Raising Point Of Impact


Dear Technoid,

I have been working on fitting myself up to my 870 TC Trap (non-Monte Carlo), with some success. I now have a comfortable stock fit, but the point of impact is still too low. When I began the stock required me to force my head down. Rather uncomfortable, and the point of impact was low, like 45/55.

I built the comb up with pieces of adhesive backed padding, the green stuff designed to stick under furniture to protect flooring. This works very well. Builds height quickly, is fairly stable, and is comfortable to the cheek. Drop at comb measured from the top of the rib is now about 1 1/8″.

I added a Morgan adjustable butt plate/recoil pad which allowed me an effective drop at heel of about 2 5/8″.

I added a 1/32″ brass shim to the left side to give a little cast off.

All this has made the gun comfortable to mount, but the point of impact is still barely over 50/50. I really would like at least 60/40 to 70/30.

I don’t want to raise the comb any more or it will get ridiculous. I already see a little rib between the mid bead and the end.

I am thinking about the following to increase the POI: Additional matching right/left brass shims in the receiver to decrease the angle between the top of the rib and the top surface of the stock. This should effectively raise the point of impact without adding more comb. However, I believe even with this approach the site picture will still show even more rib between the beads.

It’s fun to play, but this is getting weird. Perhaps I am not looking at this objectively. Any ideas?

Thanks,

John

Dear John,

It sounds as though you want to raise the point of impact without further increasing the amount of rib you want to see. This is a fairly common problem with ATA-style trap shooters who shoot constantly rising targets and don’t want to train themselves to cover the bird when they shoot. If you can get used to seeing more rib, then just keep raising your stock. Shimming between the stock and receiver will simply raise the stock and show you more rib. It’s just raising the stock by a different means.

If you can’t bear to see more rib, then I think that you have two basic choices, other than selling the gun.

1) Get a new rib installed that is higher at the rear than at the front. This will allow you a “normal” rib picture, yet can set your impact as high as you wish. Once the rib is set up right, then the stock may have to be further raised to get you eye where you want it.

2) A second approach would be to quit messing with the rib and the stock and send the gun to a good chokesmith to have an eccentric screw choke installed or ground (depending on whether you want screw ins or fixed). This is probably the cheapest approach. Yes, it will make your shot deflect at the choke (never good), but eccentric choking does work pretty well for changing direction of the shotcharge to some extent. Briley Manufacturing, <www.briley.com> can install changeable eccentric choke tubes (actually oval cross section chokes) to alter point of impact, or they can install standard choke tubes in the barrel at a slight angle. I was surprised that there is machining that can do this, but they can. If you want fixed chokes ground to raise point of impact that can also be done by any really good barrelsmith. Ken Eyster, 6441 Bishop Road, Centerburg, OH 43001, Tel: 740-625-6131 is a great choke guy, but there are many others too.

A third possible alternative is to bend the barrel. This will certainly raise the point of impact, but you will see more rib and you say you don’t want that. Bent barrels also tend to move when they get hot, so it’s not really the best alternative.

Just as an aside, the problem of point of impact very often arises in conjunction with barrel conversion problems. Very few double barrel shotguns shoot both barrels to exactly the same place. Most are “good enough”, but some aren’t. Briley’s ability to install screw chokes on an angle in a previously fixed choke gun to correct this is a huge boon. If the gun comes with factory screw chokes, then you are probably stuck with using eccentric choke tubes. They also work, but they have to be indexed perfectly and are more expensive. Also, the particular eccentric choke tube must be mated to the particular barrel. Recutting fixed chokes on a bias to alter point of impact is an old technique. I’ve used it on several guns and, when done by someone who knows that they are doing and is willing to grind/test/grind/test, it can work well though you usually do give up some constriction.

Best regards,

Bruce Buck
The Technoid writing for Shotgun Report, LLC
(Often in error. Never in doubt.)
http://www.ShotgunReport.com

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