AR Sponsor
Posted: 3/8/2012 4:40:29 AM EDT
|
So, I have my new DPMS LR-308 24" bbl and I have taken it to the range a couple times now. The first time I went, I brought some 125 grain match grade ammo. I fired through an entire magazine (19 rd) and had no issue. Between every 5 rounds, I would run a boresnake through and relube the bolt (I know, less than recommended brake-in). I would fire 4 rounds, drop the mag, and fire the 5th. Well after a while, the range when cold so I dropped the mag, and tried to clear the chamber (about 35 rounds into my day). I pulled and pulled on the charging handle, but couldn't get the round out. After a while, i spoke to the range officer and asked to attempt to fire the round and he OK'd it. I fired, but it misfired. After yanking on the charging handle more and more, i finally got the bolt open. The casing ejected, the powder spilled, and the bullet remained just inside the barrel. I looked at the casing and noted a light primer strike (perhaps all the pulling on the cartridge changed the seating of the bullet).
Well, this was the end of the day for me. I took my gun home, put my carbon fiber cleaning rod, with a plastic thread cover, down the barrel and tapped on it a few times with a rubber mallet. Bullet pops out and I start cleaning the gun. I go to the garage and use my air compressor to clean out the unburnt powder (it was sticking to the bolt lube in certain areas). I then continue to fully clean the gun, lube it, and put it back together. Next weekend, I go back to the range. I had decided to blame the fail-to-extract live round on the ammunition. I made some reloads of varying charge (168 gr SMK, BR2 primers, 41-44 gr Varget in 1 gr increments, all seated to Lyman recommended OAL +/- 0.002). I go to the range, fire using the same brake-in procedure as before, and have no issues. Range is about to go cold, I drop my mag, try to extract the live round, and it feels stuck again. This time, instead of pulling hard on the charging handle, I fire the round before the range is cold, and it fires, accurately, without issue, and the brass extracts fine. I did note on this trip to the range, that the case neck appeared to scrape against the lugs during extraction (two scratches in the neck that lined up perfectly with the lugs.) I have tried to research my problems, and I have seen that the tollerances are tight, and DPMS barrels are rough. I have seen small base dies recommended, so I ordered some and should have them tomorrow. The only case of seeing someone with a problem ejecting live rounds, said the problem continued until he had fired 200-300 rounds, and then no longer had the problem. I was wondering if anyone else had any other suggestions I should try while I'm at it. Due to weather, I probably won't get to shoot this weekend to test the issue, so I have time to order other possible fixes too. The rounds I reloaded were the first rounds inhad ever reloaded. I had an experienced reloader watching over my shoulder as I made them to make sure I wasn't doing something stupid. The brass I used was once fired, 308 brass (not 7.62x51) with Winchester and remmington head stamps. They had been fired out of my rem700 308. I did test a sized 308 casing in a Wilson LE case Gage that my buddy had, and it looked properly sized. I am pretty inexperienced with the AR world and these forums (i have a basic AR-15 223 and just got the LR-308) so please dumb things down a little if you can. I am an engineer, so I understand the concepts and catch on pretty quick on these types of things. Thanks for any help. These forums look great! |
| Sound like the problem is that the throat is not properly reamed, because you were able to force the case to eject and bullet remained. You can chamber an empty sized case to check chamber size and if ejects, good. You can use an empty, no primer or powder, sized case with a bullet seated, then use a black marker on bullet. You can first drop the unloaded round in the chamber and tap in some, then tap out, then check for marks. If you are getting marks on the bullet, you can seat the bullet a little more each time till clean of marks. Then you will know where the rifling starts. A loaded round with spec length should not touch. This is a procedure to use when loading the bullets just off the lands for improved accuracy, when you do not have a chamber mic. to measure with. |
|
I had the same problem. The issues was the bullet was hanging up on the lands. The bullet had a peculiar ogive (profile) which did not agree with the suggested OAL. In short it needed to be seated deeper. You can do what Fritzcat says to incrementally seat it further in. I went ahead and got a Hornday OAL guage so I can custom measure OAL for a specific bullet and my AR. Some guys use a black Sharpie marker and mark the bullet before chambering. This would allow you to view where the paint was scratched off and give u a better idea on how far to set it back.
I had 2 scratch marks on the neck from ejection. The extractor pulls the case out of the chamber at an angle. The case may rub against the barrel lugs (for lack of a better term). |
|
Scratches on the case neck after ejection is normal.
Have you tried any factory ammo? Sounds like you have just been using reloads. I have seen a simaler situation with reloads, the neck was getting slightly burgled While seating the bullets. Chambered fine, fired fine, but hard to extract by hand. Chamber and extract a live round and post pix of any marks on the case and bullet. This should tell you where the problem is. |
|
Quoted:
I had the same problem. The issues was the bullet was hanging up on the lands. The bullet had a peculiar ogive (profile) which did not agree with the suggested OAL. In short it needed to be seated deeper. You can do what Fritzcat says to incrementally seat it further in. I went ahead and got a Hornday OAL guage so I can custom measure OAL for a specific bullet and my AR. Some guys use a black Sharpie marker and mark the bullet before chambering. This would allow you to view where the paint was scratched off and give u a better idea on how far to set it back. I had 2 scratch marks on the neck from ejection. The extractor pulls the case out of the chamber at an angle. The case may rub against the barrel lugs (for lack of a better term). +1 I've found that some bullets hang up on the rifling, and some don't, depending on their ogive. Milsurps with steel jackets tend to be large-for-weight since they're not as dense as copper or lead, so they hit the rifling too soon. What I can shoot 7.62x51DAG What I can't shoot LC surplus (Talon) Radway Green I've just been seating my handloads a little deeper (warning: increased pressures)...and buying more DAG. If you don't want to put up with this foolishness, send your upper back. |
|
So, i incrementally sat a bullet deeper and deeper until I was able to eject without scraping up the bullet. It ended up being 0.010" deeper than the book recommended OAL for 168 SMK. I will try these at the range when my Texas weather permits it.
If I start having the same problem there, I will blame neck tension and might have to start crimping, or at least see if that will do it. Thanks for all the suggestions, hopefully it works out well |
| I never had to crimp on my AP4. The recoil pounds the point in the mag and the inertia from chambering, never moved the bullets. If you were loading the 168 SMK @ 2.800 length, then had to seat -.010, Then your throat is about .050 shorter than a M852 match chamber. Which was for the SMK 168, but still chamber any factory or milspec rounds safely. The short throat is a mistake from DPMS, because it opens them up to liability issues not being able to chamber all factory rounds without pressure issues. So you have to ask yourself if you want to be limited to short custom rounds. What if SHFT happens or you want to sell or swap the rifle. |
| You should be using a case gauge to check your brass after resizing and before priming. You should also be full length resizing on semi-autos. You could also try this. Take the upper off and drop a reloaded round into the chamber to see if it goes all the way in. If it does not and the the OAL is within SAAMI spec then I would call DPMS. Hard to tell when the bolt, under spring pressure, is slamming the round into the chamber. |
|
I think you should crimp your rds for semiautos, they slam pretty hard.
I like the LEE factory crimp die, it's a collet die If you want to see if your bullets are moving when the rd is chambering you can, Pull you rear take down pin and open the upper from the lower, load a rd by pushing the BCG closed on the rd by hand, Next insert a wood dowel in the barrel and mark it at the muzzle. Remove the round, and reassemble your upper and lower, Now load a rd with the full force of the BGC, Reinsert the wood dowel and check to see if the mark is still at the muzzle,( for saftey reasones, you may want to open the upper from the lower for this part) if it's not, your bullet is not crimped enough |
|
AeroAgg06...
Welcome to the forum. I did not know they made 125 grain Match Grade Ammo. Anyway, the bullet stuck in the lands and remaining after you eject the unfired round, sends up a red flag. The autoloader forces on the cartridge is like the kinetic bullet puller forces. The case stops traveling when the shoulder meets chamber shoulder, and the bullet wants to continue on forward. A good neck tension, or a combo neck tension and crimp will usually prevent that. If you have any of that 125 grain stuff left, color the neck and bullet continuously with a sharpie. Put one in a mag. Pull the charging handle back all the way, and let it "twang" forward like a bow string release. Now slowly pull back again and tease the unfired round back out. "Safety On" of course, and pointed away from anything you do not want to shoot. If the bullet has dislodged and moved forward any at all you will see a bright copper / brass ring at the neck / bullet junction. Now break down the rifle and remove the BCG. Use the chamber in the upper to act as a kind of gage. Select another assembled round. (OAL should be around 2.800, maybe less for the 125 grain stuff) Color the bullet with the sharpie. Push the assembled round into the chamber hard with your finger. Pull it back out and see if there are land contact marks on the ogive of the bullet (scuffs of bright copper showing through the sharpie color). If so, your OAL is too long or your chamber freebore is too short. Now select another completed round from your stock (Match or Reload) and push it hard into the chamber. With the chamber turned up vertical, the round should slide back out under its own weight. If not, you have a dirty chamber, or you have an undersized chamber. 
|
AR Sponsor