Trying to lower ES in .260 AI

[codyadams]

I have a .260 AI, 30" Krieger 1in8 barrel, using Berger 140 VLD's and H-4831sc. I'm using CCI 200 Standard Large Rifle primers and formed Lapua brass. I have loaded from 47.5 grains up to 49 grains in .3 grain increments, and the ES never improved. My most accurate load is 47.8 grains going an average of 2,980 fps, at 100 yards it shoots in the .1"-.2", but my ES hangs around 25 fps for 10 shot strings.

Every charge is weighed, CBTO is very consistent, everything about this load is very consistent accept the extreme velocity spread. My first thought is to try a different primer, and if that doesn't work I may try different powders, thinking IMR 7828, Reloader 19 or 22, or maybe Win. 780 Supreme. Any suggestions on what to try? Anyone else ran into this issue? Any help would be appreciated, My 2 goat tags and deer and elk tags are creeping up!! Thanks all!!

 

[J E Custom]

I have a .260 AI, 30" Krieger 1in8 barrel, using Berger 140 VLD's and H-4831sc. I'm using CCI 200 Standard Large Rifle primers and formed Lapua brass. I have loaded from 47.5 grains up to 49 grains in .3 grain increments, and the ES never improved. My most accurate load is 47.8 grains going an average of 2,980 fps, at 100 yards it shoots in the .1"-.2", but my ES hangs around 25 fps for 10 shot strings.

Every charge is weighed, CBTO is very consistent, everything about this load is very consistent accept the extreme velocity spread. My first thought is to try a different primer, and if that doesn't work I may try different powders, thinking IMR 7828, Reloader 19 or 22, or maybe Win. 780 Supreme. Any suggestions on what to try? Anyone else ran into this issue? Any help would be appreciated, My 2 goat tags and deer and elk tags are creeping up!! Thanks all!!

I use all types and brands of primers, and have the best SDs in the 308 class of cartridges using the
CCI BR2 primers and the best accuracy .053 5 shot group in a 7/08. the next best group was/is
.074 using Rem 9 1/2 Lg rifle primers.

The same load was used and velocity was almost exactly the same, the only difference was the improvement in SDs and group size. the SDs dropped from 14 to 09. not much but enough to
cause me to switch to the CCI BR2 primer.

SDs are normally effected most by the powder burn rate and the primer Brisance and the best combination of both, so you also may have to change powders.

It would be worth a try.

J E CUSTOM

 

[dsculley]

So you have a quandary, do I believe my chronograph or my target? Personally, if I were shooting .1 " to .2" 10 shot groups consistently I would not care what my chronograph said. Sounds like it is time to stretch its legs and see how it performs at distance. If it shoots that well at 100 yds, it should shoot well at distance.

Just for fun, if you can set up a target at 100 yds made of paper, with another target set up at 200 or 300 yds that the bullet will pass through you will get your answer. If it is shooting in the 2's at 100 you will find the groups on the longer target to be in the 2's as well.

Another good method to test them is set up a target at longer range, say 400-600 yds, that you will use as an aim point and then set up the 100 yd target in bullet's path so you can compare these targets as well. If your groups open up when shooting at the longer range, they will open up on the 100 yd target as well.

I would look at the raw data on my strings as well. List them out then sort them by string/velocity. A spreadsheet is handy for this. Are the velocities equally distributed, or do you have a clump with a smaller ES with 1 or 2 outliers? What is your Standard Deviation? It is a much better indicator as to what is going on. (By the way, 6 X SD will give you the true ES to be expected over the life of your barrel with this load.)

If the chronograph data is correct, you must be on a good, wide node. That is a good thing as minor inconsistencies in your loads won't show up on the target, which is what you are seeing now.

FWIW

 

[bigngreen]

Put it on paper at as far a distance as you can shoot well, this will tell you how your vertical is. Try changing the neck tension, this just tweaks the starting pressure of the load enough to really effect ES.

 

[Mikecr]

You didn't mention your sizing, or preps completed, or that brass is fully fire-formed or not.
There are potentials in these.
Not suggesting a 'problem' but it's hard to advise without this information.

 

[Corey Schwanz]

If you have a load that is consistently .1-.2" on a regular basis (not just a 1-time thing), I'd definitely start shooting it longer distances to see how it looks. The chrono may not be giving you the perfect numbers, but if that's how the target looks....

Stretch it out some and see if the larger ES starts to show at all.

 

[codyadams]

Brass was fire formed with a starting load of varget and 100 gr. Amax, and is being fired for the 3rd time while collecting this data, so brass is well formed. Brass was not trimmed, as it is still slightly under the trim to length on 3rd firing, but all measures within .002" in length. It has only been neck sized. My Redding sizer gives .0018" of neck tension, just under .002" and seems very consistent. I measured 10 rounds before and after seating and they were all exactly the same, so I didn't bother measuring anymore. My brass is not neck turned and I don't have a neck turning tool. Load is .005" off lands, which is where it shot the best when seating from there to .120" jump.

 

[codyadams]

If you have a load that is consistently .1-.2" on a regular basis (not just a 1-time thing), I'd definitely start shooting it longer distances to see how it looks. The chrono may not be giving you the perfect numbers, but if that's how the target looks....

Stretch it out some and see if the larger ES starts to show at all.

For some reason I didn't really think about that....I got caught up in the numbers getting frustrated with it, and I didn't think about the real world results I'm getting. I never thought about the fact that my chronograph might not be giving the correct numbers....

The attached group is from 1,325 yards that I got yesterday...This wouldn't be possible with 25 fps ES would it?

 

[scottishkat]

It's altogether to easy to start nit picking the accuracy we're getting with the 260 AI, 6.5x284 and 260 or 6.5 CM for that matter. An ES of 25 over 10 shots does not seem alarming.

I agree with the shoot it at long range crowd. But you really might end up doing some serious hair splitting if your not shooting bench rest. Neck turning sorting brass all these are going to be contributing factors to this issue. Try the rem 9.5 or BR2 or the 210m primer the CCI 200 would not be my first choice for the 260AI.

Terry Cross is using 210M primers. I would say try that or the CCI BR2 first.

Terry's Tactical Two-Sixty AI

I certainly would not be worried about your results for hunting to 6 or 700 and I don't think I would consider a shot on a mountain goat past 500.

Good luck and shoot straight

Bob

 

[codyadams]

I don't think I would consider a shot on a mountain goat past 500.

Bob

I wish I had a mountain goat tag, I meant antelope tag ha ha

 

[dsculley]

Like I said before, you gonna believe your target or your chronograph? With shots/groups like you posted I would stop worrying about ES or SD and just shoot!

We all get caught up in the numbers sometimes but targets don't lie. I will always trust my target over my chronograph. If a load shoots like that, who really cares what the chronograph says. Remember, the chronograph is just an estimation and can be affected by external factors unrelated to your load.

FWIW

 

[Greyfox]

For some reason I didn't really think about that....I got caught up in the numbers getting frustrated with it, and I didn't think about the real world results I'm getting. I never thought about the fact that my chronograph might not be giving the correct numbers....

The attached group is from 1,325 yards that I got yesterday...This wouldn't be possible with 25 fps ES would it?

Between your group size and results at long range I would say you needn't be concerned about the ES you are getting from your chrono. You didn't mention what type of chronograph you are using, but I have had similar issues with ES using optical chronographs. My groups at short and long range were perfect but my ES was very high using mu Oehler 35. This was with my 6.5x284 using Berger !40 VLD's. When I switched to !40 JLK VLD's my ES dropped to under 8 FPS. The shooting results were just about identical at short and long range though. The notable difference between the two was the dull finish on the JLK"s as compared to the high polish on the Bergers. Thinking that this could be the cause, I dulled the Bergers with a Sharpie. My ES decreased dramatically. I think the ES variation was due to the glint of the shiny surface of the Bergers effecting the readings. I have since upgraded my chrono to a Magneto Speed, and more recently a LabRadar and have not experienced this issue.
I'm not sure this is your issue, but for those using optical chronographs it may be something to keep an eye on.

 

[codyadams]

I Have a chrony f1, so like the cheapest one you can get ha ha. I did notice something about the sharpie though, I had 3 of them that were scribbled on with it that I used to double check that I was close to the lands in conjunction with my sinclair OAL gauge, and when I was shooting at 810 yards I was shooting some nice groups, but when I shot the ones with sharpie on them they hit about a full minute low, made a nice little group but we're significantly lower from my other groups. Just thought that was interesting

 

[Pdvdh]

Wrong color sharpie. Black hits low, green hits right on, red hits high. Kidding of course...

Throw your Chrony F1 away, and you'll likely sleep better.