Thanks for the detailed write up. The comment about the standard chamber vs AI was interesting and something I have been considering. My load right now is pushing a 108ELDM just over 3000fps with H1000 in a 24" barrel, so I'd likely be around the 2900 as well cut down to 20". Lack of trimming would be cool, not sure if it's worth the extra work of an AI. Seems like if a guy was going to do the extra work why not chase the extra speed with a SAUM/PRC wildcat. All things to consider.
243 AI-Any Input?
- Thread starter PathFinder
- Start date
OP
OP
PathFinder
WKR
How many grains of H1000 is that load? The load I'm using now is 47.7 grains. Went quite a bit higher, but got clickers and even an ejector mark on the Alpha brass.
49.3 in virgin Starline brass got me 3014 fps across 10 shots.
OP
OP
PathFinder
WKR
After finally purchasing a proper chronograph (replaced a glitchy Magnetospeed with an Athlon), it was time to work up to speed/pressure again. I need matching head stamp brass for an upcoming Africa trip, so the test was conducted with both Federal and Alpha brass that were previously fire formed. Alpha brass had 4-5 firings on them, Federal had one past the initial fire form. The barrel had 526 rounds down it at the beginning of this test.
I've attempted to fire form Winchester brass in the past, but about 50% of them rupture at the shoulders. They are significantly lighter, and I assume the thinner walls are what prevent them from successfully forming. Federal weigh about the same as Alpha, so hopefully they form more successfully. Components were H1000, CCI 200, and a 116 TMK. COAL of 2.920.
As always, work up, but these are the charges and velocities:
Alpha:
49: No data. ~2900 est. Had the chrony too low.
49.5: 2929
50: 3000
50.5: 3003
Federal:
49: 2886
49.5: 2913
50: 2919
50.5: 2987
No significant pressure signs from any of the loads above. No heavy bolt lift, ejector marks, or clickers. The Alpha brass, on their 2nd and 3rd firings, were prone to clickers above 48 grains. This was only a few rounds, but now on their 4th-5th firings that problem didn't resurface. The bolt lift was somewhat lighter on the Federal brass. Overall very promising, and more in line with the target velocities for this round. Targeting 3k fps in either brass is looking really good right now.
Also fire formed six more Federal brass to see how they'd hold up. All six formed successfully with 39 gr H100V and a 105 Hybrid at 2880 fps. I want to research different brass (especially Starline) to see which others might be prone to successful fire forming. There will be a separate thread to collect data, but adding brass weights here would be helpful.
Alpha: ~176 grains
Federal: ~175 grains
Winchester: ~160 grains
I've attempted to fire form Winchester brass in the past, but about 50% of them rupture at the shoulders. They are significantly lighter, and I assume the thinner walls are what prevent them from successfully forming. Federal weigh about the same as Alpha, so hopefully they form more successfully. Components were H1000, CCI 200, and a 116 TMK. COAL of 2.920.
As always, work up, but these are the charges and velocities:
Alpha:
49: No data. ~2900 est. Had the chrony too low.
49.5: 2929
50: 3000
50.5: 3003
Federal:
49: 2886
49.5: 2913
50: 2919
50.5: 2987
No significant pressure signs from any of the loads above. No heavy bolt lift, ejector marks, or clickers. The Alpha brass, on their 2nd and 3rd firings, were prone to clickers above 48 grains. This was only a few rounds, but now on their 4th-5th firings that problem didn't resurface. The bolt lift was somewhat lighter on the Federal brass. Overall very promising, and more in line with the target velocities for this round. Targeting 3k fps in either brass is looking really good right now.
Also fire formed six more Federal brass to see how they'd hold up. All six formed successfully with 39 gr H100V and a 105 Hybrid at 2880 fps. I want to research different brass (especially Starline) to see which others might be prone to successful fire forming. There will be a separate thread to collect data, but adding brass weights here would be helpful.
Alpha: ~176 grains
Federal: ~175 grains
Winchester: ~160 grains
OP
OP
PathFinder
WKR
Update:
After more testing, 50 gr H1000 is a no-go in both Alpha & Federal brass, magnum and standard primers were essentially identical for pressure and velocity. The first dozen or so I shot were ok, since then every single one has very heavy bolt lift and leaves heavy swipes & ejector marks. Average velocity for them is about 2940.
With that, I'll play around with a couple more powders just for kicks. Planning to keep the load around 2800 fps with the 115/116 grain bullets.
After this barrel is done, I'll probably leave my next one as a standard 243, or pick up one of the new 7.5 twist 6 CM barrels if they're available by then. 2800 fps can be done in an 18" barrel with less powder, no fire forming, and no special dies.
After more testing, 50 gr H1000 is a no-go in both Alpha & Federal brass, magnum and standard primers were essentially identical for pressure and velocity. The first dozen or so I shot were ok, since then every single one has very heavy bolt lift and leaves heavy swipes & ejector marks. Average velocity for them is about 2940.
With that, I'll play around with a couple more powders just for kicks. Planning to keep the load around 2800 fps with the 115/116 grain bullets.
After this barrel is done, I'll probably leave my next one as a standard 243, or pick up one of the new 7.5 twist 6 CM barrels if they're available by then. 2800 fps can be done in an 18" barrel with less powder, no fire forming, and no special dies.
OP
OP
PathFinder
WKR
Tested a couple more powders just for kicks. Staball 65 was unimpressive. Maxed out at 44 grains and 2860 fps, with pressure signs down at 2800. N560 was a little more encouraging, it made 2900 at 46 grains. Both of these were in Alpha brass.
I worked up a training load with blem 107 SMK and some 7828 SSC that was laying around. 43 grains at 2800 fps was very mild initially, accuracy was typical of this barrel at around 1.2" for ten shots. That load started showing pressure signs in the Alpha brass, velocity is the same. No issue in the Federal brass. The worst part was that two of about 20 shots in the Alpha brass had partial case head separations. I'm not sure what the deal is, but I won't be shooting any more of it. Since the Alpha brass has a substantially thicker neck, I'm thinking it may be a neck clearance issue related to fouling. The barrel now has 658 rounds on it.
Whatever the cause is, I'm over the boutique cartridges. I'll be going back to a standard 6 CM just as soon as I can get my hands on a factory Tikka 6 CM barrel. This barrel, dies, brass, etc will be for sale after this weekend. This was a fun experiment, but the more I shoot high volumes in field conditions, the more apparent it becomes that keeping things simple, cheap, and reliable is much more effective than chasing small gains in case geometry.
Reaching significantly higher velocities than other standard cases in the 243 AI just didn't work reliably with high round counts. The 6 CM has a standardized reamer, more neck clearance, correct freebore on standard reamers, more brass availability, easy die availability, no fire forming, and should reach the same velocity reliably. There's some possibility of using Peak brass too, but that would be its own rabbit hole in terms of reliability.
I worked up a training load with blem 107 SMK and some 7828 SSC that was laying around. 43 grains at 2800 fps was very mild initially, accuracy was typical of this barrel at around 1.2" for ten shots. That load started showing pressure signs in the Alpha brass, velocity is the same. No issue in the Federal brass. The worst part was that two of about 20 shots in the Alpha brass had partial case head separations. I'm not sure what the deal is, but I won't be shooting any more of it. Since the Alpha brass has a substantially thicker neck, I'm thinking it may be a neck clearance issue related to fouling. The barrel now has 658 rounds on it.
Whatever the cause is, I'm over the boutique cartridges. I'll be going back to a standard 6 CM just as soon as I can get my hands on a factory Tikka 6 CM barrel. This barrel, dies, brass, etc will be for sale after this weekend. This was a fun experiment, but the more I shoot high volumes in field conditions, the more apparent it becomes that keeping things simple, cheap, and reliable is much more effective than chasing small gains in case geometry.
Reaching significantly higher velocities than other standard cases in the 243 AI just didn't work reliably with high round counts. The 6 CM has a standardized reamer, more neck clearance, correct freebore on standard reamers, more brass availability, easy die availability, no fire forming, and should reach the same velocity reliably. There's some possibility of using Peak brass too, but that would be its own rabbit hole in terms of reliability.
Steve300xcw
WKR
- Joined
- Oct 19, 2017
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I didnt care for staball 6.5 either. Was rather spikey in the limited time I tried it.
+1 for simple/cheap
Just a boring ol 243 with h1000 and 105/108's can do pretty well btw
+1 for simple/cheap
Just a boring ol 243 with h1000 and 105/108's can do pretty well btw
OP
OP
PathFinder
WKR
That was another conclusion, that a standard 243 gives up almost nothing the the Improved. I have a 243 Tikka barrel sitting in the safe too, but I have way more Creedmoor brass and a die set already. The Tikkas being a 7.5 in the 6 Creedmoor is the final factor for the decision.
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