Promising results at jump and jam - which to choose?

[APGE]

Howdy Folks,

I'm currently working up a load for 230 hybrids in my 308 and am at the point of needing the expertise of the brainstrust.

Methodology so far has been a ladder test to find a charge window, fine tuning that charge window and now working on seating depth. The charge is 40.3 of 4895 under a moly coated 230. This afternoon I did some coarse testing of seating depth (20 thou changes) and shot groups at 600 yards. Below is a plot of the groups for 10 thou jam and 50 thou jump. Grid lines are at half inch spacing.

There was a reasonable wind blowing, explaining the wide shot on 50 thou jump. Other loads tested (10 thou jump and 30 thou jump) had significant vertical and aren't worth sharing.

Which would you pursue? What would you tweak? Jam is comfortably the smaller of the two groups, but the fifth shot threw the groups vertical from 1 to 2 inches.

As I was testing in fairly coarse 20 thou increments, I'm not sure which way to go as I suppose either the jump or jam load could improve with tweaking.

Any and all advice is welcome!

 

[JFrank]

Interesting test, .020 increments seems quite course for a seating test.
I run a course powder test on the lands to find a node then seating in .005 increments looking for the least vertical then fine tune powder.

 

[mikecr]

Did you back away from your best charge for this testing?

 

[savagedasher]

What was your ES with both
I test jump useing ES as a base
line
But I also tune with a tuner

 

[Bc'z]

I've passed on many trips to range due to not having favorable weather conditions for testing load work.
I do practice in unfavorable conditions because I hunt in them , just as alot of you shoot for score in less than favorable weather.
Personally I'd reshoot it on a calm morning.

I agree with SPJ on your coarse seating.
If you adjust in .005 increments you can watch your groups gradually tighten or open up. Then I fine tune in .001 increments in the direction of where it's getting tighter.

 

[Bart B.]

200 thru 250 grain Sierra HPMK match bullets in 308 cases have shot most accurate at long range with IMR4350. 48 grains with 200s for about 2500 fps. 46 for 220's. Don't know what David Tubb used with 250 HPMK bullets leaving about 2150 fps.

Methinks IMR4895 is way too fast a powder for any bullet over 180 grains in 308 Win cases if best accuracy is paramount.

 

[Dusty Stevens]

I think you have too many external variables to decipher. You need to get closer to your target (literally in 2 ways) then pick a couple loads to fine tune at distance. You have what we call a weather report there.

 

[APGE]

Thanks for all the advice, gentlemen - it's much appreciated

Interesting test, .020 increments seems quite course for a seating test.
I run a course powder test on the lands to find a node then seating in .005 increments looking for the least vertical then fine tune powder.

I usually do 5 thou, but decided on 20 after reading the Berger article that recommended 40 thou increments! I couldn't bring myself to do an increment that big, so I settled at 20 as a compromise, with a view to fine tuning afterwards. Still not sure which direction to head.

Did you back away from your best charge for this testing?

No - what did I miss by not backing off?

What was your ES with both
I test jump useing ES as a base
line
But I also tune with a tuner

I didn't crono the seating depth test. Es was 5 for 5 shots before playing with seating depth.

200 thru 250 grain Sierra HPMK match bullets in 308 cases have shot most accurate at long range with IMR4350. 48 grains with 200s for about 2500 fps. 46 for 220's. Don't know what David Tubb used with 250 HPMK bullets leaving about 2150 fps.

Methinks IMR4895 is way too fast a powder for any bullet over 180 grains in 308 Win cases if best accuracy is paramount.

Powder was H4895. I'd prefer to be running 46.8 grains of 4350 (which netted 2500fps vs the 2400 I'm getting), but I was having trouble with compressing the load and cases growing. That was with an 8" drop tube - maybe I need to rig up something longer and revisit? Using H4895 was intended to be a compromise that addressed the case capacity issue while offering a little more velocity than varget

I think you have too many external variables to decipher. You need to get closer to your target (literally in 2 ways) then pick a couple loads to fine tune at distance. You have what we call a weather report there.

Thank you, Dusty. I was following some advice to do my testing at the distance I will be shooting at - do you recommend something different?

 

[Dusty Stevens]

Thank you, Dusty. I was following some advice to do my testing at the distance I will be shooting at - do you recommend something different?

I prefer to work up the load closer in THEN verify/final tweak at distance. you have way too many variables at distance to see if the wind or seating depth got that wide load.

 

[mikecr]

what did I miss by not backing off?

If you don't back away from best powder load while doing full seating testing, you end up changing 2 attributes at once. A seating affect, and a collapsing load affect.

Ideally, you would be nowhere near any powder node for full seating testing.
This is a coarse seating adjustment, which you should later followup with a fine tweaking(group shaping), while at best powder load.

 

[APGE]

I prefer to work up the load closer in THEN verify/final tweak at distance. you have way too many variables at distance to see if the wind or seating depth got that wide load.

Thanks, I'll bring it into 200 yards and play.

When I do, I will work in 5 thou increments, but I still don't have any idea which area to pursue - would you tweak around the large (50 thou) jump, or the 10 thou jam?

 

[Bart B.]

Powder was H4895. I'd prefer to be running 46.8 grains of 4350 (which netted 2500fps vs the 2400 I'm getting), but I was having trouble with compressing the load and cases growing.

Probably too much pressure. That alone can cause accuracy problems.

The chamber freebore may be too short for those heavy bullets and non-compressed loads with IMR4350 in your cases. .

 

[APGE]

A sign of too much pressure. That alone can cause accuracy problems.

I should have clafiried - the cases weren't growing, the loaded rounds were. The compressed load was pushing the projectile back out of the case. Had no dramas with pressure - I physically cannot fit enough 4350 in a case for it to be a concern

 

[Ned Ludd]

I'd suggest starting the 230s at .015" off the lands, and use Varget instead of H4895. I think you'll find the results (and the recoil) a little more satisfying; H4895 is a very fast powder for 30 cal bullets that heavy. Once you find the center of the optimal charge window, go back and tune seating depth in .003" increments from about .003" off to about .027" off. The 230s should not need to be seated into the rifling.

Edited to add: H4895 should only net you about 20 fps or so more than Varget at a given node. Although I'll certainly take that, all else being equal, it's not a huge difference in velocity. You should find a node for a 30" barrel .308 with the 230s and Varget somewhere in the 2450 fps range.

 

[Dusty Stevens]

Man if your powder load is pushing your bullet back out then you should switch powder. You cant do any testing for seating depth when your depth keeps changing and youre at max powder fill with nowhere to go with your load

 

[Bart B.]

44 grains of IMR4320 under Sierra 190 HPMKs&& was very accurate in heavy M118 match cases with 24" 1:12 twist barrels.

Maybe 41 or 42 grains with 230 grain bullets and no charge compression.

 

[APGE]

I'd suggest starting the 230s at .015" off the lands, and use Varget instead of H4895. I think you'll find the results (and the recoil) a little more satisfying; H4895 is a very fast powder for 30 cal bullets that heavy. Once you find the center of the optimal charge window, go back and tune seating depth in .003" increments from about .003" off to about .027" off. The 230s should not need to be seated into the rifling.

Edited to add: H4895 should only net you about 20 fps or so more than Varget at a given node. Although I'll certainly take that, all else being equal, it's not a huge difference in velocity. You should find a node for a 30" barrel .308 with the 230s and Varget somewhere in the 2450 fps range.

Thanks Ned, I'll try a varget ladder during the week and report back. 2450fps would be quite fine.

Man if your powder load is pushing your bullet back out then you should switch powder. You cant do any testing for seating depth when your depth keeps changing and youre at max powder fill with nowhere to go with your load

Yep, it made seating depth tests flat out impossible. Actually it made shooting accurately flat out impossible!

I need a longer drop tube and I won't have the problem. Talking to other shooters using similar setups (215s generally) they are getting even more 4350 in than I was trying to but are using drop tubes literally 4 feet long.

 

[Bc'z]

Man if your powder load is pushing your bullet back out then you should switch powder. You cant do any testing for seating depth when your depth keeps changing and youre at max powder fill with nowhere to go with your load

Ok D, heres 1 for you.
Everyone agrees NO CRIMPING!
RIGHT?
Soooo what if neck tension was increased to stop powder from pushing back against the bullet?
I know it would be changing the original recipe, but seems to me if it stopped the irregular seating depth it would be worth investigating.
Thoughts?

 

[Scott Harris]

Howdy Folks,

I'm currently working up a load for 230 hybrids in my 308 and am at the point of needing the expertise of the brainstrust.

Methodology so far has been a ladder test to find a charge window, fine tuning that charge window and now working on seating depth. The charge is 40.3 of 4895 under a moly coated 230. This afternoon I did some coarse testing of seating depth (20 thou changes) and shot groups at 600 yards. Below is a plot of the groups for 10 thou jam and 50 thou jump. Grid lines are at half inch spacing.

There was a reasonable wind blowing, explaining the wide shot on 50 thou jump. Other loads tested (10 thou jump and 30 thou jump) had significant vertical and aren't worth sharing.

Which would you pursue? What would you tweak? Jam is comfortably the smaller of the two groups, but the fifth shot threw the groups vertical from 1 to 2 inches.

As I was testing in fairly coarse 20 thou increments, I'm not sure which way to go as I suppose either the jump or jam load could improve with tweaking.

Any and all advice is welcome!

So, .050" jump shows 1" vertical at 600 yards??? That is pretty darned good, don't you think? Seems like it works great off the lands, which is exactly what I find with all the hybrids. For F-class, we don't even mess with seating depth: shoot hybrids only and set them to .015" off the lands with a new barrel. Do a ladder test and that's usually it. The rest is about wind reading and gun handling IMHO. Regarding gun handling...good luck with those 230s in a TR gun!

 

[Dusty Stevens]

Ok D, heres 1 for you.
Everyone agrees NO CRIMPING!
RIGHT?
Soooo what if neck tension was increased to stop powder from pushing back against the bullet?
I know it would be changing the original recipe, but seems to me if it stopped the irregular seating depth it would be worth investigating.
Thoughts?

.005 tension wont keep it from being inconsistent