New rifle - AI AXMC in 6.5x47mm Lapua

[MCMXI]

I'm assuming that with the rifle being an Accuracy International there is little clearance between the firing pin and firing pin hole?

I don't know when AI made the change but short action AX rifles have a small firing pin. My older AW short action has a large firing pin which supposedly could/would pierce small rifle primers if there was sufficient case pressure. I've never shot SRP cartridges in that rifle although last year I did buy 200 6.5 Creedmoor Lapua cases with an SRP pocket. I haven't tried them yet though.

@WelshShooter, thanks for your input re the Varget velocity test. I did get out this morning and managed to shoot a similar test using H4350. Here are the results and to me there's no question that H4350 is a better choice than Varget in terms of velocity/pressure at least. I didn't get any major pressure signs on the brass with H4350, even at 41.8gr which supposedly generates about 64,624 psi. The sweet spot seems to be somewhere between 41.2gr and 41.8gr … hmmm … 41.5gr perhaps. So now to play with seating depth.



Three case heads from 41.8gr load

 

[WelshShooter]

@WelshShooter, thanks for your input re the Varget velocity test. I did get out this morning and managed to shoot a similar test using H4350. Here are the results and to me there's no question that H4350 is a better choice than Varget in terms of velocity/pressure at least. I didn't get any major pressure signs on the brass with H4350, even at 41.8gr which supposedly generates about 64,624 psi. The sweet spot seems to be somewhere between 41.2gr and 41.8gr … hmmm … 41.5gr perhaps. So now to play with seating depth.

I agree, your sweet spot is at the higher region again. The case heads look better than the Varget ones, but notice the case in the lower right having an ejector mark around the 'L'. 41.3gr might be a good middle of the road as it looks like the velocity has a small a jump between 41.2gr and 41.4gr, plus it's a good 0.5gr below your max 41.8gr. How do the case heads look on these two groups? When you play with seating depth (ie seating longer towards the lands) your pressure should slightly decrease unless you jam your bullet into the lands (@Nature Boy, not talking about jam on toast here!). Do you know how much distance you have to play with? Assuming you're using 308 AI mags you can load them long and still feed from a magazine.

Your primers look in good condition so you need not worry about piercing/blanking. Here's a picture of my standard CCI 400 prmires that were on the verge of piercing before I had the firing pinhole bushed. Starting load at left, each column moving up a charge. Right most column was midpoint to max charge. I stopped at the pierced primer. You can see some ejector swipes on the fourth column just before the failure at the fifth column. That's when I knew I had to change something (magnum primers and/or bushing the firing pin hole).

Ignore the faint concentric circle in the middle of the brass, that was caused by a start edge on my case holder which has since been smoothed out.

PS great shooting, looking forward to seeing more of your progress as you go along

 

[Nature Boy]

The sweet spot seems to be somewhere between 41.2gr and 41.8gr

I’d say even back to 41.0

Velocity flattens out between 41.2 and 41.4. I bet you find something good in that area

Also, do a primer test as well. It’s surprising how much that makes a difference

 

[MCMXI]

@WelshShooter, I appreciate your input for sure and good eyes on the ejector mark on that one case. I take photos of case heads using a 9X loupe and with my older eyes can't see any marks without one. Brass from lower charges looks virtually new with no discernable marks, even when viewing with a loupe. That's a very helpful image of your primers and I had a similar issue working up a load for my gf's FN chambered for 6.5x47mm Lapua. You asked about bullet jump and magazine length. I've only tested at .018" off the lands so far and could move the bullet out almost .020" and still have plenty of room in the magazine. The photo below shows a 130gr VLD loaded to touch the lands.

I feel that I could have done better yesterday but thanks for the pat on the back.

 

[MCMXI]

@Nature Boy, very nice test there with different primers. You know my next question of course …. which primer did you settle on after that test? I have all but the Remington primers on hand as well as GM205MAR and WSR, so once I get the COAL dialed in I'll do a similar test. I'm still getting used to the trigger on the AX. It's very different to the 2-stage triggers on my AW rifles and I'm not sure what it is about the trigger that's bothering me. The rifle is still too new with many changes so I haven't figured some things out yet. I do know that I shoot the AWs better but it's early days.

Both of these velocity tests were shot with new brass so I'd expect better results using fired brass that's been neck sized and had the shoulder bumped, if necessary. I've done no sorting either i.e. case weight, bullet base to ogive, bullet weight etc. Basically, this should be the worst case scenario. I'll need to get the anneal figured out too but that's a ways off yet.

I do like 41.2gr for this load … maybe 41.3gr. Pressure is good, accuracy is good, and velocity is decent. Ironically, the first two handloads for this rifle were 41.2gr and 41.5gr of H4350. I could have stopped there but inquiring minds want to know, and who doesn't like to shoot. @Varminterror might be having kittens over wasting a good barrel but I can always buy another.

How did your test go yesterday?

 

[Nature Boy]

You know my next question of course …. which primer did you settle on after that test?

Originally the 205M but a fella on the ASF forum saw my test and said to try the BR4 with another 0.1g of powder. Tried it and proceeded to clean 2 targets in back to back 600 yard F class matches.

When developing loads at 100 yards for longer distances I think it’s important to pay attention to group shape too. Two groups may have the same max spread but one is vertical and the other is horizontal. You want the latter.

How did your test go yesterday?

Good, and not what I expected. It tended to validate my original load.

Original load test 6 months ago on top, and the one I did yesterday on bottom with new lots of powder and bullets

Speed on left, charge weight on top, vertical distance to center on right and change in speed between charges underneath



My original load was 30.6g

Yesterday’s test says it’s between 30.4 and 31.0 (because there’s very little change in vertical distance to the centerline when compared to each other) Velocity change of zero between 30.7 and 31.0 tells me to look there, plus, note how the group shape changes from vertical to horizontal

And apologies for hijacking your thread

 

[MCMXI]

And apologies for hijacking your thread

Are you kidding ... this is great! Did you move the bullet too? Top target shows -0.000 and bottom shows -0.020. Is the brass new or resized? Thanks for your insights into load development and fantastic work for sure.

 

[Nature Boy]

Are you kidding ... this is great! Did you move the bullet too? Top target shows -0.000 and bottom shows -0.020. Is the brass new or resized? Thanks for your insights into load development and fantastic work for sure.

Brass was post fire forming (Ackley Improved) so at least one firing on the original test and yesterday’s test was brass with 5 firings

Original test was before I did a seating test so I just loaded them at touch. Subsequently, I did this to determine seating depth. As you can see, +0.007 and -0.020 were the winners.



I took 5 each at those two seating depths and shot them at 500 yards



Back to the group shape. Both have identical max spread of 1.5” (0.29 MOA) but the -0.020 off has half the vertical. That’s the one I went with. Interesting too is the difference in POI. +0.007 has an average of 38fps more velocity than the -0.020. I assume that’s the increase in pressure associated with jam vs jump

 

[MCMXI]

I really like your methodology here ... a good road map for even the dumbest of us to follow. It does help that you can shoot too. It's so easy to hide important data with human error.

Added in edit: Pressure can increase when the bullet can't move out of the case to relieve pressure before engraving. Also, it's my understanding that playing with seating depth changes barrel time for the bullet which is a way to fine tune the position of the barrel when the bullet exits the muzzle.

 

[C-grunt]

I don't know when AI made the change but short action AX rifles have a small firing pin. My older AW short action has a large firing pin which supposedly could/would pierce small rifle primers if there was sufficient case pressure. I've never shot SRP cartridges in that rifle although last year I did buy 200 6.5 Creedmoor Lapua cases with an SRP pocket. I haven't tried them yet though.

They changed in 2014. My AT is a 14 model and I had to talk with someone, I forget who, at Mile High to figure out if I had a small pin or a large. I ended up having a small pin.

 

[Nature Boy]

I really like your methodology here ... a good road map for even the dumbest of us to follow. It does help that you can shoot too. It's so easy to hide important data with human error.

Added in edit: Pressure can increase when the bullet can't move out of the case to relieve pressure before engraving. Also, it's my understanding that playing with seating depth changes barrel time for the bullet which is a way to fine tune the position of the barrel when the bullet exits the muzzle.

We stand on the the shoulders of those that came before us and I must give credit to Erick Cortina, current (and 4 time) Texas F class long range rifle champion for the methodology.

His accomplishments are a big deal if rifle accuracy is your hobby.

I’ve never met Erik, but like many of us these days, we learn a lot over the Internet. His process works for him and it works for me. It’s the least I can do to give attribution and pass it along to others.

Having said that, (as you have pointed out) it's necessary to have some control over the variables in order for the load data to be meaningful.

Edit: after re reading my post I want to make it clear that I'm still learning and figuring things out. If anything I've done can help someone else chase the accuracy demon then that's what I'm after. I was concerned that my tone came across as a little arrogant. It was not my intent.

 

[MCMXI]

Edit: after re reading my post I want to make it clear that I'm still learning and figuring things out. If anything I've done can help someone else chase the accuracy demon then that's what I'm after. I was concerned that my tone came across as a little arrogant. It was not my intent.

I didn't read it that way at all. I for one really appreciate your posts and value your input on load development and other topics. I've historically used the OCW method to work up a load but I like the idea of a repeatable approach that ends up with the right answer in as few rounds as possible. I enjoy working up loads but it's frustrating when 200 rounds later you're not sure if you have the best load possible.

 

[Nature Boy]

I had one more thing to try on Sunday that I’ve been wanting to do for a while and that’s shoot the same loads on a traditional ladder test at distance and see if it correlated to the 100 yard test. That would be good validation of that method.

Unfortunately our 500 yard lane was under several feet of rushing water. I’ll get to it once things dry out around here

 

[WelshShooter]

Sorry to hijack your thread MCMXI, but I didn't feel this deserved a new thread and I want to keep your thread active to promote us to update our progress!

On Saturday I went to the range to re-do some load testing for 123gr Scenar's using Viht N150 powder. I was a bit concerned when I double checked the published load data which showed that the max load of 37.8gr gives 2,805fps from a 28" barrel when the cartridge is loaded to 2.736". My freebore is a tad on the smaller side so the maximum COAL I can use for my rifle is around 2.666", so 0.070" shorter. My current pet load at 37.0gr gives me an average velocity of 2,900fps which is actually faster than the max load 0.8gr higher. I double checked this in QuickLoad and it showed me that the theoretical pressure of Viht max load being 53,121 psi and a theoretical velocity of 2,816fps (so pretty much spot on). My pet load theoretically gives 52,199 psi. Strange that it's still much lower than max pressure of 63,091psi.

Any way, I settled on running the Satterlee load development, whereby I made ten groups starting from 34.3gr and increasing by 0.2gr until I reached 36.1gr. All charges thrown and measured using my Chargemaster lite. After a charge was thrown, the pan was lifted and placed back on the scale to verify measurement. This window is far enough away from the top end of published data. I loaded three at each charge group, just like you guys have done. I used CCI 450 primers and factory new brass, where the case-head to datum measurement is only 0.002" shorter than my fired cases after I bump the shoulder back, so they should be similar to my fire-formed brass. Target was at 100m, shot from a bench, beautiful sunny but cool day (15C, or 59F for my American friends ). All shot velocities were recorded using my MagnetoSpeed sporter. Barrel remained "warm" throughout all testing and was not allowed to get hot to the touch.

Some observations:

1.) 5 out of 10 of the groups had one outlier in velocity which was much different than the other two. Is this normal? I double checked dispensed powder weight on the Chargemaster and it always read the desired charge.
2.) Average velocity chart only shows two main flat spots in velocity - 34.3gr to 34.5gr, and 34.7gr to 34.9gr. Otherwise, chart is pretty linear.
3.) Group position seems fairly consistent across all groups, aside from 35.5gr, and one strange shot for 36.1gr (I felt like this was a normal shot, unlike the two calls I made for 34.9gr and 35.1gr)
4.) Standard Deviation and Extreme Spread is amazing and identical at 34.9gr and 35.1gr (2fps and 4fps respectively), but the shift in mean velocity between the two groups (18fps) was the biggest delta observed through the test.

Conclusion:
Based on the data, it seems 34.3gr to 34.9gr have relatively small steps in velocity (20fps spread in average velocity between 34.3gr and 34.9gr) and no significant vertical dispersion. 35.9gr to 36.1gr look pretty tight too (aside from that one result I cannot explain), have negligible vertical dispersion and low velocity delta.

What do you guys reckon? Sorry for the blog post...

 

[Nature Boy]

I’m seeing the same thing you are.

A low node at 35.3-34.5 and a high node at 35.9-36.1 (with the odd flyer remaining a mystery)

I’d pick one of those as do a seating depth test

 

[MCMXI]

Sorry to hijack your thread MCMXI, but I didn't feel this deserved a new thread and I want to keep your thread active to promote us to update our progress!

No worries at all … that's a very interesting post you made so keep it coming. There's no question that 34.3gr to 34.9 gr is a wide sweet spot but it would be interesting to see your data up to 37.0gr or higher since the pressure is quite a bit below SAAMI max. Are you seeing any pressure signs at 36.3gr? Your issue with velocity outliers might be due to neck tension Did you size the new brass at all? Did the bullet seating stage give you the feeling that neck tension was consistent? There are a number of variables that affect velocity, even how much you allow the rifle to move during recoil, so it can be a can of worms chasing low ES numbers.

Nice charts by the way … very helpful.

 

[WelshShooter]

No worries at all … that's a very interesting post you made so keep it coming. There's no question that 34.3gr to 34.9 gr is a wide sweet spot but it would be interesting to see your data up to 37.0gr or higher since the pressure is quite a bit below SAAMI max. Are you seeing any pressure signs at 36.3gr? Your issue with velocity outliers might be due to neck tension Did you size the new brass at all? Did the bullet seating stage give you the feeling that neck tension was consistent? There are a number of variables that affect velocity, even how much you allow the rifle to move during recoil, so it can be a can of worms chasing low ES numbers.

Nice charts by the way … very helpful.

Apologies for the late reply to your questions...

I took some pictures of the case-heads for each load as shown below. I'm seeing ejector marks on pretty much all powder charges (but not necessarily all cases). I start seeing ejector swipes on 35.5gr (bottom left case, left of the 6; bottom right case, left of the Lapua logo) and again at 36.1gr (top case between "a" and Lapua logo, doesn't show so well on camera). The CCI 450 magnum primers look in good condition: no cratering or flattened primers around the edges. Bolt lift was not stiff, each case felt the same to extract and eject.

I did size the new brass using my Forster bench rest die. The die had been set up to perform 0.002" shoulder bump from a fired condition. The shoulders of the factory brass was 0.004" back compared with a fired case and this did not change after sizing. During seating I felt nothing out of the ordinary, or at least nothing which felt overly tight/loose compared to the other rounds.

I'm happy to be the limiting factor with these tests

 

[Nature Boy]

I don't think there's a problem. Your primers look good and you aren't seeing any other signs of pressure.

The brass is new and will be at its softest. A few cycles and I bet you don't see those ejector marks any more.

 

[LoonWulf]

Another note on ejector marks, and you guys have much nicer finished rifles than I do so this may not have anything to do with it.
I've found that some of my guns will print very slight markings on first firing on any loads unless the cases are crammed back against the bolt. I'm assuming this is due to sharp edge on the plunger hole and the cases slamming back.
Could be totally wrong, just a thought I had recently.

 

[MCMXI]

I don't think there's a problem. Your primers look good and you aren't seeing any other signs of pressure.

The brass is new and will be at its softest. A few cycles and I bet you don't see those ejector marks any more.

I agree that the brass and primers look fine. You make an interesting point about new brass being soft. When I worked at Remington I remember that the .223 brass case heads were hit twice during forming to make them harder … struck up was the term I think and no other brass got the same treatment. It seems logical that the case head slamming up against the bolt face during firing would cold work the brass and make it harder. We think about the case necks getting cold worked and needing to be annealed but not so much about the case head.

I've been so busy with projects these past couple of weeks that I haven't done any shooting. I need to change that.

 

[Gtscotty]

Do y'all shoot load development groups with a magnetospeed attached? I was always worried that the extra weight cantilevered out on the muzzle might change barrel vibration and affect groups.

 

[MCMXI]

Do y'all shoot load development groups with a magnetospeed attached? I was always worried that the extra weight cantilevered out on the muzzle might change barrel vibration and affect groups.

I've wondered about that too, but based on results from @Nature Boy, @taliv and @WelshShooter they really seem to have this figured out. I use a LabRadar and last year bought the microphone attachment to improve trigger performance when shooting suppressed. If this unit ever fails I'd definitely buy another if it couldn't be fixed.

 

[Nature Boy]

I saw similar ejector marks working up my first 6BRA loads with new brass and thought I was seeing pressure signs but after the 3rd firing there’s no sign of it anymore

 

[WelshShooter]

I saw similar ejector marks working up my first 6BRA loads with new brass and thought I was seeing pressure signs but after the 3rd firing there’s no sign of it anymore

View attachment 842723

That's good to know! Did your ejector marks disappear through tumbling or not? My only thought is seeing two sets of ejector marks on three times fired brass and wondering if two of them overlapped or if the marks no longer appeared at all!

I need to do some confirmation tests this weekend on the two nodes. I have 20 unfired cases left or around 80 once fired cases. I think I'd struggle doing confirmation tests on two loads with twenty cases but I don't want there to be any potential variances using fired cases instead of factory.

Thoughts?

 

[Nature Boy]

Did your ejector marks disappear through tumbling or not?

Yes, don't see them any more