Sighting Question for 870/Mossberg DRS

cvbrewer · October 30, 2010, 02:18 PM

I test fired some slugs at the range today with my 870 express, which has a new Mossberg slug barrel with deer rifle sights. A few slugs grouped well, especially copper solids, but at 25 yards, all slugs were at least 4" high. The copper solids are supposed to zero at 50 yards and be only 1/4"high at 25 yards.

Even with my rear sight "bottomed out" for elevation, I am still too high with all the slugs. Am I correct that I should be lowering my rear sight to lower my point of impact? If so, where to I go from here?
Thanks,
CV

hogdogs · October 30, 2010, 04:08 PM

Yes you lower the rear sight to drop the point of impact.

I would put the rear sight at about mid way and check it at 100yds, then 80 then 60 then 40... I would then make a decision regarding adjustment.

The "supposed ta' " doesn't take into account, the rear stock design, the way you weld your cheek nor the size of your head...

Just a starting point...
Brent

zippy13 · October 30, 2010, 05:36 PM

Raise the front sight, or remove some material from the top of your rear sight to lower your POI (point of impact). But, only after following Brent's recommendation for incremental verification

Remember, the slug's trajectory crosses the aim line twice. The height of the sights above the bore plays a major factor in determining at what distances the cross points occur. An old rifleman's trick is to mount their sights high to increase their point blank* range. It's one of the reasons modern battle rifles have higher sights than they did back in the day.

*point blank: The range where your POA (point of aim) and POI are close enough to insure a kill without adjusting your sights or holding high or low.

cvbrewer · October 30, 2010, 07:14 PM

Thanks very much. This is exactly the info I was looking for.

I was considering taking some material off the rear sight, as the front sight is adjustable only for windage, not elevation. Of course the idea of smithing my sight is little intimidating.

After reading your posts, I realize that I'm not at that point yet, and that I need to get some more slugs and do some incremental testing at longer ranges.

The idea of high sights to increase PBR is interesting. That seems to be how my sights are configured.

Back to the range!
CV

October 30, 2010, 02:18 PM	#1
cvbrewer Junior Member Join Date: September 20, 2010 Posts: 8	Sighting Question for 870/Mossberg DRS I test fired some slugs at the range today with my 870 express, which has a new Mossberg slug barrel with deer rifle sights. A few slugs grouped well, especially copper solids, but at 25 yards, all slugs were at least 4" high. The copper solids are supposed to zero at 50 yards and be only 1/4"high at 25 yards. Even with my rear sight "bottomed out" for elevation, I am still too high with all the slugs. Am I correct that I should be lowering my rear sight to lower my point of impact? If so, where to I go from here? Thanks, CV

October 30, 2010, 05:36 PM	#3
zippy13 Senior Member Join Date: August 23, 2008 Location: SoCal Posts: 6,442	Raise the front sight, or remove some material from the top of your rear sight to lower your POI (point of impact). But, only after following Brent's recommendation for incremental verification Remember, the slug's trajectory crosses the aim line twice. The height of the sights above the bore plays a major factor in determining at what distances the cross points occur. An old rifleman's trick is to mount their sights high to increase their point blank* range. It's one of the reasons modern battle rifles have higher sights than they did back in the day. *point blank: The range where your POA (point of aim) and POI are close enough to insure a kill without adjusting your sights or holding high or low.

October 30, 2010, 04:08 PM	#2
hogdogs Staff In Memoriam Join Date: October 31, 2007 Location: Western Florida panhandle Posts: 11,069	Yes you lower the rear sight to drop the point of impact. I would put the rear sight at about mid way and check it at 100yds, then 80 then 60 then 40... I would then make a decision regarding adjustment. The "supposed ta' " doesn't take into account, the rear stock design, the way you weld your cheek nor the size of your head... Just a starting point... Brent

October 30, 2010, 07:14 PM	#4
cvbrewer Junior Member Join Date: September 20, 2010 Posts: 8	Thanks very much. This is exactly the info I was looking for. I was considering taking some material off the rear sight, as the front sight is adjustable only for windage, not elevation. Of course the idea of smithing my sight is little intimidating. After reading your posts, I realize that I'm not at that point yet, and that I need to get some more slugs and do some incremental testing at longer ranges. The idea of high sights to increase PBR is interesting. That seems to be how my sights are configured. Back to the range! CV