New 6mm Advanced Rifle Cartridge

lennyo3034

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How much shoulder bump is everyone using for their gas guns? I started loading today and started with the headspace comparitor. Using the B .350" bushing:

Factory Ammo: 1.184"
Once fired factory brass: 1.191"

Does .007" growth seem high? It's out of a gas gun so I'm expecting it to stretch a little more.

I just resized the brass to 1.189" for a .002" shoulder bump, but I'm wondering if that's too little. Being a gas gun the case stretches a bit during extraction so the measured 1.191" may not be representative of actual chamber dimensions.
 

eddie102870

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most say .003-.004 for gas guns from what ive read, have you tried any through the gun with the .002 bump?
 

GONE BAD

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I just resized mine today. New brass .007 shorter than once fired. Bumped back .002 and chambered fine. New brass my not have fire fromed to chamber (.001 spring back). I'll load these up and see how it goes.
Didn't anneal this time as it was easy to bump back. I'll anneal next firing. Brass being as hard to come by, I don't want to over work it! Probably got to make this batch last till sleepy joe gets out of office !😱
I'll run loads just hot enough to allow the rifle cycle properly at this point in time 🙃
 

LRRPF52

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How much shoulder bump is everyone using for their gas guns? I started loading today and started with the headspace comparitor. Using the B .350" bushing:

Factory Ammo: 1.184"
Once fired factory brass: 1.191"

Does .007" growth seem high? It's out of a gas gun so I'm expecting it to stretch a little more.

I just resized the brass to 1.189" for a .002" shoulder bump, but I'm wondering if that's too little. Being a gas gun the case stretches a bit during extraction so the measured 1.191" may not be representative of actual chamber dimensions.
I’ve found most factory ammo to be undersized relative to base-to-shoulder datum as a rule so it will run in a wide range of chambers.

So yes, you’ll typically see a lot of shoulder growth upon firing. You don’t have to re-size to that short factory dimension though.

I use a stripped bolt with the same face depth and lug lengths to determine how far I need to move my shoulders back, along with the Stoney Point/Hornady headspace gauge set. When setting up my sizing die, I incrementally turn the die down until I get reliable bolt lock-up with the stripped bolt in the chamber I’m loading for.

For those that are trying to make sense of what we’re talking about, we’re measuring the distance from the base of the cartridge/case to a middle point on the shoulder as a way to set headspace. Too long...and it won’t chamber. Too short with repeated re-sizing to that length, and you over-work your brass, which reduces its life.

Unfired factory Lapua brass:

20170818_194516_zpsqfww3xps.jpg



Fired:
20170818_194614_zpsbtxr8shd.jpg
 
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alamo5000

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I scored some 6mm ARC ammo. Hornady 105's @ Palmetto. I probably got screwed a little but I got them to the door for $1.75 p/r shipping and tax included.

All I really wanted to do is have some on hand for when I get my barrel and to also be able to harvest some brass.

After I get these in hand I will be able to at least reload. Got a bunch of powder and primers. I just need some 6mm bullets.

Note: I was just going to buy brass only but if you can find it it's almost a buck per piece.
 

lennyo3034

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Shot reloads for first time through the ARC. Today was OCW testing. Went from 28.0 to 29.4 in .2 grain increments, focusing on velocity. I’ll worry about seating depth and tuner settings next trip.

28.0: 2587
28.2: 2617
28.4: 2638
28.6: 2671
28.8: 2695
29.0: 2704
29.2: 2730
29.4: 2758

Looks like a good node between 28.8 and 29.0. I’ll load some at 28.9 for the seating depth test.

24” Bartlien barrel, 105 berger hybrids jumped .070” (limited by elander mag length), once fired Hornady brass.
 

lennyo3034

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Brass from 29.4 load. I don’t see any pressure signs.
 

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newageroman

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When you say stripped bolt, do you mean no Firing Pin or is there more to it than that. I'd like to confirm my measurements a bit more in this area. I have the Hornady comparator set.

That looks great results on the reloads! If you zoom in close you can see the center of the primers starting to protrude back out just a tad. On some of my hotter loads it is a little more pronounced than that even, but I don't haven any hard primers so im stuck in the 2600ish range for now. Whats the deal with the sharpie mark, did you hand feed and index them or something?

I just got some new glass on the Poverty Pony. No excuses this time. I went with the Valdada 16x56 fixed power MOA. It's pretty nice and I think I can get most all my target yardages with holdovers only and no dialing - sight in this weekend hopefully.

I just hot washed and deprimed ~250 cases of starline converted brass last night. I think some of it was also annealed after firing but most wasn't so I'm just saving it for annealing next range trip.

After that though, I will be forming it with the body die/bump (~4 thou) no center spindle/expander ball, Manderal Die expand, then check trim len. champher/deburr and run'em again on the D650. The theroy being that the manderel die will center the necks a tad more.
 

LRRPF52

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When you say stripped bolt, do you mean no Firing Pin or is there more to it than that. I'd like to confirm my measurements a bit more in this area. I have the Hornady comparator set.
When I say "stripped bolt”, I mean extractor and ejector removed. The ejector is the main thing that won’t allow you to get correct headspace readings since it has so much force behind it with the ejector spring.

I used one of my bolt disassembly tools to punch out the roll pin that retains the ejector and I keep that bolt in that state specifically for determining headspace for my sizing process.

I seat a sized empty case in the chamber and then see if I can rotate that stripped bolt into a locked position in the barrel extension. If it won’t turn easily, I keep sizing the shoulder back until it will reliably do so with several pieces of brass.

The last time I did it with Grendel, it worked out to be the same headspace across all my semi autos and Howa bolt gun, which was fortuitous.

That Hornady comparator set is a great tool to have for this reason, far more effective than case generic gauges.
 

newageroman

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Sweet - This is now on my list of to dos. Let me ask this as a follow up:
Right now I run a lightweight BCG but have a spare normal BCG
How can I measure the lugs per se to make sure they are the same.
When doing this process would it be advantageous to have both bolts out and testing at the same time to see which one locks up first?
I'm new to ARs - thx for the tips.
 

lennyo3034

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For those who have conducted seating depth testing with Berger 105s: where did you end up at?

Here is my target for today. Corresponding jump values next to target. I tried to go in .003” increments but the Hornady dies don’t have a micrometer.

Looks like it doesn’t like being between .040-.050 jump. I could maybe try a .035” jump but I’ll be pretty close to mag length. .052” or so may be the ticket. I’ll go back with 5 round groups at .052-.060 next.
 

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FLIGHT762

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I tried to go in .003” increments but the Hornady dies don’t have a micrometer.
Hornady sells a micrometer top for their seating dies. The great thing about them is you can buy 1 mic and use it on your other Hornady rifle dies. You just note down the mic readings for whatever bullets you're using on the other caliber dies.


Seems everyone is out of them right now, but for $30.00, they are a good deal. Get on a backorder list.
 
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LRRPF52

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Sweet - This is now on my list of to dos. Let me ask this as a follow up:
Right now I run a lightweight BCG but have a spare normal BCG
How can I measure the lugs per se to make sure they are the same.
When doing this process would it be advantageous to have both bolts out and testing at the same time to see which one locks up first?
I'm new to ARs - thx for the tips.
As long as the lug lengths and bolt face depth are the same, the headspace will be the same for the test bolt vs the bolt being used.

I’ve measured a lot of Grendel bolts and found that most of them have the same lug lengths and face depth.

I’ve seen some that other people wanted to use for builds that had too deep of a face (excess of the .136” depth), but I don’t recall any right now that were shorter. The Grendel bolt is -.003” allowable, no + allowable.

The main dimensional variation I’ve seen is bolt overall length, with a lot of imitation bolts being 2.800” vs the 2.810” required to use standard firing pins.
 

lennyo3034

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Whats the deal with the sharpie mark, did you hand feed and index them or something?
No, that's just how I mark my brass. I've been squaded with people at PRS matches that use the same brass and same color exterior marking as me before so this is an additional mark.

Also it helps keep tabs on how many loadings are on the brass. I use 1 mark for every time I load it.
 

Yondering

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Sweet - This is now on my list of to dos. Let me ask this as a follow up:
Right now I run a lightweight BCG but have a spare normal BCG
How can I measure the lugs per se to make sure they are the same.
When doing this process would it be advantageous to have both bolts out and testing at the same time to see which one locks up first?
I'm new to ARs - thx for the tips.

Better to just swap your current bolt to the new carrier if you're going to change.

Headspace should be fine with either one, but like any mechanical parts that work together, your bolt starts seating against the carrier more evenly as parts wear together. This is a good thing for even bolt lug loading and longevity, but swapping bolts around starts the whole process again.
 

lennyo3034

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So I think I have to call my seating depth testing a fail. Doesn’t look like it matters how much I jump, I get the same accuracy results.

Bullet jump values next to respective targets below.
 

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Dino11

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I find that the Berger bullets don't like a long jump. I am loading them to 2.950 to 2.300 OAL. But I am now shooting their 115 grain bullets in my bolt action and they do very well. The Nosler RDF's I load on the other hand love a longer jump, but do well with a short jump to. You usually find a couple nodes when testing. I change my jump in .030 increments and find the tighter groups and then fine tune from there.

Your groups look pretty good, but each barrel likes something different, I have four ARC's and each one likes a different load, would love to find a universal load for my gas guns though. I may work on that but one of them has a match grade barrel on it to compete in PRS gas gun, and my bolt gun is a totally different animal all together, I have to keep that brass segregated from the gas stuff.
 

Yondering

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So I think I have to call my seating depth testing a fail. Doesn’t look like it matters how much I jump, I get the same accuracy results.

Bullet jump values next to respective targets below.
You didn’t test across a very wide range so you might just be missing the best node. I try to cover a range spanning.100”-.150” for a good seating depth test, depending on the situation. If it were mine, I’d be testing both less jump and more. Maybe .010”-.110” etc.

The other part of a seating depth test is to find the depth that is most tolerant of variations in velocity or powder charge. To do that, I like to mix 5 different charge weights for each seating depth. For example maybe 30.0gr to 31.2gr in 0.3gr increments for each seating depth. This shows more dispersion at some depths and let’s you zero in better on the right jump.

Hope that makes sense. Might sound confusing at first but it’s actually fairly simple and works well.

(The powder charges I said above are not a recommendation for your load, just an examI used myself not long ago.)
 

lennyo3034

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I was being somewhat facetious with that last post. While it was true, getting consistent .3-.5 moa out of a gas gun is plenty good for me. The fact that I don’t have to worry about chasing lands is even better.

I tested between .030-.080 jump in .003” increments. Any less jump and I run into mag length issues. Deeper and I start compressing load and spiking SDs. These groups were where I suspected the best nodes may be.

Below is chrono data. 105 berger jumped .061 29.0gr lever evolution. Can anyone with quick load run that and see what pressures I’m around? I could probably push higher but don’t see the need to yet.
 

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Ledzep

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    E-lander and ASC 15 rounders have been solid for myself and a couple buddies. E-lander 25's are fine unsuppressed in my experience, but the extra fouling from a suppressor will cause the magazine to run slower than the bolt.
     

    newageroman

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    Shot the Valdada fixed yesterday at 100 yds to zero. Glass is great and the side focus is nice. I've only seen a few great glass scopes so I can only compare to what I have (all < $200). Fire Formed about 50 more cases. Looking forward to stretching the legs with the new glass and holdovers.

    The scope is also MUCH lighter than all the ATN stuff. I was amazed at how close to bore the scope/rings were when installing and didn't even make any adjustments until I got to the range and then it was ony ~1" high and right - super easy to sight in. So close in fact I wished I had just started at the 300 yd range but stuck at 100 for the day - whatevs...

    I'm running Duramags with the blue follower, they are GTG. 10 rounders for load dev (usaually only shoot 5) and the longer ones for fun time.

    Also scored 3 cans of W748 for free! - It's in the old antique bottles but I'm gonna run it in the new 6ARC. I have some old primers to use too. thinking old/new...
     

    Bantam1

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    I'm patiently waiting for my 20" Proof carbon to get here. Supposedly July shipment. I have everything to build the rifle but the barrel, but no components to load still.
     
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    LongRangeAggie

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    Did a ladder test with the ARC over the weekend.

    Enviro:
    -85 F
    -70% RH
    -600' Elev

    Load:
    -Starline 6.5 Grendel brass
    -Berger 108 Elite Hunter
    -Hodgdon Leverevolution 27.2 - 30.0grs in 0.2gr increments
    -Federal AR Match primers
    -CBTO 1.655" (0.060" off lands)
    -COAL (E-Lander mag length) ~2.25"

    Rifle:
    -20" 1:7.5 +2 rifle Rock Creek by Craddock Precision
    -AGB
    -Silencerco Omega

    27.2 - 2479
    27.4 - 2521
    27.6 - 2543 light ejector marks started
    27.8 - 2580
    28.0 - 2594
    28.2 - 2611
    28.4 - 2630
    28.6 - 2648
    28.8 - 2698
    29.0 - 2693
    29.2 - 2702
    29.4 - 2749 heavy ejector marks started
    29.6 - 2726
    29.8 - 2757
    30.0 - 2798

    Had some light ejector marks on the factory 105s. Need to adjust my AGB as well.

    I also loaded 5 rounds at 29.0grs but didn't have time to shoot them. It looks like that is going to be the sweet spot, the same as many of you on here found.

    Brass pic starts at 27.2 on the left and ends at 30.0 on the right, as well as the two factory 105s on the bottom.

    I'll report back when I shoot 5 round groups near the node.
     

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    lennyo3034

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    Did a ladder test with the ARC over the weekend.

    Enviro:
    -85 F
    -70% RH
    -600' Elev

    Load:
    -Starline 6.5 Grendel brass
    -Berger 108 Elite Hunter
    -Hodgdon Leverevolution 27.2 - 30.0grs in 0.2gr increments
    -Federal AR Match primers
    -CBTO 1.655" (0.060" off lands)
    -COAL (E-Lander mag length) ~2.25"

    Rifle:
    -20" 1:7.5 +2 rifle Rock Creek by Craddock Precision
    -AGB
    -Silencerco Omega

    27.2 - 2479
    27.4 - 2521
    27.6 - 2543 light ejector marks started
    27.8 - 2580
    28.0 - 2594
    28.2 - 2611
    28.4 - 2630
    28.6 - 2648
    28.8 - 2698
    29.0 - 2693
    29.2 - 2702
    29.4 - 2749 heavy ejector marks started
    29.6 - 2726
    29.8 - 2757
    30.0 - 2798

    Had some light ejector marks on the factory 105s. Need to adjust my AGB as well.

    I also loaded 5 rounds at 29.0grs but didn't have time to shoot them. It looks like that is going to be the sweet spot, the same as many of you on here found.

    Brass pic starts at 27.2 on the left and ends at 30.0 on the right, as well as the two factory 105s on the bottom.

    I'll report back when I shoot 5 round groups near the node.
    Looks like you have the same node and same jump that I ended up with. Not surprising since mine is also from Craddock and likely same reamer dimensions if not same reamer itself.
     
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    newageroman

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    Awesome data! - Are those AR Match primers hard primers? When I load up to 29.0 gns with 105s I get cratered primers and a couple pierced primers, backed off a bit. Need the hard primers... Your brass pics help gauge a lot as far as what is a bad ejector swipe - thx for sharing.
     

    LongRangeAggie

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    Awesome data! - Are those AR Match primers hard primers? When I load up to 29.0 gns with 105s I get cratered primers and a couple pierced primers, backed off a bit. Need the hard primers... Your brass pics help gauge a lot as far as what is a bad ejector swipe - thx for sharing.
    Appreciate it, just trying to contribute.

    Yes the AR primers are harder to protect against slam fires and the harder nature of AR's vs bolt guns I think.
     

    Yondering

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    Awesome data! - Are those AR Match primers hard primers? When I load up to 29.0 gns with 105s I get cratered primers and a couple pierced primers, backed off a bit. Need the hard primers... Your brass pics help gauge a lot as far as what is a bad ejector swipe - thx for sharing.

    What primers are you using? Sounds like they are too soft for these pressures, although anything that handles 5.56 pressure will handle this cartridge easily since the pressure is lower.

    If you’re not using a thin primer like Remington’s 222 / 22 Hornet primers or a pistol primer, it might be an indication of an oversized firing pin hole in the bolt. Something to check anyway.
     

    Yondering

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    Did a ladder test with the ARC over the weekend.

    Enviro:
    -85 F
    -70% RH
    -600' Elev

    Load:
    -Starline 6.5 Grendel brass
    -Berger 108 Elite Hunter
    -Hodgdon Leverevolution 27.2 - 30.0grs in 0.2gr increments
    -Federal AR Match primers
    -CBTO 1.655" (0.060" off lands)
    -COAL (E-Lander mag length) ~2.25"

    Rifle:
    -20" 1:7.5 +2 rifle Rock Creek by Craddock Precision
    -AGB
    -Silencerco Omega

    27.2 - 2479
    27.4 - 2521
    27.6 - 2543 light ejector marks started
    27.8 - 2580
    28.0 - 2594
    28.2 - 2611
    28.4 - 2630
    28.6 - 2648
    28.8 - 2698
    29.0 - 2693
    29.2 - 2702
    29.4 - 2749 heavy ejector marks started
    29.6 - 2726
    29.8 - 2757
    30.0 - 2798

    Had some light ejector marks on the factory 105s. Need to adjust my AGB as well.

    I also loaded 5 rounds at 29.0grs but didn't have time to shoot them. It looks like that is going to be the sweet spot, the same as many of you on here found.

    Brass pic starts at 27.2 on the left and ends at 30.0 on the right, as well as the two factory 105s on the bottom.

    I'll report back when I shoot 5 round groups near the node.

    Looks good. I’ve noticed that Starline brass is pretty tough in this cartridge and handles a lot of pressure and abuse. In my 4 rifles that use this brass, it can be pushed way over pressure without showing pressure signs.

    All of those cases look ok except the last couple; those ejector hole imprints are concerning since it’s Starline. If you haven’t, it’d be worth making sure your shoulder bump is correct; too much bump (creating excess headspace) can cause those imprints at higher pressure. The danger is that it also resulted in impending case head separation for me after a few loads and the brass was junked. Reducing bump down to minimum with the same loads let this brass handle 12 loads without any pressure signs.

    Hope that helps.

    I have a few disagreements with that method of load development but will keep it to myself because some people take it personally. The one thing I’ll say is that results on target matter a whole lot more than results over the chrono, and primers are hard to get right now...
     

    LongRangeAggie

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    Looks good. I’ve noticed that Starline brass is pretty tough in this cartridge and handles a lot of pressure and abuse. In my 4 rifles that use this brass, it can be pushed way over pressure without showing pressure signs.

    All of those cases look ok except the last couple; those ejector hole imprints are concerning since it’s Starline. If you haven’t, it’d be worth making sure your shoulder bump is correct; too much bump (creating excess headspace) can cause those imprints at higher pressure. The danger is that it also resulted in impending case head separation for me after a few loads and the brass was junked. Reducing bump down to minimum with the same loads let this brass handle 12 loads without any pressure signs.

    Hope that helps.

    I have a few disagreements with that method of load development but will keep it to myself because some people take it personally. The one thing I’ll say is that results on target matter a whole lot more than results over the chrono, and primers are hard to get right now...
    Thanks for the advice. Now that these are fire formed I will know exactly what to bump the Starline in the future. Hopefully the 29.0grs shoots well and I don't have to develop much after that.
     

    SWFShooter

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    I was being somewhat facetious with that last post. While it was true, getting consistent .3-.5 moa out of a gas gun is plenty good for me. The fact that I don’t have to worry about chasing lands is even better.

    I tested between .030-.080 jump in .003” increments. Any less jump and I run into mag length issues. Deeper and I start compressing load and spiking SDs. These groups were where I suspected the best nodes may be.

    Below is chrono data. 105 berger jumped .061 29.0gr lever evolution. Can anyone with quick load run that and see what pressures I’m around? I could probably push higher but don’t see the need to yet.
    The previous chrono data you posted of the OCW testing does not line up with the 2718 fps of this post, but calibrated to the 2718 fps, pressure is estimated over 57K. (Without calibrating to actual velocity, the estimated velocity was lower, and the pressure was just under 54K, so between 54K and 57K is mu best guess) The optimal barrel time for a 24" barrel at node 5 is 1.228 ms, so I highlighted the node. In an AR15, with the gas block changing harmonics slightly, I find that 10-20fps faster than the node will shoot the best with lowest ES and SD, so I would suggest targeting 2670 to 2690 fps and see if that has the lowest ES/SD and smallest group. And yes, I know everyone wants to go fast, but run a ballistic calculation and see how little impact 30 or so fps has on the solution. (spoiler alert, not much)
     

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    Yondering

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    Skagit Valley, WA
    The previous chrono data you posted of the OCW testing does not line up with the 2718 fps of this post, but calibrated to the 2718 fps, pressure is estimated over 57K. (Without calibrating to actual velocity, the estimated velocity was lower, and the pressure was just under 54K, so between 54K and 57K is mu best guess) The optimal barrel time for a 24" barrel at node 5 is 1.228 ms, so I highlighted the node. In an AR15, with the gas block changing harmonics slightly, I find that 10-20fps faster than the node will shoot the best with lowest ES and SD, so I would suggest targeting 2670 to 2690 fps and see if that has the lowest ES/SD and smallest group. And yes, I know everyone wants to go fast, but run a ballistic calculation and see how little impact 30 or so fps has on the solution. (spoiler alert, not much)
    Seems to me you’ve made some assumptions and correlations that don’t actually carry over from one barrel to the next. Barrel harmonics for example are highly dependent on barrel profile, not just length. And the optimum accuracy node from harmonics does not necessarily correlate to lowest ES/SD; those are independent of each other. You might see both of these occurring simultaneously in your barrel with that load, but it’s a bad assumption to conclude it works that way in other examples too.

    I know that people who’ve spent good money for a software program don’t like to hear this, but this is a good example of the fact that just because you can generate a bunch of data doesn’t mean it’s accurate or useful.
     

    SWFShooter

    Private
    PX Member
    Minuteman
    Feb 24, 2017
    43
    29
    Seems to me you’ve made some assumptions and correlations that don’t actually carry over from one barrel to the next. Barrel harmonics for example are highly dependent on barrel profile, not just length. And the optimum accuracy node from harmonics does not necessarily correlate to lowest ES/SD; those are independent of each other. You might see both of these occurring simultaneously in your barrel with that load, but it’s a bad assumption to conclude it works that way in other examples too.

    I know that people who’ve spent good money for a software program don’t like to hear this, but this is a good example of the fact that just because you can generate a bunch of data doesn’t mean it’s accurate or useful.
    I don't think my comment was misleading as I referred to the numbers as "estimated", numerous details were not provided to make any sort of true analysis. Garbage in equals garbage out. Even noted the chrono data does not match up, and I selected only the last to use to this estimate. And based on the numerous calculations I have provided for AR clients seem to pan out that the effect on OBT times that gas blocks, muzzle devices, etc. tend to push the assumed node a few fps higher, based on ES/SD and group size. Suppressors in particular impact the estimates. Also, calibration to actual velocities will skew the pressure estimates, so I identified an estimated range as my "best guess". I remind my clients of this because so many are used to the bolt gun numbers being spot on when we do a full analysis. This however was a "quickie estimate" to answer the question, in which I used saved criteria from other 6mm ARC clients, so it is obviously "ballpark", not exact.
     

    Yondering

    Sergeant
    PX Member
    Minuteman
    Mar 16, 2017
    1,126
    698
    Skagit Valley, WA
    I don't think my comment was misleading as I referred to the numbers as "estimated", numerous details were not provided to make any sort of true analysis. Garbage in equals garbage out. Even noted the chrono data does not match up, and I selected only the last to use to this estimate. And based on the numerous calculations I have provided for AR clients seem to pan out that the effect on OBT times that gas blocks, muzzle devices, etc. tend to push the assumed node a few fps higher, based on ES/SD and group size. Suppressors in particular impact the estimates. Also, calibration to actual velocities will skew the pressure estimates, so I identified an estimated range as my "best guess". I remind my clients of this because so many are used to the bolt gun numbers being spot on when we do a full analysis. This however was a "quickie estimate" to answer the question, in which I used saved criteria from other 6mm ARC clients, so it is obviously "ballpark", not exact.

    You're still assuming correlations that don't exist. One is your comment about optimum barrel time and harmonics leading to lowest ES/SD; those are independent things and one does not cause the other. Another one is your assumption that you can estimate optimum barrel time based on barrel length alone.
    Good for you if it's worked for you and your "clients" but IMO you're promoting bad understanding of how this stuff works.

    In my experience if you just start off with good load development practices (NOT things like the velocity "node" search someone used above) you often end up at a very different result than trying to follow these predictions, because they lack enough input data to be actually useful.
     

    Dino11

    Private
    Minuteman
    Nov 11, 2019
    97
    65
    60
    Ohio
    The first thing that I saw that caught my attention was the input data on case capacity in H2O, it was 34.8, that seems a bit high.

    Bad data in...