Pinning or Shimming an 870 barrel with a cantilever mount.

[engineer40]

Well I was very curious if I pinned/shimmed my 870 barrel if it would improve accuracy. It is a cantilever mounted scope. I understand both theories; 1) Probably won't help with accuracy because the scope is on mounted to the barrel 2) Might see some improvement because any movement is considered bad movement (like bedding an action of a rifle).

I found some very detailed instructions on shimming your barrel. I took my time and did a really good job. I was quite impressed with my work and got it shimmed probably 340 degrees of the 360 degree round shank. Very tight! Fit was perfect!

The test results are in!

No improvement in accuracy. At 100 yards, I was shooting 4 inch 5 shot groups before. And I'm shooting 4 inch 5 shot groups now. Bummer.

It's hard to look at 4 inch groups when I spend most of the year shooting rifles that are sub MOA...

 

[hammer111]

I would say you limitations are in barrel and ammo. I have a 20ga 870 and put a Hastings slug barrel on it and it's deadly. I shoot Accutips or federal. I made a mistake and shot a copper solid but it worked.

Yes the Hastings barrel is worth more than the gun and scope. But boy does it shoot.

 

[snox801]

I did the same thing with my 870 shimmer then pinned nothing. Save your headache and quickly find an HR doesn't have to be the thumbhole. My light barrel standard shoots just as well all hole usually touch. Hell I get under a two inch group at 208 yards third drop line on my scope. If interested I know a place not to far from us that still has a few of both sitting around.

 

[jdemocko]

I had my barrel pinned and the barrel hand lapped on my 870 and the groups shrunk.