Why can pistol loading data be so inaccurate?

[JRWhit]

It kinda irks me that most all of the pistol data is found with a 10" barrel.
You would think that the powder manufacturers would be better equipped to find the best performance while testing it in something similar to what it will actually be used in.

It may likely be that they test in what would likely generate the highest pressure in order to avoid bad things from happening to the end user, but even if that be the case, you would think it would better to list velocities,"even calculated or estimated",that better represent what it will be most likely used in.
Somewhere, somebody with 10" Thompson contender has little to complain about.

 

[LiveLife]

Most published load data were developed using single shot universal test barrel fixtures instead of actual pistols. So us reloaders, especially with autoloaders, must conduct our own load dvelopment to ensure our rounds reliably feed/chamber from the magazine, cycle the slide, extract/eject spent cases and produce accuracy which the single shot universal test barrel fixtures cannot do.

So why do some published load data use such short OAL/COL? That maybe because the leade/freebore length of the test barrel was shorter for the bullet type used and would not allow longer OAL to fully chamber in the test barrel and not because it was the ideal length that would reliably feed/chamber from the magazine.

I normally take manual inconsistencies with a grain of salt.

124gr bullet data. Winchester/Hodgdon website shows 3.9-4.4. Speer shows 4.0-4.5, ok pretty much the same. I recently looked at Hornady for the first time and it shows 4.7-5.3, now that is pretty different. I have read of many settling in on a 4.8gr for their favorite load. Looks like I have more experimenting to do.

Different test barrel length, groove diameter, leade/freebore length, bullet type, OAL/COL, etc. all contribute to how chamber pressures are generated. Variation in one or more of these can require different amount of powder charges to produce the same average maximum chamber pressures.

Even with all variables being the same, small difference in barrel groove diameter can require considerably more powder charge to produce the same chamber pressures. 9mm 124 gr bullets work well around 4.3-4.5 gr of W231/HP-38 in my barrels with .355"-.356" groove diameter but with oversized barrels at .357"-.358", more powder would be needed to produce same muzzle velocities.

 

[Toprudder]

One of the worst inconsistencies I have seen lately were two data points from the same source.

I picked up a pound of Shooters World "Auto Pistol" powder. It is relabeled Lovex D-036 powder. The label on the container had load data for a few calibers, including 45acp. The label data showed a Nosler 230gn FMJ with a max of 9.3gn. If you go to their website you can find the Lovex "Explosia" reloading manual, where they list an S&B 230gn FMJ with a max of 7.3gn. I was trying Xtreme 230 RN, so I went with the much lower charges in the Lovex manual. I got virtually identical velocities compared to the Lovex data. If I had gone by the label data and started 10% lower, I believe I would have been way over pressure.

This is one reason why I like having multiple independent sources for data.

 

[300Whspr]

LOL, I'm one of those guys with a Contender saying "what are they complaining about??!!??" LOL

Universal receivers with test barrels, usually have SAAMI minimum chambers, or tighter, so that they will show pressure signs fastest. They also will deliver the highest velocities for a given powder charge.

As far as Accurate Arms data, in my experience it has been fairly accurate for the chamberings that I reload for, particularly their 22PPC data... dead nuts on. I think the biggest disparity between actual results and published data has been with Hodgdon's data... I can never seem to match their numbers, even with a 2 inch longer rifle barrel...

 

[Hondo 60]

I could write pages about the discrepancies.
I have yet to find a factory ammo that shoots as fast as they say on the box.

But they're using a pressure barrel with no gaps.

1 mfg claims it's 22lr shoots at 1250fps - I get about 900 with a revolver & maybe 950 with a semi-auto.

The same goes for my reloads.
I don't even bother with checking their claims.

 

[Toprudder]

Yeah, the 22LR is all measured from a rifle if I am not mistaken.

I was in the LGS one day, and a guy wanted to buy some 22LR ammo for his suppressed pistol. He was asking for subsonic 22, and I told him the standard velocity would be subsonic from his gun. I don't think he believed me.

 

[Slamfire]

Accurate Arms data has been fantastical many times. I don't know why their results are so different from my results, but I believe my results.

 

[H&R Glock]

Chronograph Lie detector?

I just got my first Chronograph for Christmas. It makes a good lie detector when used with reloading manuals.
True I used plated bullets with my 6" barreled 38/357 pistols, and used lead bullet data, but when the smoke cleared, I found loading manuals were just a low guess at velocity.
Squib loads can result in a bad day at the range.

 

[ny32182]

Using lead data with plated bullets, your velocity is going to be low for sure.