Diagnosing cast 9mm - right of POA

[Dahak]

I have my pistol (M&P 2.0 9mm 4" barrel) set up for 147 gn Brazos cast bullets. However, I recently obtained a 147 gn MP mold, though with my lead alloy, the boolits come out at 154gn. Okay, adjust from 3.1 to 2.9 of Titegroup to account for the weight shift. However my hits were consistently 1" to the right at 7 yards (vertical was within my margin of error). What could account for the point of aim shift? I was testing 5 round groups rotating between the Brazos and my boolits and the results were consistent through all 50 rounds of my test batch.

My initial reaction is that I adjusted too much on the powder reduction for the weight shift. If I saw that shift at 25 yards I would adjust the sights and call it good, but that's a lot of shift at 7 yards. Can anyone give me some guidance on what might be going on?

[Dusty Bannister]

You may expect some diagonal movement of bullet impact on the target when you change bullet weight and powder charges. That changes the recoil impulse as well as the dwell time as the bullet leaves the barrel.

[Finster101]

Bump the charge up just a little.

[mdi]

IMO; different bullet weights, different powder charges, = different load. Equals Different POI...

[mnewcomb59]

In my 357 rifle I run two basic loads. 2-2-96 AC and 2-2-96 WD. I need the WD for good penetration at 10-30 yards when deer driving. When ambush hunting I use the AC bullet because shots will be broadside and probably further than a deer drive shot where you need to shoot them quartering or Texas heart shot. The same bullets out of the same pot of alloy get powder coated one color then water dropped, and the rest get PC a different color and air cooled.

The AC and WD bullets hit different POI left and right from each other. I sight in for the AC and figure I will need the precision for a 100-150 yard shot and the WD is more than 2 inches right or left at 100 yards.

In my M&P 2.0 5" 9mm I am sighted in with pulled 124 HSTs at 1250-1300 fps and they are centered but 1" high at 25 yards. Perfect. My 124 cast bullets hit the same spot when cast hard, and my 124 NOE HP that is 9BHN hits a few inches left. Tulammo 115 steel jacketed hits about 3" low and 3" right. The hardness of the bullet torques the barrel as soon as the rifling is engaged. Softer bullets might skid a bit on the first driving band, then bite hard, and they put a lower, spread-out-over-time torque impulse on the barrel. The Tulammo with a hollow base and steel jacket must torque the barrel much more abruptly and strongly than a brass jacket HST to cause the POI to change so much.

[44MAG#1]

I have my pistol (M&P 2.0 9mm 4" barrel) set up for 147 gn Brazos cast bullets. However, I recently obtained a 147 gn MP mold, though with my lead alloy, the boolits come out at 154gn. Okay, adjust from 3.1 to 2.9 of Titegroup to account for the weight shift. However my hits were consistently 1" to the right at 7 yards (vertical was within my margin of error). What could account for the point of aim shift? I was testing 5 round groups rotating between the Brazos and my boolits and the results were consistent through all 50 rounds of my test batch.

My initial reaction is that I adjusted too much on the powder reduction for the weight shift. If I saw that shift at 25 yards I would adjust the sights and call it good, but that's a lot of shift at 7 yards. Can anyone give me some guidance on what might be going on?

My first response would be, what are you going to use the gun for? What bullet are you going to use the most, the one it is sighted for? If for self defense are you going to use the cast bullets or one of the Whizbang JHP loads?
If for just practice why worry about it?
Are you going to shoot more than 7 to 12 yards?
If not going beyond 12 yards I wouldn't give it a seconds thought much less a minutes thought.
Now if I were going to shoot much longer distance I would give it a thought.
Just for practice I don't worry if one load shoots a little different than another.
Kinda like the Gnat and Camel thing.
BTW. To diagnose it I would say bump the powder charge up slightly if it is safe to do so. You should know whether it is or not.
Not as much torque as the other load if you are right handed.

[Dahak]

UPDATE: Loaded up another 50, this time at 3.1 grains. Point of impact issue solved, primers looked good. I was able to clean the dot torture drill at 3 yards except for the one-handed exercises, but that is 100% on me and is one of my summer self-improvement projects.

As for my goals with this load - practice/plinking and local IDPA matches with a match director who puts 15-25 yard shots on about a third of the stages.

I don't understand _why_ the lower power load went right and the higher power load straightened out, but I do know that boolits require experimentation and experimentation requires good notes and so my reloading journal has been updated. I'll do some longer range testing to make sure that solved really means solved and then start some serious-for-me production because SPP have been starting to appear at 5.50/100 locally.

[fredj338]

I would not expect any POI diff at a mere 7y. COuld just be a bearing surface thing. Could just be the TG too. Never got great results with cast/coated & TG.