450B case trim length: Contradiction & Confusion

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450B case trim length: Contradiction & Confusion

Postby pitted bore » Tue Sep 04, 2012 11:54 am

Part 1 - Background

Lots of words follow. Please join me in mourning the electrons that have given their all in their production.

Short version of the whole thing: Hornady has published contradictory information about 450B trim length, and has published a very confusing statement relative to trimming.

Case length and trimming to length can be significant factors in reloading the 450B. The cartridge headspaces on the case mouth. The length of the case from base to mouth determines headspace relative to chamber length. If you get case length wrong, you can have trouble (… with a capital T and it rhymes with P and it stands for Poof ! - or Kaboom!)

In a recent thread, a forum member made a statement about trim length as described by Hornady. The statement contained a typo, but even corrected it didn't make much sense otherwise, and I replied to that effect. Since writing that reply, I came across the likely source of the confusion of his statement. I've apologized to the forum member 450 Bushy help needed.

Let's locate the contradiction first, starting with the information in the 8th edition of Hornady's Handbook. The information about the 450B begins with a list of some critical measurements. Here's a scanned image of these.
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H_img1.jpg
From Hornady Handbook #8
H_img1.jpg (38.54 KiB) Viewed 2531 times

The 450B max case length is 1.700", trim is 1.690", with a 0.010" difference. We note this difference of 0.010" is the usual specification for most cartridges, rifle and pistol, in the Handbook.

However, there are quite a few exceptions, mostly straight-walled cartridges that headspace on the mouth of the case. For such cartridges, trim length is 0.005" less than max. These include the 380 Auto, 9mm Luger, 38ACP, 38 Super, 9x18, 40 S&W, 10mm Auto, 41 AE, 44 Auto Mag, 45 Auto, 45 Win Mag, and 50 AE.

This makes obvious sense. Trimming affects how these cartridges headspace in the chamber, and too much trimming produces excessive headspace, resulting in various problems.

So, we can make a general rule from the Handbook information. Cartridges that headspace on rims, belts, or shoulders will have trim lengths 0.010" less than max. Cartridges that headspace on the mouth will have trim lengths 0.005" less than max.

Alas, there are exceptions to our general rule. The Handbook lists four straight-walled cartridges that headspace on the mouth and have 0.010" trim differences, not the expected 0.005". These include the 25 auto, 32 auto, 30 Carbine, and the 450 Bushmaster.

(For the nit-pickers, the 30 Carb ctge doesn't have straight walls, altho the chamber walls are straight. There are still other exceptions to the general rule. I counted six, but these cartridges are odd in other ways.)

A possible simple conclusion: The 450Bushmaster falls with the 25 auto, 30 carbine, and 32 auto in the exceptional group of cartridges that headspace on the case mouth, but have a Hornady-specified trim length 0.010" shorter than the max.

So what's the big deal? See next post.
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Re: 450B case trim length: Contradiction & Confusion

Postby pitted bore » Tue Sep 04, 2012 11:57 am

Part 2 - Hornady's contradiction

Hornady has released reloading information for the 450B at three different times. First was the widely-distributed hand-written set of data sheets from 2008. Second was a pdf page for the 450B on the Hornady web site. Third was the Handbook, 8th edition, 2010.

The critical information about powder charges and bullets is the same for all three. (Yay!). The first data sheets included no trim specifications.

As shown above, the Handbook gives a trim difference of 0.010". However, a page on the Hornady web site shows a trim length of 1.695", for a difference of 0.005" from maximum.

Here's the current link to the page: http://www.hornady.com/assets/files/ftx_load_data/450_bushmaster_ftx.pdf

Here's an image of the specifications listed on that page, just in case the link breaks in the future:
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H_img2.jpg
Hornady web site
H_img2.jpg (29.19 KiB) Viewed 2530 times

Which Hornady-specified trim length are we to use? Which one is "correct"? Only Hornady knows.

To be conservative, we could decide to use 1.695". Unfortunately, some Hornady brass comes new from the factory shorter than this. In practice, Hornady appears to be using the 1.690" length.

How can we resolve the contradiction between the specified differences of 0.005" and 0.010"? I tried. See next post.
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Re: 450B case trim length: Contradiction & Confusion

Postby pitted bore » Tue Sep 04, 2012 12:07 pm

Part 3 - Can SAAMI clarify? - Nope

The Sporting Arms and Ammunition Manufacturers' Institute (SAAMI) sets specifications and tolerances for most commercial cartridges. I attempted to resolve the Hornady contradiction by checking their technical drawings. ( Current link to SAAMI index)

The straight-walled cartridges listed in Part 1 above (380 Auto, 9mm Luger, etc.) that headspace on the mouth have a SAAMI case length tolerance of 0.010".

It looks like Hornady is taking a conservative approach to tolerance, because for these cartridges the handbook lists 0.005" for trim length difference, which is half the SAMMI tolerance value.

Hornady maintains this approach also for the 25 Auto and 32 Auto. For these two, SAAMI shows a case length tolerance of 0.020"; the Handbook shows 0.010" trim length difference, which again is half the SAAMI value.

Following logically from this half-SAAMI value conservative approach, we can conclude that Hornady's 450B trim length specification of 1.695" on the web page is correct. (That would make the Handbook value of 1.690" an error.)

However, this conclusion gets messed up when we check the SAAMI specs for the 30 Carbine. Like the 450B, the 30 Carbine it has a SAAMI tolerance of 0.010". The Handbook shows a trim length 0.010" less than max length. For these two cartridges, the Handbook departed from the conservative approach.

Here's a listing of the above info in tabular form, with an explanation:
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H_img3A.png
Hornady trim & sammi tolerances list
H_img3A.png (11.81 KiB) Viewed 2530 times

#1-7: Follow the general rule:
---If headspace on rim, belt, shoulder, SAAMI tolerance=-0.020", Hornady diff=0.010".
---If headspace on mouth, SAAMI tolerance=-0.010", Hornady diff=-0.005"
---Shows usual Hornady approach of half SAAMI tolerance

#8-9: Exceptions: These two cartridges headspace on mouth, but unusual SAAMI tolerance=-0.020", Hornady diff=-0.010" Usual Hornady approach of half SAAMI tolerance

#10: Exceptions: Headspaces on mouth with usual SAAMI tolerance=-0.010", Hornady diff=-0.010" . An exception to usual Hornady approach.

#11: 450B #1, from Handbook 8. Usual SAAMI tolerance=-0.010" for headspacing on mouth, Hornady diff=-0.010", an exception to usual Hornady approach

#12. 450B #2, from web pdf page. Usual SAAMI tolerance=-0.010" for headspacing on mouth. Hornady diff=-0.005, the usual Hornady approach.

Here's an image diagramming the SAAMI specs, which may help in comprehending what's going on:
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H_img3.jpg
sammi length specs for 450B
H_img3.jpg (22.13 KiB) Viewed 2530 times


More confusion coming up in next post.
Last edited by pitted bore on Tue Sep 04, 2012 12:13 pm, edited 1 time in total.
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Re: 450B case trim length: Contradiction & Confusion

Postby pitted bore » Tue Sep 04, 2012 12:11 pm

Part 4 - Hornady's Blurb of Befuddlement

On the web page pdf mentioned in Part 2 above, Hornady included a statement about loading FTX bullets in the 450B. Here's an image of what is written on the web page:
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H_img4.jpg
statement on FTX bullets from 450B Hornady web page
H_img4.jpg (29.96 KiB) Viewed 2530 times

This statement may cause massive confusion about trimming. Most obvious is the sentence about trimming to shorter than the suggested 0.010" under SAAMI max that Hornady usually recommends. This statement is placed right next to the 450B specs showing a trim length of only 0.005" under max. How are we to make sense of this?

Then there is the suggestion that cases might have to be shorter than 1.690" or 1.695" when loading the FTX bullet. What's going on? The statement says to follow trim lengths as presented for the FTX bullets. But no such lengths are presented. This makes you go Hmmmmmmmm!

Here's what I think happened. The statement about trimming cases for use with FTX bullets is a generic one, but does not apply to all cartridges. The warning should not have been placed on the web page describing loading the FTX bullet in the 450B.

Extra trimming so that cases are shorter than SAAMI is appropriate for some cartridges. For example, here's the Handbook specifications given for the 45 Colt cartridge.

H_img5.jpg
Colt 45 specs from Hornady Handbook 8
H_img5.jpg (46.74 KiB) Viewed 2530 times

The trim length is modified when the 225-grain FTX bullet is loaded, producing a shorter case:
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H_img6.jpg
45 COlt with FTX bullet trim length
H_img6.jpg (48.42 KiB) Viewed 2530 times

I measured some 225-grain 0.452" FTX bullets #45218 that I have on hand. As far as I can determine, the shorter case length is needed to crimping the Colt case in the FTX cannelure while keeping C.O.L. within spec.

Modifications of trim length for FTX bullets are given for other cartridges, included 444 Marlin, 44 Rem Mag, and 45-70 Govt.

In brief, Hornady made a mistake in putting the blurb about shortening cases for the FTX bullets on the 450B web page. Such shortening would compromise head space, and it is not needed to accommodate a cannelure because the 250-grain .452 FTX does not have one.

I may be mistaken about this whole matter. Comments and suggestions are invited.

--Bob
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Re: 450B case trim length: Contradiction & Confusion

Postby longnkrnch » Tue Sep 04, 2012 5:42 pm

So are you suggesting that 1.695 is the correct trim? Hope so, since thats what I'm trimming to.
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Re: 450B case trim length: Contradiction & Confusion

Postby pitted bore » Tue Sep 04, 2012 8:48 pm

longnkrnch wrote:So are you suggesting that 1.695 is the correct trim? Hope so, since thats what I'm trimming to.

longnkrnch-
You can't go wrong with a 1.695" trim length with respect to headspacing of the case in the chamber. Your cases will be less than max, and will fall within the SAAMI tolerance of 0.010" less than max.
--Bob
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Re: 450B case trim length: Contradiction & Confusion

Postby stevewix » Wed Sep 05, 2012 8:58 am

Source for confusion can be found here: http://www.hornady.com/assets/files/ftx_load_data/450_bushmaster_ftx.pdf.

"Loading FTX™ bullets requires some specialized techniques in certain
cases. To achieve a high ballistic coefficient we had to lengthen the
ogive, or nose, of the bullet. Sometimes this requires that the cartridge
case to be trimmed shorter than the suggested .010" under SAAMI Max
length that we recommend for conventional bullets. Follow prescribed
trim lengths exactly as presented in the FTX™ data for optimum results."
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Re: 450B case trim length: Contradiction & Confusion

Postby pitted bore » Wed Sep 05, 2012 10:31 am

stevewix-

Thanks for confirming the source of your confusion. I posted the same link above, as well as an image of the problem paragraph. The Hornady proof readers were asleep at the switch.

Playing with cases shorter than SAAMI tolerance lengths in rimmed and belted cartridges is not a problem. We shoot 22 shorts in 22 lr chambers, 38 specials in 357 chambers, 44 specials in 44 RM chambers, etc. Hornady applied the blurb about trim length to all cartridges with FTX bullets; it was a mistake to do so for the 450B.

Keep the forum informed about how things work out with your rifle and handloads.

--Bob
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Re: 450B case trim length: Contradiction & Confusion

Postby 450b-recluse » Wed Sep 05, 2012 2:50 pm


using this info, I would have to discard about 25-30% of my factory brass for being too short!!!
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Re: 450B case trim length: Contradiction & Confusion

Postby BD1 » Wed Sep 05, 2012 6:49 pm

I'm going to go out on a limb here and suggest the the trim to length of the .450 Bushmaster should be 1.70, the same dimension as the case length spec, and in fact you should never need to trim a Hornady factory .450B case.

I make this bold statement based on two factors: First, all straight wall cases get shorter every time they are re-sized, in my experience this is true across the board with no exceptions. There is no need to trim them once they are within spec. Second, I have never heard of a reported Hornady factory .450 B case longer than 1.70. if anyone has experienced such a case, please report it here. My problem with Hornady factory cases is that they become too short, (under minimum length for correct headspace), long before they wear out or split.

I have never trimmed a Hornady factory case, and have no intentions to ever do so.
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