Powder charge, bullet, vertical Point of impact

I fount this interesting today. I have a Persian Mauser. Plus I took some Iranian 8mm rounds that I disassembled then loaded up with the average charge from the pulled bullets of 45grains. OAL is nearly identical to the Iranian ammo with less crimp than the Iranian ammo. Zero signs of over pressure. I had previously ran sample loads of 40, 41,42 43 and then 45 grains looking for over pressure before I loaded up 20 rounds of the 45 grains.
So, with the Persian Mauser and the Persian bullets/powder loaded into PPU cases, the POI across 10 rounds was pretty decent I would say. Vertical was spot on at 50 yards and a tad left. Groupings were as good as it gets with me, my eyes and bags at 50Yards with one flyer.

I then ran 6 rounds with my German K98K and the POI was high about 4" at 50 yards.

Next was PPU 196g and it was about 3" low at 50yards

This got me thinking about matching the load to the gun. When I ran the Original Iranian Ammo, everything was left and nearly center vertical but groups were bigger. The Iranian ammo primers are known to delay and I attributed the grouping to such. Seems like the powder, bullet and sights for the Persian mauser all matched to give the proper POI (or close to it, I have not shot at 100 yards yet).

Got me thinking if there were some known rules about vertical POI and powder, bullet weight, barrel length etc.
The Persian Mauser is a longer barrel and a bit heavier than the German K98K. I'm speculating that is a factor in why the K9K posted higher POI. But why the lower POI for the PPU? Less energy and thus less recoil? Faster powder burn?

Both bullets are about 196grain.
Iranian is a boat tail. And a really tapered rear and boat tail. Not as much area contacting the rifling compared to the PPU.
The PPU is a soft point non-boat tailed


YES, the targets are rotated and YES what you see is the proper vertical of the target when on the stand.

Many factors can affect the POI, not just linear relationship between pressure and trajectory. Some of the things I know about (and I am far from an expert at high precision shooting)

Assuming all rounds were fired in the same weather and wind conditions:

Barrel erosion at breech and muzzle

Flex of the barrel during bullet travel down the barrel

Differences in neck tension between rounds

Imperfections in the geometry of the projectile, both during manufacture and assembly of cartridges

Slight differences in actual charge weights ( I had a range office tell me that he had disassembled some Russian ammo and found steel filings mixed in with the powder. Suggested that rather than change the equipment setup to account for a batch of powder with different burn properties, they just added steel filings so the same grain weight still applied)

debris in the free float space between the barrel and the stock

Barrel Temperature

There is discussions on other threads about rifles being rated for Minute of Angle precision (MOA) I would expect that rifles with a smaller MOA rating are specifically built to reduce these and other factors as much as possible to increase precision. Does anyone have a sense of the max precision an armory new rifle of the models listed above SHOULD be, with perfect ammo?

I recommend
Understanding Firearm Ballistics by Robert A. Rinker

It explains things in simple terms but includes all the formulas for the math if you want to dig deeper.

https://www.amazon.com/Understandin...F8&qid=1545156573&sr=1-20&keywords=ballistics

Ergonomics of design will influence impact from one firearm to another. Until velocity beyond fairly short range there are some generalities for the same firearm.. Beyond shorter ranges relative to the cartridge, the lessened flight time of higher velocity gives gravity less opportunity to pull the projectile down.

Given same relative power a heavier projectile will strike higher than a lighter one;
Given the same bullet weight higher velocity will strike lower than a slower velocity.

OP, your tests illustrate how a given firearm has prefences for specific ammunition. Also the lack of chrono data didn’t allow you monitor how a change of cases (volume and pull weight) and crimp (pull weight) effected to outcomes relative to load performance. I read and reread more to the changes of impact relative loads in the specific guns more than between guns. But your shooting and loading care lends credibilty to your data. Nice job.