Strange results from a seemingly perfect barrel

[flightsimmer]

I was reading the other day about a fella that was having problems with a rifle he had bought and it was shooting all over the place and it reminded me that I had one like it, not the same model or brand but it shoots all over the place.
Now I’m not new to firearms by any means and I thought I could figure out what the problem was but so far no luck.
I have a stainless 16” barrel from a 10mm carbine that slugs a perfect .401 and is uniform from chamber to muzzle (by feel resistance) and looks to have a clean and true cut crown. The rifling is 1 turn in 16” and is 6 land and grove of about .004, much the same as my super accurate 5” Delta Elite, Bar-Sto 10mm barrel. There is no stock on this barrel and I consider it to be a free floating blow back operated barrel.
I have not shot any jacketed bullets in it, just mild (by 10mm standards) 175gn. TC cast lead like I use in my Delta Elite and they work great in it. At first I thought it might be the sights but I have tried several different ones with the same results so I’m still left searching for answers. Got any ideas?

10mm, when you care enough to send the very best.

 

[Certaindeaf]

What's the measured diameter of your cast slugs?

 

[25cschaefer]

Maybe the rail you are mounting the sights to?

 

[Certaindeaf]

A carbine will send them faster of course. If it's over about 1400fps and they are plain base, there's your (a) likely problem.

 

[flightsimmer]

Quote: What's the measured diameter of your cast slugs?

Sized to.401

Quote: Maybe the rail you are mounting the sights to?

I cannot find any looseness in the sight or base. I first thought it might be a defective red dot sight but I've tried several.

Quote: A carbine will send them faster of course. If it's over about 1400fps and they are plain base, there's your (a) likely problem.

Yes, that may be a possibility, I've got a new Chrony but have not got to use it yet. I may try it in my garage since I can't get to a range yet.
Jacketed bullets might do much better in that case but I'll need to get to somewhere where I can try it outdoors.

Their building a new indoor range close to me but it will be a while yet on account of building permits.

 

[rcmodel]

10mm carbine that slugs a perfect .401

It should slug .400".

Sized to.401

They need to be sized .402" - .403" for a .401" bore.

rc

 

[flightsimmer]

OK, today I chrongraphed my normal hand load at 1279 fps from the 16" barrel, hardly to fast for a lead bullet. I also chronographed the same load in my Delta Elite at 1055 fps.
Still looking for a cause.

 

[Ludasmith]

You are still using the same cast bullet? I'd try a box of factory ammo, maybe a couple different brands/weights/whatever and see if it's possible it just doesn't like that load.

 

[ball3006]

It is your ammo. Try different brands and bullet weights...chris3

 

[flightsimmer]

Quote: It is your ammo. Try different brands and bullet weights...chris3

I don't disagree but it's seems strange that I get excellent results from my Delta Elite but not the carbine. I re-slugged the carbine and checked the specs and the only difference I can see or measure is that one has a right hand twist and the other has a left hand twist.