A question about .30-30 trajectory

[Rock_Steady]

Alright, I'm stumped.

I have gone back to semi-buckhorn sights on my Marlin, taking off the 4X scope that I had put on there - that I decided just ruined the lines.  So I go out two times now, funning through some ammo, trying to get a good zero and get things rolling.  As I'm shooting with open sights, I'm starting at about 50 yards and moving up.  I have 2 problems.

1.  As the barrel heats up, my POI gets higher.  First group of 3 is 1" high, dead center.  Subsequent groups climb right off the sheet.

2.  Moving out to 100 yards, my shots climb even higher.  Is this the fault of the bullet's trajectory (shooting 150gr remington core-lokt, 80 degree day, calm winds) or the shooter?  

I have a hard time with the semi-buckhorn.  I loved using peep sights in the army, but with the factory sights here I'm finding it hard to get a good clear sight picture.  

I'm pretty sure that I'm doing my part, as the groups are nice and tight, but I'm running out of elevation on the sights when the barrel gets hot.  Ideas?

[Winter Hawk]

Since you liked a peep sight in the military, why not get one for the Marlin?  Williams Foolproof is about as good as you can get in my opinion.  The WGRS (Williams Guide Receiver Sight) is rugged and simple.  If you want a "ghost" sight, just remove the aperture.  For sighting in or target work, use the smallest diameter aperture Williams sells.  They sure don't mess up the lines of the rifle and you can wrap your hand around it at the balance for a comfortable carry.

Williams has the 5D which is similar to the Foolproof except without screw adjustments.  It costs less than the Foolproof.  In fact, 5D stands for 5 Dollars which is what they cost when Williams first came out with them (Foolproofs went for $18.50, IIRC)

-WH-