Cast load windage issue.

[Mctrigger]

I recently loaded up some 210 grain commercial gas checked round nose Bullets @ .312 for my Finn m39 7.62x54 that specs out at .310. They are over IMR 4198 in PPU brass and large rifle federal primers. No Dacron or filler. I did groups from 22 grains to 32 grains. Had promising 100 yard groups at 28 and 30 grains. However these groups fall 10”+ left from POA. All 11 strings fall in this area. elevation is low but I expect this. My standard for windage is factory jacketed 203 grain rounds that shoot very well out too 600 yards my max range. Any advice as to what I may be experiencing? I’m new to cast and have very limited experience.

[TCLouis]

When you shot it with jacketed bullets you established the POA/POI for full power jacketed bullet loads.
Knowing nothing about that rifle I have no idea how nor how easy windage adjustments might be.
That said, as I remember they have a reputation for fine accuracy.
Contrary to what one would expect the point of impact may hold close for cast boolit loads or may move significantly up, down, left or right. I have found elevation to be least affected with with cast boolit loads.
Since they all fall in that area, you are experiencing POA/POI relationship for that rifle with that sight setting with cast boolits.
Switch over to mostly cast Boolit shooting, set the proper windage and enjoy the heck out of your rifle!

Testing some 45-70 loads recently, just changing powder type shifted POI 3 inches right at 50 yards with no change in elevation.
Velocities of both loads were likely pretty close to the same.

Don't ever try to guess the change the POI from a change in loads, you may well be fooled.

BEST of luck to you in your BOOLIT shooting quest!

[samari46]

Have a Finn model 27. Set it up for cast bullets (Lyman 314299) and never touched the sights again. The sight leaf on the Model 39 is kind of an odd duck as most are marked starting at 150 meters. If you look at the front sight you'll see a series of dots around the adjustment screws. one dot to another is supposed to be good for 5/8th's of an inch. But that is for jacketed ammunition. Cast bullets have a much lower velocity as I estimate my 314299 is only going between 1600-1700 feet per second. On the model 27 my rear sight is set for 550 meters for 100 yds. But
the m27 rear sight is much different than the one on the M39. Hope this helps. There is/was a gent on the gunboards.com forum who sells or sold a peep type sight for the rear sight and a taller front sight for the m39. I have a set I bought from him last year but as yet I haven't installed it as all the local ranges are closed due to covid. Frank

[Mctrigger]

Thanks guys. I’m ok with the elevation. I can run a cheat sheet for that. It’s the huge windage swing that seems odd. I’ve never touched front. It’s currently center. and I don’t believe it has ever been adjusted. But I think I’d have her pinned all the way one side damn near. At a 100 I held to the far edge of the target 10-14” change of aim to impact. But like I said I’m just beginning here. Wanted to hear some advice from you guys in case it’s a error. I did have a clean bore and shot 40 rnds jacketed prior to this test if that’s a issue.

[astroturf3040]

Had the same experience with a K31. Windage way off with usual 30 cal loads. Ending using 30.0 gr IMR 4198 with the NOE 180 gr gc. Centered up windage to mechanical zero.

My m39’s shoot the 311466 and red dot to poa, groups well at 200 and banged the gong often at 300 off hand. 311299 shots well.

Thanks!

[TCLouis]

Use the calculator here to see how much sights would have to be moved.

https://www.dillonprecision.com/sight-correction-calculator.html

Typically surprisingly little.

If you are going to be shooting cast and coated bullets then drift changing sights is out!

[GooseGestapo]

My Izvesk 91/30 does the same thing, except with 147gr vs 185-204gr jacketed bullets. It shoots similar weight cast to same windage as jacketed.
I’ve settled on the PPU 180gr .311” jacketed bullets and Lee .312”180gr RNGC bullet. Over (cast bullet) 24.0gr of #2400 it shoots 4moa at 100yds and uses the 400m sight elevation setting.
Though the crudest of my milsurp rifles, it does hold its own!
It also shoots well with a powder coated Lee 155gr w/o gc, from 6-cavity mold over 20.0gr of #2400. Uses 500m setting. Shoots to left 4” at 50yds.

The horizontal shift is due to barrel harmonics.

[GoodOlBoy]

In all honesty you're getting pretty good advice from everybody on your issue. One thing I would like to point out is that in my experience there are some rifles and handguns that for some reason, or no reason, just don't like a certain type, brand, weight, shape, etc bullet. Chalk it up to harmonics, rifling depth, or being built under counter astrological signs from the gun itself.

Cursed items are also very real IMHO. I've got a bullet mold buried around here somewhere for a 160 or 200 grain (can't remember which) .452 that casts dang near perfect without needing resize (even tried resizing them). Got it from a member here years ago who wanted to see if I had any luck with it in my old 1911. I couldn't hit the side of a barn from inside the building with that bullet (same problem he was having). Some buddies and I got together. We tried it in 3 different 1911s, a schofield, and four 45 long colts (yeah I know it isn't a great bullet for a 45LC). Same thing. All over the place. The mold was checked every which way. Tried with multiple lead types, multiple powders, different lubes, etc. One guy's Uncle or Dad had the same mold. Bullets cast from HIS mold worked pretty well. From MY mold... you'd be better off chunking the ammo at the target, though I honestly think there would be a risk of it "boomerang-ing" into the back of your head. I gave the mold away and a year later it was back in my collection because the guy I gave it to, and two of his friends had the EXACT same problems.

I've got an RCBS 30 Remington (not ar) resizing die that is cursed as well. No press in the world with no amount of resizing lube will put a piece of brass all the way in it. You couldn't drive it in with a sledgehammer. Took two big boys and 3' of cheater pipe to pull the last piece we tried to force into it back out, cracked the wood the press was mounted on in the process. The die went back to RCBS THREE times. They couldn't find a problem, and couldn't get the die to work. It went to a custom die maker. He couldn't find a problem with it. It has been checked every which way you can. Won't work. Finally (nearly 14 months of fighting with it) RCBS sent it back with a full refund. They didn't even want the thing in their shop. Bought a lee whack-a-mole 30-30 set (needed one anyway) while waiting for it, and resized the brass with very little effort...

I've had cursed brass even. I always mark any "problematic" brass (splitting, dented, etc). Had a couple of pieces of 45-70 brass (a short hornady, and a remington) that no matter what I did or do they will NOT successfully eject without a rod to pop 'em out of the old single shot H&R Handi. They have been full length sized, deburred, refired multiple times. I call that little baggie the Bob Marley's, cause they always be jammin'. I keep 'em cause I can always use them as a last resort, but I won't use them unless it IS a last resort.

Dad had a box of Black Talon 45 acp given to him years ago because the person who bought them was having heck. Every other round took multiple primer strikes to fire, one round went off when the slide closed on it, and the rest wouldn't hit a pulpwood truck at three feet. He fired them up at the old Carter's Country range on Treaschwig Rd in Spring Texas in 1996. The very final round was literally hand chunked downrange by the RO when three different 45s gave it multiple strikes and nothing...

Try a different brand, weight, something and see what you get. Heck get some White Label lube or LLO and tumble lube 'em and try it. Then chalk it up to the wrong diet for your rifle, and move on. Life's too short, range time is too limited, and powder and primer are too scarce to beat your head against a wall over it. Or at least it is for me these days.

God Bless.

Richard

[Winger Ed.]

A slower cast boolit has a longer time of flight, so the wind has more time to push on it.

I also think difference in barrel harmonics with the different powder charges will move POI sideways also.
It might also move it up & Down too, but we usually chalk that up to weight and velocity differences.
Harmonics seems to be the reason target/bull barrels are so thick, in order to minimize the effect.

[Eddie1971]

I got 2 M39's both mint both VKT made. One shoots cast like a champ the other just so so. IMHO bump up your load to another powder. Mine seem to like a charge of 36 grains of Winchester 748. Both would string to right with a similar charge of IMR4895.

[jimb16]

You are dealing with 3 issues, wind drift due to longer flight time, barrel harmonics and gyroscopic precession. All 3 can move the bullet to the right or left (depending on the twist of the barrel). The slower the shot, the more each can effect the movement. Have fun! They can drive you crazy!