SBS velocity loss.

When it comes to shotguns, we have all heard the "Don't get an SBS, it limits your range!" and then we have people chime in saying "No it doesn't, with equal chokes, you get nearly equal patterns, and with slugs, they are just as accurate", to which the rebuttal "But the velocity will be less and the shot/slug won't hit nearly as hard from your SBS as from a "full size" tactical shotgun barrel like an 18.5 or 20""

Then we are left with a bunch of conjecture and confusion and very little real data and both sides kindof walk away without having actually unpackaged anything from the debate.

I have long held the opinion that with at least low-recoil ammunition, the girth matters more than the length, when it comes to shotguns. Bore VOLUME is what matters, and considering the amount of powder in a shotgun shell vs. length vs bore ID, there has, in my mind, always been plenty of bore volume to make up for lopping off several inches of length because of the large ID of a 12 gauge bore.

Regardless, conjecture is what we want to get away from, so I decided to actually test the theory and see if the bore ID of the 12 gauge made up for the bore shortening in the case of the SBS. Today, I tested low recoil ammunition, since it's so popular. Tomorrow, or soon, I will also test full-power ammunition, and see if the trend changes because of the larger amount of powder involved.

Average velocity of 14" firing LEB127LRS (rated velocity, 1300fps)
1180.6fps, calculated kinetic energy (assuming 438gr), 1356ft-lb

Average velocity of 18.5" firing LEB127LRS (rated velocity,1300fps)
1215.2fps, calculated kinetic energy (assuming 438gr), 1436ft-lb

Average velocity of 14" firing LE13200 (rated velocity, 1145fps)
1088fps, (energy per pellet, assuming 50gr pellet weight) 131ft-lb

Average velocity of 18.5" firing LE13200 (rated velocity, 1145fps)
1125.25fps,(energy per pellet, assuming 50gr pellet weight)141ft-lb

With the slugs, the 14" SBS gave up 34.6fps, and 90ft-lb of kinetic energy. With buckshot, it gave up 37.25fps, and 10ft-lb per pellet (90 total) of kinetic energy. This is the equivalent of 6 yards in distance of flight travel, presuming a G1 BC of 0.07.

Across Federal's low-recoil LE ammunition, this is a very uniform result, and I have a high level of confidence in its accuracy due to this.

____________________________

 

Full power ammunition:

Fiocchi 1560fps 1oz slug
Chronographed at 3m from muzzle

14":1358.6 fps /// 1794.8 ft-lb (assuming 438gr slug)
18.5": 1429 fps /// 1985.7ft-lb (assuming 438gr slug)


70.4fps deficit for the 14" barrel. Translates to 190.9 ft-lb (presuming 438gr slug weight, which this slug weighed in at when dissected, although the wad is attached and I did not account for it.)

Federal LE12700 1325fps Buckshot
Chronographed 3m from the muzzle


14": 1244.6 //// FPE per pellet @ 50gr per pellet: 171.9
18.5": 1261.2 //// FPE per pellet @ 50gr per pellet: 176.6

*Chronographing the buckshot proved problematic, only 3 rounds registered properly from the 14", and all 5 registered from the 18.5" barrel, although one round was low, at 1202, but was included in this average. The average would rise to 1276, without it.

Based on this data, I plan to run the low-recoil LE13200 and 1300fps rated low recoil Truball slugs from my shotguns, both. Shooting either at night makes a HUGE difference in flash signature, the noise and concussion is notably different, and recoil doesn't much matter to me and my split times don't seem to care, but I do feel less beat up after shooting a lot with the LR stuff, but mainly, it's wear and tear on the gun that while I'm sure it will take it (The military tested the M4 to over 4 million rounds during development across their samples, and derived a 25,000 round between major part replacement schedule from such), I see no need in it, given the other factors.

Original Post

Excellent work!  Thanks for posting that.

Interesting that there's more of a difference in the full power stuff.

For the record, I use a Hogue short pull stock on my 870.  The rubber pad is so much more comfortable than anything else I've tried.  I can shoot the shotty all day, and I'm not a big guy either.

Any details on the barrels? (Vang Comp treatment, choke, etc)

______________

"A pistol is what you carry when you do not expect a problem. If you expect a problem you can't avoid, and you are not taking a long gun, you are not very smart." - DM

 

Joined: 04Nov2007         Location: Indiana

Thank you very much for this post WS6; I've often wondered how much one gives up when using a 14" SBS vs a standard 18" barrel and now I know.

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