Difference in function 18.5" vs. 20" barrel (12ga)?

[Plinkeriffic]

Anyone know the functional difference between a 18.5" vs. 20" barrel on a 12 guage? For a little length in the barrel a pump shotgun can increase capacity by 1/3, but any functional difference (defense/sport)?

Thanks!

-Plink

 

[chuckusaret]

I prefer the 20" because of the added capacity with no change in function

 

[dasanii19]

In my eyes, with a 20" barrel your adding weight and losing a little maneuverability in a HD situation.

 

[deputy tom]

Not much performance or function difference either way.I like them both.The plus to a 20" bbl. is if using a factory magazine extention the bbl. and mag. tube will be even at the muzzle in most cases.YMMV.tom.

 

[Fred Fuller]

increase capacity by 1/3

???

It's the magazine tube that governs capacity, not the barrel. Given non-fixed length magazine tubes- that is, a design that will take an extension- it's possible to have a magazine longer than the barrel. Perhaps not wise, and somewhat odd looking, but I have seen 3-gun shooters with scatterguns set up that way.

For designs with fixed length magazines like the Mossberg 500, various High Standard pumps, etc., this might be a consideration with some models. But it can't be generalized quite so broadly, I'm afraid. With guns that have pull-through cleanout magazine tube designs, magazine capacity has nothing to do with barrel length. No shotgun magazine is ever big enough anyway, IMHO it's more important to learn to load the gun than it is to try to get the longest magazine possible.

That said, there's little difference IMHO in practical funtion between an 18", 18.5" or 20" barrel. Personally I like the 18 or 18.5" but I can sure live with a 20" if that's all I can get. Last two spare 870 barrels I got decent deals on were both 20", one CYL bore bead sight and one ImpCyl rifle sight, and I happily paid for both of them.

lpl

 

[Youngster]

Very little difference in handling, however the 20" length seems to have a rather substancial unexplained shortfall in velocity in all of the bbl length to velocity chronograph results I've seen.

 

[Plinkeriffic]

The 20" barrell less velocity than 18.5"?

This would be an important consideration, I would not have thought 1 1/2" would make much difference or if anything get better performance than a shorter barrel. is there more to it? Thanks!

-Plink

 

[Eric-WA]

Someone correct me if I'm wrong, but I believe that in a standard 2 3/4" 9 pellet 00-buck round the powder will burn completely in the first 13 inches or so.

If this is the case, and I believe that it is, wouldn't the velocity be the same for anything beyond that initial 13". I'd always been led to believe that barrel length is purely determined by the activity you plan to use the gun for. Most deer barrels are at least 20" and go up to 24" which I'd imagine is a by-product of the need for a longer sight radius. The typical defense barrel being 18"-20" is purely a design of maneuvarabillity.

So . . . . . .Having said all that it boils down to if you don't mind the additional weight and desire the added capacity then go 20"

 

[Youngster]

Someone correct me if I'm wrong, but I believe that in a standard 2 3/4" 9 pellet 00-buck round the powder will burn completely in the first 13 inches or so.

If this is the case, and I believe that it is, wouldn't the velocity be the same for anything beyond that initial 13". I'd always been led to believe that barrel length is purely determined by the activity you plan to use the gun for. Most deer barrels are at least 20" and go up to 24" which I'd imagine is a by-product of the need for a longer sight radius. The typical defense barrel being 18"-20" is purely a design of maneuvarabillity.

So . . . . . .Having said all that it boils down to if you don't mind the additional weight and desire the added capacity then go 20"

The powder may burn up that quickly but it still needs additional bbl length to allow it to expand and impart its energy to the payload. The chart below seems fairly typical of what to expect, although the velocity drop at 20" isn't always so severe.

 

[Plinkeriffic]

Wow, that dropoff for 20" just seems anomolous and bizarre for hust that one barrel length (and not a dip in fps around the ones of similar size). I'm pretty sure it's not going to dissuade me; I'm getting the slightly longer (by 1 1/2" barrel) but 33.3% greater capacity of the same model shotgun. 9 is such a nice number . . .

 

[rcmodel]

Seems more likely a crony anomaly, or he didn't test enough shots.
Notice he didn't say if he shot 1, 5, 10, or 100 shots at each length to gather the data.

It could be normal standard deviation if he didn't crono enough loads at each length to get a statistically meaningful sample.

There is really no internal ballistics reason that could explain it.

rc

 

[oneounceload]

At HD distances, it isn't going to matter one bit.....shoot the barrel length you like....period - the rest is mall ninja BS

 

[Youngster]

Wow, that dropoff for 20" just seems anomolous and bizarre for hust that one barrel length (and not a dip in fps around the ones of similar size). I'm pretty sure it's not going to dissuade me; I'm getting the slightly longer (by 1 1/2" barrel) but 33.3% greater capacity of the same model shotgun. 9 is such a nice number . . .

The 20" dip seems consistant with every multi barrel length shotgun shoot I've seen, although not always so drastic, the chart above just happened to be the only one I had available to post here. Who knows why that is but the world of ballistics is filled with weird and counterintuitive happenings and it seems especially true of scatterguns.

Personally if I'm going to go longer than 18.5", I'll jump right up to 23-24" even on a defence gun, it's not so much about the ballistics or patterning but that the noise and muzzle blast seem to drop off noticably when it gets to that length.

 

[jakemccoy]

I ended up buying both barrel sizes (18.25" and 20"). I didn't feel like researching the issue. If you handled my 870s with these two different barrels, I doubt you would appreciate much of a difference.

I barely can tell a difference between the two lengths. The 18.25" barrel is on my primary HD shotgun. I took off the mag extension and any other extra stuff. This HD shotgun setup is most comfortable for me: