Author Topic: COAL when switching bullet styles  (Read 4304 times)

Offline Stein

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COAL when switching bullet styles
« on: May 27, 2010, 09:10:56 PM »
I have reloaded about 400 rounds so far, so consider me a beginner.

Up until now, I have been loading 9mm, 115 g FMJ Winchester bullets to a COAL of 1.165".  I recently bought 1,000 Montana Gold JHPs which are obviously shaped different.

The MG bullet measures 0.550" long and the Win measures .595.  My line of thought was that the critical thing is how much of the bullet is in the case, so I figured I would subtract .550 from .595 and shorten the COAL by the same amount.  If I seat them to that depth, the MG COAL would be shorter, but the same amount of bullet would be in both cases.

This gives me a difference of .045" and subtracting this from 1.165 = 1.120.  Surprisingly, when I loaded the first MG JHP, it measured 1.11" which is remarkably close to what I was aiming for.  I loaded up 10 rounds and plan on shooting them tomorrow but then started second guessing myself.

If you have a load and switch bullet types (FMJ to JHP), but keep the same weight and powder charge, can you simply adjust the COAL as I described?  The load I am using is toward the low end so I am not worried about an overcharge, simply a bit concerned about the seating depth since 9mm is a high pressure cartridge.

Any advice?  It seems that most JHPs will have a somewhat different length since they are all have a slightly different shape.

Offline 19114life

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Re: COAL when switching bullet styles
« Reply #1 on: May 27, 2010, 09:29:20 PM »
the bullet will sit deeper in the case in different rounds.  The thing to think about is if it is a compressed load or not.  If you shoot heavier bullets they will be set deeper in the case.  With really heavy bullets you will get a compressed load but you reloading manual is normally good at telling you if it will be a compressed load.  The depth depends on alot.  My .223 shoots better if I seat deeper and have the bullet jump to the rifling, some rifles/ pistols are opposite.  As long as your not over the COAL you will be fine. 

Offline cohutt

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Re: COAL when switching bullet styles
« Reply #2 on: May 28, 2010, 04:42:16 AM »
to answer the question in regards to the pistol rounds you are loaded:

You logic is sound and you should be good to go.   

The pressure is a function of the amount of powder (obviously more = more pressure) and
the volume of space inside the case (less space = more pressure)

So therefore the calculation you did (to work off of where the base of the bullet is seated) is the correct and conservative way to approach it.

(Practically speaking it is likely overkill if you are loading well below published max for the powder you are using.)

The thing to remember is the characteristics of the new MG bullets may cause them to perform differently through the same gun even though you loaded them to the same theoretical pressures as the Wins.   Finding the sweet spot combination for you gun is where the science of reloading stops and the art kicks in....

On powder compression:

Some powders work OK with slightly compressed loads, ie there isn't a pressure spike that appears immediately upon the case being full of powder.   Examples of powders that I have used in some loads that tolerate a little compression are Varget in 223 and Unique in 9mm.

Offline joeinwv

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Re: COAL when switching bullet styles
« Reply #3 on: May 28, 2010, 06:56:25 AM »
I don't have any reloading books in front of me, but I usually try to keep my OAL fairly consistent. Once I find a length that is accurate and will head space properly, I like to leave that variable alone.

So, if you are loading a longer bullet, then it will seat deeper in the case, which reduces the case volume, which increases pressure. If you were already using a starting charge of powder, you should be fine. If your previous load was near max, I would back off by 10-20% and evaluate.

The other factor that I did not note from your post was the relative weight of the 2 bullets. If you are increasing or decreasing the weight, that makes a big difference as well.

As always, start low and work your way up and if you can find a published load that emulates what you want to load, follow that to start.

Offline Stein

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Re: COAL when switching bullet styles
« Reply #4 on: May 28, 2010, 09:07:08 AM »
Thanks for the replies.  The weights of both bullets is 115g.

The thing that is quickly becoming apparent is that reloading data only goes so far.  Most books only list their powders or their bullets.  If you go with a bullet whose manufacturer doesn't publish load data you are basically on your own.  I have reloaded about four powder/bullet combinations and I have yet to find load data that matches exactly what I am doing even after looking through 6-8 books.

Offline cohutt

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Re: COAL when switching bullet styles
« Reply #5 on: May 28, 2010, 11:09:11 AM »
It's a science based art I tell ya.


;)


Offline jawjaboy

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Re: COAL when switching bullet styles
« Reply #6 on: May 29, 2010, 06:42:10 PM »
Agreed.

Offline dannynkc

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Re: COAL when switching bullet styles
« Reply #7 on: June 05, 2010, 04:17:26 PM »
Here

« Last Edit: June 05, 2010, 04:21:37 PM by dannynkc »

Offline Stein

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Re: COAL when switching bullet styles
« Reply #8 on: June 07, 2010, 08:54:11 PM »
I just noticed that Lee lists the minimum Bullseye at 5.0 grain for the load and most other book list a maximum of 4.9 or less.

I used to like Lee quite a bit, but their tables are horrific.  If you use their Auto-Disc settings you will be fine, but if you weigh out to their tables - all I can say is wow.

I loaded 4.7 grain under the Montana Gold 115 g JHP and shot an IDPA match.  There were about 10 comments about what brand flamethrower I was using.  It ended up being hotter than the IDPA guy's Speer Gold Dots in +P.  Lee says I should have loaded 5.0 grain at a minimum.

They should drop the weight and stick with the Auto-Disc settings only or actually get tables that reflect reality.  I like their equipment, but I pretty much ignore anything they say on loads.

Offline outdoorlady79

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Re: COAL when switching bullet styles
« Reply #9 on: June 07, 2010, 10:40:00 PM »
I just noticed that Lee lists the minimum Bullseye at 5.0 grain for the load and most other book list a maximum of 4.9 or less.

I used to like Lee quite a bit, but their tables are horrific.  If you use their Auto-Disc settings you will be fine, but if you weigh out to their tables - all I can say is wow.

I loaded 4.7 grain under the Montana Gold 115 g JHP and shot an IDPA match.  There were about 10 comments about what brand flamethrower I was using.  It ended up being hotter than the IDPA guy's Speer Gold Dots in +P.  Lee says I should have loaded 5.0 grain at a minimum.

They should drop the weight and stick with the Auto-Disc settings only or actually get tables that reflect reality.  I like their equipment, but I pretty much ignore anything they say on loads.

Having pretty much relied on the lee manual up till now you are scaring me a bit Stein.  Think I'll be doing some more research on what charges we are using compared to other publications.