• Watch Out for Scammers!

    We've now added a color code for all accounts. Orange accounts are new members, Blue are full members, and Green are Supporters. If you get a message about a sale from an orange account, make sure you pay attention before sending any money!

IMR 8208 XBR and Hornady 68gBTHPs

I think it's tangent ogive vs secant ogive and also the berger hybrids.

So besides Sierra and Berger who else makes good tangent ogive bullets.

I asked a factory rep for hornady and all I got was crickets.

Talking on the phone with Berger rep about a gun I have he was strait forward and said thier vld's would also not work in my application.

He took time to explain about ogives and design. Most helpful!

I've had good luck with standard Hornady match bullets. 68 and 75s in 223 and 178s in 308.
 
Last edited:
Well sir thats good but I have a couple of needs for tangent or hybrid applications.

1: 223 for several rifles same load. Different jump.

2: 308 bolt gun with a short magazine length.

No place for a secant ogive bullet in iether case for me anymore.

And in general not at all happy with hornady bullets performance in several calibers.

I am putting them at the bottom of my shopping list if at all.
 
Well sir thats good but I have a couple of needs for tangent or hybrid applications.

1: 223 for several rifles same load. Different jump.

2: 308 bolt gun with a short magazine length.

No place for a secant ogive bullet in iether case for me anymore.

And in general not at all happy with hornady bullets performance in several calibers.

I am putting them at the bottom of my shopping list if at all.

Cant beat SMK but Lapua Scenars shoot great too and arent jump sensitive.. 308 and short magazine length is a match for SMK's
 
What is your testing procedure?? Are you just loading charges and deciding on load by group size? Forgive me, but thats what it appears since you refernce not finding small groups... You do know, you are NOT looking for group size when doing this part of the test.. You should be shooting your different charges, (0.2gr increments I see which is good) in Round Robin style. You should be use same headstamp brass when doing this. Biggest reason why, case capacity differences causing different pressures. That will skew your results right off the bat...

You are looking for consistent POI (Point of Impact) to identify the node. 23.2-23.4gr is pretty consistent and right there in the known 77smk/8208XBR node... 23.6gr - 24.0 POI drops down a little and is pretty consistent across those charges. You have options here. I would load up 23.3gr and do a seating depth test.

Your next step is to do a seating depth test. That is the step where you look for group size. If done properly, I guarantee you will find one group that shrinks right up and stands out from the rest....

Here is my load development with 8208XBR and 77smk out of a WOA 20: 1:7 SDM barrel all at 100yd

This is my initial OCW looking for the node (consistent POI across various consecutive charges).. You can see, my POI is very consistent from 23.2gr to 23.8gr. I picked 23.6gr being pretty much in the middle of this very wide node... If not knowledgable about how to do proper load development, you would think Im crazy as 23.6gr is one of the largest groups. But doesnt bother me, because Im NOT looking at group size. You have to ignore it.







Now, Ive selected 23.6gr so I load up a bunch of rounds with 23.6gr and I do a seating depth test, again shot Round Robin style at 100yds..







Now here you can see the clear stand out of the seating depth my barrel/load likes. It shrunk right up, just what I was looking for. Im now ready for load confirmation test.


Here is my final load confirmation test @ 100yd. Load is confirmed, very consistent and very accurate.





Time to test at distance for final load confirmation. Not bad 0.6moa @ 546yd in a 15MPH crosswind.. I call it good at this point




This is my process for EVERY load I develop. Is it a lot of work? Yep. Does it work, time after time. Yep, every single time. Start with some same headstamp brass and restart your testing.

I do all my precision AR shooting with prepped 1xLC. There is no need to use Lapua in an AR unless you have money to burn and dont care about beating the shit out of it or loosing it.... I found zero accuracy difference testing my loads in Lapua vs prepped LC (flash holes deburred, pockets uniformed, annealed, sized, chamfer/debur).


Update: I finally got enough brass in to work with. I went with Lapua (overkill but it’s done now). Headspace using my comparator was pretty consistent across all 200 pieces at 1.458” +/- 0.002 (most were +/- 0.001), but trim lengths were a tad more deviant. Did find two badly deformed case mouths. Uniformed all Primer Pockets, FL Resized without bumping the shoulders back as they were all just under where I like them to be anyway, then trimmed all to 1.750”.

I then revisited OCW test with 68g BTHPs, and also did as you recommend, and tried a Seating Depth Test with my 77g SMKs at 23.3g of 8208 XBR load. These were done round robin with 10min cool time between each flight. No Chrono this time. Forgot it🤦🏻‍♂️. Here’s what I got:

1596514718659.jpeg

Not sure what to do with the 68g load. POIs are moving around from starting left, to centering up, to ending right. 23.2 maybe then Seating Depth Test? Your thoughts are welcomed.

The 77g SMK Seating Depth test below was fun, but this was a first firing for the brass, and I’ll admit, it’s hard for me to break that many shots consistently, so I’m not sure if I was as precise as I should have been on my technique. Anyhow, my interpretation is that slightly over 2.250 COL at the 1.861 CBTO is looking good, but I’m all ears if you have any thoughts or recommendations.
1596514790812.jpeg
 
  • Like
Reactions: Formosan
Update: I finally got enough brass in to work with. I went with Lapua (overkill but it’s done now). Headspace using my comparator was pretty consistent across all 200 pieces at 1.458” +/- 0.002 (most were +/- 0.001), but trim lengths were a tad more deviant. Did find two badly deformed case mouths. Uniformed all Primer Pockets, FL Resized without bumping the shoulders back as they were all just under where I like them to be anyway, then trimmed all to 1.750”.

I then revisited OCW test with 68g BTHPs, and also did as you recommend, and tried a Seating Depth Test with my 77g SMKs at 23.3g of 8208 XBR load. These were done round robin with 10min cool time between each flight. No Chrono this time. Forgot it🤦🏻‍♂️. Here’s what I got:

Not sure what to do with the 68g load. POIs are moving around from starting left, to centering up, to ending right. 23.2 maybe then Seating Depth Test? Your thoughts are welcomed.

The 77g SMK Seating Depth test below was fun, but this was a first firing for the brass, and I’ll admit, it’s hard for me to break that many shots consistently, so I’m not sure if I was as precise as I should have been on my technique. Anyhow, my interpretation is that slightly over 2.250 COL at the 1.861 CBTO is looking good, but I’m all ears if you have any thoughts or recommendations.

I'm in a similar boat, shooting 77smk with IMR 8208, I chose 23.2grains. Neighboring nodes with similar POIs. Low ES and SD. Sorry, i didnt mark up the targets but i started shooting from the top left. The tightest targets seem to be seated 1.846, 1.843, and 1.828 CBTOs, so I loaded up 10 more of each and will test them out tomorrow. Tac didnt make the cut lol.

I was hoping to get touching holes like some folks, but that just doesnt seem possible to me any more. Looking at your results, our group sizes arent that far off, but your 1.836 & 1.861 CBTOs do look promising.

My original goal of 1/2 moa doesnt look possible, I will settle for 3/4 moa 10 shot groups now lol

IMG_20200731_221930.jpg


IMG_20200802_103247.jpg
 
Keep in mind guys, getting 1/2moa groups out of ANY gasser is not easy. While sometimes you can get lucky on components when building an AR, the recipe is a well built, properly tuned AR with a high quality custom match barrel (Bartlein, Kreiger, etc).

The other half is you, the indian....Everyone thinks they should be able to shoot tiny groups with an AR cause they do it with a bolt gun...completely different animal. Fundamentals and practice are key...good solid shooting position, square to the rifle, exaggerated mechanics of follow throw, trigger reset.... you have moving parts in a gasser. You can get away with poor Fundamentals with a bolt gun, but you find out real quick with an AR that's not the case. Even more magnified when you step up to a large frame gasser (308,6.5cm).

This is just info, not directed at anyone specific. I'm just saying, don't be hard on yourself. Don't always think it's the load....could be the barrel, you, the load, or a little bit of all of that... when you hear "I have a 0.5moa AR all day" on the internet 95% of the time its bullshit.....0.5moa is NOT easy out of an AR. Shooting a 0.5moa or smaller group is NOT a 0.5moa gun...

Just some thing to keep in mind when your setting expectations for your AR loads and what to look at and work on...
 
what do you guys mean when you say your are shooting " red robin" ?
 
  • Haha
Reactions: Formosan
what do you guys mean when you say your are shooting " red robin" ?

LOLOL, Its Round Robin, not Red Robin... funny stuff

It means, you DO NOT shoot 3 shots of the first charge weight and move to the next, and shoot those 3, etc. Thats not Round Robin.

Round Robin means you shoot 1 shot of the first charge, then move to the next target and shoot 1 shot of the next higher charge, then move to the 3rd target and shoot 1 round of the next higher charge and so on till you have fired exactly 1 shot of each charge weight in consecutive order from lowest charge weight to highest charge weight.... When your done, you go back to the lowest charge weight and you shoot it at the same target you shot that 1st shot at, then again shoot the 2nd round of the next charge weight and so on. Your firing 1 shot of each charge weight at a time.. Rinse and repeat till you have fired all shots of all charge weights, round robin style..
 
  • Like
Reactions: Gustav7 and sid
oh :) ok i get it, i never heard of the term ( i have only heard of red robin, maybe thats why my hands typed red instead of round :)
 
Today 3 groups at 300 yards to confirm 23.2gr imr8208 with 77smk 1.846" to ogive. Seems to be around 3/4-1 moa.

Maybe if I anneal the brass it will shrink the groups?

When measuring the bullet seating depth to the ogive with the Hornady tool, I usually measure 8 times while turning the cartridge. If I get 1.846 on all 3 sides of the cartridge, but 1 side I get 1.849, should I seat the bullet deeper until that 1 side measures 1.846, even if the 3 other sides.may measure 1.843?
 

Attachments

  • IMG_20200809_122142~2.jpg
    IMG_20200809_122142~2.jpg
    533.8 KB · Views: 43
No, annealing your brass is not going to shrink groups...thats not what annealing does...your measuring tools are not capable of accurately reading to the .001 consistently every time. Even thought your calipers may read to .001...pressure at which you apply, how you hold, etc...set your die to get you very close to 1.843 then load all your ammo..

Your getting 1moa @ 300yd....what more do you want out of that AR? Get a custom bartlein if you want any better but its not gonna be 0.5moa at 300yd....
 
  • Like
Reactions: Formosan
Today 3 groups at 300 yards to confirm 23.2gr imr8208 with 77smk 1.846" to ogive. Seems to be around 3/4-1 moa.

Maybe if I anneal the brass it will shrink the groups?

When measuring the bullet seating depth to the ogive with the Hornady tool, I usually measure 8 times while turning the cartridge. If I get 1.846 on all 3 sides of the cartridge, but 1 side I get 1.849, should I seat the bullet deeper until that 1 side measures 1.846, even if the 3 other sides.may measure 1.843?

8 times... damn. Personally I don't think you need to get that involved with it. IF you start chasing 1 thou here or 1 thou there after measuring multiple times on the same bullet you're gonna end up going in circles.

What I do is get my bullet seating depth to within 0.005 of my target depth, then I load 5-10 using the exact process I'll use to load all 300-500 or so, then measure each one of those for seating depth. I typically only measure the bullet (at the ogive) once, but if it looks a little cockeyed or I feel I don't have my calipers set consistently, then I'll turn the bullet and measure a 2nd time. Sometimes I adjust the die a bit, and sometimes I'm close enough that I'm good with it. Depends on what my seating depth test showed me. This last test, all the seating depths were pretty decent, with all tests coming in at sub-moa 5 shot groups.

If I do my part and my process is in sync, I'm usually seating to +/-0.001ish. I think my last run of 300 rounds, 90% of my rounds fell into a 0.003 window, so +/- 0.0015. The other 10% fell within a 0.004 window. Thats good enough for me, and after all they're getting ran in an AR, so I'm happy with that.
 
  • Like
Reactions: Formosan
I'm in a similar boat, shooting 77smk with IMR 8208, I chose 23.2grains. Neighboring nodes with similar POIs. Low ES and SD. Sorry, i didnt mark up the targets but i started shooting from the top left. The tightest targets seem to be seated 1.846, 1.843, and 1.828 CBTOs, so I loaded up 10 more of each and will test them out tomorrow. Tac didnt make the cut lol.

I was hoping to get touching holes like some folks, but that just doesnt seem possible to me any more. Looking at your results, our group sizes arent that far off, but your 1.836 & 1.861 CBTOs do look promising.

My original goal of 1/2 moa doesnt look possible, I will settle for 3/4 moa 10 shot groups now lol

View attachment 7392807

View attachment 7392808
Been offline awhile and just now seeing your post. I think your rifle and loads are doing great. This stuff is fun. What I find fascinating about reloading is the opportunity to optimize whatever rifle platform you have to it’s fullest potential. I don’t think I have a 0.5moa gun, and I’m certainly not a 0.5moa technique guy behind the rifle, but I’ve seen some cool differences in what my rifle likes versus what it doesn’t like thru reloading. It’s an awesome feeling to go from only having a few very specific factory loads available to me (if they aren’t sold out or on Backorder 😂) that will shoot decent in my rifle, to having the option to tailor make an optimal reproducible round at home whenever I choose to. I also like the unknown in reloading in that you never know just how good you can get an average grade stock gasser shoot (in my case) until you try out a few things at the reloading bench. I went from shooting baseball & bigger sized groups with factory Fed XM193s to shooting consistently an inch an usually under with my reloads. That’s very comforting!
 
  • Like
Reactions: Formosan
Keep in mind guys, getting 1/2moa groups out of ANY gasser is not easy. While sometimes you can get lucky on components when building an AR, the recipe is a well built, properly tuned AR with a high quality custom match barrel (Bartlein, Kreiger, etc).

The other half is you, the indian....Everyone thinks they should be able to shoot tiny groups with an AR cause they do it with a bolt gun...completely different animal. Fundamentals and practice are key...good solid shooting position, square to the rifle, exaggerated mechanics of follow throw, trigger reset.... you have moving parts in a gasser. You can get away with poor Fundamentals with a bolt gun, but you find out real quick with an AR that's not the case. Even more magnified when you step up to a large frame gasser (308,6.5cm).

This is just info, not directed at anyone specific. I'm just saying, don't be hard on yourself. Don't always think it's the load....could be the barrel, you, the load, or a little bit of all of that... when you hear "I have a 0.5moa AR all day" on the internet 95% of the time its bullshit.....0.5moa is NOT easy out of an AR. Shooting a 0.5moa or smaller group is NOT a 0.5moa gun...

Just some thing to keep in mind when your setting expectations for your AR loads and what to look at and work on...
I totally agree with everything you just said. To me, it’s all about optimizing what you have, and trying to get both the rifle, and the shooter as precise as both can get. It’s also about perspective and having realistic expectations. In my case, I wanted a 0.5moa gun, but I didn’t have the money to buy one. I also didn’t have knowledge or expertise to know how to build one, or the ability to consistently break the shots with proper technique required to be an all day 0.5moa shooter 😆. I’m trying and practicing hard to get there one day tho. I do enjoy shooting with a passion, and I’m learning more & more about this reloading stuff every day. It’s starting to click for me. I just reaped the benefits first hand of doing an OCW and Seating Depth Test. I didn’t understand what I was looking at the first time I did one, but now, after gaining a better understanding of what the tests are designed to show from your explanations, I got a more consistent load working than I ever would’ve gotten just picking best groups. Friday evening just before dark, I got a chance to push my 77gSMK load in development out to 500yds. I saw enough consistency there to try them at 1000yds. I know in theory the .223 is not really designed to shoot remarkably reliably beyond 600yds, but I figured wutha heck, I’ll try it, and was making hit after hit after hit with ridiculous ease at 1000yds. Groups at 1000 were not super impressive, but the fact that it hit the 3x3 plate with regularity was more that impressive to me. I never thought for a second my rifle was capable of doing that before the reloading OCW & Seating Depth tests. Thanks for your help!
 
  • Like
Reactions: Formosan and padom
I totally agree with everything you just said. To me, it’s all about optimizing what you have, and trying to get both the rifle, and the shooter as precise as both can get. It’s also about perspective and having realistic expectations. In my case, I wanted a 0.5moa gun, but I didn’t have the money to buy one. I also didn’t have knowledge or expertise to know how to build one, or the ability to consistently break the shots with proper technique required to be an all day 0.5moa shooter 😆. I’m trying and practicing hard to get there one day tho. I do enjoy shooting with a passion, and I’m learning more & more about this reloading stuff every day. It’s starting to click for me. I just reaped the benefits first hand of doing an OCW and Seating Depth Test. I didn’t understand what I was looking at the first time I did one, but now, after gaining a better understanding of what the tests are designed to show from your explanations, I got a more consistent load working than I ever would’ve gotten just picking best groups. Friday evening just before dark, I got a chance to push my 77gSMK load in development out to 500yds. I saw enough consistency there to try them at 1000yds. I know in theory the .223 is not really designed to shoot remarkably reliably beyond 600yds, but I figured wutha heck, I’ll try it, and was making hit after hit after hit with ridiculous ease at 1000yds. Groups at 1000 were not super impressive, but the fact that it hit the 3x3 plate with regularity was more that impressive to me. I never thought for a second my rifle was capable of doing that before the reloading OCW & Seating Depth tests. Thanks for your help!

There you go. Putting in the work with load development pays off. Especially when you walk that load out to distance. That's where you see guys loads fall apart that just picked tiny groups at 100yds...
 
There you go. Putting in the work with load development pays off. Especially when you walk that load out to distance. That's where you see guys loads fall apart that just picked tiny groups at 100yds...
I guess it goes without saying, but just for clarification, it was a 3ft by 3ft steel plate i was rattling at 1000yds, lol. If I could hit a 3x3” plate with my rig... I’d go buy a lottery ticket ASAP 😂.
 
My load is pretty much the same as everyone else with the 77 SMk in my 18" Douglas barrel. 23.5 of 8208 and 1.850" to the ogive. I run .003" neck tension and anneal the brass. SD varies from 3-6fps. ES is usually 10-12. The groups vary slightly from .3-.8 MOA. I get the same numbers in my LC and Lapua brass which surprised me.

My upper and lower fit very tight but I still have to pull the grip towards me to get the groups to be a little more consistent. If I get lazy the groups open up. If I make sure to repeat how I grip the rifle they shrink back up. Play with changing your grip and see if it affects the way the rounds print.

Solid performance to 800 or so. I have pushed them to 850 but spotting misses is tough when I don't make a good wind call. I have not tried to push them further because they are going pretty slow at that point.
 
My load is pretty much the same as everyone else with the 77 SMk in my 18" Douglas barrel. 23.5 of 8208 and 1.850" to the ogive. I run .003" neck tension and anneal the brass. SD varies from 3-6fps. ES is usually 10-12. The groups vary slightly from .3-.8 MOA. I get the same numbers in my LC and Lapua brass which surprised me.

My upper and lower fit very tight but I still have to pull the grip towards me to get the groups to be a little more consistent. If I get lazy the groups open up. If I make sure to repeat how I grip the rifle they shrink back up. Play with changing your grip and see if it affects the way the rounds print.

Solid performance to 800 or so. I have pushed them to 850 but spotting misses is tough when I don't make a good wind call. I have not tried to push them further because they are going pretty slow at that point.

How do you like the Douglas barrel? I was looking at those and the WOA's for my next barrel... I just don't think I need or want to spend the cheddar on a Bartlein
 
How do you like the Douglas barrel? I was looking at those and the WOA's for my next barrel... I just don't think I need or want to spend the cheddar on a Bartlein

I'm happy with it. I have some odd looking gas port erosion, almost looks like chunks missing or gouges, but it shoots fantastic. It prefers a little fouling to shoot really well. The best groups are in the .3's but it seems to be a solid half MOA capable barrel. It shoots the Federal 73 Berger factory load well and the Hornady 75 Match. The BH red box 5.56 77 shot about .75-1+" groups. I have shot maybe 100 rounds of factory ammo through it. The rest have been my hand loads with Sierra 77 or Hornady 75 which it shoots equally well. I can't have a suppressor here in CA so I can't comment on it shooting suppressed.

Mine came through Centurion arms years ago when he was still in CA and a relatively new brand for the AR market. He claims the chamber is "optimized for MK262" 5.56mm. I have no idea if there have been any changes to their barrels or chamber in recent years. I know the WOA have a great reputation and to be honest, once this thing is shot out I will probably replace with one of their barrels. In the end it's an AR with a regular forged upper and lower. I can only expect so much from it without going to something like a JP for example. I will also probably change to a 20" to get some extra velocity too. My current loads run 2670. I have pushed them faster but lost accuracy. I went to an adjustable gas block and all it did was eliminate some of the ejector swipes I would get here and there.

I am very happy with Bartlein in my bolt action rifles. I wouldn't mind trying one of their barrels in my AR. I might build a 6ARC next year and I will run a Bartlein for that build more than likely.
 
Interesting update on my developing loads. 68gBTHP seems fine. Shoots lights out at 100yds and 500yds, but have only tried a few shots at 1000yds with it, and i got a couple hits at 52MOA and stopped. At home with better lighting, I saw ejector swipes in my 77g SMK load in development on about 1/4 of my brass at 23.1g of 8208 set at 1.861 CBTO. I’m shooting consistently around 3/4” groups & under at 100yds at 23.1g with this load, and hammering steel at 1000yds at 48MOA (Only a 16” Barrel). My initial OCW was done with mixed head stamp LC, and folks tried to tell me that Lapua Brass was overkill for an AR, but that’s all I could find at the time without tapping resources that I didn’t wanna trouble at the time. My question is this. I’ve heard Lapua has a smaller case volume than LC, and since my Unfired Lapua measured 1.458 to headspace datum line, and 1.464 to the headspace datum line Fired, could the excess headspace in Unfired Lapua (plus the smaller case volume as compared to LC) be responsible for the ejector swipes at 23.1g IMR 8208 XBR with 77g SMKs? That seems to be a fairly safe load when I research what others are loading. My second question is if I reduce by 0.2g, will I need to redo my seating depth test?
 
(No feed or eject issues other than occasional lack of locking back on empty Mag. No adjustable gas block, and Ejection Pattern is consistent at 4-5 O’clock thrown around 1 meter out)
 
Interesting update on my developing loads. 68gBTHP seems fine. Shoots lights out at 100yds and 500yds, but have only tried a few shots at 1000yds with it, and i got a couple hits at 52MOA and stopped. At home with better lighting, I saw ejector swipes in my 77g SMK load in development on about 1/4 of my brass at 23.1g of 8208 set at 1.861 CBTO. I’m shooting consistently around 3/4” groups & under at 100yds at 23.1g with this load, and hammering steel at 1000yds at 48MOA (Only a 16” Barrel). My initial OCW was done with mixed head stamp LC, and folks tried to tell me that Lapua Brass was overkill for an AR, but that’s all I could find at the time without tapping resources that I didn’t wanna trouble at the time. My question is this. I’ve heard Lapua has a smaller case volume than LC, and since my Unfired Lapua measured 1.458 to headspace datum line, and 1.464 to the headspace datum line Fired, could the excess headspace in Unfired Lapua (plus the smaller case volume as compared to LC) be responsible for the ejector swipes at 23.1g IMR 8208 XBR with 77g SMKs? That seems to be a fairly safe load when I research what others are loading. My second question is if I reduce by 0.2g, will I need to redo my seating depth test?

Isn't the Lapua brass 223? The LC is 5.56, hence the higher pressure its able to tolerate.
 
Isn't the Lapua brass 223? The LC is 5.56, hence the higher pressure its able to tolerate.

I’m not sure. The box says “.223 (5.56 x 45mm)”, so I assumed it was rated for 5.56 NATO pressures. Hoping it’s just a one off combination of new brass that has a smaller case capacity, which is also .006” shorter than my chamber headspace that is creating a false positive sign of pressure. I’m thinking smaller volume cases will have greater pressure with an equal sized charge in a higher volume case like LC, and being .006” short of chamber headspace, I’m guessing the case is slamMing back into bolt face a bit aggressively. I will probably just back off 0.2g, repeat my seating depth test, and if no pressure signs, just pick the best group, and go from there. I’ve already resized the cases, and now they are at 1.462 give or take a thou, where when fired, they read 1.464. Hopefully my theory and plan will work out.
 
Isn't the Lapua brass 223? The LC is 5.56, hence the higher pressure its able to tolerate.

To my knowledge, brass is brass. The alloy that LC is made of may be slightly different, but I've never heard of any brass manufacturer having stronger brass than Lapua. Maybe just as strong. Its not like Lapua's brass is only rated to SAAMI pressures but LC is somehow rated higher. Guys using Lapua brass in bolt guns are running loads over book max (over NATO max) and Lapua continues to deliver longer life than other brass manufacturers.

The difference in SAAMI vs NATO pressures for 5.56 has to do the with the chamber of the rifle. A .223Rem chamber is spec'd to SAAMI pressures(~55k psi), an AR15 with a 5.56 nato chamber is spec'd to NATO pressures (~62-65k psi).
 
  • Like
Reactions: Formosan
My question is this. I’ve heard Lapua has a smaller case volume than LC, and since my Unfired Lapua measured 1.458 to headspace datum line, and 1.464 to the headspace datum line Fired, could the excess headspace in Unfired Lapua (plus the smaller case volume as compared to LC) be responsible for the ejector swipes at 23.1g IMR 8208 XBR with 77g SMKs? That seems to be a fairly safe load when I research what others are loading. My second question is if I reduce by 0.2g, will I need to redo my seating depth test?

The smaller case volume could account for higher pressures, and therefore ejector swipes. Keep in mind, Lapua is great brass, and to have the life that Lapua brass has, its generally thicker...and since the outside dimension must remain the same, you lose volume on the inside. If you ticked the load back 0.1 or 0.2gr you may find you reduce that pressure and keep your original velocity from the LC brass load.

From what I've learned on here, less headspace actually reduces your pressure (counter intuitive). This is because more energy is required to expand the smaller brass, which results in less energy given towards the bullet and chamber, resulting is slightly lower pressure.

My guess is, the smaller volume of the Lapua Brass has driven up pressure a bit. I would reduce to 22.8-23.0gr and try it again over a chrono and watch for pressure signs
 
The smaller case volume could account for higher pressures, and therefore ejector swipes. Keep in mind, Lapua is great brass, and to have the life that Lapua brass has, its generally thicker...and since the outside dimension must remain the same, you lose volume on the inside. If you ticked the load back 0.1 or 0.2gr you may find you reduce that pressure and keep your original velocity from the LC brass load.

From what I've learned on here, less headspace actually reduces your pressure (counter intuitive). This is because more energy is required to expand the smaller brass, which results in less energy given towards the bullet and chamber, resulting is slightly lower pressure.

My guess is, the smaller volume of the Lapua Brass has driven up pressure a bit. I would reduce to 22.8-23.0gr and try it again over a chrono and watch for pressure signs
The counter intuitive part made my head spin at first, but I totally get what you are saying. Thanks for explaining that. Yessir, gonna tone it back 0.2g and recheck. With any luck, my velocities will still be comparable as I really liked the way it shot.
 
  • Like
Reactions: Gustav7
Fired 20 rounds of 77gr smk at the 600 yards today. 2 shots went off the paper. Didn't hold over for cold bore, left 0.2 mils. Wind hold was about 0.3 mils right, I can see that now. My ballistic calc app had me low 0.2 mils.

Brought the wrong battery cable with the Chrono and was not able to get velocities. I wonder what caused the 2 high and 1 low.

Maybe it's time to clean the gun? Bore and upper hasn't been cleaned in ~900 rounds.
IMG_20200822_111844.jpg
 
Last edited:
  • Like
Reactions: Lunchbox27
Fired 20 rounds of 77gr smk at the 600 yards today. 2 shots went off the paper. Didn't hold over for cold bore, left 2 mils. Wind hold was about 3 mils right, I can see that now. My ballistic calc app had me low 2 mils.

Brought the wrong battery cable with the Chrono and was not able to get velocities. I wonder what caused the 2 high and 1 low.

Maybe it's time to clean the gun? Bore and upper hasn't been cleaned in ~900 rounds.

What was wind? Around 15mph?

Im curious how your app had you 2 whole mils low? What info did you input? Lol... that’s like a little less than half your total vertical adjustment
 
What was wind? Around 15mph?

Im curious how your app had you 2 whole mils low? What info did you input? Lol... that’s like a little less than half your total vertical adjustment

Sorry, i meant 0.2 mils.

I'll correct those mistakes.
 
  • Like
Reactions: Gustav7
Fired 20 rounds of 77gr smk at the 600 yards today. 2 shots went off the paper. Didn't hold over for cold bore, left 0.2 mils. Wind hold was about 0.3 mils right, I can see that now. My ballistic calc app had me low 0.2 mils.

Brought the wrong battery cable with the Chrono and was not able to get velocities. I wonder what caused the 2 high and 1 low.

Maybe it's time to clean the gun? Bore and upper hasn't been cleaned in ~900 rounds.
View attachment 7405309

Awesome that you were on paper right out of gate at 600. Tells me your app and data are close. Hard to say what to do next without the velocity data. In my limited experience, I’ve tweaked the MV in my app when off paper to true it up. Sometimes I’ll play with the BC when it’s true at one distance, bit it doesn’t hold up farther out. Maybe try slowIng it down in the app 40-60fps, and see if the slow down will add 0.2mils to the required hold?

Edit: My apologies. I misunderstood the original question. Read it too fast, & thought you were referring to the 0.2mil low. After looking more closely at the Target, if the squares are 3” across, the bulk of your vertical dispersion seems to be around 6” or close to 1MOA at 600yds. The high and low shots could’ve been anything from changing conditions to rest/shot break to load related inconsistency. Hard to say. That looked plenty impressive to me.
 
Last edited:
Awesome that you were on paper right out of gate at 600. Tells me your app and data are close. Hard to say what to do next without the velocity data. In my limited experience, I’ve tweaked the MV in my app when off paper to true it up. Sometimes I’ll play with the BC when it’s true at one distance, bit it doesn’t hold up farther out. Maybe try slowIng it down in the app 40-60fps, and see if the slow down will add 0.2mils to the required hold?

Edit: My apologies. I misunderstood the original question. Read it too fast, & thought you were referring to the 0.2mil low. After looking more closely at the Target, if the squares are 3” across, the bulk of your vertical dispersion seems to be around 6” or close to 1MOA at 600yds. The high and low shots could’ve been anything from changing conditions to rest/shot break to load related inconsistency. Hard to say. That looked plenty impressive to me.

Thanks. I agree with your conclusions. Today I tried some 10 shot groups at 100yards to really dial in my technique. With 10 rounds left, I decided to dry fire and noticed the gun moves up to 0.2 mils when the hammer hit the firing pin. So then I started gripping the sides of the stock wfirmly wth my support hand to keep it from moving side to side and fired my.last 10 rounds. The group
IMG_20200913_104244~2.jpg
right in front of the scope cap is a 10 shot group the 3 that went left was from the cold barrel I think. Once it's warm, it started hammer them 1/2" at 100 yards