View Full Version : Bullet tumbling
I'm out with my friend today to zero his rifle. He has an upper completely built by bravo company and is shooting some federal M855. The barrel is 16" with a 1:7 twist
We are at 36y since that is the zero he wanted. He shoots a 3 shot group to make sure he is on paper and it is all over the place. The cliff notes version of the story is that this ammo is actually tumbling out of the gun. We found 2 places where the bullets struck the card board completely sideways. (Sorry, didn't think to take a picture)
Then he switches ammo to something else (not sure what he was using at this point) and it starts grouping fine.
Any ideas what was going on? Is m855 a no go in a 1:7 barrel?
M855 is fine in a 1:7... something else is going on.
Sent from my SM-G900P using Tapatalk
SuaSponte175
10-25-14, 22:32
M855 is fine in a 1:7... something else is going on.
Sent from my SM-G900P using Tapatalk
Hit the nail on the head. OP - what brand is the XM855, was it Federal Lake City or a different brand?
SuaSponte175
10-25-14, 22:46
Hmmm, 1:7 will have no problem stablizing M855. We shoot it out of 10.5" 1:7 rifles without issues. There is definitely something going on with the ammo, I would say.
Perhaps the flash hider is loose???
The muzzle device is my suspicion too, I can't think of what else it might be at this point.
If that were the case though would changing ammo actually fix that?
It's fairly obvious since switching the ammo fixed the problem, it's an ammunition problem. It seems like there is more missing here....
Thats scary. I want to know what's up, too. *shoots suppressed mostly*
Is this a BFH or standard barrel? Although XM855 isn't exactly primo ammo, I'm having a hard time believing that it's keyholing solely because of the ammo.
If it were my gun, I'd have a riflesmith with pin gauges check the barrel out.... just for peace of mind. 1/7 is way more than needed to stabilize 855 bullets. I've shot them here at my altitude out of a 1/12 and got them to get to 80 yards pretty stabile.
Interesting.
I was shooting XM855 (headstamp LC11) (lot# SMQ11H303S095) yesterday out of a BCM 16" BFH barrel, and while I the ammo didn't keyhole, it was the most inaccurate ammo I've ever fired. Not only large groups, but sometimes shifting in location when firing 3 shot groups. We are talking 50 yards here using a 1-4 (that Vortex has just checked out and given a clean bill of health) shooting off sandbags. The groups should have been the size of a quarter at worst.
Confused by this I fired my last 10 rounds of 90's produced SS109, which were about touching each other.
If I ever even THINK about buying a can of XM855 again, someone please kick me in the nuts... repeatedly...
10mmSpringfield
10-26-14, 09:55
I have two boxes of 120 of XM855 sitting around and I thought about what was said...
It's not accurate but doesn't keyhole.
Oddly, it shoots great out of my Shrubmaster ACR... finally found a use for that thing.
If I ever even THINK about buying a can of XM855 again, someone please kick me in the nuts... repeatedly...
:sarcastic:
10mm, I read somewhere that 855 shoots much better with less twist, as in groups half the size with a more reasonable twist rate (don't remember the exact rate). The faster twist is for tracers but significantly reduced accuracy of the standard 855.
turnburglar
10-26-14, 19:18
Definitely trying different ammo, is a quick and easy variable to check. However at 36 yards a decent shooter should be able to make all holes touch, even with 3-4 moa ammo.
Back in the Force I shot thousands of rounds of m855 and never had an issue with the 25m zero. It was always one clover leaf shaped hole.
I'm not sure what it would take for a barrel to keyhole at 36 yards. If memory serves, filthy 14 was still shooting 1.5" groups at 50 yards with close to 50,000 rounds. That barrel was smoked and probably would key hole at longer ranges, but not 36 yards. If the projectiles were actually tumbling and key holing the cardboard at 36 yards, it must be ammo. Unless someone swapped the barrel to 300 BLK while you were snoozing....your brass might look a little funny though.
Is the flash hider factory installed?
Cincinnatus
10-26-14, 20:31
Were you shooting at the target through intervening brush or tree branches?
If the bullet skids along the rifling, it won't be spun fast enough and will tumble in flight.
If the crown is damaged or fouled, it could cause bullet tumbling.
Doesn't M855 have some kind of penetrator core or something that's not bonded to the jacket?
556BlackRifle
10-26-14, 20:53
I was at the range the other day and an older fellow was trying to zero is newly purchased AR at 50 yards. All the experts were telling him that the bullets were tumbling. I suggested raising his POA to the top of the paper. Guess what? He had a nice little group at the bottom of the page. What everyone thought were tumbling bullets were actually rocks being kicked up by hitting the ground 10 feet in front of his target. No dust because the ground was damp due to recent rain. A few turns with my front sight tool and he was zeroed in perfectly.
I'm not saying this is what's happening with you but it's worth looking into..... Good luck!!
People should actually re-read the OP's post. He states- ammo was changed and then it grouped fine. So unless something is totally lost in translation here, the only reasonable explanation is that there was something wrong with that ammo.
If it was me I'd pull a bullet and mic it.
Next logical step would be to try the ammo in a similar (1/7) gun. If the ammo shoots fine/stabile in a similar barrel, you have to look at the original barrel as the potential problem.
I have a barrel that shoots near MOA with SMKs, but spins 50 gr softpoints apart. Now I know the bullets are ok, and 1/7 twist at .223 velocities from a 14.5 inch barrel should not create enough RPMs to spin a 50 gr apart, but it's happening.
Update: went to the range yesterday. Zeroed the rifle with some 55gr. Incredible group too, 4/5 pretty much through the same hole. So the shooter and rifle are definitely solid
Then shot some more green tip. We didn't get any sideways action this time but it still didn't group for a damn.
So a missing detail is that two days ago it was windy and rainy. Had some gusts at over 10 mph. I wouldn't think that would matter at 36y but maybe?
We don't have another 1:7 but my barrel has a 1:8 so running some through my gun is a good idea
Strange. Couldn't hurt to try the round in the 1/8 I suppose.
I have a new 11.5" BCM upper and Lake City XM855 doesn't group worth a damn through it at 50 yards. No key holing though. I made the switch to Wolf (gasp) 62 gr hollow points and cut my group size roughly in half. I won't be buying any more XM855.
All M855 is horribly inaccurate in my experience.
All M855 is horribly inaccurate in my experience.
855's were never designed to be target ammunition. It was designed to poke holes in light armor. I will be happy if my new 16" ELW barrel shoots 5" groups at 200 with M855.
Renegade04
10-27-14, 18:53
855's were never designed to be target ammunition. It was designed to poke holes in light armor. I will be happy if my new 16" ELW barrel shoots 5" groups at 200 with M855.
Exactly. :smile:
steyrman13
10-27-14, 18:58
Were you shooting from prone or a bench? How high was the target off the ground?
Suwannee Tim
10-27-14, 19:23
The rifling may not be what is marked on the barrel. You can check it with a cleaning rod and a tight fitting patch. Allow the rod to twist as you push it though, measure the distance it takes to make one revolution.
Prone, with bipod and rear bag and the target was 3 feet ish off the ground
steyrman13
10-27-14, 19:45
Prone, with bipod and rear bag and the target was 3 feet ish off the ground
Was there any chance your bore was too close to the ground or there was a hump in the ground/ brush/grass inline with the target that could have cause the bullets to tumble?
It was pretty much all gravel where we were so no grass. I don't recall seeing any bumps in the terrain that were interfering. It was a fairly flat area
855's were never designed to be target ammunition. It was designed to poke holes in light armor. I will be happy if my new 16" ELW barrel shoots 5" groups at 200 with M855.
Yeah, I know. And though that may be true, the lack of accuracy is flat out unacceptable.
I say mic the bullet, and/or try a new lot and see what happens. Sounds like some really crappy bullets.
I'm not sure what it would take for a barrel to keyhole at 36 yards. If memory serves, filthy 14 was still shooting 1.5" groups at 50 yards with close to 50,000 rounds. That barrel was smoked and probably would key hole at longer ranges, but not 36 yards. If the projectiles were actually tumbling and key holing the cardboard at 36 yards, it must be ammo. Unless someone swapped the barrel to 300 BLK while you were snoozing....your brass might look a little funny though.
Is the flash hider factory installed?I bought a 5.45x39 barrel marked Spikes Tactical and it keyholed at 25yd with 7N6 because it was a 5.56 bore rather than a 5.45 bore. I think it was a .219 bore when 5.45 wants a .214-.216 bore... I might be a little off but it's something like that at least. Never did manage to get them to replace it either.
855's were never designed to be target ammunition. It was designed to poke holes in light armor. I will be happy if my new 16" ELW barrel shoots 5" groups at 200 with M855.
I've shot worse groups with a 10X optic on a 24" DMR style Colt with Winchester M855 (Q3269). With PPU M855, I shot sub 2 MOA 10-shot groups at 200 with it.
Powered by vBulletin® Version 4.2.5 Copyright © 2024 vBulletin Solutions, Inc. All rights reserved.