Subcal .375

[Dave W]

Have been playing around with a new duplex and decided to post this to show how finicky this stuff can be.
Me and the wind do not get along, I tend to hammer the trigger, trying to time shots when shooting in gusty conditions like yesterday which had prevailing 15mph winds. Probably 3/4 value at the target and full value at the bench. Didn't really want to shoot in those conditions but it was my last chance to shoot in sub freezing temps before some above average temps set in.

Temp was 28* with wind chill in the teens. Components:
.375 260gr Nosler Accubond
.037 bushing
Fed 209A
6/69 N110/I4350

Had already shot a 5/70 ratio in colder temps with veggie wads but the group was not satisfactory and the booster level was probably too low for this setup since it did not respond well to an additional primary powder increase. Hence the change in ratio to 6/69. Started out with felt wads, shots 1 & 2 timed 2610 & 2676fps, erratic velocities and grouped horribly. Went to a bare bullet and shots 3&4 both timed 2583fps and cut holes. Had plans to fire a 5th shot but my cold hands dropped the primary charge and spilled it on the ground.


Next and the main reason for making a range trip, I changed the ratio to 6/70 to see how the velocity would respond. 3 shots timed  2615-2624-2622fps for an average of 2620fps and an ES of 9. Think I am on the right track for the booster level but requires more testing.
Printed a .560" ctc group which I was happy with considering the conditions.


The first target shows how something as simple as a change in wads, or no wads in this case, can make a drastic change in group size and velocity. Wise to keep an open mind when testing and experiment a little.

THIS LOAD APPEARS SAFE IN MY GUN, MAY NOT BE IN OTHERS.

[jims]

Nice group. Cold hands often mean cold fingers, hard to get good groups when the trigger finger is like a block of ice.

[rambler]

Good shooting given the circumstances.

[rossman40]

Real good shooting! Proves you do not need those 350gr lawn darts for (at least midrange) hunting.

[alex]

Good report Dave, did you ever shoot a straight load of I4350? If so how did it compare?

[Deleted]

Nice shooting.

[Dave W]

Jan 30, 2016 15:42:49 GMT -5 alex said:

Good report Dave, did you ever shoot a straight load of I4350? If so how did it compare?

It was back in warmer temps. Velocity was lower than QL projections with 260 & 270gr bullets. A heavier bullet or tighter bullet fit may help with efficiency but I would rather stay with a lighter bullet with this gun and this choked Kreiger makes a tight fit impossible.

[schunter]

Nice shooting in those conditions. Was the second target also shot bare?

[Dave W]

Feb 1, 2016 8:49:22 GMT -5 schunter said:

Nice shooting in those conditions. Was the second target also shot bare?

Yes, bare bullet for both ratios.

[Savage Shooter]

Just a swag here but tend to think raising velocity a bit more might be in order. Using N110 under 4350 I would think 2,675-2,700 would be awful close to the right spot. Of course it was 28 degrees so that may be where your at already. Can see what speeds do as temps come up.

You for sure on the right bullet!

[Dave W]

Feb 1, 2016 13:43:56 GMT -5 Savage Shooter said:

Just a swag here but tend to think raising velocity a bit more might be in order. Using N110 under 4350 I would think 2,675-2,700 would be awful close to the right spot. Of course it was 28 degrees so that may be where your at already. Can see what speeds do as temps come up.

You for sure on the right bullet!

Estimating off of a 5/70 trace, think I am close to 49-50kpsi now with the 6/69.

[Savage Shooter]

You may be that high on pressure based on your speeds. Do you have trace with the 260 Accubond instead of the Partition. I have seen them be at completely different max loads before due to construction. Seeing you mention the Accubond is why I said that.

[Dave W]

Conflicting data. Guy shot both 260's, Nos. Part. & AB, with a large single. The NP was faster, which based on the design with the flat exposed lead base made sense to me. When I shot both on the same day with the 5/70 load, the AB averaged 2612fps, the NP averaged 2560fps. My data may be skewed though since I had sized the Partitions with his die a while back before my die had arrived. Even though the bullets load with similar resistance, the bullets sized with his die mic to a smaller diameter than the AB's sized in my die.

[Savage Shooter]

Yes I see what you mean. Depending on burn rate faster can mean more pressure and with a different bullet faster can actually be less pressure. Have loaded a truck load of both accubonds and partitions in several different centerfires and from caliber to caliber and bullet to bullet max can be different on the 2 bullets. Only reason i mentioned is that I don't know in the .375 which makes pressure quicker. I think back over the loads tested and would tend to think that in most loads the accubond can be pushed to higher speed than the partition but not always. I think the center solid section in the partition has more to do with pressures than lead base, and in most uses will build pressure a bit quicker than the AB. Your ES's coming down makes me think like you said, your on the right track.

Of course the solid center in the partition may be halting obturation and make less pressure than the AB.... what i do know is get this combo giving desired results and NOTHING on the planet can walk away from it, with either bullet.

[Dave W]

Adding this to show how much difference 1 grain of booster can make in this caliber. Different bullet also, but the same weight.

[rambler]

That's a pretty significant rise all things being equal.

[jims]

Pressure can be pretty significant on some of those smaller subcalibers.

[Dave W]

Took the 6/69 load out to 200yds yesterday. Temps were in the upper 30's, with very little wind,  started with a clean barrel since I had not cleaned it in awhile. Fouler and then 3 shots, tough to tell by the pic but shots 2 & 3 ended up in the same hole and they timed at identical speeds. I thought the hole enlarged some on the 3rd shot looking through the scope but had to walk down to verify that my eyes were not deceiving me and then checked the hole diameters with the calipers when I got home. Measured 1.015" ctc.

Compnents:
260gr Nosler Accubond
Fed 209A
No wad
6/69 N110/I4350
Timed: 2723-2729-2729fps  Avg-2726fps ES-6



The troublesome part is the speeds jumped up 143fps with only an approximate 20 degree temp change from the last time I shot this combo. Have seen worse temp related load sensitivity issues from other calibers and loads but the accuracy was never this good on those occasions.
Possible causes- faulty chrono readings, seating resistance change, temp sensitivity.
 
I had heard of bullet shrinkage from sub freezing temps so I checked it for myself. Took a sized bullet and put it in the freezer for an hour, checking it with a mic several times on all sides before and after being in the freezer. The bullet OD was .00005-.00015 smaller after being in the freezer. I had checked the bullet diameters with a mic prior to shooting this load on both occasions. We are talking about a small difference in diameter but the gun loaded much stiffer yesterday than it did in sub freezing temps.
 Whether it is a fouling issue or bullet diameter issue, I am not sure? What I do know is that seating resistance changed and even though the accuracy is good, I am not happy with the increase in speed over such a small temperature change window. If the chrony was giving accurate readings? Was overcast yesterday, chrony was shaded the last time I shot this load.

Need to see if TG will run a seating resistance change trace with this load and shoot it again to satisfy my curiosity.

Thoughts anyone?

[Savage Shooter]

Just guessing here but when I see velocities bounce up with tighter loads I reduce the loads energy potential, just a guess but the N110 in this smaller bore is prolly the driving factor. A slower booster may be in need. I suspected this from the traces above when 1 grain booster change entire load 30+psi/grain. I have found reasonable temp stability in the 600psi/grain range like where you are now. Load that is pressure sensitive (load tighter) will nearly always be temp sensitive too, so you got 2 factors moving speed around.

Would be worth trying H4198 as a booster instead just to see. Have always found H4350 to be both less pressure and temp sensitive as compared to I4350 also.

My first reaction is that N110 to fast a booster.

Just Thoughts

[Savage Shooter]

I noticed to that TG traced Varget at 70 grains. I would tend to think that 70 grain total is the upper end of charge weights for the .375 with 260gr bullet and Varget or RL15 fit this best. The more the total the more the "energy potential". I think that with load totals in the 65 - 70 grain range you will see this go away.

I prefer to tend toward more closely matched burn rates for duplexes now days as can get better temp stability. If I was building this load I would start with 60 grains of varget or RL15 then add H4198 under couple grains at a time keeping main the same to start. Goal velocity would be bout 2,625 to start and trace........ can prolly reach 2,650 +/- with lot better stability.

When feeling around in the dark I do 2 shot tests over chrony, one "tight" and one "loose". When pressure is built more from bullet weight and less from bullet fit you will see velocities in the normal es range i.e. 15-20fps. I intentionally under and slight oversize bullets for this instead of trying to make them perfect on size, will tell you all you need to know on the chrony!

Then you know that anything you can load by normal hand pressure on the ramrod will stay in your normal es's. Then test accuracy. I always stabilize load first. Remember in general less pressure sensitive will normally be less temp sensitive and may actually see loads that are just a tad faster when really cold (barrel tight). I see where TG's Steel/H4350 trace shows this very anomaly, most pressure and speed at colder temps...... it can be done.

[Dave W]

Don't think I have ran H4350 with the 260's but with a 270 HSP, it runs hotter than QL predicts. My chamber and the efficiency probably makes it a remote possibility for duplexing. For instance, if you look at TG's Steel/H4350 traces with a 260gr bullet, I am hitting comparable velocity with a single and a 270gr bullet. Guy has shot stout singles of that powder with a 260 AB and efficiency doesn't fall off, still runs hotter than predicted.
Had plans to try a mixture of 6/71, to see if it would smooth the raggedy curve of the 6/70, but the session got cut short. H4198 is an option, have pounds of it and no caliber to shoot it in.

[Deleted]

Nice shootin. Keep up the testing!!!

I need to see the backer

[Earnhardt]

I would have done 2.5 cartwheels for ya if all 3 were in the same hole at 200... But since you only put 2 in the same hole I'll just give you an "Atta boy"...

[Dave W]

Guessing the chrony had a bad day.
Warm weather brings the horde out plus I had to wait until late in the day for the sun to get off the field so I only got a couple shots off.
Started out with the 250 SBT and 6/69 N110/I4350 due to the pressure getting up there if the chrony was accurate and it was even warmer than last time I shot.
Timed-2695- cold fouled bore-2686-2682- Avg.-2688fps ES-13 @63* This was down approx. a 100fps from what 6/70 timed in the upper 30's.
CTC-.366" @100yds.

Tried to get a group in with the 260 AB but the chrony only picked up the first shot due to darkness and people wanted to pull targets and leave so I packed it in. The first shot timed 2642fps.

It appears the load has some  temp stability issues, maybe not as bad as I thought, hard to tell with the chrony readings.

[rambler]

Good shootin!

[subcalshooter]

Glad to see all your work and testing are paying off. Good shooting!

[Deleted]

Good shooting.