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Posted: 2/22/2006 7:28:06 PM EDT
[#1]
You need to Reload for the barrel at hand, and not hope that former loads for an old barrel may work.
Also DPMS does chamber their DCM barrel in 5.56 Nato, but again, the chamber is new/rough/tight and full sizing should be used for the first time out of the gate to break the barrel in, and get the needed reloading readings/feed back (chamber dimension expansion-working pressures), then you can go back to just bumping the shoulder if you so desire. Myself, I full-size for all of my DCM rig's, since un-slinging to dig out a stuck case breaks my concentration. Plus, you only get to call an alibi once, and if you stick a case the second time, you better work quickly and get it cleared as the clock it ticking (read work threw the jam since you call an ammo failure twice and your going to get yanked off the line and out of the match for unsafe ammo). |
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Posted: 2/23/2006 12:52:27 AM EDT
[#2]
Dano:
OK, what factory ammo should I get to check out the new dimensions on this chamber? anything available out there? thanks for the help. billy |
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Posted: 2/23/2006 6:21:45 AM EDT
[#3]
If you want factory ammo, Black hills or Fed gold would be a good way to go,
On the other hand, since you do reload, just full size the cases and start the loads off reduced and work up from there. Also, the throats on the DPMS DCM barrels are on the long side (read Nato chamber), so you may as well figure the long load for sled’g @ 600 (read not a snow balls chance in hell of the ogive even getting close to the lands coming out of the mag). Also it wouldn’t be a bad idea (got to love double negatives) to install a #60 O-ring around the extractor spring until the chamber polishes out threw live fire (should be about the same amount of rounds until the barrel settles in). |
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Posted: 2/24/2006 2:56:27 AM EDT
[#4]
Dano:
The O ring idea sounds good. OK, I did FL size the cases; shoulders pushed to the minimum on my Redding die. I do not break in barrels too often; setting up the front site on mech. zero with the 4 set screws is one major PIA. What is your ballpark estimate on how many rounds till she breaks in? Till the gas port burr gets shot off? thanks for the help! bill d |
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Posted: 2/24/2006 4:44:18 AM EDT
[#5]
If you keep the bore semi clean, the lands/throat/muzzle should unify in around 200 rounds, and depending on how hot you get the barrel, it should tension relieve in about the same amount. In regards to the chamber self-polishing threw live fire, if there is no major reaming burs, 200 to 300 rounds.
Also a little FYI: I am running a DPMS DCM barrel (hand lapped) on a loaner/practice rig, and the barrel lasted over 4500 rounds before starting to push up daisies (groups opening up + 2MOA from the 1.2 MOA it used to hold). When I get a chance, I need to pull the barrel and re-crown the muzzle to see if I can get another thousand or more rounds life out the barrel. |
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Posted: 2/26/2006 6:52:05 AM EDT
[#6]
Dano:
OK, full length sized 30 cases and loaded 10 ea with Win 748, 25.0, 25.4, and 25.8 gr with the Sierra 69 gr bullets. Shoulders pushed all the way back on Win cases. Pressure tested one round from ea category, all is OK, primers look good. Shot remaining 9 rnds of 25.0 gr, all is OK. Then I shot 5 rnds of 25.4 and everything was good so far, functioning is great. The next 5 rnds of 25.4 and 3 rnds of 25.8 were all fails to eject. All eight had flattened primers as well. It was 24 degrees F where I was in Central Jersey this AM. None of the rounds sat in the barrel prior to shooting them. I shot 'em both single shot and rapid fire. The bolt comes all the way back and locks up; looks like I am getting enough gas. What is going on? Chamber still too rough? Loads too hot for the Saami chamber? Next time bring chrono? Any help is appreciated, still lost. thanks Bill D |
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Posted: 2/26/2006 8:29:27 AM EDT
[#7]
Dano:
sounds like a brain you know what. Sounds like a good case of chamberitis. What say you? bill d |
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Posted: 2/26/2006 11:25:35 AM EDT
[#8]
You have to remember that the AR gas system was designed around faster burning gunpowder’s with bullets in the 55/62-grain range. When you use slower burning powders, coupled with heaver bullets, the residual gas pressure in the barrel is higher than the norm at unlock, and this will lead to problems.
For now (until the chamber polish out), looks like you found your max load of 25gr for the brass/primer combo that are using, and is time to start backing down the load from that point to really see what powder weight makes the barrel sing. No reason to try to push a bullet/load to scream down range, only realize that it will not find its target. Note: the only time that a max load may work in your favor is when the wind is just blowing beyond hard, and you are trying to buck it at the 600 line. |
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