philnie

Hi Guys,

I've recently increased powder charge from 85gr by volume to 90gr, then again to 100gr.Shooting a White UMag in .504, SSB 375gr sabot, CCI #11 mag percussion caps.What I don't understand is why I didn't see a noticable increase in POI at 100yds going from 90gr to 100gr?I shot my best 3 shot group at 100yds using 100gr too - approx. 1.4" V x 1.7" H so there's wobble room in my group size.I started spit swabbing and dry patching between shots for the first time too so the crud ring didn't surface, but the ole UMag got way more dirty using the higher powder charges. The SSBs load with medium pressure, not too hard or too easy.

Is it perhaps its just not far enough to realize POI changes due to 10gr charge increase? Any of you guys shooting something similar have average velocity for this load?

thank you!
phil

PS: if anyone wants more SSB 375 bullets - I ordered more from Cabelas a couple weeks ago and their CS is telling me they'll fill my order tomorrow ...

cayugad

Well anytime you change and aspect of your load, be that powder, sabot, bullet or even ignition.. there is a CHANCE in can change the POI but that is no guarantee it will. Besides, you're shooting a very high quality rifle able to handle powder and pressures very well. I really am not surprised that the POI did not change all that much. Sounds like a nice group. I shoot the same Buffalo Bullet 375 grain SSB with 100 grains of Pyrodex RS out of my Ultra Mag with amazing accuracy.

lemoyne

Check it at long range and you will see a differance.

philnie

Ok, thank you guys! I'll check at 150yds orso to see what happens to POIusing the two powder charges and keeping the POA the same. That's probably my maximum range given my abilities, iron sights, my old eyes and so on ... hopefully I'll get within 100yds though! I know Redclub's advice to use the smaller peep aperature helped shrink my groups - ordered a Merit adjustable insert as a result too!

thanks again!
phil

txhunter58

Another weird quirk is that sometimes by increasing the powder, you can lower the point of impact. In other words, I have had bullets from 100 grains hit lower at 100 yards than those shot with 90 grains when using the same bullet.

The 100 grain loads should not fall as fast once you change your sights to get them to hit where you want. And, as stated above, at 150 yards you should see more drop off in the 90 grain load.

lemoyne

txhunter58
That's one of the reasons a person needs to actually check the trajectory. The recoil on a load of less velocity can raise the barrel before the bullet exits there for changing the poi where as the heavy load may get the bullet out of the barrel before the barrel raises as much. Lee

philnie

Hmmm, that's very interesting txhunter58 and lemoyne. I hadn't considered muzzle rise effects as a result of increasing or decreasing powder charge. I'm really curious now to see how these two loads shoot at 150yds ...

thanks again!
phil