Stringing eith garand cast load.

[300blk]

Im getting some pretty serious stringing with my cast loads in the garand, looking like horizontal variation is less than .750 inch but the vertical variation is almost 3 inches!
This is at 50 yds, loaded with 36.8 grains varget- over checked and lubed 311-299.This load cycles the action and is a real pleasure to shoot. I did not use a filler (dacron etc. ) i wasnt able to use a chrony, however stringing like that usually is an indication of velocity deviation. Will using a filler help with this problem? Anyone have any experince with this? I would like to get near my jacketed groups of .450 @ 50 yds but would be satisfied with 2 moa.
Any suggestions welcome.
300blk

[Silverboolit]

You could try weighing your boolits..sometimes I find some that are up to 2 grains different. 2 tenths difference may group your shots a little better..

[geargnasher]

It's not a muzzle velocity deviation, it's an ignition deviation causing erratic harmonics with the extra-whippy M1 barrel, or you're sneaking up on a good vibration node. You are almost "there". Check the load for "headroom" on book loads and try increasing the charge in two-tenth-grain increments and see if it doesn't close that vertical stringing. Forget about fillers for the moment. I'll pass on a tip from a friend's experiences, those rifles are very picky with anything upsetting barrel vibrations, and just exactly where you hold or rest the rifle (pressuring the barrel) can make huge changes in group dispersion. Sounds like you have enough things working for you with your components and techniques that all you need is the powder charge fine-tune and pay attention to shooting position.

Let us know how it turns out, and don't go changing a bunch of things yet, you're CLOSE right now.

Gear

[300blk]

I will weight sort a little more closely right now am using 1 grain tolerance, before lube and checks. Will move down and use the lighter ones in blackout.

[300blk]

It's not a muzzle velocity deviation, it's an ignition deviation causing erratic harmonics with the extra-whippy M1 barrel, or you're sneaking up on a good vibration node. You are almost "there". Check the load for "headroom" on book loads and try increasing the charge in two-tenth-grain increments and see if it doesn't close that vertical stringing. Forget about fillers for the moment. I'll pass on a tip from a friend's experiences, those rifles are very picky with anything upsetting barrel vibrations, and just exactly where you hold or rest the rifle (pressuring the barrel) can make huge changes in group dispersion. Sounds like you have enough things working for you with your components and techniques that all you need is the powder charge fine-tune and pay attention to shooting position.

Let us know how it turns out, and don't go changing a bunch of things yet, you're CLOSE right now.

Gear

I think ill be reducing charge instead of increasing.
Luckily my shooting position is the same, prone unsupported, slung up rifleman-style.
36.8 was the low end. Worked up to max of 38 of varget 2/10 gr at a time. Worst group was 5 inches !!! with 37. 4 Grains.
Since all cycled action i will reduce 1 grain and work up to 36.8 in .1 grain increments.

[300blk]

Thanks for everyones input so far keep it coming.

[geargnasher]

I know you don't understand why I told you what I told you, but if you want to learn, how about trusting me? If you're safe to increase without bending your op rod (you make that call), that is the direction you should go, not down. And don't increase by much. It will only take you ONE en-bloc to find out.

Your other option is to drop back several grains to the previous harmonic and work up, but you might get into ignition consistency issues with that powder before you can find the next lower node. Finding the next node down might also require a powder change.

The sling technique is horrible for creating vertical stringing, although it should show up in your J-word loads as well to a lesser degree if you're inducing the stringing via barrel pressure. Cast is a LOT more sensitive to such things.

Gear

[300blk]

Thanks, i can try those same loads again, I did increase the loads up to max of 38 grains 2/10s at a time. are you suggesting to go above max load?
I can shoot from a rest but if the barrel sensitivity is that bad then there would be no point that i can see, as i use my sling with that rifle nearly always.
My jacketed loads yeild147 fmj bt@ 2902 avg @ 10 ft and hold sub moa at 50 and 100 yds(by a hair) while using the sling.
No issues with op rod have a '54 with cut op rod and has had no issuesup to 220 jacketed at max loads.

[madsenshooter]

Lots of room before the gasport pressure becomes an issue. It would be over 39gr, which would produce around 29,234psi chamber pressure, 2000fps velocity, and only 8275psi port pressure. Standard Garand loads produce around 10,500psi port pressure.

[300blk]

I see, my cast lyman book lists 38 grains as max.

[runfiverun]

that's is their max for the bullet not for the powder or pressure.
you have two choices.
more powder or a filler. [basically the same thing....kinda, but different]
a third is a different powder looking for the next node.
the simplest is to increase the powder looking for a round group.

[300blk]

What do you mean by round group? As in not stringing?
I got some butgroup sizes were abysmal. 3.5-5 inches.@ 50 yards.
That is entirely unnacceptable..
Will work up from 38.2- 39 grains before using filler.
Am i not understanding correctly? If 36.8 is producing stringing but overall little horizontal variation and the cause is inconsistant ignition would afiller keeping powder from layng flat in the case not solve the problem?
Can someone explain this to me a litttle better?

[zomby woof]

My load is 33 Varget with that boolit, I use a filler. Works great.

[geargnasher]

What do you mean by round group? As in not stringing?
I got some butgroup sizes were abysmal. 3.5-5 inches.@ 50 yards.
That is entirely unnacceptable..
Will work up from 38.2- 39 grains before using filler.
Am i not understanding correctly? If 36.8 is producing stringing but overall little horizontal variation and the cause is inconsistant ignition would afiller keeping powder from layng flat in the case not solve the problem?
Can someone explain this to me a litttle better?

I can try to explain it. There are ignition inconsistencies and there are barrel vibrations. The two aren't necessarily the same problem, but one affects the other greatly.

The barrel vibrates when fired like a guitar string. Just exactly at what point in the whip the boolit ejects from the muzzle determines where it will strike the target. Slight variances in boolit/muzzle timing that are beyond your control will dictate the stringing, scattering, bugholes, etc. Group shape is a way to determine which part of the node your load is in, and which way to make adjustments to where these inconsistencies are minimized and the muzzle is most still when the boolit exits. you have to time the load to the right point and have a powder charge that lights exactly the same way every time in order to get small, round groups. You are below ideal, coming up on it, and probably way past the sweet spot of the last node. Google is your friend for finding tons of great information on harmonic barrel vibrations and how to load for them. Same principle applies to cast as to jacketed here.

Gear

[runfiverun]

once the vertical stringing starts coming together.
you can tune the oal.
you are having ignition consistency issues causing issues with the accuracy node.
once you get the more consistent powder burn you can tune it further.
that's what changing the oal will do for you.

looks like gear was typing while I was. :lol:

[geargnasher]

Ya, I was trying to save some wear and tear on your keyboard! You should be able to read my mind by now, are the Rocky Mountains breaking up the waves again? :kidding:

Gear

[300blk]

Thanks for your patience. This then is no different than loading match loads for my 260 remington then, its just the limited powder charge was throwing me... No pun intended. I will bump up the powder and watch for leading and pressure signs.
At what point do you suggest increasing the oal? Soon after the stringing opened up . 4 gr the groups increased in size to 3 inches. So maybe tryto adjust oal from 37 grains?

[runfiverun]

quite often it's shortening the oal that you want to do.


i think the Jetstream has dipped down again and is blowing the antenna off.
:lol:

[300blk]

Ugh this is backwards as hell... On match load workups i start low and work to or nearly to the rifling. Will do. Gonna try a couple of loads at different oal to hopefully get a useful load, i will post results and may have further questions. Thanks to all.

[geargnasher]

Read Run's last sig line. Lot of truth there. Lot of truth to both of them, in fact.

Gear