Hard extraction at mild load problem

[ghostwriter247]

So I was testing loads in a dpms lr308 with the 18 inch barrel for my dad and the rim of the cartridge has bad extraction marks not on the back but on thw interior almost immediately. Even at 39 grains of imr 4064 behind a hornady 150 spire point they started

at 42 grains they bent the case rim backward a bit. It's federal brass. These seem like really mild loads and we aren't getting good fps, maybe 2400 at 41.5.

I kno I can't load it like my bolt gun but expected better than that.

Even the federal American eagle crap was running 2700

Is it the brass? Or should I switch powders?

I don't understand adjustable gas blocks but would one solve this problem? I wouldn't want to run a 150s at 2400fps.

Thanks

 

[bj1126]

I'm confused by this line:

Even the federal American eagle crap was running 2700

Are you saying the factory American Eagle was running fine in your gun or in other guns?

 

[wxl]

Could be head space. How far back did you bump the shoulder when you resized? If you did not bump enough, brass will be hard to chamber or stick in chamber. Federal brass is also soft.

 

[ghostwriter247]

It wasn't sticky or hard to chamber. I've got a pretty tight chamber in my ba and it chambered fine. I didn't set bump just left it at the factory bump. Also there were no scrape marks on the side of the brass or flattened primers like I'm used to see with a hot load, which 39 grains isn't.

I was wondering if it was just soft brass but bending a rim seems pretty extreme for once fired brass when there isn't any other signs of pressure

He had some federal American eagle we put thru afterwards and it ran just fine. No extraction marks. 2700 fps

 

[ghostwriter247]

I forgot to mention this particular gun has way more apparent recoil than I'm used to in a 308.

 

[bj1126]

Sounds like something with your load is causing early extraction. That'd account for the recoil I imagine as well. I'm total newb when it comes to reloading so not qualified as to comment on powder choice or load.

 

[ghostwriter247]

Any others?

 

[arnie19]

Might be over gassed ? Is the gas tube a rifle length or mid length ? it might be worth investing in an adjustable gas block .

 

[Sledge1]

I'm going with headspace problem too. Bump the shoulder back a couple more thousandths and try it. Bet it goes away.

 

[ghostwriter247]

I'm gonna try the shoulder bump and go from there. Thanks

 

[ghostwriter247]

Would three thousandths bump be enough or would you go five?

 

[Temp9]

Sounds like an over-eager extraction to me. The gun is trying to extract the cartridge too early, when the case is still at high pressure and sticking to the chamber wall. An adjustable gas block will decrease the amount of gas used to extract the cartridge and will slow down the time before the case is extracted. This will likely give enough time for the case to release from the chamber wall. Over-gassing also will result in the increased recoil you feel on the gun, as the bolt is traveling rearward faster when it smacks the back of the buffer tube.

 

[ghostwriter247]

temp 9,

I think it is that too with the excessive recoil. I did a bunch of reading on other forums and sounds like its a bit of everything. The federal brass is definitely too soft. i have no idea if its bumping back the shoulder enough and given the recoil and over eager extraction sounds over pressured and overgassed.

Once I get the bump issue resolved, Im gonna switch to lake city brass, try polishing the chamber just to cover the rough chamber base and see where we are at with the over gas issue.

 

[wxl]

As for over/under gas, where does brass eject relative to 3 o'clock?

 

[ghostwriter247]

It's back about 5oclock 10 feet back give or take

 

[tipper]

I kno I can't load it like my bolt gun but expected better than that. Do run IMR 4064 in your bolt gun.

 

[ghostwriter247]

i do. im just finishing up load testing in it. i should get back out to the range to put my final groups together this weekend.

 

[LawnMM]

Its over gassed, and there is no "factory bump" you have to size cases and set them to bump the shoulder the desired amount.

Are you using a bump gauge? How about a small base die?

 

[ghostwriter247]

i guess i should have elaborated. i didn't set the bump on my rcbs dies, so the bump is what ever it is set at with the factory. It is a standard rcbs die so i don't think they are small base correct? My bump guages are on the way from brownells as we speak.

 

[BCP]

What you need to do is screw the die down to where it meets the piston on the upstroke, then lower the piston and screw the die down another 1/8th or so of at turn. Check to make sure that when you size it it's going all the way up into the die with little to no daylight between the shell holder and die. You want to feel it camming over when you size your brass. If you have already done that then you might want to try a small base die, I needed one for my DPMS 308.

Second of all use your factory 308 ammunition that works well as a baseline for sizing and pressure. Measure the new cartridges vs your resized ones, measure the fired factory brass vs your fired handloads. If it's an 18" DPMS 308 with the short gas system then it will be especially hard on brass but I don't think that is your problem.

Federal brass is soft. It will bend the rims a bit and after 2-3 you will probably end up with really loose primer pockets (no resistance when priming case = bad). Best luck for me has been lake city, it takes a lot of prep work because of the crimps and blown out machine gun cases but it will last the longest.

43.5 IMR4064 with a 150 grain bullet in that fed or lc brass, or 45 in winchester, should be about right.

 

[ghostwriter247]

bcp,

thanks for the input, and confirming the small base die use. i was going to check the bump as soon as i get my gauges. i needed it for my Bolt anyway. i just got 1000 rounds of prepped lake city. I keep hearing about small base dies for dpms 308. can you explain what the difference is? Im confused at what they do. most threads i've read assume you know what it is. Doesn't rcbs make a small base die? Ive heard redding quite a bit for small base dies.

 

[wxl]

i guess i should have elaborated. i didn't set the bump on my rcbs dies, so the bump is what ever it is set at with the factory. It is a standard rcbs die so i don't think they are small base correct? My bump guages are on the way from brownells as we speak.

What others have posted on bump. There is no factory bump. It is how much you screw the sizing die down that determines how much the shoulder on the brass is reformed or bumped. By trial and error you can screw the die down 1/4 turn, size brass and try to chamber.

Also as also posted, 5 o'clock is too far back and should change to lighter buffer weight (if you are using heavier than carbine standard weight or also use lighter spring). Does bolt lock back on empty mag? If it does not, you are short stroking because of the heavier buffer/spring and is worst with your low velocity ammo trying to push the bolt back.

 

[ghostwriter247]

the bolt locks back, its the stock dpms spring and buffer.

 

[LawnMM]

You need to use the bump gauges to set up the dies. The makes contact and add 1/4 turn method is imprecise and it sounds like you haven't set the dies up at all. You should read a reloading manual and ask questions here on the hide. I'm not trying to get on your case but reloading can be dangerous for experienced guys and you are loading ammunition without any idea how the dies are set up or what your headspace looks like. I only pray you are checking starting and maximum loada and aren't just dumping powder in as well.

Auto loading guns are much more finicky about ammo than bolt guns, its not a good place to get your feet wet. A small base die will size the brass to minimum specifications but you still have to measure and set the dies for headspace.

Read up a bit I don't want the gun blowing up in your face and this is how it happens.

 

[ghostwriter247]

Lawn,

I appreciate you input, and Im sure your heart is in the right place but you are making some unwarranted assumptions. I actually do more reading than most.

Not only do i check my manual for minimum and maximum charges i also cross reference it with the powder maker and bullet makers website.

perhaps i was less than clear in how i phrased my questions. i have a reloading manual and pull it out on a regular basis. I've read it quite a bit. I think if you would review my posts you would find I ask quite a few questions here on load development. Ive also read all the reloading stickies numerous times both here and on accurate shooter. I do understand the danger involved. risk management has been ever present in most of my jobs and yes i set up my dies. I did them by the numbers instructions in hand.

The 1/4 turn method is imprecise i agree, however has worked for most of what i have done up unto this point, without pressure signs, which i watch for carefully.

Ironically, i had just been looking for bump gauges as I was wanting a more precise setting for my headspace for my guns, when i ran up on this problem in my dads gun.

Honestly most of the time i already have the answer i think by reading old threads and my manual before i ask questions. I ask them here as a quality backup to my thought process. I haven't gotten an answer here I hadn't already come to, but its nice to know i wasn't wrong and hadn't missed anything.

 

[BCP]

Maybe I'm just lucky but I have always figured my shoulder bump for gas guns by feel and have never had problems with brass life or case separation. Once you get your small base die and start putting some powder behind those squibs (a factory pressure load would be 42.5-43.5 grains for a 150 in FC brass at least) your problems should go away.

I know this because when I had my DPMS SASS I had the SAME problems with a regular FL die. Small base and never had a problem again.

Especially if the rifle runs fine with factory ammunition. That should be your biggest clue that it is due to some gremlin in your reloading process.

Do you have any 168 or 175 grain bullets? If you do load 5 rounds of each in that FC brass, small base sized and generously shoulder bumped, with 42 grains of 4064. I bet they cycle fine an eject about 2-3 o'clock.

 

[LawnMM]

Lawn,

I appreciate you input, and Im sure your heart is in the right place but you are making some unwarranted assumptions. I actually do more reading than most.

Fair enough and I'm glad to hear it. I wasn't assuming, I was hoping you weren't diving into this without a clue. I feel better having read your last post but you have to understand that talking about a factory bump on dies gives cause for concern. That sounds like a lack of understanding or education regarding a dangerous hobby.

That quarter turn method needs to be stricken from reloading manuals. I tried that when I first started reloading and by the fourth firing I had impending case head separations. You need bump gauges to do it right. They cost all of about 30 bucks, we should all just buy a set at the word go.

 

[ghostwriter247]

Lawn,
true enough on the 1/4 turn. I think it should be mentioned in the threads using a bump gauge isn't just a precision issue. its a safety issue as well. Im getting away from the bulk reloading and getting more into the handloading for precision. i put off the bump gauges too long. Right before i ran into this i got a coal length gauge, bullet comparators but they didn't have my bump gauges locally. They came in friday from brownells.

Im shooting a savage 10 ba thats a hammer and im trying to wring every ounce of accuracy i can to see what she does. I just got a WHidden micrometer die and am waiting on my custom chamber die from them.

UPDATE: the shoulder on the fired brass from the lr308 is 1.627 i measured five, pretty much spot on every time. The shoulder on the unfired FL sized brass is 1.617 to 1.621. so its pretty sloppy but definitely over the 3 to five thousandths. Would too much bump cause this? Ive never seen that issue addressed.

Dad's bringing out some factory stuff this afternoon so i can measure it just to cover all bases.

BCP,

Dont ya hate it when you live in the sticks. Ill have to order a small base die set to see how that works out. takes a few days to get it in.

Since the bump is good i am going to try to run some lake city 175 smks through it and see how it does this afternoon after i clean the chamber. A few of those should tell a story since the bump is good. they were resized with the same die. Honestly dad likes reusing his brass but I personally stay away from the federal just because of what I've read about it being soft. and lc is cheap good brass. I have 100 pieces of Winchester unfired sitting around though.

Thanks for the info.

 

[LawnMM]

The shoulder is only part of the case, some people get away with regular dies on a gas gun. Some people can't get it feeding right without a small base die. Keep in mind you are switching multiple variables here. Different cases, different dimensions, different brass.

I'm betting you are getting hosed by soft brass. You might need a small base die for Federal brass, you may or may not need one with the Lake City.

 

[reelserious]

I was having the same problem with one of my Ar 10s. Now I only use SB dies and set the shoulder back to min dimensions and it runs great now.

 

[mtrmn]

Soft brass could definitely be the problem. Especially Federal IME.
4064 is within the preferred burn rate range for gassers. I've never used 4064, but about 42 gr of 4895 or TAC was where I got my best accuracy performance with 150 gr bullets. About 2600 to 2650 fps IIRC. Maybe try different powder if all else fails.
All the talk of SB dies and bumping the shoulder more/less is fine and good if you were having FEEDING/CHAMBERING problems. If your rounds are chambering/firing, then your dies have done their job and the act of firing UNDOES the work your dies have done. Your rounds will NEVER be as tight in the chamber before (or after) firing as they are DURING firing. From your description you are having problems with EXTRACTOR damage which only comes into play during the firing/extraction sequence.
MARKS on your brass rim could be something as simple as sharp edges/burrs on the extractor.
BENT rims on the other hand are usually from the extractor trying to pull the brass out of the chamber while it's still under pressure from firing. During this time the brass is supposedly expanded against the chamber walls so tight that it is "welded" in there and there's no way in hell that extractor is going to remove it. If it tries, the weakest link is going to give up=either the extractor will slip off the rim or it will tear a chunk out of it. YOUR problem is just the first signs of this. Rather than slipping or tearing out chunks, it's just bending the rims. It also is a sign of reaching near max loads, but I'd think you would get better velocity in that case.

To fix this, unlocking/extraction needs to be delayed another microsecond or 2 to give chamber pressure time to drop off a little more. This will allow the brass to contract a bit and turn loose of the chamber walls. A stronger buffer spring and/or adding weight to the reciprocating mass will help to delay the process a bit. Turning the gas down a bit with an adjustable gas block is the best way, but if you have a weak spring anyway this may mask another problem. The extra recoil you mentioned is not typical in a properly set up AR 308, so I would kinda lean towards sticking a new spring/heavier buffer in it.

All this is just my opinion based on my experiences working on my POS AR's over the years. YMMV

 

[ghostwriter247]

Thanks for the input guys. It's spot on with what I'm thinking. I'm going to run a few lightly loaded lake city to see where I'm at but I see an adjustable gas block as the most likely thing that will need to be done as well.