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Overpressure vs Speed

Discussion in 'Ammunition & Reloading' started by CrossHairs, Feb 18, 2010.

  1. CrossHairs

    CrossHairs Tigard Active Member

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    I loaded up some .223 rounds for my AR and got them to the range last weekend and threw them over the chrony. Here's the stats

    LC brass, BL-C(2) 26gr and 27gr with a Hornady FMJ BT 55gr round in it. CCI 400 primers.

    After shooting off a couple I checked the cases as I always do and then the primers. I noticed that the primer was certainly flatter than I've seen on any of my loads previously (for my Savage 12 VLP), yet speed wise, I was only getting 2600 and 2700 fps (give or take ten or so fps) respectively.

    One of the things you read/hear is load till you see the pressure signs using the chrony to see if your nearing the max.......but the max of what? In this case, the speeds are nowhere near what I would have expected for a max load....and what would I expect...well certainly something on the high side of 3000 fps and up...or am I just misguided?

    I immediately suspected that the primers are a little softer than factory ammo because I also threw in a few loads that had gone through the Savage, and they too appeared to have a little flattening, yet I did not notice that when I fired them from the savage.

    Thoughts? Warnings of dire consequences?
     
  2. the4thshake

    the4thshake Portland Active Member

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    What is your barrel length?

    Pop some of the primers out and see if they look like mushrooms.

    Have you tried another brand of primer?
     
  3. CrossHairs

    CrossHairs Tigard Active Member

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    It's a colt LE6920 with a 16" barrel. And yes, one or two mushroomed, but I just noticed that some other quite tame loads had mushroomed on my Savage rounds. and no, I've not tried another primer, I definately think I should though. Finding some might be the challenge!
     
  4. the4thshake

    the4thshake Portland Active Member

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    It is very well possible the burn rate of that powder is just too slow for that weight of bullet in the shorter barrel. I would try a faster burning powder if I were you.
     
  5. CrossHairs

    CrossHairs Tigard Active Member

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    So I took the same loads to the range today and ran them through my Savage, as expected they are heading out of the barrel much faster, 3026 fps average, and here is the weird part, not a single sign of flattening of the primer....bear in mind that this is the same brass, same bullets same powder same primers....different gun!

    So, I suspect that the AR is playing some part in this, and I really don't think that the load is particularly hot.

    I may run a few more through the AR to see. As for the speed....I'm really after a plinking round anyway, so it was not top speed I was after, just something that got out to 100 yards tops with some degree of accuracy, but would be more likely to be hitting 50 yds targets with the dot sight.
     
  6. rudedog04

    rudedog04 oregon-roseburg Member

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    if bullets get up near lanz also creates pressure. also look at case heat did it leave any marks from extractor?
     
  7. CrossHairs

    CrossHairs Tigard Active Member

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    There were some marks on the base of the brass from the extractor.

    I have to say, I did not consider the OAL as these rounds are seated to book specs....but I do have a guage, I'll take a look tomorrow and see if for some odd reaon, the FMJ BT's are somewhat longer to the point of the ogive. Either way, I could certainly set them back a little and see if that helps.
     
  8. branchbuster

    branchbuster Albany Active Member

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    Might be a headspace issue with your AR or case sized too short.
     
  9. RVTECH

    RVTECH LaPine Well-Known Member

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    Are you using Military brass or stock .223 Remington brass? Some military brass is heavier with a much thicker case neck which can create pressure issues depending on gun's chamber size and headspace. I ran into this problem many years ago reforming .308 brass for my .243. Got rid of all the reformed .308's and went with stock .243.
     
  10. Gunner3456

    Gunner3456 Salem Well-Known Member

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    You will get lower velocities out of the AR with the shorter barrel and semi-auto mechanism than you will out of the Savage.

    Using LC brass and CCI primers I don't have any damaged case or primer issues pushing the 55gr bullets to 3150 in an AR-15, 16" barrel. I do have to load to the higher end of the powder recommendations, but not beyond it. I do this with several types of .223/556 appropriate powders because for the past couple of years I didn't always have a choice of powders to buy.

    I worry more about primers bulging out on the outside, or even backing out of the case's primer pocket than anything else when looking for pressure problems. I don't ream LC brass primer holes. I swage them. I've had no problems at 3150 fps, but ymmv.
     
  11. CrossHairs

    CrossHairs Tigard Active Member

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    Interestingly enough, I tried some IMR4064 which is slightly faster than the BL-C(2) as I had some on hand. Velocity was slightly slower but comparable yet did not exhibit the same problem. Might just stick with some of that powder for a few rounds. Also picked up some IMR 4198 to try it's up the scale in terms of speed. Let's see how that pans out.
     
  12. Gunner3456

    Gunner3456 Salem Well-Known Member

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    Have you tried H335? Please check and double check the max recommended load and don't take my word for it. I could be brain dead or guilty of a typo.

    I get 3150 fps and great accuracy with a 55gr bullet with 25.2 gr of H335 in a 16" 1:9 twist barrel. I show no case or primer stress. This is with LC brass and CCI primers. You will do worse with standard commercial brass for several reasons including but not limited to case capacity and resultant pressure differences. Also, I would not be comfortable loading commercial brass that hot, even though I believe the load is within specs.

    Double check me on that max recommended load please.
     
  13. CrossHairs

    CrossHairs Tigard Active Member

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    Thanks for the heads up Gunner, H355 appears somewhere below 322 on the powder speed chart, I have not tried it, but I do have a little 322 to have a go with too. I'll keep the 355 in mind if I can grab some.

    To re-iterate, not so worried about getting these rounds to max velocity either, as long as it falls somewhere between 2700 and 2900(preferably closer to the latter) they should be just fine for 50 yard plinking with a dot sight. So I'll be avoiding too many full charges for now.
     
  14. Gunner3456

    Gunner3456 Salem Well-Known Member

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    It's H335. 335. :thumbup:
     
  15. CrossHairs

    CrossHairs Tigard Active Member

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    Damn! Was typing on the iPhone....things great until you need to actually write something !!!!
     
  16. CrossHairs

    CrossHairs Tigard Active Member

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    OK, so I've been experimenting.

    I've used H322, the BL-C(2) as previously mentioned, IMR 4198 and IMR 4064.

    It seems, that no matter what the load I'm getting some primer flattening. Today I tried some H322 with 21, 21.5, 22 and 22.5 gr loads behind a 55 gr FMJ BT. And earlier in the week I used the 4198 with 19, 19.5 and 20 gr loads. All of these are low to midway through the speed charts.

    Also, the powders are considerably faster than the IMR 4064 and BL-C(2) on the burn rates scales.

    Interestingly, the IMR4198 and H322 gave me almost identical performance of 2585 average with both the H322 and the IMR4198 at the mid loads of 21.5 and 19.5 gr.

    I checked the headspace...I'm no where even close to the lands in the barrel, can't remember the exact measurement right now, but it was pretty substantial. I also measured the casings near the base for expansion and can see none that was discernable.

    So, I am lead to believe that the primer flattening is caused by something else and not the load. If I can lay my hands on some mil type primers, I'll see what happens, but for now, I am 'fairly' confident (make that almost convinced, but not quite) that this is not an overpressure issue. Shots using the same rounds from the savage just don't lend me to believe that the load is too hot.

    If someone else has anything the add...I'd be happy to hear it.
     
  17. Gunner3456

    Gunner3456 Salem Well-Known Member

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    Can you please describe "primer flattening?" What is happening - what are you seeing, exactly?
     
  18. CrossHairs

    CrossHairs Tigard Active Member

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    Here. Same load fired from my Savage 12 VLP and my Colt LE6920. The left case came out of the Colt.
     
  19. Gunner3456

    Gunner3456 Salem Well-Known Member

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    I don't see unusual flattening of the primer. I certainly don't see bulging from over pressure. I see a very hard primer strike from the Colt's firing pin which has upset the metal around the pin strike area.

    Factory XM193 has a harder, thicker primer than you are probably using, even in CCI.

    I don't see anything that I would worry about but if you want you could find a lighter firing pin spring for the Colt, or you could switch to the mil spec primers from CCI. It might be CCI #41, but I can't remember. Someone else here will know. I think it's this: Link

    I wouldn't worry about it unless the Colt ever, even once, punched a hole in a primer or slam-fired (fired more than one round per trigger pull.) I've never bought the mil spec primers and I've never had a real problem.
     
  20. CrossHairs

    CrossHairs Tigard Active Member

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    Thanks Gunner, I don't feel there is an issue either, I was just very aware that the primer looked a little different than I expected. And yes, I chose that case as a worst case of cratering the primer, not all showed that particular condition. So, unless I drill a hole into a primer or get a slam fire, I'll just carry on as I am.

    Thanks for the input, that's whats great about the forums.