading for a CZ-75 SA, using 124gr LRN bullets and Titegroup.


The problem I'm having is that, using the "plonk" test, I'm getting a working OAL of around 1.115. Even this is a bit tight, and during shooting the gun locks up now and then, so I'm probably going to need them even shorter.


This is a little scary for me - I can certainly back off on the powder charge, but I've heard that weird things start to happen when you go too far past the recommended OAL.


What should I do?


I think the issue is the overall shape of the bullet. Should I continue making rounds, or trash the bullets (1000 of them.... sigh...) and load something more streamlined?


Thanks!




Online chfields

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Re: COL woes
« Reply #1 on: January 05, 2015, 06:15:08 PM »
Check to see what your minimum OAL is and work from there. If that still doesn't work then you will probably need different bullets.
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Offline Rodolfo Fierro

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Re: COL woes
« Reply #2 on: January 06, 2015, 10:23:28 AM »

I'm loading for a CZ-75 SA, using 124gr LRN bullets and Titegroup.


The problem I'm having is that, using the "plonk" test, I'm getting a working OAL of around 1.115. Even this is a bit tight, and during shooting the gun locks up now and then
What happens when the gun " locks up" ? 
1.115 is not that much over the recommended OAL and might even be within the recommendations for this particular bullet.  Do you have the ability to measure the velocity of the bullets?  That will give you an indication that you are nearing a maximum load.  Do these reloads feel hot?  Loads for lead bullets are usually pretty tame. 

Offline fmiller

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Re: COL woes
« Reply #3 on: January 06, 2015, 12:00:26 PM »
Hi


Thanks for your reply. Sorry I was so vague in describing the gun 'locking up' - there are actually several things that are happening (all of which I -believe- are the result of the cartridge being too long).


First, and most common, the gun will chamber the round but I can't rack the slide to eject it. I only noticed this after a light primer strike - the gun went 'click' and I couldn't eject the round.


The other problem I had was the slide not going fully into battery. Thankfully, the gun did NOT fire then.


I made up some dummy rounds last night and found that a COL of 1.10 worked. Should I progress with loading or shelve these bullets?




Offline Rodolfo Fierro

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Re: COL woes
« Reply #4 on: January 06, 2015, 03:34:35 PM »
If the 1.115 OAL cartridges are not ALL allowing the slide to close properly don't shoot them.  Get a bullet puller and you can save the primed brass by resizing them in a die without the de-capping pin in it.  You can save the powder, and maybe the bullets.  Check that the bullets are still .356". 
  Try the 1.110 OAL with a small batch.  You can test them without firing them.  Just fill a magazine and work the slide manually.  If any don't chamber properly pull them and try a shorter length.  BTW The results of the push test are .010" longer than the cartridges that you want to load.

Offline noylj

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Re: COL woes
« Reply #5 on: February 21, 2016, 02:27:52 AM »

Find out what your problem is and fix it. Don't just start changing things.
The concern about COL is about going a lot shorter than used in the manual. The COL in a manual is usually pretty close to the minimum working COL (and sometimes I wonder if they even check functioning or just did all testing in a single-shot Universal Receiver).


     Per Ramshot:
"SPECIAL NOTE ON CARTRIDGE OVERALL LENGTH “COL”
It is important to note that the SAAMI “COL” values are for the firearms and ammunition manufacturers industry and must be seen as a guideline only.
The individual reloader is free to adjust this dimension to suit their particular firearm-component-weapon combination.
This parameter is determined by various dimensions such as
1) magazine length (space),
2) freebore-lead dimensions of the barrel,
3) ogive or profile of the projectile and
4) position of cannelure or crimp groove.
• Always begin loading at the minimum "Start Load".
• Increase in 2% increments towards the Maximum Load.
• Watch for signs of excessive pressure.
• Never exceed the Maximum Load."

Your COL (OAL) is determined by your barrel (chamber and throat dimensions) and your gun (feed ramp) and your magazine (COL that fits magazine and when the magazine lips release the round for feeding) and the PARTICULAR bullet you are using. What worked in a pressure barrel or the lab's gun or in my gun has very little to do with what will work best in your gun.
Take the barrel out of the gun. Create two inert dummy rounds (no powder or primer) at max COL and remove enough case mouth flare for rounds to chamber (you can achieve this by using a sized case—expand-and-flare it, and remove the flare just until the case "plunks" in the barrel).
Drop the inert rounds in and decrease the COL until they chamber completely. This will be your "max" effective COL. I prefer to have the case head flush with the barrel hood. After this, place the inert rounds in the magazine and be sure they fit the magazine and feed and chamber.
You can also do this for any chambering problems you have. Remove the barrel and drop rounds in until you find one that won't chamber. Take that round and "paint" the bullet and case black with Magic Marker or other marker. Drop round in barrel (or gage) and rotate it back-and-forth.
Remove and inspect the round:
1) scratches on bullet--COL is too long
2) scratches on edge of the case mouth--insufficient crimp
3) scratches just below the case mouth--too much crimp, you're crushing the case
4) scratches on case at base of bullet--bullet seated crooked due to insufficient case expansion (not case mouth flare) or improper seating stem fit
5) scratches on case just above extractor groove--case bulge not removed during sizing. May need a bulge buster.
 

Offline frgood

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Re: COL woes
« Reply #6 on: February 21, 2016, 08:08:48 AM »
If the slide is getting tight during lock-up (going into battery), I might suspect the issue that i had last year.

Bulgie!Are you using range brass? Chamber check your rounds before heading out to the range and confirm they fit properly. Simply drop the round into the barrel and ensure it fully seats. That is where I found the cartridge getting wedged pretty solidly.

If the cartridge diameter is too large (near the base as the resizer may not go ALL the way to the bottom), you can use a Lee Bulge Buster to get your rounds back into spec.

In my case, I find my TS .40 chamber has a tighter tolerance that most pistols, which adds to its precision. 

Offline Dvrdwn72

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Re: COL woes
« Reply #7 on: February 24, 2016, 08:14:47 AM »
I load a few unprimed rounds and chamber check them. I then can seat the bullet deeper and check until I get the seating depth the gun likes.