Help me explain this ???

The loss of velocity can be because the little 55 grain bullet doesn't have enough bearing surface to hold back the pressure. A buddy and I both have 24 inch Valkyrie's. Mine is 250 FPS slower than his with the same round but still accurate. A lower charge with a 50 grain bullet out of it is faster than a 40 grain bullet with a higher powder charge. Pressure is escaping past the 40 grain bullet because of a loose bore and smaller bearing surface but still accurate.
 
Finding Jam Length ... I use two differing methods
1. I will use a dummy cartridge seated long then working in length shorter checking with the bolt handle NOTE grease the bullet ogive to prevent sticking it in the bore each time you put the dummy in. Once the bolt closes take the dummy out and measure again don't forget to subtract your 3 or 5 thousand when setting the depth

2. in my AR's or gas guns I'll put just the bullet in the bore and use some thing small enough to gently push the bullet into contact hold it and insert a cleaning rod to find the ogive (usually a proper jag that has the tip broken giving me a flat surface) touch the bullet mark on cleaning rod which I've got a section of masking tape with a pencil concentric to the muzzle. Now remove the bullet from the bore close the bolt insert cleaning rod again until contact with bore face. take it out now measure the two marks now you have length subtract 3,4,5,10 thousands. now play with your loads.

Usually my first set is to find the upper limit using a ladder some like to go 0.5grs increments, personally I use 0.3gr increments. once you see pressure or a hard bolt lift STOP that is redline your hottest load. subtract 0.3 or 0.5grs from that and make up your desired test in 3 or 5 shot groups or Shoot a ladder test.

What I have listed is NOT the only ways others will chime in ... with another method ... I'm just stating my method
 
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Here I have just barely seated a 69gr into a 6mm CM case... I used the same lube aka grease that I use to lube my cases to prevent the bullet from sticking.
In this case I didn't need to seat deeper and the bolt handle actually "cammed" over (slight resistance, thus moving the bullet into the non primered non loaded case)


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Here using a bullet comparator I'm measuring the JAM length or where the bullet contact in the bore. 2.2425" subtract for my desired jump be that 0.005 or 0.010" that is your start point .... Most refer to this as a CBTO (Cartridge Base To Ogive) if I measure from bullet tip to base in my case it's 2.7145" that is the C.O.A.L which I would use the same method subtract 5 or 10 thousands to avoid being into the throat or lands thus establishing my length to start at.

so that said I would set my loads to test at 2.2375" (5 thou off jam) or say 2.2325" (10 thou from jam) CBTO.
For COAL say a 5 thou off jam = 2.7095" or a 10 thou you guessed it 2.7045"
I like using 10 thou math is easy in my head using that method

HTH

(call it luck I JUST got done earlier setting and headspacing this 6mm CM barrel into the action today so yeah this simple tutorial was to my benefit as well, as I planned on shooting the 69gr Barnes match burner flat base which while heavier will be sort of close in length to your 55gr boat tails. BT are always longer than a FB)

Note in this I do not call this to the lands ... simply because I don't know for a fact that it's truly the lands that is making contact all I know it's something in the throat that has made contact. This is why I say "jam" I have jammed into something ....
 
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I have a tool made by an old member/mod that was on here years back (RagnCajun). Basically a rod with 2 discs that slide on the rod and have set screws to lock them in place. Slide the rod down the bore from the muzzle end till resting on the bolt face. Slide discs down to the muzzle and tighten set screws. Remove rod and bolt. Insert bullet to be used into the chamber and hold in place with a pencil or dowel. Insert rod in bore till it touches the nose of the bullet. Loosen the set screw on the disk closest to the muzzle. Slide it down the rod to rest on the muzzle and re tighten set screw.
Measure between the discs to get the coal.
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Hm1996 sent me a tool similar and it works well easy and fast.
and yes sir @crapshoot that is right there with my second method pretty much same principal, actually yours is a neat setup

But I figured to show a method that didn't involve obtaining tools except what most have on the bench
 
Sgt_Mike said:
View attachment 28053

Here I have just barely seated a 69gr into a 6mm CM case... I used the same lube aka grease that I use to lube my cases to prevent the bullet from sticking.
In this case I didn't need to seat deeper and the bolt handle actually "cammed" over (slight resistance, thus moving the bullet into the non primered non loaded case)


View attachment 28054

Here using a bullet comparator I'm measuring the JAM length or where the bullet contact in the bore. 2.2425" subtract for my desired jump be that 0.005 or 0.010" that is your start point .... Most refer to this as a CBTO (Cartridge Base To Ogive) if I measure from bullet tip to base in my case it's 2.7145" that is the C.O.A.L which I would use the same method subtract 5 or 10 thousands to avoid being into the throat or lands thus establishing my length to start at.

so that said I would set my loads to test at 2.2375" (5 thou off jam) or say 2.2325" (10 thou from jam) CBTO.
For COAL say a 5 thou off jam = 2.7095" or a 10 thou you guessed it 2.7045"
I like using 10 thou math is easy in my head using that method

HTH

(call it luck I JUST got done earlier setting and headspacing this 6mm CM barrel into the action today so yeah this simple tutorial was to my benefit as well, as I planned on shooting the 69gr Barnes match burner flat base which while heavier will be sort of close in length to your 55gr boat tails. BT are always longer than a FB)

Note in this I do not call this to the lands ... simply because I don't know for a fact that it's truly the lands that is making contact all I know it's something in the throat that has made contact. This is why I say "jam" I have jammed into something ....
Click to expand...
This is genius im going to give this a try for sure
 
LOL the method I showed is over a hundred years old, the only add on was using the comparator vs using just calipers measuring COAL.

There are tricks to full length sizing as well to prevent over working your brass.

ES and SD can be very useful if the sample size is large enough, If I recall the Athlon allows you to set for a certain rifle and load and as such you could run one load validating it over time and hit the desired 30 plus shots and have useful data to show the average velocity for your rifle and your load. As well as Extreme spread and Std Dev.
Plant one is a proponent of the ES and SD method in load development, I'm positive he will glad to assist you if you want to use that method.

New barrels shoot slower than the same barrel with say 50 to 100 rounds so the rule of thumb is new they will speed up level off then as they start to wear out will start slowing down again. Again just a rule of thumb, a guide not set in stone. some (actually most) will retain accuracy for a while then the bottom will fall out. Honestly don't get hung up on velocity. Sure we all want to shoot as fast as we can, and as accurate as we can. But speed won't help you until you can connect with the target.

All of the members that have responded to you in your thread are very versed in loading and development all you have to do is ask they will be more than happy to assist you.
Heck I ask them questions sometimes....
 
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All this "lands measuring" info is good knowledge to have, but I doubt it's going to help the OP much in this particular case. He's shooting a 55 grain (very short) 6mm bullet out of a 6 Creedmoor, which is by default throated for long bullets. I would guess when touching the lands, the bullet will be nearly out of the case.
I have several rifle / bullet combos like this, in which case I try to seat the bullet to where the top of the boattail is at the neck/shoulder junction, and go from there.
 
Since it appears we are working with a hunting rifle, shooting jam loads is asking for a field problem. Extracting an unfired round and the bullet remains in the bore(and powder is dumped into the action). You want to know TOUCH and than seat test away from that. Typically I start testing 0.015 to 0.020 off touch for hunting rifles. Loading non lead(like a Barnes or Hammer bullet) you will likely be starting 0.050 off touch. Also something pretty common when load testing-- group size can go in and out a couple times as you change powder charge weights, seating depth. Your goal is a load that is tuned to the harmonics of your specific barrel.
 
Sgt_Mike said:
Bingo!!!! no truer words spoken ... to actually get something a Minimum of 30 shots is required for ES and SD to almost be a indicator, more shots are better.
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ES and SD do matter at smaller group counts - just like starting accuracy testing in load developement counts when using only 3 shot groups for initial load developement.

how you ask? because everyone knows "the sample size is just too small with only 3 shots"

eric cortina pointed this out why 3 shot groups and data are actually valid starting data points, and i paraphrase

if the group doesnt meet our accuracy demands at 3 rounds, adding more rounds to the group isnt going to shrink it. we can throw that test powder charge out from testing right now. just like ES, and most of the time SD. especially with the numbers OP was getting.

so if you have a 3 round group thats 2 MOA but we're looking for ½ moa accuracy - you can add 400000000 shots to that same dataset, and you're never gonna get BELOW 2 moa. Same goes for ES - if youve got an ES of 100 (just to throw a number at it) with 3 rounds... adding 40 more test rounds to the data set, or even 400 more is never going to shrink that ES.

you can clean up SD by making your dataset larger - but how much?

in this example from the OP, with the SD being as bad as 120... you might be able to shrink the sd to what? 70? 60? maybe even 50? still way bigger than most of us are going to be comfortable with for an accuracy based load

lets be serious.. most of us want SD's in the single digits and ES no more than in the mid to high teens...



so discounting the data "just because its 3 shots" is silly. 3 shots in a load testing ladder that give BAD data should be thrown out and eliminated from further testing.

its the 3 rounds that give amazing data - regardless if thats accuracy, ES or SD.. or even all 3 - that we need to go back and test further with larger sample sizes.

thats what step two of starting to prove your load test by doing - just as an example - 3x 5 rounds groups with that next test load that shot great at 3 shots and starting to average the data from those 3 groups to give us a better idea of the true cone of accuracy of that specific load combo.
 
Im making a move away from the 55 grain and going to go with a heavier bullet, i learned alot from trying to turn my 6mm creeedmoor into 22-250 proformance . Its just not meant for that . Im going to load some 80 grainers and go from there . I can not seat that little 55 grainer out for enough to get the velocity I was hoping . I will specify so i dont get killed on here !! Accuracy is my first priority . I was trying to achieve speed as well , i liked the idea of shooting a 55 grain at almost 4000 fps something the 22-250 can't quite achieve . I can with a 50 grainer in a 22-250 but not a 55 grain , but now understanding i probably should have bought a 243 instead . Well I learned alot and know that I need to focus on what the cartridge was designed for the heavy longer bullets .
 
With the influx of new cartridges and specific barrel characterists designed for them(part of marketing) it seems fairly common for shooters to experiment. Big selling points have been heavy, high bc bullets for caliber. These often are for long range steel games(also when consistent minimum velocity spreads are important). Actual hunting ammo is still purpose based, type of animal tends to dictate the bullet and to lesser extent distance to target. The information shared is based on personal experience, but experiences vary greatly. Your chronograph is an important part of safely reloading ammo, continue to use it as you continue load development. Very important to know if you have a hot, average or below average powder lot.
 
Plant.One said:
lets be serious.. most of us want SD's in the single digits and ES no more than in the mid to high teens..
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Agreed, not saying that ES and SD can't be good data points for repeatability sake, a accumulative data set of say 30 rounds is usually a good point to have confidence in the data.
Understand I'm not advocating shooting a bad load. say I'm working a load up , my intent is to shot five shot groups. The first three shots plant on target at a MOA far exceeding my desire. I'll stop and check the equipment to ensure the rifle and equipment are ok. if so I'll abandon the load immediately. But the ES and SD are not what causes me to abandon the load. It's the group size, it could have a small ES and SD.

But to evaluate a load solely on the ES and SD, yet the dispersion (group) presented on target is greater than desired. Yeah not a way to proceed imho.

It makes perfect sense for the deviation of shot to shot to be as small as possible for accuracy especially at beyond say 300 yards. The larger the sample size the better data set for average velocity , ES, and SD is available.
The chronograph is a invaluable tool to get a load settled quicker than without. So no I'm not advocating abandoning it.

@Plant.One yes sir I tend to listen to Eric Cortina when he releases a new reloading video. It is hard to ignore a world champion F-Class shooter when they are sharing their methods. But the groups size (dispersion) rule the data sets, one can lower the ES and SD with various methods neck tension, primer type to name a few.

The reason I sounds so anti ES SD is Not the OP or on this Forum I've seen those whom advocate solely on the ES and SD ignoring the dispersion presented on target. Let me be clear YOU are NOT one of those types we, you and I have discussed too much in the past for me to think that.
I don't discount the value of the SD or ES, but place a higher focus on the group sizes when it repeats it self. Key word is repeatability. one of the secerts of the data set is to keep accumulating the data when you shoot that load. The chronograph that the OP has that ability IIRC he can set up his to just that rifle and load return and add dat to the calculation.

I have my reason I've pretty much discarded the three shot group, and went to the 5 to 10. But if someone is totally sold on three so be it, ha ha I actually recall the gun writer and the article whom basically started this three shot group for evaluation. He stated simply "I can tell how a express rifle will preform in three shots" . Note he didn't say he could determine the true accuracy of his gear, simply said he could evaluate how his first three shots would perform with that rifle. He was a Big Game hunter whom wrote for a gun rag, before the actual internet came into common usage.

Bottom Line is You, and I don't disagree, I'm merely cautioning against letting ES and SD rule the roost. Simply because those values can be lowered by larger data collection sizes, neck tension, primer selection (LR vs SR) and the list goes on.

I was actually hoping that you would pop in here to guide the OP through what the ES and SD actually mean, and how to use it effectively.
After all at one time most thought only ES was the answer, now we are chasing both ES and SD.
 
SupressYourself said:
All this "lands measuring" info is good knowledge to have, but I doubt it's going to help the OP much in this particular case. He's shooting a 55 grain (very short) 6mm bullet out of a 6 Creedmoor, which is by default throated for long bullets. I would guess when touching the lands, the bullet will be nearly out of the case.
I have several rifle / bullet combos like this, in which case I try to seat the bullet to where the top of the boattail is at the neck/shoulder junction, and go from there.
Click to expand...

Very true in many respects can't argue with your observations.
The nosler 55gr bt should be about 0.787" per JBM Ballistic bullet data set.
The Barnes 69grs Match Burners I used are about 0.842" again per JBM. (0.055" longer)
I did use a 6mm CM barreled action in order to be as close to apples to apples as possible. I also chose the bullet that was as close as I had on hand in length. Not exactly a perfect example, but because ogive profile differ so much between bullet makers, he may or may not make contact. Change bullets and because of the ogive profile may make contact.

The direction that the OP is going is the way I want to go once I get that action stocked.
Now will I have to select a different length/ weight probably maybe. The 85gr sierra Match King does have a rounder more proud ogive profile which like will make contact allowing it to be place deeper in the neck IDK (this last part is for my thought on selection the OP may have no interest in that combo).
 
But wouldnt that data change with different ambient temp and barometric pressure?
And as far as that feature on the Athelon, i haven't figured out how to do it on mine. But im not one who reads manuals. A lot of the time i just FAFO.
 
I don't have the Athelon, however did use one, a gent was kind enough to allow. As well as the Garmin I liked both of them.
Decades ago My shooting chrony had a fatal for it accident long story involving my son... I wound up recently with a labradar gifted to me. Not as slick as the pervious mentioned Chronograph's (Garmin & Athelon). But will work for now.
On the weather changes yes I think it would, and in my simpleton mind would be true data set than just 1 session. Which I'm sure no one on here is actually doing that, rather collecting data over time.
I guess now is a good time to test my thoughts on that, now that I have the labradar which is better than the shooting chrony I had.

(note to self I need to quit posting on this thread, The OP has hit his determination. Which should end it.)
 
Your targets don't mean all that much with respect to diagnosing the issues. The two things that absolutely scream for your attention should be the huge ES and the soot on the outside of the neck and shoulder of your cases. Those are two dead give aways for low pressure, inefficient loads. The soot is from the low pressure not expanding the case necks not expanding quickly enough to seal the chamber. That allows the blow back that you are seeing on the cases. The big ES is the result of inefficient powder burn. Load single cases with increasing powder until you run into a sign of pressure. Somewhere along that progression you will see the soot go away on your cases. Test that load for ES and I'd make a bet your chronograph numbers will have improved significantly.
 
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