Subsonic Stability Testing

[J. W.]

Worked up some .300 BLK subsonic loads the other day for a 1:8 8” barreled AR. Bullets were 194 Lehigh ME. Noticed that when I tested them at 100 yds (no suppressor), I got a little bit of “swipe” on the bullet holes. Holes were still very round, but with the carbon/lead smear only on one side of the hole.

These rounds are intended for close use, and at 30 yds there was no noticeable swipe, so I function tested them with the can on and had no issues in the 10-15 rounds I shot.

Anyway, it made me wonder how much instability is necessary to end up with a baffle strike? Anyone found out the hard way? Am I flirting with trouble running these?

 

[Old Man with Gun]

Are the swipes on the bottoms of the holes? At 100 yds, subs have dropped a fair bit. Remember you are aiming higher than the bull and bullet stays parallel to bore. At 100 they fly nose up in relation to the target.
But regardless Round holes at 100 I would not be concerned at all.

 

[J. W.]

Are the swipes on the bottoms of the holes? At 100 yds, subs have dropped a fair bit. Remember you are aiming higher than the bull and bullet stays parallel to bore. At 100 they fly nose up in relation to the target.
But regardless Round holes at 100 I would not be concerned at all.

Makes sense. Bottom right, if I remember correctly. I also shot some 220 gr round nose, no swipes with those, so it made me wonder.

 

[Macht]

Makes sense. Bottom right, if I remember correctly. I also shot some 220 gr round nose, no swipes with those, so it made me wonder.

What he posted is nonsense, the average motion of the bullet tip tracks with the trajectory in almost all circumstances. Fail-to-trace is really only a thing in artillery for quadrant elevations above 70 degrees.

 

[Old Man with Gun]

What he posted is nonsense, the average motion of the bullet tip tracks with the trajectory in almost all circumstances. Fail-to-trace is really only a thing in artillery for quadrant elevations above 70 degrees.

I'm always open to learning, but you need to give me more than calling what I said nonsense.

When I shoot my 300BO at 100 yds the absolute drop is 16.4", so by definition the axis of the bore and bullet is pointed 16.4" high. The only way to get a perfect circle in the target is for it to go perpendicular through.
If the bullet spinning and remains parallel to the bore, neither the bullet or trajectory are perpendicular to the target.
Even if the bullet defies the gyroscopic forces and changes it's axis to point down with the trajectory the path is still not perpendicular to the target.
I don't know artillery or fail to trace, but the target smudges OP discussed matches what I see when I shoot subs.

 

[Old Man with Gun]

Just to cover all bases, a bullet that is not stabilizing completely can have a bit of wobble and still get decent groups. It will tare a rougher hole, but still is safe for suppresor use. As long as groups are of a reasonable size, a little yaw doesn't scare me. People win matches with loads that yaw some.

What is dangerous for a suppresor are bullets that are coming apart or tumbling in flight. If there are indications that jackets are coming apart, or bullets tumbling that scares me.
If the target has oval but consistent holes in decent sized groups I believe it is just the rainbow trajectory of the round.

 

[Macht]

Sure, there's a couple different ways to look at it.

First: If your supposition that the bullet remains parallel to the bore is true, it's trivial to calculate the angle of impact of the projectile given your 16.4" drop number (.261 degrees). This will produce a hole indistinguishable from a bullet hitting exactly perpendicular to the paper. Your own explanation doesn't produce the result you think it does. I've included an image showing two bullet holes, one is yawed .261 degrees.

Second: Bullets simply don't fly like that. I mentioned earlier that the "average" motion of the projectile tip tracks with the trajectory. Technically speaking, that isn't quite true; the average tip motion is centered about the yaw of repose (which is generally tiny, especially at short ranges). The total yaw at any given point is the vector sum of the epicyclic yaw and the yaw of repose. You don't have to take my word for it though, straight from McCoy:

 

[mtrmn]

Sure, there's a couple different ways to look at it.

First: If your supposition that the bullet remains parallel to the bore is true, it's trivial to calculate the angle of impact of the projectile given your 16.4" drop number (.261 degrees). This will produce a hole indistinguishable from a bullet hitting exactly perpendicular to the paper. Your own explanation doesn't produce the result you think it does. I've included an image showing two bullet holes, one is yawed .261 degrees.
View attachment 8300211

Second: Bullets simply don't fly like that. I mentioned earlier that the "average" motion of the projectile tip tracks with the trajectory. Technically speaking, that isn't quite true; the average tip motion is centered about the yaw of repose (which is generally tiny, especially at short ranges). The total yaw at any given point is the vector sum of the epicyclic yaw and the yaw of repose. You don't have to take my word for it though, straight from McCoy:
View attachment 8300225

 

[J. W.]

straight from McCoy:

And how do we know this is the real McCoy?

Seriously though, I’ll let you fellas sort out the academics of it. I don’t feel like doing differential equations, and honestly it’s been so long I’m not sure I still could do the math.

The fact that those 220 gr LRNs didn’t swipe and had an even, concentric carbon ring around the hole seems to suggest those Lehighs were slightly less stable.

I just want to know if I’m asking for a damaged suppressor. Sounds like I’m probably ok, and the rounds I shot through it seem to corroborate that so far, albeit the sample size was tiny.

I don’t care about stability downrange anyway, as long as it’s good coming out of the can. This is ammo for inside 50 yds.

 

[Old Man with Gun]

Good info. I shoot the Maker 200g Rex and it is 1.415 long and a full .30 cal for over an inch. I get oval holes at distance and believe it is the long projectile and the drop. It is consistent and more pronounced at longer range. I'm willing to bend on my theory, but that else can it be?

 

[mtrmn]

And how do we know this is the real McCoy?

Seriously though, I’ll let you fellas sort out the academics of it. I don’t feel like doing differential equations, and honestly it’s been so long I’m not sure I still could do the math.

The fact that those 220 gr LRNs didn’t swipe and had an even, concentric carbon ring around the hole seems to suggest those Lehighs were slightly less stable.

I just want to know if I’m asking for a damaged suppressor. Sounds like I’m probably ok, and the rounds I shot through it seem to corroborate that so far, albeit the sample size was tiny.

I don’t care about stability downrange anyway, as long as it’s good coming out of the can. This is ammo for inside 50 yds.

This^^
Shoot a few up close and if you don't get any sideways profile holes you're probably good. JMO

 

[Old Man with Gun]

And how do we know this is the real McCoy?

Seriously though, I’ll let you fellas sort out the academics of it. I don’t feel like doing differential equations, and honestly it’s been so long I’m not sure I still could do the math.

The fact that those 220 gr LRNs didn’t swipe and had an even, concentric carbon ring around the hole seems to suggest those Lehighs were slightly less stable.

I just want to know if I’m asking for a damaged suppressor. Sounds like I’m probably ok, and the rounds I shot through it seem to corroborate that so far, albeit the sample size was tiny.

I don’t care about stability downrange anyway, as long as it’s good coming out of the can. This is ammo for inside 50 yds.

Sorry for the full nerd deep dive.

 

[Pharmseller]

View attachment 8300240

That’s funny as hell.





P

 

[Macht]

Good info. I shoot the Maker 200g Rex and it is 1.415 long and a full .30 cal for over an inch. I get oval holes at distance and believe it is the long projectile and the drop. It is consistent and more pronounced at longer range. I'm willing to bend on my theory, but that else can it be?View attachment 8300244

That is a super long bearing surface, so any amount of yaw will look more pronounced for sure and all bullets are flying with some amount of yaw.

If it's getting worse with range it could be a dynamic instability, no idea if those particular bullets display that behavior.

 

[Alabama556]

I don’t know if this helps but I have a Remington 700 sbs with a 12 inch barrel. Douglas 1/8 twist in 300 whisper. It shoots leighigh’s fine but I switched to 220 grain outlaw state exot. I get great groups with the outlaw state on deer and on paper. 3/4 inch when I do my part at 100.

I get nice groups and round holes at 100 yards ( that’s the only range I ever shoot paper) with both bullets mentioned above plus my plinking load which uses a 225 hornady eld.

Maybe my longer barrel stabilizes them better.

I did the same thing you did when I 1st got the gun and chopped the barrel. I shot it at 10 yards to see if the holes were round. I use a 12 inch suppressor and have never had any issues.

If I had it to do over I might get a 1/6 or 1/7 twist.