Question about 5.56mm M855 and 62grn handloads

[Charlie98]

I've been working on some handloads for a 62grn BTHP bullet for my AR's, using LC brass, and over a charge of H335. Using LC M855 as a baseline, I see velocities at or above 3000fps with both my 16" and 20" AR's, which is about what I expected. As I understand it, M855 is loaded using the non-canister version of H335.

Researching data for 62grn bullets, I'm seeing velocity expectations around 200fps, give or take, below factory M855 velocites. My test load velocity, so far, basically mirror the data's expectations, so I'm getting what I expected from my handloads, even as I near max book data.

Question: Pressure being what it is, and understanding that I'm looking at Service Rifle data for AR's, why can I not expect to load to M855 velocity using similar components... that is, a 62grn bullet over H335 in an LC case, lit by a #41 primer... without blowing past published data max to get there?

 

[entropy]

You probably can. I'd start a bit lower and work up, of course. When you come up with a good load, let me know; I've got 500 62. gr bullets coming my way, and I've never loaded 62 gr. before.

 

[jebova2301]

You'll probably be at/above published max load data to get there. When manuals are published, they put out data that is typically quite conservative(especially Hornady). Remember, when a major operation(federal, Hornady, winchester, etc) have the equipment to test the pressure on their loads, and have the capability to blend and mix lots of powder to make it right. There will always be some variation from lot to lot of powder that you buy. Typically, it is quite minimal, but publishers that put out load data have to factor in a safety factor that some lots of powder will be hotter than others. They also have to tread lightly from a legal standpoint, because if they put out data that is blowing up guns left and right, they can potentially be held liable, and it will also annihilate their reputation and credibility.

If you really want to hit m855 velocity, your best bet is to just do a ladder and keep going up until you get pressure signs.

Another thing to think about is why are you wanting that specific velocity? I would be looking for the most accurate load, not the fastest.

 

[entropy]

FWIW, I've found M855 more accurate than I am out to 600 meters. I can't blame Charlie 98 for wanting to duplicate the load.

 

[Charlie98]

If you really want to hit m855 velocity, your best bet is to just do a ladder and keep going up until you get pressure signs.

Another thing to think about is why are you wanting that specific velocity? I would be looking for the most accurate load, not the fastest.

FWIW, I've found M855 more accurate than I am out to 600 meters. I can't blame Charlie 98 for wanting to duplicate the load.

Well... pressure 'signs' are nebulous, of course, without the validation of a pressure tester. I'm getting the velocity the data suggests... and I might say that this particular set of data is probably closer to published velocity than any other cartridge I've tested, and that includes something as simple as .45ACP, or even 55grn FMJ 5.56mm loads. Strange but true. I'm starting to see flat primers... not mashed flat/sharp edges, as high pressure suggests... but they are getting there, and I'm .5grn under the max load two sets of data suggests (Speer and Hodgdon.) I wish Hornady Service Rifle included a 62grn bullet. Accuracy isn't the only thing I'm looking for... there is certainly a accuracy node lower on the velocity totem pole, but then I'm giving up range, and possibly bullet stability, too; I found that loading .308 for my M1a.

I also know there are significant differences between any commercial 62'ish grn bullet, and the LAP 62grn M855 (et, al) bullet, including a longer bearing surface. I'll probably run my next test lot up to book max and see what it tells me.

I figured I'd post this question here... I know some of you have significant experience loading and shooting for the AR. Thanks, guys!