Slugs dropping low after several rounds?

[harveyce]

Took my M4 to the range today to sight in my optic for slugs.   Dialed it in at 25 yards and consistently shot about three inch groups of three.  Moved to the 50 yard range and the first three shots hit about the same, maybe around 4 to 5 inch groups, but then the next 4 or 5, depending on how many shells were in the gun, were much lower, maybe a foot or so, and kept creeping downward.   Thought maybe it was me but this happened every time I stopped to reload and check shots.  Shooting from a bench and practicing what I consider good technique.  Using the stock choke as well, modified if I remember correctly.  Any ideas what I'm seeing here?

[Evolution]

4 hours ago, harveyce said:

Took my M4 to the range today to sight in my optic for slugs.   Dialed it in at 25 yards and consistently shot about three inch groups of three.  Moved to the 50 yard range and the first three shots hit about the same, maybe around 4 to 5 inch groups, but then the next 4 or 5, depending on how many shells were in the gun, were much lower, maybe a foot or so, and kept creeping downward.   Thought maybe it was me but this happened every time I stopped to reload and check shots.  Shooting from a bench and practicing what I consider good technique.  Using the stock choke as well, modified if I remember correctly.  Any ideas what I'm seeing here?

With the M4 having a screw-in choke, you probably should not be shooting slugs using the modified choke that comes with the M4. The M1014 has a thicker barrel mouth and even tho it is a modified choke diameter, that thickness allows for shooting slugs safely.

Benelli says it is not safe to shoot rifled slugs thru any choke other than a cylinder or improved cylinder choke. The exception being the M1014, not having a screw-in choke.

https://www.benelliusa.com/support/faq

Not saying that is absolutely what caused the anomaly you are experiencing but, try using a Cyl or IC choke.

Edited December 6, 2023 by Evolution

[RxArms]

Was your barrel fully seated and tight?  Might be a cause if it loosened itself.

as the comment above I have shot thousands of slugs through the M4 stock choke, even though they say not to… (apparently)

[harveyce]

Thanks for the info.  I'll swap out the choke for a cylinder choke and see what happens on my next range day.  Yeah, the barrel was tight.  I checked the cap to make sure it was on correctly several times.  It almost seems like an optic issue but there is no way it went back to the zero I started with... I supposed I'll have to burn up some more slugs trying to figure it out.