M855A1 projectiles.......cores spin?

[Palladan44]

Just for the sake of fun, I picked up a batch of M855A1. 62gr projectiles.
Curiosity has got the best of me, as usual.
Couple thoughts#1
They are lead free, and have a similar length to SMK 77gr. so I'm curious where to start as far as data. The closest I can find would probably be the Barnes data for their 62gr lead free projectile, which seems to have a long bullet.
I have H335, Benchmark and CFE223.
I'm leaning towards CFE223 and starting around 25.5gr.

Thought #2
On many of the projectiles, about 1 in 5 or so, you can physically spin the penetrator tip that's pressed into the copper bullet body. Using my imagination and what I know of physics, there is no way in blue hell that can be a good thing....the rotational acceleration of the bullet body with that tip sitting still and then slowly spinning up like a top......then spinning back down.....eeeek. or it's nothing.

 

[Odd Job]

If that was me I would test it in ballistic gel:

1. Find a cartridge with a bullet that has a loose steel insert
2. Draw a line from the tip of the insert to the cannellure with a Sharpie
3. Carefully single-load that cartridge into the chamber of the gun
4. Fire in gel and retrieve the bullet

Then see if the sharpie mark is the same as when the cartridge was chambered.
It may well be that there is enough of a squeeze on the bullet as it engages the rifling that the looseness is eliminated. I don't know enough about the mechanics involved and whether the insert extends low enough into the bullet to facilitate this.

 

[Zerodefect]

I'd shoot the spinning ones away first.

M855 isn't all that accurate anyways.

 

[Laphroaig]

M855's are not known as accurate projectiles. Maybe the loose tip is a reason, or maybe there are other factors. I doubt if its worth worrying too much about. Blast away!

 

[Palladan44]

If that was me I would test it in ballistic gel:

It may well be that there is enough of a squeeze on the bullet as it engages the rifling that the looseness is elimeliminated

I'm thinking this is probably the case, I don't know why I didn't think of this...

 

[WestKentucky]

I'm thinking this is probably the case, I don't know why I didn't think of this...

Even if it’s not the case just think of the incredible amount of friction acting between the 2 separate pieces as the main part of the bullet engages against the smaller insert. Even after accelerating out of the barrel, that insert is taking the majority of the wind resistance and pushing it rearward jamming it into the spinning mass of the larger portion. I can’t really imagine the insert spinning separately from the main portion of the bullet. There may be some slippage, but it won’t be much.

 

[NIGHTLORD40K]

The French actually designed a 105mm tank gun projectile with a rotating outer sleeve that could be fired from from a rifled barrel, but the HEAT core would remain stationary since spin degrades the performance of shaped charges.

Never heard of any accuracy issues with it, but then I wasn't in the French armored corps in the '80s, lol.

I just tried a few PMC green-tips and I couldn't get any of them to spin....hmmmm.

 

[Charlie98]

M855 isn't all that accurate anyways.

I would agree. I've found cheapo M193 (55grn) to be much more accurate than M855... of any flavor. I quit buying M855....

I just tried a few PMC green-tips and I couldn't get any of them to spin....hmmmm.

M855 and M855A1 are two completely different bullets. There is no exposed tip on Green Tip M855... the core is internal.

 

[NIGHTLORD40K]

I would agree. I've found cheapo M193 (55grn) to be much more accurate than M855... of any flavor. I quit buying M855....



M855 and M855A1 are two completely different bullets. There is no exposed tip on Green Tip M855... the core is internal.

Huh, I coulda sworn at least some manufacturers made the cap over the penetrator a seperate part, but I guess not. Couldn't find a cross section of any like that, anyway.