Please Help, chasing bullet lot variation?

[03machstock]

So I had a load worked out for my rifle, origin action, pva prefit 1:7t .223. Shooting 75gr eldm’s over 24.8gr of 2520. Was shooting good. I ran out of bullets so I ordered a bunch more that are from a different lot and the groups opened up to huge. 2 things changed. 1. The lot of bullets. The old ones measure .566 base to ogive. The new ones measure .576 base to ogive, so a .010” difference. 2. The brass from the old load was shot out of a rem 700 before this, full length resized, and loaded. The new loads were the same brass as before, but have then been shot through this gun and full length resized. Both loaded rounds were 1.988” base to ogive. So, do I reduce my charge, or seat my bullets out an additional .010”, or start over from the beginning? I have a shoot next weekend and a class the following week so I’m feeling anxious.

Top 2 on the left were the old combo, all the other groups are the new combo.

 

[straightshooter1]

So I had a load worked out for my rifle, origin action, pva prefit 1:7t .223. Shooting 75gr eldm’s over 24.8gr of 2520. Was shooting good. I ran out of bullets so I ordered a bunch more that are from a different lot and the groups opened up to huge. 2 things changed. 1. The lot of bullets. The old ones measure .566 base to ogive. The new ones measure .576 base to ogive, so a .010” difference. 2. The brass from the old load was shot out of a rem 700 before this, full length resized, and loaded. The new loads were the same brass as before, but have then been shot through this gun and full length resized. Both loaded rounds were 1.988” base to ogive. So, do I reduce my charge, or seat my bullets out an additional .010”, or start over from the beginning? I have a shoot next weekend and a class the following week so I’m feeling anxious.

Top 2 on the left were the old combo, all the other groups are the new combo.

For #1, this kind of difference in bullet's BTOs' between lots is common. I would NOT reduce the charge. Yes, I'd seat the bullets out an additional .010" (assuming the same correlation in BTO where your seating stem makes contact on the ogive AND you've got enough space to the lands). This way the base of your bullet should be pretty close to where your old lot was.

For #2, sounds like you've got a different number of firings on the two sets of brass. Keep in mind that every time you fire the brass and resize the brass, work hardening is taking place each time, which will change how the bullet is released. If you're combing brass with different number of firings, they're not going to be as consistent at brass with the same amount of firings. And to some extent, this is true even for brass that's of the same number of firings within the same lot and why people like myself will anneal brass after every firing to get them as uniform as possible.

 

[hafejd30]

If you don’t have a hornady OAL tool I’d get one. I find a certain bullet (Sierra smk for example) shoots best at .010” or .015” off the lands. So just loading a bullet like you have in your case may seat me into or close to the lands. Which can cause pressure issues

Instead of setting next lot to previous measurements I’d remeasure the distance to the lands with the new lot. Then set to load those .010” etc off or whatever your previous loads shot best at

After that I’d test on either side of your previous powder charge. Likely a chrono would show any serious variations in ES changing or just speed in general

 

[03machstock]

For #1, this kind of difference in bullet's BTOs' between lots is common. I would NOT reduce the charge. Yes, I'd seat the bullets out an additional .010" (assuming the same correlation in BTO where your seating stem makes contact on the ogive AND you've got enough space to the lands). This way the base of your bullet should be pretty close to where your old lot was.

For #2, sounds like you've got a different number of firings on the two sets of brass. Keep in mind that every time you fire the brass and resize the brass, work hardening is taking place each time, which will change how the bullet is released. If you're combing brass with different number of firings, they're not going to be as consistent at brass with the same amount of firings. And to some extent, this is true even for brass that's of the same number of firings within the same lot and why people like myself will anneal brass after every firing to get them as uniform as possible.

My brass prep is as follows.
1. I anneal on an annealeeze.
2. I dry tumble in either walnut or corn cob.
3. I lube the brass with the lanolin/alcohol spray.
4. Full length resize/ deprime on first stage in Redding full length sizing die with neck bushings. However, I just keep feeding them in and spinning the turret to let them land in the loaded cartridge tray so I’m not putting in and taking out every piece, just putting them in.
5. I trim/chamfer/deburr on a giraud case trimmer.
6. I put the cases in my ultrasonic cleaner out in the shop to take the lube off them. Still haven’t found the recipe for solution I like, might try boretech next, but I only really care about getting the lube off.
7. I blow the cases out with compressed air, and I’ll throw them in the oven at 150 for a few minutes if I want to load right away, but just let them dry normally if not.

I’ll try seating them out .010, thanks!

 

[03machstock]

If you don’t have a hornady OAL tool I’d get one. I find a certain bullet (Sierra smk for example) shoots best at .010” or .015” off the lands. So just loading a bullet like you have in your case may seat me into or close to the lands. Which can cause pressure issues

Instead of setting next lot to previous measurements I’d remeasure the distance to the lands with the new lot. Then set to load those .010” etc off or whatever your previous loads shot best at

After that I’d test on either side of your previous powder charge. Likely a chrono would show any serious variations in ES changing or just speed in general

I have a Hornady OAL tool, I didn’t think of remeasuring he new bullets in the barrel, I’ll do that, thanks!

 

[918v]

I would do plus .002”, .004”, .006”, etc and minus the same increments from your current setting. And then buy in bulk from the same lot.

Plus .010” from the current setting means your seating depth is the same. But that doesn’t mean it’s jumping .010” closer. That is an assumption people make that is often wrong because your comparator doesn’t contact your bullet in the same way your rifling does.

 

[03machstock]

So, my old bullets measured .566 base to ogive of the bullet, 2.003 base to ogive to the lands. My new bullets measure .576 base to ogive of the bullet, 2.023 base to ogive to the lands. So the bullets are .010” different, but the base to ogive to the lands is .020” different. So maby I’ll load some up same charge, .010 longer, and .020 longer. Any other ideas welcome but thank you guys for everything so far!

 

[nn8734]

So, my old bullets measured .566 base to ogive of the bullet, 2.003 base to ogive to the lands. My new bullets measure .576 base to ogive of the bullet, 2.023 base to ogive to the lands. So the bullets are .010” different, but the base to ogive to the lands is .020” different. So maby I’ll load some up same charge, .010 longer, and .020 longer. Any other ideas welcome but thank you guys for everything so far!

How close is your current charge weight to your overpresure threshold charge weight?

If you have some room before hitting pressure, up your charge weight a little (.3-.4g more) if those other adjustments dont bear fruit. If you're up against it, drop by .3-.4g... You're using one of the best powders for 5.56 out there and may have a little room to increase the charge before you hit overpressure.

Otherwise I agree with varying your current seating depth at .010 increments (two or three 3-shot groups per seating depth change is sufficient to get a prelim read on things). Go .020 deeper also, unless you've already tried that.

Hopefully you'll solve the problem with one of those test groups.

 

[03machstock]

How close is your current charge weight to your overpresure threshold charge weight?

If you have some room before hitting pressure, up your charge weight a little (.3-.4g more) if those other adjustments dont bear fruit. If you're up against it, drop by .3-.4g... You're using one of the best powders for 5.56 out there and may have a little room to increase the charge before you hit overpressure.

Otherwise I agree with varying your current seating depth at .010 increments (two or three 3-shot groups per seating depth change is sufficient to get a prelim read on things). Go .020 deeper also, unless you've already tried that.

Hopefully you'll solve the problem with one of those test groups.

I’ve got plenty of room to go pressure wise, no pressure signs yet and I tried up to 25.2 grains, 24.8 just yielded better accuracy. I’ll load up some with a few tenths more as well. Thanks!

 

[nn8734]

I’ve got plenty of room to go pressure wise, no pressure signs yet and I tried up to 25.2 grains, 24.8 just yielded better accuracy. I’ll load up some with a few tenths more as well. Thanks!

Try the seating depth tests first. Ideally that will fix it before you have to tweak the charge weight.

FWIW, all my carbines and mk12 mod 1 consistently print their tightest groups at 24.8-25.1 g (I use the exact same 2520-based load using the 77smk, loaded on the same equipement via the same process for all of them).

 

[MarshallDodge]

Some say the 75 ELD is easy to tune but I have had to play with the OAL a little more to get them to shoot. Typically between 10 to 20 thousands off the lands.

 

[03machstock]

So the first string of shots today showed no hope. I tightened up the action screws a little bit and group C tightened up some, not sure if that’s why. I’ll re load c again, and go out another .010” and try that as well as going the same in. A was .010” out from my old bullets load, B was .020” out from my old bullets load, and C was .020” out, with the charge increased from 24.8 to 25.2. (B and C are .015” off lands, which is where my old bullets shot good).

 

[03machstock]

Any ideas @bohem ? I know the gun will shoot, ever see anything like this?

 

[918v]

Your coal increments are too large.

 

[03machstock]

Your coal increments are too large.

I just loaded up some .002 .004 .006 .008 .010, .012 plus and minus of my “C” load above, I’ll shoot them tomorrow and report back.

 

[MakeSawdust]

Load development is very over blown. I doubt the different bullet length caused the issue. Probably either a different issue with the bullet (maybe diameter small, or cores are shit with voids, etc) or an issue with gun or optic.

I would guess the problem is something wrong with gun (i.e. mechanical or something loose), a problem with the optic or mounts, or the new lot of bullets is shit. I have never seen a good gun shoot bad with Lapua brass, a good powder, and Berger bullets. I can literally pick a speed and shoot. As long as it is not over pressure a 223 is going to shoot that brass and bullet with say 4895, varget, or xbr into 3/8" to 1/2" at 100 yards for 5 shots. Pretty much all reasonable charge weights and a jump that is .040" or larger will do that. Also, just touching the lands seems to shoot damn good in everything as well.

It is rare for load development to take a 2 moa load and make it a 1/2 moa load unless the 2 moa load is over pressure or very low pressure (case not sealing chamber right away). I will say, I had a coyote/whitetail gun I wanted to shoot Hornady 105 bthp out of. Same gunsmith as usual, known good powder, bartlein blank, Peterson brass. After a bunch of fucking around I had a 3/4 moa gun at 450 yards, and I was pissed. I called the gunsmith and asked what I was doing wrong. He said stop shooting hornady. I'm a stubborn ass, so I sorted all the Hornady bullets by oal into lots of .002". Like magic I turned it into a .5 moa gun at 450 yards for 5 shots. I shot 6 5 shot groups to confirm. Largest was right at 2.375" with some running under 2".

There is a reason benchrest shooters like to use custom bullets. I would check scope rail, rings, and scope for problems, check the bore with a borescope, check for bedding issues, and test again. If they are still shooting like that I would be making a call to Hornady.

When I want cheap bullets I have found that sorting the hornady bthp match bullets by oal will usually shoot well. When I want to shoot sub 1/2 moa for 10 shot groups, you guessed it, berger or custom bullets.

I will give sierra a little credit and say that I have ok luck with them, but not as good as Berger. Hornady has been very hit and miss.

 

[Haney]

Load development is very over blown. I doubt the different bullet length caused the issue. Probably either a different issue with the bullet (maybe diameter small, or cores are shit with voids, etc) or an issue with gun or optic.

I would guess the problem is something wrong with gun (i.e. mechanical or something loose), a problem with the optic or mounts, or the new lot of bullets is shit. I have never seen a good gun shoot bad with Lapua brass, a good powder, and Berger bullets. I can literally pick a speed and shoot. As long as it is not over pressure a 223 is going to shoot that brass and bullet with say 4895, varget, or xbr into 3/8" to 1/2" at 100 yards for 5 shots. Pretty much all reasonable charge weights and a jump that is .040" or larger will do that. Also, just touching the lands seems to shoot damn good in everything as well.

It is rare for load development to take a 2 moa load and make it a 1/2 moa load unless the 2 moa load is over pressure or very low pressure (case not sealing chamber right away). I will say, I had a coyote/whitetail gun I wanted to shoot Hornady 105 bthp out of. Same gunsmith as usual, known good powder, bartlein blank, Peterson brass. After a bunch of fucking around I had a 3/4 moa gun at 450 yards, and I was pissed. I called the gunsmith and asked what I was doing wrong. He said stop shooting hornady. I'm a stubborn ass, so I sorted all the Hornady bullets by oal into lots of .002". Like magic I turned it into a .5 moa gun at 450 yards for 5 shots. I shot 6 5 shot groups to confirm. Largest was right at 2.375" with some running under 2".

There is a reason benchrest shooters like to use custom bullets. I would check scope rail, rings, and scope for problems, check the bore with a borescope, check for bedding issues, and test again. If they are still shooting like that I would be making a call to Hornady.

When I want cheap bullets I have found that sorting the hornady bthp match bullets by oal will usually shoot well. When I want to shoot sub 1/2 moa for 10 shot groups, you guessed it, berger or custom bullets.

I will give sierra a little credit and say that I have ok luck with them, but not as good as Berger. Hornady has been very hit and miss.

"Load development is very over blown. I doubt the different bullet length caused the issue. Probably either a different issue with the bullet (maybe diameter small, or cores are shit with voids, etc) or an issue with gun or optic."...

Overblown ? What a joke . And then you go on talking like a rookie even more .

 

[03machstock]

I just loaded up some .002 .004 .006 .008 .010, .012 plus and minus of my “C” load above, I’ll shoot them tomorrow and report back.

Results are less than promising.

 

[918v]

Try again using the original power charge that shot good with the old lot of bullets.

 

[Tmm01]

Results are less than promising.

.002 jumps are too small to see anything worthwhile, and at the end of the day are you going to chase the lands to keep it in tune? Being a .223 it would be more of a stroll after the lands . I would jump those bullets starting at 20 thou and 40 thou off the lands with your original powder charge and see what you get, the 75gr eldms like to jump.

I edited my suggestion on the jump recommendation's, I still can't find my old notes, but remember they have a limited amount of bearing surface. I would see what you can get away with.

 

[MakeSawdust]

Try again using the original power charge that shot good with the old lot of bullets.

^^^THIS. If it goes back to shooting call Hornady and ask for a better lot of bullets. Hornady elds aren't garbage, but they aren't premium either.

 

[Haney]

Start from scratch like this never happened .

Try again using the original power charge that shot good with the old lot of bullets.

Your advice wastes time and money . It;s been proven already .

 

[918v]

Start from scratch like this never happened .

Your advice wastes time and money . It;s been proven already .

You are a waste of organic material.

Whenever I change lots of bullets I keep the same charge weight and adjust the coal in small increments. I always get the accuracy back that way.

So fuck off.

 

[03machstock]

Ok guys, ended up playing around with seating depth with no luck, did a down and dirty ocw test, found one that actually shot decent, it infact shot decent with the original bullets too. Original seating depth. It’s a slower charge that’s why I picked the faster one last time around, but the new bullets won’t shoot for shit with the higher charge. A is a different seating depth, ignore it. B is the new load with new bullets, slow, but it will get me through the week until I can do another proper load development with other powders. And I had some of my good loads still loaded up with my old bullets which is C, just to make sure I wasn’t crazy haha. Don’t pay attention to the poi, I was playing with my elevation knob between groups. Thanks for all the help!