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Old October 25, 2012, 07:06 PM   #1
robfromga
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Hornady 55gn vmax h335 powder charge ?

Just got 1000 of the 55gn vmax/zmax projectiles. Was planning loading them tonight and realized they are significantly longer than the 55gn fmj that I typically load. .83" vs .71". The tip to the canalure is the same length so loading the same length would put more bullet in the case.

So the questions, follow my load data for my powders ? Namely h335 and blc2.
My seating die will seat to the canalure but will this be an over pressure ?

Last edited by robfromga; October 25, 2012 at 08:02 PM.
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Old October 25, 2012, 07:56 PM   #2
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The Hornady loading manual says OAL of 2.250 for the 55gr vmax
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Old October 25, 2012, 08:01 PM   #3
robfromga
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I'm good on the oal.

I'm not communicating correctly. The 55gn is significantly longer than a 55gn fmj. Seated to the longest length to fit an AR magazine would probably cause a over pressure using 55gn fmj powder charges.

So my question is for powder charges. Using h335 any clue of a max and starting charge ? I feel that using the fmj data would be risky, given the added bullet length.
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Old October 25, 2012, 08:42 PM   #4
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Quote:
Using h335 any clue of a max and starting charge ?
The 0.012" difference in bullet length isn't significant. If you start at the listed starting charge you should be fine. Regarding the max charge, that needs to be developed based on your rifle, brass, primer selection, powder lot, elevation, barometric pressure, chamber dimensions, throat, yadda, yadda, yadda.

Watch for signs of pressure and work up from the starting load based on your components based on your rifle and loads to determine your max loads.
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Old October 25, 2012, 08:47 PM   #5
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I use the 55gr Vmax (same as the zombies with a red tip.) I load with 25.3grs of H335 and am getting .5" groups at 100yrds
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Old October 25, 2012, 08:59 PM   #6
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Oh wow ! OK... I've got some good luck with 24.6gn , even though 25gn is max think its safe to start there ? I'm developing this for my AR's. I'm not interested in super accurate. I'm sure it will be acceptable, just shooting for safe.

Pun intended :-)
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Old October 25, 2012, 09:01 PM   #7
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A couple posts ago, you were worried about a difference of .012 being unsafe and now you want to start at max load?!
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Old October 25, 2012, 09:47 PM   #8
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How is 24.6gn a max load ? My chart shows 25.3gn as a max with 55 fmj. The Vmax is slightly longer, the .12". Not being a math wiz I don't want pressure problems at 24.6gn, which was my planned starting point, until I measured the Vmax projectile.
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Old October 25, 2012, 10:27 PM   #9
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I loaded the 55 gr Vmax and worked up to 24.9 of H335 with coal of 2.250. I shot them today and got 1/2 groups at 100 yards. But I worked up to that load from 23.0 checking for signs of pressure along the way. Just work it up slowly checking for signs of over pressure. I have a friend with a RR Ar b15 and his accuracy load is 24.3 of H335, so you can see all rifles are somewhat different when it comes to the most accurate loading.
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Old October 26, 2012, 07:46 AM   #10
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I shoot a S&W 16" carbine AR-15 and those same bullets. I'm loading at 25.0 with no signs of pressure at the same OAL your using. I agree that 25.3gr is suppose to be the max.
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Old October 26, 2012, 08:05 AM   #11
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Thanks straight shooter... your like the 5th person on multiple forums to say they run 25gn. The extra length worried me and I few people have said 25 was way over the max for that round. But for h335,there's no listing for that loading, just a 60gn vmax
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Old October 26, 2012, 08:12 AM   #12
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Quote:
Originally Posted by robfromsc
How is 24.6gn a max load ?
It's not, apparently your sentence is just poorly worded....

Quote:
I've got some good luck with 24.6gn, even though 25gn is max think its safe to start there ?
The implication being "there" is 25gr, since it's the most recent subject in the sentence and you don't generally jump back past a comma to find the subject being identified by an ambiguous word.

Regardless, conventional wisdom indicates a reduction of at least 5-10% when changing components. Length of the bullet isn't the only variable.
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Last edited by Brian Pfleuger; October 26, 2012 at 10:03 AM.
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Old October 26, 2012, 09:23 AM   #13
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Thank you Brian for the grammatical and reloading lesson. I'll try to do better in my next endeavor.
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Old October 26, 2012, 09:29 AM   #14
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I'm not trying to be a jerk. It's important that you're clear about your meaning when you're talking about something that generates 50,000+ psi and it should be important to you that your readers understand your intentions anyway, to avoid this very conversation.

Regardless, it doesn't change the main point. If you're changing components, conventional wisdom dictates a charge reduction of 5-10% from max and working back up. That means starting at around 22.5gr if 25.0 is the listed max load.
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Old October 26, 2012, 10:25 AM   #15
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Correcting an error and providing some numbers

Rob,

The issue you were originally concerned with is called seating depth. It is how far below the case mouth the bullet extends.

Seating Depth = Case Length + Bullet Length - COL

So, for the first bullet:

Seating Depth = 1.750"¹ + 0.71" - 2.250" = 0.210"

For the second bullet:

Seating Depth = 1.750" + 0.83" - 2.250" = 0.330"

The difference in the two depths is 0.120" and not 0.012" as was miscalculated earlier. That is a significant difference.

Since your bullet jump will be about the same in both instances, the 0.120" difference can, according to QuickLOAD, raise pressure about 11% with H335 in your charge weight range. It would raise pressure about 13% with BL-(C)2 loaded to the same starting pressure (but that's a heavier load and compressed; H335 is a better choice for this bullet weight). Reducing the H335 powder charge about 3% or about 0.7 grains should bring the longer bullet load back to level with the shorter bullet load. Other factors like jacket hardness and ogive radius can also affect actual pressure, so reducing the charge weight 5% and working back up in 1% increments still is the prudent approach based on safety.

All that said, are you sure about your bullet length differences? Most of the 55 gr. FMJ's I have lengths for are 0.735"-0.745" long and the Hornady 55 grain V-max I have at 0.811". I wondered if you reversed the least significant digits in your numbers; if your 0.71" and 0.83" weren't meant to be 0.73" and 0.81", for 0.08" difference in length?

Regardless, I would still be knocking the load down 5%, assuming you haven't changed cases or primers, and work back up in 1% steps. That's just 6 rounds to check for pressure signs before getting back to your original charge, and not a lot of extra shooting.


¹ Note that I used a standard case trim-to length here and not your actual case lengths (which I don't know, anyway). The reason for using a standard length rather than actual length in this calculation is that it is the space under the bullet we care about, so it is really the distance between the inside of the case head and the bullet base we are trying to control. By sticking to a constant case length we get a more realistic representation of that, since you don't change your seating die setting every time a case is a little shorter or longer.
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Last edited by Unclenick; October 27, 2012 at 10:39 AM. Reason: typo fix
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Old October 26, 2012, 12:25 PM   #16
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Thanks Unclenick! That helped alot!
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Old October 27, 2012, 03:07 AM   #17
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Robfromsc

I don't want to try and confuse you, but I received load data from a rep at Sierra for .223 and 5.56 NATO. It was interesting to see that the same bullet, weight and all had two completely different starting points. For example the .223 started at 23 and maxed at 25, then for the 5.56 the starting load was at or just below the max of the .223. Those are not the exact numbers but close, I did that from memory. I just don't feel like turning on my other computer where all my load data is.

Oh yeah, the reason for that is because you need higher pressure to cycle the AR's. too low of a pressure will slowly damage your rifle, so I hear. <----don't take my word on that
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Old October 27, 2012, 07:06 AM   #18
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I loaded 10 at 24.4gns. They grouped fine, 4 within a 1" at 100yds. No signs of over pressure. I'll leave it at 24.4. Here in Ga there's no real world shot that open, 100 yds. There will be a branch or tree or something between you and the intended target. Even if more power would tighten it up, its pretty rare that its needed here.
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Old October 27, 2012, 11:47 AM   #19
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Eastern woods are the same. 75 yards seems to be about maximum, with 50 or less being typical.


Mohr308,

The AR will function fine with lower pressure loads. The only reason the 5.56 loads use more powder is the NATO peak pressure spec is higher than the SAAMI spec. The CIP has the NATO spec as 430 MPa, which converts to 62,366 psi. SAAMI has it as 55,000 psi. More interesting is that the CIP also has .223 Remington at 62,366 psi. How did two standards organizations end up with such different numbers? And why is SAAMI only giving 55,000 psi as the Maximum Average Pressure, when its older copper crusher MAP is 52,000 CUP? All the other cartridges SAAMI had with 52,000 CUP MAP's under the old system have 60,000-65,000 psi MAPs under the new system today. You'd expect the CIP number to be where they would actually land.

I really need to ask SAAMI this question, but I suspect it's likely because of a military practice of measuring pressures on the m.11 copper crusher in CUP, but the editors of specs and TM's reporting those CUP's as psi, despite them having actually been measured on copper crushers. Board member FALPhil has a good article on this misunderstandings created surrounding .308/7.62 pressure ratings, here.

From MIL-C-63989C(AR) for M855 ammunition {with italicized comments by me}:
Quote:
3.7 Chamber pressure. The average chamber pressure of the sample cartridges, conditioned at 70° ±2°F shall not exceed 55,000 psi {actually CUP}. Neither the chamber pressure of an individual sample test cartridge nor the average chamber pressure plus three standard deviations of chamber pressure shall exceed 61,000 psi {actually CUP}.
I think SAAMI probably just looked at that "55,000 psi" and didn't realize it was actually CUP and decided that the military knew its guns best and they didn't want to mess with their number. But the bottom line is the weapons actually work with a pretty wide range of pressures from SAAMI spec to military spec.


Edit:
P.S., Sierra will have provided you the same data that's in their printed manuals. As you say, they have different COL's and the same load data, but that doesn't tell you how the seating depths are varying. It also doesn't mean the pressures and velocities are truly identical. If they stay within 50 fps of the same number in the same test gun across the span of bullets given, they can round it to the stated velocity number. Since their data is in 100 fps steps, that actually gives them a span of 100 fps to play with.
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Last edited by Unclenick; October 27, 2012 at 01:36 PM.
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