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Short OAL - Plunk Test w/147 .356 BB


IVC
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I ordered some Blue Bullets sized to .356 (listed at 147, BB states they are 150, most measure around 149) and was doing the plunk test in several guns after my usual 1.145 OAL caused some feeding issue in S&W 952-2 yesterday at the range. The test was for several guns I intend to shoot in local steel matches and for fun at the range. For reference, I used factory 115 FMJ ammo that easily passes in all barrels because it's a longer and narrower bullet. 

 

The problem is that BB are not only longer because of weight, but also have a "fat profile" so they tend to stick at longer OAL. As I shorten the OAL and make them pass the test, it's getting pretty short. Combined with longer bullet itself, it leaves much less room in the case. I'm worried that if I load to the shorter OAL I will have to start reducing the amount of powder and then look for the signs of over-pressure as I work it back up, possibly not getting to the PF I need (it's only minor, but this is more about the principle...). 

 

Here are the OAL for various guns, sorted in descending order:

1.145 Glock 34 (passes easily, could pass longer; this was the starting point)

1.120 CZ SP01

1.115 S&W 952-2

1.105 CZ TS

1.100 CZ P01

 

As expected, CZ-s have shorter chambers and like shorter OAL. The P01 is not the one that I would reload for, so it's not really a concern, but it's pretty short at 1.100. The TS is the one that I use for steel from time to time and I would like to have it run reliably. It's barely longer, at 1.105. 

 

So, here is the question: Can I go from 1.145 to 1.105 safely by just loading shorter and/or adjusting the powder charge, or are there some additional concerns when loading heavier bullet this short? 

 

My standard load is 3.26 grains of N320 (I measure 10 loads as thrown by 1050, then repeat several times; I include the second digit if there is consistency over 10-load measurements) loaded at 1.145 . This works well in Springfield Armory 1911 (not included in the list above because it passes long). I'm getting just north of 130 PF out of semi-autos and just south of 130 PF from a couple of S&W 929 revolvers, so it's a good compromise load. 

 

Any thoughts or suggestions? 

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Cz's do have short chambers as you stated. I load my 125's to 1.100 for my shadow and TS. I should go a little shorter as some rounds still dont plunk. A lot of guys will load to 1.085-1.095 for cz. And yes you should decrease your powder as you go shorter. Like you said the less case capacity the higher the pressure will be. I'm no expert but I would drop a couple tenths and chrono it. 

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You can decrease the charge but unless you were on the ragged edge (more than published max) to begin with it won't matter in terms of safety. I load 3.6gr of Titegroup at 1.09 because my CZ limits my length. I could tailor my loads to each pistol but I'm not that anal so that load makes 130ish in my shortest barrels and progressively more as the barrels get longer.

Edited by 4n2t0
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I found my PCC to be the same way with their 125gr RN bullets. They look to be using the same profile as Missouri (who say to load to 1.080"). I asked Blue about it but they refused to comment on *any* loading data. My initial load was 1.125" and it passed the plunk test but when put into chamber by force it became extremely difficult to eject.

 

It's most certainly a bullet profile issue because 124gr NATO WWB is close to 1.155" yet it has no problem getting stuck.

 

 

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4 hours ago, IVC said:

 For reference, I used factory 115 FMJ ammo that easily passes in all barrels because it's a longer and narrower bullet. 

 

 Can I go from 1.145 to 1.105 safely by just loading shorter and/or adjusting the powder charge, or are there some additional concerns when loading heavier bullet this short? 

 

Using a 115 FMJ for reference doesn't accomplish much, but you made up for it by

doing The Plunk Test (that's necessary whenever you change bullets - not just the

weight, but also the brand).

 

No other "additional concerns" that I've ever heard of - safest, but probably unnecessary

for the load you are using, to drop the charge and stick the bullet in shorter.  You are

NOT in unchartered waters with the load and OAL you're discussing - many people are

doing the same thing.

 

BUT, safest to drop the charge and work up slowly with a chrono.    :)   

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If I load them short, it will be for SP-01, not shorter. Probably to 1.120 or 1.115 to account for variability of bullets within a batch. It's for C/O and steel. Based on my tests, it should work in most of the guns I tested above.

 

I will pay attention to the brass and look for any signs of overpressure. The load was initially around 130 PF, so I have some room for maneuvering. I'll make sure I try it out in the least favorite gun first, just in case... :)

 

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I will tell you what I just did. I had a 147 blue load I had been using in my PCC. Found it was too long for some pistols and decided to shorten it up. I didn't get as short as you need to but you can get an idea what your getting into. I do 10 powder drop average to get to x.xx grains too

 

Load comparison shot in sig x5 legion

PCC load 3.28gr universal @ 1.145 PF 128 

Shorter load 3.28gr universal @ 1.135 PF 136

load development 3.00gr universal @ 1.135 PF 126

New load 3.10gr universal @ 1.135 PF 128

 

The New load 3.10gr universal @ 1.135 makes 136 PF in my pcc and get the ejection where it needs to be and locks back on an empty mag 

Edited by Chillywig
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This is why a lot of us throat the barrels in our shorter chambered guns. I run Walthers which have “CZ Short” chambers, so I went so far as to have a carbide reamer made which can cut a hardened barrel.

 

The case wall on a 9mm begins to thicken roughly .300” down from the mouth. A 147 is a much longer bullet than a 124, so you’re already stuffing it back into the mouth a decent amount at 1.125”. Shorten that load up to 1.100” and you’ll see a lot more case gauge failures from the case wall developing a bulge during the seating process.

 

All of my guns (including CMMG Guard PCC and my Walthers with their notorious chambers) can take any bullet profile out to 1.145” now.

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2 hours ago, MemphisMechanic said:

The case wall on a 9mm begins to thicken roughly .300” down from the mouth.

 

This is where case selection by headstamp can make a big difference, because that internal taper varies a lot between different brands. Older FC brass for example has more than double the space before the internal taper compared to CBC and a couple others. 

 

That .300" number is an approximation that actually varies so much it's not really a useful guideline IMO. 

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1 minute ago, Yondering said:

That .300" number is an approximation that actually varies so much it's not really a useful guideline IMO. 


There’s no way I’m sorting brass by headstamp for anything smaller than an Area level match or Nationals.

 

The .300” is a useful approximation because if I  stay well above it, perhaps 2 rounds out of 500 fail to gauge.

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On 10/17/2019 at 9:23 AM, MemphisMechanic said:


There’s no way I’m sorting brass by headstamp for anything smaller than an Area level match or Nationals.

 

The .300” is a useful approximation because if I  stay well above it, perhaps 2 rounds out of 500 fail to gauge.

 

I'm not saying you necessarily need to sort by headstamp, but for some longer bullets it is necessary to either sort or accept deformed bullet bases. With shorter bullets or loading long it doesn't matter much.

 

What I am saying is that .300" number is a theoretical spec that does not match the reality of mixed headstamp brass. If a guy is going to load long bullets or seat deeply, it helps to be aware of how the brass dimensions work with that.

 

I've done a fair amount of measuring this; easy to check my numbers yourself with a pair of calipers. The ONLY brass headstamp I've found that consistently has .300" or more straight section is older FC; everything else has less space. 

Here's what I've seen for some of the more common headstamps:

 

FC: .320"-.340"

 

PMC, *FC*, Blazer: .260"-.280"

 

Win, R-P, some S&B: .200"-.250" (Win and R-P are inconsistent)

 

CBC, Aguila: .130"-.160"

 

Obviously, seating a long 147gr bullet into something like CBC or even a lot of Win brass either causes a bulge or deforms the base of the bullet, depending how the ammo is processed and how soft the bullet is. 

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@Yondering : I haven’t measured how much bullet is actually in the case when I seat a 147 blue to 1.145-1.150” but I wouldn’t be surprised if it’s around .200” to .250”

 

When I think to do so, I’ll mark one then pull it and take an exact measurement. I’m now curious.

 

I just knew that longer loads with heavier bullets resulted in much more consistent(ly gauging) ammo. Thanks for the insight as to why. ;) 

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I first started looking into this when I got into loading heavy subsonic bullets for suppressor use, and was surprised at the differences between headstamps. Other calibers vary a little bit, but the 9mm seems unique in the large differences between one brand and another. I designed my own 178gr, 168gr, and 165gr subsonic 9mm bullets, and because of their length, older FC brass is the only headstamp I can use without causing the brass to bulge and the bullet bases to be sized down. Running those bullets in something like Win brass through a Lee FCD just caused the bullets to be pushed back out of the case and become loose.

 

Of course those findings got me curious so I had to measure everything else too. As a result, I do separate out CBC and Aguila for everything except 115gr or lighter bullets. I can get away with using it for 125gr but the bullet bases get damaged, which leads to lead smoke (coated cast bullets) and I try to avoid that. 

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