870 20 inch barrel vs 28 inch

[303carbine]

I patterned my 870 12 gauge today and got some unexpected results.
First shot was with a 28 inch barrel with a Rem Full choke,it patterned Federal 3 inch mag 00 buck into an 18 inch pattern at 50 yds.
I tried the same load and choke screwed into a 20 inch barrel and it patterned the 00 buck into an 11 inches at 50 yds.
I was surprised when the short tube produced a tighter pattern than the long one.
Anyone have an explanation???

 

[MauserMike]

I think you are using too much choke. Try modified.

Here is one theory - you are getting a slightly higher muzzle velocity with the long barrel and the tight choke is deforming the shot slightly and opening the pattern.

 

[303carbine]

I think you are using too much choke. Try modified.

Here is one theory - you are getting a slightly higher muzzle velocity with the long barrel and the tight choke is deforming the shot slightly and opening the pattern.

For deer,I think it will work perfectly. I tried the Rem Mod choke and it spread out over 3 feet at the same distance,the IC choke pattern was even bigger. I was using everything the same except for the barrel length.

 

[Covey Ridge]

I think that is a great pattern. Why the difference? Who knows? I would speculare on a few things. The actual bore dimensions prior to the ckoke threads could be different? The longer tube may deform more or cause more of a string? The longer tube may cause the plastic wad to slow more and separate quicker leaving the shot to spread quicker. When shot through the shorter barrel it may still contain the shot and hold the pattern tighter? Again, who knows? But all of those 00 in 11 inches at 50 yards? Lethal

 

[MauserMike]

The pattern board doesn't lie, does it? Go with what works best and good luck bagging a deer.

 

[303carbine]

There was 6 or 7 pellets out of 12 in the 11 inch pattern,the rest were hard to trace because of all the 303 holes in the target..

 

[warrenb]

The reason:

choke the same, load the same, barrel different;

I'd go with the barrel.

Seems a good pattern with the short barrel though.

 

[870P]

Anyone have an explanation???

That's shotgun barrels for you, another batch of 20" and 28" barrels would probably produce different results each time. A friend and I own 18.5" IC choked 870s with consecutive serial numbers and they don't share much in common as far as pattern size with whatever given load.