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Posted: 5/3/2010 7:36:12 PM EDT
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Great suppression, and wonderful accuracy... but pressure signs seem higher than when shooting without the can. This is with a Rem 700 .308 Winchester bolt-action, not a gas gun. Is this normal? unsuppressed left, ............................................................. suppressed right  Thank you |
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Quoted:
Great suppression, and wonderful accuracy... but pressure signs seem higher than when shooting without the can. This is with a Rem 700 .308 Winchester bolt-action, not a gas gun. Is this normal? Thank you Suppressors always increase back pressure. Are you shooting factory ammo? I could see handloads that are on the top edge of safe pressure going a little over pressure with a can attached. |
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By the time a bullet reaches the interior of a suppressor, the pressure has dropped to less than 9K psi, AKA muzzle pressure. I know that the "dwell time" is increased, but that I think is more a function of gas guns. Still, I haven't met Jack S... so maybe you are on the money. Appreciate the response. |
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I don't know if it's "good", but that small primer flow around the firing pin happens to alot of my handloads wih the can on. Only full-power though, the sub loads don't do it. I guess until you asked, I never thought about it bening the can's fault. Sometimes it'll even flatten the primer out pretty good if the load is right at the top end. I have figured out that with a can attached, as a general rule I stay about 10% off the top of any load.
Thanks for sharing. Were those handloads? Cheers, Benji |
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Very interesting.
Do you have a friend with another can to try it out with? I have a feeling that any can would do that... maybe a reflex can would act differently for you? I've never had that problem with cans from Gemtech, SWR, Ops, Surefire, or AAC in .223, .308 or .300 weatherby on my reloads or factory ammo. Semper Fidelis, Kent |
| How often does this happen? If it's just these two, then it might be coincidence. If you shot 20-30 rounds with and without, would the groups be this distinguishable? The one on the left still has some pressure signs (raised material around the firing pin strike) so it's also on the edge. It might just be pure randomness at this point. |
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The silencer is an AAC Cyclone, the ammunition was "loaded" in new Lapua cases, CCI BR2 primers, 175 SMK's and 1/2 grain under "book maximum." I agree that "Book maximum" is a meaningless term... Yes, the rifle has a Sako extractor, and yes there should never be case head deformation. Round count is barely over 1K Silencer was tried on another rifle with the same loads and no discernable difference was noted there. A different Cyclone was shot previousily, but not enough rounds to know what was going on. I appreciate the experience of the forum and the help rendered...Thanks |
| The primer flow in the left pic is normal with modern day remingtons. Irritated me to no end so I sent my bolt to Gre-tan rifles to have the bolt face bushed. The case head flow in the right pic is not. Definite sign of overpressure, and yes a supressor can cause it. |
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What's surprising in this is that the results above suggest that peak pressure can be raised from use of a silencer. That seems counter intuitive simply because the highest pressure should logically occur long before the bullet reaches the end of a typical rifle barrel, and the expansion chamber of a suppressor should cause pressure in the chamber to drop substantially from what was present before the bullet exited the barrel.
From what I've heard Lapua brass is on the lower side of volume. It may be smart to reduce your load at least 1/2 a grain because with Lapua brass you may be over the max load of an American loading manual. Accuracy is more important than velocity anyway and most guns should shoot a little better with a slightly reduced load than with a max load. Have you measured your loaded OAL? Is it within spec? Do you have load data for the exact bullet you are using? After reading your post on Snipers Hide it would seem that your barrel may be getting fouled and this may contribute. Hard to say. It still sounds like the load is probably very close to dangerous. Different powders can cause different pressures at the same bullet exit velocity. This would seem to suggest you may be able to switch powders and keep the same velocity and drop pressure depending on where your powder falls regarding that. |
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Quoted:
What's surprising in this is that the results above suggest that peak pressure can be raised from use of a silencer. That seems counter intuitive simply because the highest pressure should logically occur long before the bullet reaches the end of a typical rifle barrel, and the expansion chamber of a suppressor should cause pressure in the chamber to drop substantially from what was present before the bullet exited the barrel. From what I've heard Lapua brass is on the lower side of volume. It may be smart to reduce your load at least 1/2 a grain because with Lapua brass you may be over the max load of an American loading manual. Accuracy is more important than velocity anyway and most guns should shoot a little better with a slightly reduced load than with a max load. Have you measured your loaded OAL? Is it within spec? Do you have load data for the exact bullet you are using? After reading your post on Snipers Hide it would seem that your barrel may be getting fouled and this may contribute. Hard to say. It still sounds like the load is probably very close to dangerous. Different powders can cause different pressures at the same bullet exit velocity. This would seem to suggest you may be able to switch powders and keep the same velocity and drop pressure depending on where your powder falls regarding that. There are a lot of variables that aren't being shared and I haven't read the Snipershide thread. Its pretty much a guess at this point. Could be a hot load, could be a load that was safe at lower temps but is now unsafe with spring temps rising, could be a carbon ring in the throat, could be a bad lot of powder. As said by Skillshot, we need to see a larger sample and need to see exactly what is going on with the load. Personally I'd scrub the barrel clean and then I'd run the load across a chronograph with and without the can ( I predict less than 20fps difference though). |
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This .308 Win 26.5" barreled rifle has a known behavior and tolerance for both accuracy and pressure.
Using new Lapua brass and a known load after shooting about 12 rounds very slowily (25 minutes) the pressure begins to build. I removed the AAC Cyclone and shot several rounds and pressure appeared to diminish. I then reattached the unit and pressure began to rise again after about 5 rounds. I had ten rounds remaining and fired without the unit and even allowing rounds to cook a bit could not generate similiar visual signs of pressure. The signs were; very slightly stiff bolt lift, extruded primer material into the firing pin hole occasionally, ejector marks and brass jamming the ejector assembly. This was that other post (most of what was technical in it.) The 26.5" barrel for me really makes the idea of the silencer increasing pressure hard to believe. |
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Quoted: What's surprising in this is that the results above suggest that peak pressure can be raised from use of a silencer. That seems counter intuitive simply because the highest pressure should logically occur long before the bullet reaches the end of a typical rifle barrel, and the expansion chamber of a suppressor should cause pressure in the chamber to drop substantially from what was present before the bullet exited the barrel. From what I've heard Lapua brass is on the lower side of volume. It may be smart to reduce your load at least 1/2 a grain because with Lapua brass you may be over the max load of an American loading manual. Accuracy is more important than velocity anyway and most guns should shoot a little better with a slightly reduced load than with a max load. Have you measured your loaded OAL? Is it within spec? Do you have load data for the exact bullet you are using? After reading your post on Snipers Hide it would seem that your barrel may be getting fouled and this may contribute. Hard to say. It still sounds like the load is probably very close to dangerous. Different powders can cause different pressures at the same bullet exit velocity. This would seem to suggest you may be able to switch powders and keep the same velocity and drop pressure depending on where your powder falls regarding that. OK, what has been done is to try the load both suppressed and un suppressed. When shot in the "conventional" un suppressed manner there are no indications of excess pressure. What appears to be happening is that dwell time of the pressure has been increased, and yes I do think the load was right at the top end, but safely there. Now what has been done is to reduce the powder charge using the OBT - OCW method and with 8/10 grains less of the Varget all is well once again. I am going to shoot more extended strings between cleaning and see if there is any difference in that. I wholly agree that it is counter intuitive that a longer barrel could increase pressure, however... the length of time or dwell is apparently the culprit. Mike Mers answered a PM addressing the barrel length as most likely the problem. Appreciate the input, in all cases. |
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Quoted:
The silencer is an AAC Cyclone, the ammunition was "loaded" in new Lapua cases, CCI BR2 primers, 175 SMK's and 1/2 grain under "book maximum." I agree that "Book maximum" is a meaningless term... Yes, the rifle has a Sako extractor, and yes there should never be case head deformation. Round count is barely over 1K Silencer was tried on another rifle with the same loads and no discernable difference was noted there. A different Cyclone was shot previousily, but not enough rounds to know what was going on. I appreciate the experience of the forum and the help rendered...Thanks Was it a hot day? 1/2 under max wouldn't surprise me flowing the case into the boltface if you worked it up on a cool day and then shot it hot. OR you shot it with a HOT chamber and the chamber warmed your powder. I'm running 175 OTMs, 42.5 of Varget, WLR Primers, and Lapua brass and have never had that problem before in my Remington 5R. I've even run up to 45 grains and never had those kind of impressions on LAPUA brass. Lapua brass is VERY strong on the casehead so I really expect you've got an overpressure problem. I've never even seen that with 338 Lapua and top end loads on a hot day (300 OTMs with 89.0 RL25 in Lapua brass, Fed 215M primers). Sounds to me like you need to back of your load, probably 2 grains for use on hot days or with a hot gun (or with a can). -David Edgewood, NM |
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Lapua has less internal volume as noted above. There's a hint right there.
Instead of coming down from a perceived Max load, which may actually be over-pressure, I suggest working up from start load as with any new load. This will show at what point the pressure signs are developing. At the very least drop down to the mid range of the load, half way between Start and Max, and make a comparison. A thorough inspection/cleaning goes without saying. Calling the Can Maker might also be a good 10-15 minute investment. Good luck. Be safe. |
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