How much does Boolit Size Affect POI?

[wv109323]

I was trying to to get a load to shoot a good group out of my Marlin 94 in .44 Mag.
I had put together two different loads with the only difference being bullet size.
The boolit was a 245 gn. SWC out of a Lee mold. The load was 9.0 gn. Unique with Winchester SP Primers.
The first boolits were sized .429 with a RCBS sizer, The second group was "as-cast" at .4315 and tumble lubed with Lee Alox.
Firing was done at 50 yards. The .429 Boolits printed a 5 shot group of 2 1/4" and was in the black of a 25 yd slow fire pistol target.
I fired some of the .4315 boolits and they were off the target. The POI had shifted at least 10".Has anyone experienced anything similar?
I would not expect such a drastic POI change between two loads with only a small difference in loading.

[popper]

You made 2 changes, size and lube. I assume PB, same powder load. PSI should go up slightly with larger CB. I've had lube change POI by 6" in 30-30. Don't know why but I'm guessing base damage or a case resizing problem. Any leading?

[wv109323]

These were gas checked boolits but I was not using gas checks ,I was shooting them plain base. There were leading issues and the lube was Micro-Lube on the .429 and as mentioned Lee Alox on the as-cast.

[243winxb]

How does the .4315 boolits group? 10" POI change @ 50 yds is a lot.

[wv109323]

How does the .4315 boolits group? 10" POI change @ 50 yds is a lot.
I did not get a chance to get a group of the .4315 bullets. I only loaded ten rounds and they were off the paper. I am in the process of reloading a few rounds and see what size group I get.

[wv109323]

If that is a microgroove Marlin 44 mag, I would suggest biting the boolit and adding the GCs. If it is one of the "Ballard Rifling" variety, I would expect it to work OK in the 44-40 velocity range with plainbase boolits.

I can't say that I've had huge POI changes with seemingly small sizing changes. Leading could be the result of too small diameter boolits regardless of lube type.
It is a Micro-Groove barrel. The reason I am not using the gas checks is due to problems with them.. I bought some aluminum gas checks and I am not satisfied with them. They will not stay on the bullet when the bullet is sized and they are too large to use un-sized. I only have a .429 sizing die for the RCBS. If the .4315 bullets shoot well I am going to get a sizing die for my Star Sizer. I just don't know what size to get right now.

[Wally]

It is a Micro-Groove barrel. The reason I am not using the gas checks is due to problems with them.. I bought some aluminum gas checks and I am not satisfied with them. They will not stay on the bullet when the bullet is sized and they are too large to use un-sized. I only have a .429 sizing die for the RCBS. If the .4315 bullets shoot well I am going to get a sizing die for my Star Sizer. I just don't know what size to get right now.

I make my own Aluminum GC's and shoot the .44 Mag (USRA 94AE)...I too had them come off when lube/sizing..I found I had to make them from thicker aluminum for them to stay on. However shooting the loose ones proved not to be a problem. Some do come off after they leave the barrel, but are still quite accurate. Also if you press down hard on the bullet, when sizing, it will often make the GC stick better and not come off when you remove it from the sizing die. Another option--pan lube and size in a Lee sizer die. I do use a Lyman .431" sizer die...the .429" is just too small.

[popper]

WW alloy? I've heard that annealing will help keep GC on. I just use the Cu which works for me. Don't think the diff in size (.0025) is the problem. Did you fire the smaller first? Slight leading in my MG marlin doesn't cause me a problem, major does. Pound an as cast down an oiled bbl and check the size. Do you have any 2400 to try? It's a lot slower. Try LLA in both to see if lube is the problem. Just some ideas.