Deeredriver Posted September 13, 2015 Report Share Posted September 13, 2015 I have a .260AI with a tight neck, .290''. After waiting a very long time the H4831sc has arrived. I loaded up some test rounds and went out to test this morning. My first load was 47gr H4831sc pushing a 139gr Scenar seated .010'' off the lands. This produced a good 7 round group of .6' having shot three then setting up the chrono while waiting for the barrel/mod to cool before shooting the next 4 into the same cluster. The bolt had some resistance on opening. Speed was 2830fps with a low ES. The next round was 47.5gr but this time the bolt had a fair bit of resistance and the brass showed high pressure signs so I stopped there. This didn't concern me at the time, so while I had the chrono out I thought I'd recheck my usual loads, 43.7gr H4350/139gr Scenar. Again this load showed very high pressure with flattened primers, and extractor/plunger marks on the base. I've used this load for the last 400 plus rounds with no previous problems. The rifle was fine the last time I used it. So has anyone any idea as to what has happened? Link to comment Share on other sites More sharing options...
MJR Posted September 13, 2015 Report Share Posted September 13, 2015 Are the 4350 rounds made with the same lot of powder or a new canister from a different batch? If a difference thatch you might have to rework your load. How clean is the throat of your rifle? Have you got a ring of carbon in there increasing pressure? How much neck clearance do your loaded rounds have in the tight neck? Check the lugs on your bolt to check they aren't gauled. Link to comment Share on other sites More sharing options...
Andrew Posted September 13, 2015 Report Share Posted September 13, 2015 Is there a chance that your brass is work hardened and tired? My 220AI would start showing "pressure signs" when the case (not the neck) lost the elasticity to grip the (largely parallel) sides of the chamber walls at peak pressure. Fresh brass cured the problem.~Andrew Link to comment Share on other sites More sharing options...
Deeredriver Posted September 13, 2015 Author Report Share Posted September 13, 2015 Double post. Link to comment Share on other sites More sharing options...
Deeredriver Posted September 13, 2015 Author Report Share Posted September 13, 2015 Are the 4350 rounds made with the same lot of powder or a new canister from a different batch? If a difference thatch you might have to rework your load. How clean is the throat of your rifle? Have you got a ring of carbon in there increasing pressure? How much neck clearance do your loaded rounds have in the tight neck? Check the lugs on your bolt to check they aren't gauled. Hi, thanks for the suggestions. The H4350 rounds are the same batch as used before so I'm assuming it's a problem with the throat/chamber?? The bolt lugs are fine, I always clean the rear of the lugs and re-grease before use. I'm running .002'' clearance on a loaded round. A carbon ring is a possibility, I normally clean after every use with a combination of Wipe Out using a bronze brush/patches and Forest foam. I've never suffered with this before, but this is my only tight necked rifle. Is there a chance that your brass is work hardened and tired? My 220AI would start showing "pressure signs" when the case (not the neck) lost the elasticity to grip the (largely parallel) sides of the chamber walls at peak pressure. Fresh brass cured the problem.~Andrew The brass is Lapua and has only been sized three times, so far it's been very stable. Link to comment Share on other sites More sharing options...
Leeman Posted September 13, 2015 Report Share Posted September 13, 2015 I would suggest you're maybe not running enough neck clearance. Without knowing what cases you've used to form the improved version from, is it possible you have a doughnut at the neck/shoulder junction or maybe the case necks have just thickened enough to push pressures upwards. I'd sacrifice a couple of cases and either run a neck reamer through or just turn a couple of thou off the neck. A simple check would be to see if you can push a bullet into a fired case without resizing the neck. If no, you've definitely not enough clearance, in my opinion. Richard. Link to comment Share on other sites More sharing options...
Deeredriver Posted September 14, 2015 Author Report Share Posted September 14, 2015 I would suggest you're maybe not running enough neck clearance. Without knowing what cases you've used to form the improved version from, is it possible you have a doughnut at the neck/shoulder junction or maybe the case necks have just thickened enough to push pressures upwards. I'd sacrifice a couple of cases and either run a neck reamer through or just turn a couple of thou off the neck. A simple check would be to see if you can push a bullet into a fired case without resizing the neck. If no, you've definitely not enough clearance, in my opinion. Richard. I spoke to Neil McKillop who barrelled the rifle and he suggested the same. I'm going to turn down a batch a couple of thou more then retest. Link to comment Share on other sites More sharing options...
MJR Posted September 14, 2015 Report Share Posted September 14, 2015 So how much clearance are you running and what has changed if you are using the same brass/powder as before? Link to comment Share on other sites More sharing options...
Deeredriver Posted September 14, 2015 Author Report Share Posted September 14, 2015 I've been running .002'' clearance. Same batch as before, but the brass have now been fired three times. I spent last night giving the barrel a good clean, just in case there is a carbon build up. Link to comment Share on other sites More sharing options...
Swarovski1 Posted September 28, 2015 Report Share Posted September 28, 2015 Sounds like it's either the neck clearance or carbon fouling or both.just get a 6.5 06 mate Link to comment Share on other sites More sharing options...
bewsh Posted October 13, 2015 Report Share Posted October 13, 2015 I had a lot of (as in a particular production rather than quantity) lapua .243 brass work harden in 2-3 firings annealing solved it Link to comment Share on other sites More sharing options...
onehole Posted October 13, 2015 Report Share Posted October 13, 2015 I would suggest you're maybe not running enough neck clearance. Without knowing what cases you've used to form the improved version from, is it possible you have a doughnut at the neck/shoulder junction or maybe the case necks have just thickened enough to push pressures upwards. I'd sacrifice a couple of cases and either run a neck reamer through or just turn a couple of thou off the neck. A simple check would be to see if you can push a bullet into a fired case without resizing the neck. If no, you've definitely not enough clearance, in my opinion. Richard. Agree with this,,,,I think 2 thou is ok as long as your being real clean,,,,favouring a doughnut ,,,,re neck turn and eat a bit more into shoulder?,,,,hope you have some luck,,,,,,,O Link to comment Share on other sites More sharing options...
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