Slug Groups and Pattern Spread (101)....


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Dave McCracken
October 31, 2008, 05:22 PM
Like groups shot with rifles and handguns, slug groups are best measured center to center. To do this, measure the longest distance from edge to edge, then subtract the nominal diameter of the slug.

In 12 gauge, that's about .729". No one here will cast stones at you if you round off to .75".

20 gauge, .62" will get you in the ball park.

Doing it this way gives apples to apples results.

My best slug shooter does about 3.9" groups edge to edge at 100 yards with the best slug, so center to center is about 3.15 or so. Of course, that's with bore diameter slugs. Sabots differ.

A question I get frequently runs something like.....

" What level of accuracy is acceptable with slugs on deer and similar game?".

The answer, at least in my opinion, is.....

I'd not take a shot I had serious doubts about. If you think you may miss or worse cripple, you probably will.

If it's at a distance and angle where I can keep them inside 6" from field positions or if hunting from a stand where I have a fixed rest, I'm ready to take that shot. IF.....

I look at the deer and think,"This animal is dead if I choose to make it thus"....

Lost, wounded critters bother me way more than unfilled tags.

As for pattern spread for sporting purposes......

Spread is a result of choke, load and distance.Ideally we want as much spread as we can get to ensure hitting the target. However, it's not that simple.

The pellets must pack enough energy to break the clay or inflict enough shock and damage to a live target like a bird to drop it. Of course, on live game, we also want enough moxie to kill quickly, without pain.

Those who know more than me say on smaller game birds we want a retained energy of 1 foot lb and a pellet density of 1 pellet every two square inches of target.

Load and choke are the conjoined twins of Shotgunning. We want a load and choke combination that will give us that energy and density at a given distance.

Shotgun gurus commonly recite stuff about a 30" spread. In the real world, it's few loads and chokes that will give that density and still have a 30" spread of real utility.

More common is a real effective spread of 26-28". There will be some pellets out there further, but these are invariably deformed, unround ones fast leaving the shot cloud.

Shot clouds have a core and a fringe. Cores contain round pellets that will keep speed as much as any sphere will. Fringes contain those that have been deformed. These bleed velocity and veer out of the pattern.

Of course, fringe pellets do sometimes hit targets, but the results are not dependable or repeatable.

Pattern your load and choke at a given distance. Eyeball the USABLE spread and mark it. Measure it and repeat for a couple more times.

If the usable spread is less than 24", try the next choke tube you have with less constriction.

If it's more than 28" but there are thin spots, tighten up the choke or use a better grade of shell.

Sometimes, even using the same brand, 7 1/2s will not pattern well in a given barrel and choke but 8s may. Or vice versa, there's few absolutes in Shotgunland.

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Gord
October 31, 2008, 05:43 PM
It seems that slugs have kind of a tendency to hit left of POA from my own experiences and some of the posts I've seen here (at least from your average 18" IC bead barrel). Can this generally be corrected by finding whatever brand of slug a barrel happens to like, or is it something that just has to be compensated for?

In my limited slug testing, I was shooting three-round cloverleafs at a roughly estimated 50 yards (fifty long strides) but I was having to compensate for them going about 2" low and 4-5" left from POA.

Dave McCracken
October 31, 2008, 06:49 PM
I haven't noticed any drift to port as a rule, though Frankenstein does shoot slugs a bit left at 50 yards with its old barrel.

Gord
November 1, 2008, 03:22 AM
Well, I'd hardly call it "data," but I've seen a couple of threads here regarding slugs shooting left (something like four or five) and my 870 exhibits the same behavior out of both the original 26" Mod barrel and the 18.5" IC I strapped onto it shortly after rescuing it from the pawnshop.

I've only got access to Remington Sluggers locally, so it looks like it's time to start up the mail-order program. Funds, funds, funds...

earlthegoat2
November 1, 2008, 03:29 AM
My slugs keep shooting to the starboard. Guess its cause Im left handed.

Dave McCracken
November 1, 2008, 10:16 AM
OK, this may explain drifts to port, or starboard.

Many shotguns have triggers of more weight than optimum. For slugs, I'd really like less than 4 lbs. Few meet that, and oft the pulls near the weight of the gun.

Few of us have great bench technique. Fewer still can shoot many slugs and remain unrocked. Combine that with a heavy, nasty trigger. The result, the trigger's not pulled straight back but some side pressure happens. For RH people, that moves the POI left.

With shotguns KNOWN TO BE EMPTY, try dryfiring a few rounds and see how the barrel drifts when some side pressure's applied.

Also work in live fire bench work to exert the pressure straight to the rear. Betcha the groups are closer to POA.

Gord
November 1, 2008, 02:23 PM
Dave,

My cloverleafs were shot offhand - it never occured to me to benchrest a shotgun before, but both your suggestions are good ideas. I was thinking that maybe my mount was a little off - it all looks right looking down the barrel at the target, but it wouldn't take much for a few inches at 50 yards - but now that you mention it, the trigger does seem like it'd be the more likely culprit.

I really like reading these 101 threads and seeing immediate improvements once the advice is applied. :D Thank you for taking the time to share your experience with others - it makes a big difference!

Dave McCracken
November 1, 2008, 03:50 PM
Aw shucks.....

Thanks. My day just got better.

New User
November 1, 2008, 05:25 PM
Bad triggers + bad trigger pulling = groups to left

I just tested this hypothesis with my empty Mossberg 500 and a Mini Mag-Lite down the barrel. I pointed the empty gun towards the upper corner of my room and dry fired on some snap caps. What do you know, the light drifted to the left right before the break.

I tried the same thing with an older Spanish double that I have and the results were slightly better, but the trigger on that gun is far better than the trigger on my Mossberg.

I really need to work on my trigger technique.

Thanks for the 101 post.

Dave McCracken
November 1, 2008, 06:00 PM
You're very welcome.

Thanks for actually checking this and providing verification.

RMc
June 16, 2010, 12:42 AM
You might want to try using the same technique used by double action revover shooters - pull the trigger smoothly with the first joint instead of the pad of your trigger finger. You will have better leverage to manage a heavy trigger.

W.E.G.
June 16, 2010, 12:44 AM
Good enough for scattergunning...

http://i227.photobucket.com/albums/dd7/rkba2da/targets/2008-10-31-3000-slug.jpg

http://i227.photobucket.com/albums/dd7/rkba2da/shotguns/DSCN3238.jpg

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