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Gas Gun & Ejecter Swipe

Bigwheels

Gunny Sergeant
Full Member
Minuteman
  • Jun 16, 2007
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    Anacortes WA
    How much ejector swipe is "normal" for a DPMS LR 308?
    I just started a ladder test with Varget, & 208 A Max. Loaded to mag length, which is in there a lot. I went from 39.0-41.7 but didn't get that far. Over 41gr I was seeing pretty hard cratering, & obvious ejector swipe. BUT I also had some lower charges that showed swipe, & didn't on the next one. Seems random. My 150gr BT load also does the odd one. I also noticed that as the charge increased the brass began ejecting farther to my side. The lower charges landed more forward.Say 2:00 position on the lower charges, & almost 3:00 for the heavier ones. This is the 1st gas gun I've ever done load work up on.
    Thanks.
     
    Re: Gas Gun & Ejecter Swipe

    I think that ejector swipes are a warning sign, in any degree, gas gun or bolt. By the time you're getting that hot, pressures are probably already excessive.

    I would also suggest that anything beyond 175gr is getting a bit heavy for a semi.

    When you're loading for a semi, accuracy and LR reach are only a part of the equation. Good operation and operational reliability become real issues.

    Starting in the days of the Garand (oh, yes; I know it's a very different beasty), basic lore has strongly suggested avoiding slower propellents and heavier projetiles for semis in general. The AR system negates some of that need, but I stiil suggest that following such advice makes life easier for the semi's handloader.

    I have done extensive load development for the AR-15, M1 Garand, M1A, and SKS, and have seldom found an instance where heavier bullets and slower projectiles paid any significant dividends.

    My first semi was the Norinco SKS, and with glassbedding and load development, I was able to shoot competitively among the NRA NJ Highpower N/M League shooters at 200 and 300yd. Not a world beater, but good enough to keep me coming back until I got my Garand. These days, I still have the SKS and Garand. I found I could live well enough without the others up until very recently. Maybe I still could but I'm still looking for a Varmint AR.

    Greg
     
    Re: Gas Gun & Ejecter Swipe

    The main reason I ask is that I get swipe on the odd one using factory loaded ammo as well. Is that normal, or is there something I should be looking for in my BCG, or something?
     
    Re: Gas Gun & Ejecter Swipe

    A heavier buffer or an ajustable gas block are your two options other than changing loads. You are the first I have seen trying to launch 208 grain bullets
    so it's new territory to me. 175's are as heavy as I ever loaded and the 155's are
    my favorite. Greg hit it right on. Powder speed is the first thing I change if I want
    to make a good bullet work and have problems. I can't see a 208 at much over 2400
    fps from an AR. You are using gas gun loading data?
     
    Re: Gas Gun & Ejecter Swipe

    Never seen a load book for gas guns. So no, I'm using the data from Hodgdon for 200gr, & proceding slowly. I'm not expecting to get over 2300, but with a .650 BC even @ 2300 the bullet is SS past 1000yd @ SL, & bucks the wind better than anything. I'm giving it a try simpilly because I have a bunch of them left over from when I switched to the 225's in my 300WM.
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Greg Langelius *</div><div class="ubbcode-body">I would also suggest that anything beyond 175gr is getting a bit heavy for a semi.</div></div>

    I agree with Greg.

    In order to push the big heavy bullets, you want a) longer barrel, b) slower burning powder. This causes the pressures in the gas operating mechanism to increase dramticaly, shortening the life of the action even if no excess pressures are found. So Varget is probably not the correct powder for these heavies, and heavies are probably not tthe bullet of choice for these guns.

    Its no wonder you are seeing pressure signs.
     
    Re: Gas Gun & Ejecter Swipe

    If you want to run heavies in the AR you really need to choke down amount of gas that is cycling the BCG and run heaviest buffer you can.

    Varget/RL15/N-140 or similar burn rate is fine with the 208s but to make it work you'll need an adjustable gas block and heavier buffer then comes with factory DPMS rifle.
     
    Re: Gas Gun & Ejecter Swipe

    You never run bolt gun load data through a gas gun in .308. Just not the same
    as a .223/5.56. Sierra and Speer (iirc on the speer) have gas gun data.
     
    Re: Gas Gun & Ejecter Swipe

    OK. At least it was learning experience. I guess I'll just tune up some 150-155's, & accept what I get. I have a 300WM for the real long stuff. Just everyone has banned it from comps for hitting the steel too hard.
    Thanks guys.
     
    Re: Gas Gun & Ejecter Swipe

    I'd stick with the bigger bullets, you'll be happier in the long run.

    175/178 min, 190 is what I run in my personal AR, no reason to not run the 208s just need a few minor adjustments to the overall system.
     
    Re: Gas Gun & Ejecter Swipe

    Well, I wouldn't immediately swear off everything bigger'n 155's, 168 could end up being an ideal bullet for the rifle's capabilities. In any case, if the 150/155's are a new experience, it'll probably be a learning experience too, and maybe a profitable one at that. My only goal here is to help you find something you'll like better and like longer.

    Also, just because ammo comes from a factory doesn't mean it's OK in a semi. I wouldn't use <span style="font-style: italic">any</span> hunting load in a Garand, and we have already covered the Hornady Superformance loads in AR's here. Very good ammo, just maybe not so good in a semi.

    Greg
     
    Re: Gas Gun & Ejecter Swipe

    I thought about using the 150-155's due to having a TON of 147 NATO surp I have. I'm not against trying the 165-168's etc. But I only have a 16" brl, so I'm not going to get much velocity out of anything I run. I see 2600 out of the 150's.
     
    Re: Gas Gun & Ejecter Swipe

    I am showing 1225 feet per second at sea level with a Berger 155.5 @ 1000 with your 2600fps launch. They
    are an extremely accurate bullet as well. Many say better than the Lapua.
     
    Re: Gas Gun & Ejecter Swipe

    Well, here's my experience:

    Don't sweat it. I ran ladders with 175smk and Varget, from 41gr - 45.5gr, in my LR308 SASS.

    I got swipes on every single one (and I ran a pair of identical ladders). Not only that, but I got JUST as much swipe @ 41gr than I did at 45.5....perhaps more.

    Also, the rifle stovepiped on one of the 41gr charges, and very obviously was NOT overpressure.

    Lastly, while not a "great" indication of pressure, primers were totally rounded - not even starting to flatten in the lower charges.

    It's good of you to raise an eyebrow when you see the swipe, but at leadt in my LR 308, it isn't an indicator of pressure.
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Well, here's my experience:

    Don't sweat it. I ran ladders with 175smk and Varget, from 41gr - 45.5gr, in my LR308 SASS.

    I got swipes on every single one (and I ran a pair of identical ladders). Not only that, but I got JUST as much swipe @ 41gr than I did at 45.5....perhaps more.

    Also, the rifle stovepiped on one of the 41gr charges, and very obviously was NOT overpressure.

    Lastly, while not a "great" indication of pressure, primers were totally rounded - not even starting to flatten in the lower charges.

    It's good of you to raise an eyebrow when you see the swipe, but at leadt in my LR 308, it isn't an indicator of pressure.</div></div>

    You're getting swipes all the time because you're running Varget, gas port pressure is higher. I do too in my POF P-308, regardless of load. IMR4895 doesn't do this, but I like Varget so I stick with it.
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Well, here's my experience:

    Don't sweat it. I ran ladders with 175smk and Varget, from 41gr - 45.5gr, in my LR308 SASS.

    I got swipes on every single one (and I ran a pair of identical ladders). Not only that, but I got JUST as much swipe @ 41gr than I did at 45.5....perhaps more.

    Also, the rifle stovepiped on one of the 41gr charges, and very obviously was NOT overpressure.

    Lastly, while not a "great" indication of pressure, primers were totally rounded - not even starting to flatten in the lower charges.

    It's good of you to raise an eyebrow when you see the swipe, but at leadt in my LR 308, it isn't an indicator of pressure. </div></div>

    If you want to run your gun that way it's up to you. It's hard on the gun and
    hard on the brass. I am at a loss to understand how a stovepipe indicates
    pressure in any way?
     
    Re: Gas Gun & Ejecter Swipe

    Well, the jury would appear to indicate that swipes are not a reliable pressure indicator for this rifle, and I'm giving better credence to the rounder primer edges corresponding with expected <span style="font-style: italic">chamber</span> pressures.

    Slower powders (in this case, that should include Varget) would suggest a higher <span style="font-style: italic">port</span> pressure, and that's a good reason to stick with faster burn rates. IMR-4895 is a well respected gas gun propellent for just this reason. It is realistic to expect significantly increased action and brass stress with higher port pressures.

    Greg
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bigwheeler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: turbo54</div><div class="ubbcode-body">Well, here's my experience:

    Don't sweat it. I ran ladders with 175smk and Varget, from 41gr - 45.5gr, in my LR308 SASS.

    I got swipes on every single one (and I ran a pair of identical ladders). Not only that, but I got JUST as much swipe @ 41gr than I did at 45.5....perhaps more.

    Also, the rifle stovepiped on one of the 41gr charges, and very obviously was NOT overpressure.

    Lastly, while not a "great" indication of pressure, primers were totally rounded - not even starting to flatten in the lower charges.

    It's good of you to raise an eyebrow when you see the swipe, but at leadt in my LR 308, it isn't an indicator of pressure. </div></div>

    If you want to run your gun that way it's up to you. It's hard on the gun and
    hard on the brass. I am at a loss to understand how a stovepipe indicates
    pressure in any way? </div></div>

    If an autoloader typically shucks brass out 3 or 4 feet and never stovepipes, then all the sudden you try some "starting loads" and it only allows the brass to trickle out of the ejection port, or even stovepipe, that is a good indicator you've got low power/low pressure ammo.

    Hope this helps!
     
    Re: Gas Gun & Ejecter Swipe

    Both my DPMSs (308 & 260 uppers) have an adjustable gas block, tames them down nicely.
     
    Re: Gas Gun & Ejecter Swipe

    I reload for my Bar short track. I was using Reloader 15 and was no where max load from any book, and although it was really accurate, it beat the crap out of the gas system, almost to a point of having to start replacing parts, and that was only 100 rounds. As a rule of thumb, I will not use any powder in my gas 308 that is slower then IMR's 4064. I went back to H4895 as it didn't beat the gas system up and its accurate. I'm also working with Tac but haven't found a load it likes yet but I'm sure I will given the time.
     
    Re: Gas Gun & Ejecter Swipe

    I've been doing some reading about this, & did some comparisons with the load data from Hodgdon's website.
    Between Varget, & H4895 with the 155, 168, & 175's Varget shows a higher AVE velocity with slightly lower pressure for the 155, & 175's, but H4895 shows higher velocity with lower pressure for the 168's.
    After looking over the BC's, & probable velocities for my brl length I've narrowed it down to the 155's, or 175's. Probably the 178 A Max.
    So does the pressures they state actually have any relation with the gas system pressures? As in will the Varget still hammer the BCG harder than H4895 even thoe the pressures seem lower with Varget? It's more about the pressure @ the gas port right? Not the max pressure?
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">It's more about the pressure @ the gas port right? Not the max pressure?</div></div>

    That is my understanding, but let the more knowledgeable loaders chime in before you take my advice.
     
    Re: Gas Gun & Ejecter Swipe

    I believe that it is not only the max pressure at the gas port, but also the sustained pressure.

    Basically, if the pressure in the chamber is still 40,000 psi when the gas reaches the BCG and starts to turn the bolt, you will get swipe on your brass. It really makes no difference what your max pressure is.
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GreatGonzo</div><div class="ubbcode-body">I believe that it is not only the max pressure at the gas port, but also the sustained pressure.

    Basically, if the pressure in the chamber is still 40,000 psi when the gas reaches the BCG and starts to turn the bolt, you will get swipe on your brass. It really makes no difference what your max pressure is.</div></div>

    This is correct. Max pressure is not indicated by swipes, I look for flattened primers and case head expansion.

    Varget has lower chamber pressure overall because its slower than H4895, but because of this it is still burning and the pressure fed back into the gas system is higher at the gas port/block. So it has a longer pressure duration, creating the higher velocities.

    My gas gun has a 16.5" barrel, so the velocity gain is minimal with Varget over H4895. I didnt have any H4895 when I got the rifle, I had IMR495 and Varget. Like I said in my previous post, IMR4895 didnt produce ejector swipes, but it's not temp stable which is a requirement for me as I hunt year round in Texas and it could be 30*F in the morning and 90*F in the afternoon in the same day. When this Varget is done I'm going to switch to H4895 as it's temp stable, and if I give up a little velocity or accuracy I'm ok with it. I've just always had good luck with Varget in the 308, it's so hard to change.

    I'm not running max loads so I don't anticipate a problem with the rifle, if I were shooting an M1A I would choose differently as they're known(correctly or not) to be breakable with slower powders.
     
    Re: Gas Gun & Ejecter Swipe

    OK. That was what I was getting at. So as I'm in this for a tactical comp gun, & want to be able to use my 147gr NATO surp ammo, I should use H4895, & the 155gr bullet for best overall performance of the gas system, & be happy with what I can get? I want to keep the gun stock except for a trigger. I just don't have the $$ to upgrade the gas system, etc as well, & I only have a 16" brl so I think I'll try the 155 A Max, & maybe the 178 A Max with H4895, & see what I can get. From looking at the expected MV with these 2 bullets. The 155 is a little flatter shooting than the 178, & goes sub sonic only about 10 yds sooner, so I guess that's going to be the ticket.
     
    Re: Gas Gun & Ejecter Swipe

    Bigwheels et. al. -

    I am reading this thread with great interest, as I too am trying to develop a tac comp worthy load for my OBR. I am working through the same issues as you, with no clear direction yet. I haven't yet started to work with the 155s - I am heading there next.

    I have found a few loads with Varget and 175SMKs that are quite accurate, but all at the upper end of velocity/pressure. I am not seeing any real signs of pressure, but don't want to beat up the rifle too much for a few extra fps.

    A question: has anyone here tried ARComp powder yet? I've only read a bit about it, but it seems it might be worth looking at.

    Kombayotch has perfromed some temp sensitivity tests and it performed quite well. Better than Varget.
     
    Re: Gas Gun & Ejecter Swipe

    In my 16.5" I'm shooting the 155 AMAX for exactly the reason you're thinking about it. Im not shooting past 400 yards, but im gonna get to it eventually, maybe not with this rifle. The 155 AMAX was the best compromise between wind resistance and getting a reasonable velocity. Even so I can only get 2680 FPS before I get pressure signs with Varget at 46.3 grains which is below the 47.0 grain book max. Im going to try H4895 next, OR maybe IMR8208XBR, as its about the same burn rate and may do better. AR Comp is right next to Varget on burn rate I think, so if it were that ir Varget I wouod stick with Varget based on past good luck with it.

    Going out with my AR this weekend for deer and hogs for the first time, really looking forward to seeing how the lighter AMAX does on game. I shoot heavier Berger VLD's in all my other guns.
     
    Re: Gas Gun & Ejecter Swipe

    I think I'm just going to go with the 155 A Max, & H4895, & be done with it. As long as I can get that combo to shoot sub moa. I still have my 300WM for "long range" so the 155 out to 700, or so will do fine I think.
    Good luck with your hunt, & let us know how the 155 A Max performed. I will still be using my DPMS for "short range" hunting as well as comps.
     
    Re: Gas Gun & Ejecter Swipe

    On my rifles i have one with the JP adjustable block & one with the adjustable gas tube (cheaper)
    - JP super easy to install & sell old block to make up a few bucks
    _ Adjustable gas tube - would work great on lighter weight barrels - on the DPMS heavy i had to drill 1/4" hole on top of hand guard tube, and also had to bend tubing new the gas block to clear the barrel/valve clearance (at one point i though i may have cracked the tube - but all is good) (would not suggest this bending of the tube - easy to fu*k it up, and was not going to grind a recess in the barrel for it to sit)

    ? if i had a nice drill press i would make my old block into an adjustable
     
    Re: Gas Gun & Ejecter Swipe

    Ryedaddy,

    I think the 8208XBR may be the real ticket for the 155s. Very temp stable and should produce excellent velocities. Many bolt gun guys are starting to run it as well for that bullet.
     
    Re: Gas Gun & Ejecter Swipe

    <div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: GreatGonzo</div><div class="ubbcode-body">Ryedaddy,

    I think the 8208XBR may be the real ticket for the 155s. Very temp stable and should produce excellent velocities. Many bolt gun guys are starting to run it as well for that bullet.
    </div></div>

    Great minds think alike. I had a post a while ago asking about 8208, and it really sounds perfect for this application. I can get it in 8 lb jugs locally and may go that route, I've still got over 6 lbs of Varget left, but I may save it for other guns and just move on to a new powder in the gas gun. Im running a POF P-308.
     
    Re: Gas Gun & Ejecter Swipe

    That powder does sound like a good choice. I wonder if their testing for SASS weapons involved the use of an adjustable gas block? I think I'm still going to just go with H4895. Easier to find too I'm sure.
     
    Re: Gas Gun & Ejecter Swipe

    I do not think the ejector damage to the rims of cases is due to pressure. I think it is due to mechanical action of the ejector/extractor on the rim. I have tried to take some 600 grit sandpaper to my extractor and it has reduced it. I need to play with it more, but I am going slow, so i dont have failure to extract.
     
    Re: Gas Gun & Ejecter Swipe

    This has got me thinking about what ammo the millitary is using in the SASS. Anyone know the specs, & whether it has an adjustable gas block? I'll try google.
     
    Re: Gas Gun & Ejecter Swipe

    I dont know what they issue but the data for M118 is as follows, states its loaded with IMR4895, go figure. Ive read elsewhere that M118LR is loaded with Alliant RE-15.


    TM 43-0001-27
    ARMY AMMUNITION DATA SHEETS
    SMALL CALIBER AMMUNITION
    FSC 1305

    CARTRIDGE, 7.62MM, BALL, SPECIAL, M118

    Type Classification: STD - MSR 07798001.

    Use: Rifles, 7.62mm, M14, M21, M24, and M40A1. The
    cartridge is intended and specifically prepared for use in
    high accuracy weapons.

    Description: BALL Cartridge. The cartridge is identified by
    cartridge case head stampings with NATO design mark,
    manufacturer and year.

    Tabulated Data:
    DODAC........................ 1305-A136
    UNO serial number ..... 0012
    UNO proper shipping name ....................... Cartridges for weapons, inert projectile
    Weight ........................ 390 gr
    Length.......................... 2.83 in. (71.9 mm)
    Tracer .......................... NA
    Primer ......................... Percussion
    Fuze ............................ NA

    Explosive:
    Type ........................ NA
    Weight ...................... NA
    Incendiary:

    Type ........................ NA
    Weight ..................... NA

    Propellant:
    Type ........................ WC 846 and IMR 4895
    Weight ..................... 44 gr
    Projectile: Weight ...................... 172 gr
    Performance: Chamber pressure ....... 50,000 psi
    Velocity ....................... 2640 fps

    Shipping and Storage Data:
    Quantity-distance class/SCG.......................... 1.4S
    Storage code ............... Class V
    DOT shipping class ..... C
    DOT designation ......... SMALL ARMS AMMUNITION
    Drawing number .......... 8597555

    References:
    SB 700-20
    TM 9-1005-223-12P
    TM 9-1300-206


     
    Re: Gas Gun & Ejecter Swipe

    Yup. Google found the same thing. So now all I have to do is decide whether I want to use the 155, or 178 A max with H4895. I'll have to look over those drop charts again, & pay more attention to the wind drift as well.