I've been doing some load development a new AR-15 in 350 Legend. This weekend I tried Lil' Gun powder, Lehigh Defense .355" 118 grain Xtreme Defense (solid copper) bullets, Starline Brass and CCI Small Rifle Magnum primers. I fired 3 five round strings and the average velocity decreased as the powder increased.

27.5 gr - 2509 fps
28.0 gr - 2490 fps
28.5 gr - 2431 fps

In my reloading experience I have seen velocity remain relatively unchanged with small powder increases but have never seen it drop like this. Has anyone else had this experience? What do you think caused it?

Powder not optimal for lighter projectile in your barrel length ?

Do you have a lot of unburnt powder in the barrel or spent case?

Yes. Usually it means you have reach max pressure and adding more powder won't get you any more velocity. I'm not familiar with that caliber, bullet, and powder combination, so I'm not sure on the load data. Or the barrel may be getting seasoned in or fouled in.

What Chronograph?

I didn't notice any unburned powder.



Labradar

Chad's answer is the one I have heard before.

What length barrel? I have seen it a few times where more powder velocity starts dropping.

Barrel length is 16".

I think PP is correct and the bullet is too light for the powder type/burn rate and there's not enough pressure created. The brass and primers show no signs of over pressure and no unburned power in the case. I thought that since the bullet is solid copper there would be enough friction to generate sufficient pressure. The bullet has grooves that reduce bearing surface/friction and I think the pressure is just too low.

I may need to try a faster burn rate powder or just live with 2500 fps.

Thoughts?

Is there any chance you got them mixed up and shot them out of order? I know it seems obvious, but it would make the most sense.

That's the first thing I thought of, I am very meticulous and have a system I follow when reloading to prevent that kind of thing.

Same seating depth from the lands?

Yes, the rifle is an AR-15 so I'm not measuring from the lands but COAL is the same for all the rounds. I'm running some more loads over the Labradar this weekend will see if this reoccurs.

Sharing this for what it's worth. No idea as to what length a bedding issue would be applicable to your specific rifle but your problem came to mind as I was reading this source article.

"One re-occurring mistake I have seen is hand loaders misreading bedding problems as signs of maximum pressures. Many hand loaders have been caught out with this and I dare say many readers have probably had the same problem. In this case, the shooter buys a new rifle, works up loads one grain at a time and discovers that at X grains, groups open right up. Later on, the load is put over a chronograph and it is discovered that the load is traveling 300fps slower than what should be the optimum pressure/velocity. The culprit is the bedding - as powder grains are increased, so does recoil torque to the bedding platform. If the bedding platform is unsound, groups will open up. Shooters using magnum powered cartridges are prone to this trap and often the load is 300 to 400fps below the optimum balance of velocity versus accuracy once the rifle is properly bedded."

Source

That does not mention the OP’s issue.

I sincerely hope you find relief for your dementia or your addiction, soon, whichever it is. It’s truly sad to see.

From the OP...

"In my reloading experience I have seen velocity remain relatively unchanged with small powder increases but have never seen it drop like this. Has anyone else had this experience? What do you think caused it?

Does this explain the drop in velocity described in the OP? I don't know enough to say yes. My post was only to share information related to what can result in slower velocities as powder is increased.

Nowhere was a DECREASE in velocity mentioned in the article. Up your meds, Dan.

Last chance...

"Later on, the load is put over a chronograph and it is discovered that the load is traveling 300fps slower than what should be the optimum pressure/velocity.

Slower than what should be equals an increase in powder charge and decrease in velocity? Again, that was not stated. In the article, they worked up a load and found it lacking. They said nothing about an increase in powder charge and a decrease in velocity.

You’re retarded.

"In this case, the shooter buys a new rifle, works up loads one grain at a time and discovers that at X grains, groups open right up. Later on, the load is put over a chronograph and it is discovered that the load is traveling 300fps slower than what should be the optimum pressure/velocity."

Again, I honestly don't know if this tip applies to the problem described in the OP. I'm sharing it only because it relates to a slowing in velocity with increasing levels of powder noted in the question asked in the OP.

Never mind you are just trolling