tight extraction, flat primer, but...

[skyhawk]

Hi everyone. Hoping to get some help or advice with this one.

My daughter has a Savage 10BA .308 with about 600 rounds through it. The first 260 or so were factory Federal GMM and worked fine. Then I neck sized the brass, reloaded with 42 or 43 grains Varget (43 seemed better), SMK 168 bullets, Federal primers, and that worked fine also. Then reloaded the brass a second time, but neck sizing was tight going in, so full length sized with Lee die, trimmed the cases, used the same load, powder, bullets and primers, but after the second reloading they went in easy, but extraction was tight on some, and lately a few have actually flattened the primers. So I reduced the powder to 42 grains, and then 41.5 grains, but they both stick a bit and still flatten primers. I'm about 20 thou from the lands. Factory GMM appear to be at the lands in this rifle.

With my chrony on this gun the factory GMM average 2750 41.5 grains 2652 42 grains 2675

I didn't chrony the 43 grain rounds, but they have to be somewhere between factory and the 42s, which looks like a safe load with reasonable velocity so "probably" no overpressure... but I don't know that for sure because it sure looks like overpressure except for the moderate velocity, they do stick and flatten primers.

More info. I had a few rounds reloaded for a my own gun, which is a Savage 10TR. GMM that were only once fired and reloaded with 42 grains of Varget, full length resized, trimmed, same everything else, and I tried them in the 10BA and they worked fine, in and out easy, and no flat primers. Factory loads still work fine also in the 10BA.

When I was working up a load for the 10TR I got the following Chrony results on it Factory 2715 43.5 grains 2779 but I shoot it at 42 grains, seems most accurate. The reason I say this is that factory velocity on GMM 168s is published 2650. My chrony seems to read a bit higher than that on both guns. It's consistent.

I'm at a complete loss on this one. The evidence shows that the only difference between working fine and sticking with flat primers seems to be the brass after that 2nd reloading. I'm not annealing the brass, don't know if that would make a difference. I have not tried the twice reloaded brass in the 10TR, so don't know if the gun makes a difference, but this makes no sense to me.

I have some Lapua brass on order, maybe that will make the problem go away, but it seems such a shame to throw out all of the GMM brass only twice fired.

Any help or ideas about this would be much appreciated. or any ideas of other things to try (that won't damage the rifles or me !).

Thanks !

 

[jonbearman]

How do you measure .020 off the lands? What is your cleaning process? Could you have a carbon ring buildup in the neck portion of the chamber.It could be a couple things. Do you weigh or throw charges?

 

[308warbird]

Sounds like carbon ring issues.

 

[2506]

Are you trimming your cases. If the case is too long you will raise the pressure because it has less or no room to expand forward when fired. I always trim my cases to the trim to length at EVERY reload.

 

[brian50stang]

Hi I have a 10ba I had the same issue with factory ammo worked great but reloaded I had problems extracting the case once fired. From what I learned the 10ba's have a shorter chamber than most 308's. I bought a go-gauge to check it and that was fine. I found out my rcbs sizing die was not bumping the shoulders back enough. I got a Wilson bushing bump die that works awesome. Plus all my brass was fl sized. Hope this helped

 

[skyhawk]

Thanks so much for the ideas.

We used to clean after every time out, 10 or 20 shots, but lately get better accuracy cleaning every 60 rounds or so. I use a bore guide, Hoppes number nine and a bore brush one direction only. I don't think it's a carbon ring, but how would I check that.

Measured the position of the lands using a gauge. It came out to a fairly consistent COAL measured to the ogive of 2.2300 I load to 2.2100 for a 20 thou set back. As a reasonableness check, the average COAL with my bullet comparator of GMM 168s is 2.2300, putting it just touching the lands. I marked a factory load with black marker, chambered it, and it did indeed contact the lands. I think this is fairly accurate and sounds reasonable.

I weigh charges on an RCBS beam scale to within less than a line width on the index, and recheck the zero every 5 loads or so. (I'm a little OCD about that stuff) Double checked a couple from the batch of loads in question, exactly on.

That's why I'm so baffled about this. I'm new to .308, but have been loading .270 for 20 years. Everything is precise and consistent, at least according to the tools and measuring devices I have. BUT something IS causing this, or perhaps a combination of things ?

Ah, more posts have come in.

I trim every case. Found that neck sized cases trim very little, full length sized though need quite a bit trimmed off.

brian50stang, That sounds pretty much like what is happening, if my twice fired cases are not resizing as well as the once fired ones in the full length die. I decided to order a field gauge thinking this might be a long headspace issue, but never thought of a short chamber issue. I have never used a shoulder bump die, will look into the Wilson one. What do you mean all your brass is FL sized. Is that using the bump die only ? or did you FL with the RCBS then bump with the Wilson ? May I ask you more questions about this to learn more ? Thanks !

 

[brian50stang]

Ok so this is what I do, the Wilson bushing die is a full length die. The bushing is just so you can change neck tension on the bullet, the important part for my cases were to make sure the shoulders got bumped back .001 at least you can go more but it's just gonna work the brass more as I'm sure you know. I make sure to lube the whole case outside on an rcbs pad and esp the inside with a q tip or brush with lube on it. If it's not lubed good the expander ball catches the neck and pulls the shoulder back out sometimes as far as .002 in the wrong direction. It takes extra time to measure the shoulder before and after but it's worth it once at the range

 

[BoydAllen]

IMO you have been cleaning with an ineffective regimen. Do you know anyone with a bore scope?

I have a number of barrels that will shoot in the low twos to the high ones that have been carefully brushed quite a lot, with the brush going in both directions.

Just for grins, wrap a lightly oiled patch around a used brush so that the patch extends about an eighth of an inch past the bristles, work some JB bore cleaner into the front half inch of the patch, insert this into the barrel to the point that you feel it stop at the front of the chamber neck, grab the rod and twist it about 20 times with forward pressure. Then lightly oil another patch and work some JB into it and short stroke the throat and back half of the barrel going up and back in short strokes (2") a half dozen times. (The patch needs to have a snug fit in the bore.) Then do another patch to the muzzle, but not out, the full length of the barrel perhaps 10 times. After that use Hoppes and patches to clean out every bit of the JB.

Make sure that your cases are trimmed to minimum spec, after FL sizing. If you do not have it, buy the proper tool to measure shoulder bump, and set your FL die so that shoulders are bumped back .002 from a tight case , measured with the primer removed.

Before seating bullets, verify your length to touch.

Let us know your results.

 

[artbosco]

You just described the quagmire associated with neck sizing. FULL LENGTH size, from day one, with new brass. The future should be brighter.

 

[SmokinJoe]

One other thing that needs to be done is measure the chamber OAL so you know what trim length should be. Get the little spud from Sinclair's & make the gaging tool; it's very simple to do. I have found chamber OAL's run all over the place & measuring is the only sure way to know what you actually have.

 

[lpreddick]

when fl resizing if one pushes the shoulder back too much(.003+) can firing such a round result in excessive bolt thrust and case expansion resulting in the observed hard extraction and flatten primer? my rem 700s with firing pin/spring removed gives a very good assesment of headspace on fired cases and tells me just how much to push the shoulder back. could this be a headspace issue?

 

[skyhawk]

Thanks for all of the info and advice. I need to digest this and try some of the suggestions, and I will report back. One thing that keeps sitting in the back of my mind is still why is it fine with the once fired brass, but not with twice fired brass, all else being equal ? Still many questions, but I've got some things to try and test now. Thanks everyone!

 

[jsthntn247]

Not sure what causes it but I've noticed that once brass gets tight to extract and the bolt clicks at the top of extraction, it wil happen with that brass every time from then on. I think of it as the brass at the case head being like a paper clip that is flexible until a point, when you put a kink in the paper clip it is no longer flexible as it once was. You fired the brass and the case head expanded past its stretching point (chamber too big near base or load too hot?) but was still elastic enough to spring back, but after the second or 3rd firing the brass has lost it elasticity and will no longer spring back anymore and you get tight extraction and clicks from then on.

 

[243winxb]

Soft Brass ?

Soft Brass ?

One thing that keeps sitting in the back of my mind is still why is it fine with the once fired brass, but not with twice fired brass, all else being equal ?

Hot loads expand the web, reduce powder charge. Trimming a lot is another sign of HOT. Velocity has nothing to do with pressure. http://www.shootersforum.com/handloading-procedures-practices/58763-pressure-signs.html Lapua brass may require a new workup, as pressure may be even higher.

 

[snert]

I just obtained 4000 308 FGM 1x fired (and yes it was 1 time fired because I was responsible to order it, supply it to my guys) brass. As I started looking it over, i noted more than the occasional head with clear ejector extrusion. This is FACTORY 1x fired Fed GM. Most were fired in 700 or 40X (Hart built) or Blaser type rifles. There were NO reports of extraction issues, no odd groups (we chart EVERY shot), no abnormalities. In fact the ammo shot great. BUT, I am seeing signs of soft brass. As I am sizing, trimming sizing next I will be watching for other signs of premature brass wear.

snert

 

[PREMOD70]

Another possibility that's an easy fix is making sure the brass and chamber are squeaky clean. Sometimes the lube one uses to F/L size remains on the brass and the resultant high pressure signs are a result, good luck.

 

[Erik Cortina]

I did not read all the replies but sounds like your case head has expanded to the point where it gives you problems. This is a common issue when neck sizing only. Make sure you F/L size always.

 

[243winxb]

Tight necks may increase pressure, bulging the web area

Here a guy claims the Federal brass will not chamber, but all other brands will. Problem would seem to be larger than normal neck diameter of loaded rounds. But could not be measured by him. May also be a custom barrel problem?

We both agreed that Federal probably had the thickest necked brass and that was the problem.

?? http://thefiringline.com/forums/showthread.php?t=548462

 

[bigedp51]

when fl resizing if one pushes the shoulder back too much(.003+) can firing such a round result in excessive bolt thrust and case expansion resulting in the observed hard extraction and flatten primer? my rem 700s with firing pin/spring removed gives a very good assesment of headspace on fired cases and tells me just how much to push the shoulder back. could this be a headspace issue?

Just one of the reasons military rifles have longer headspace is because it reduces bolt thrust, this is because when the case is fired the brass must stretch to meet the bolt face. In the simplest terms the brass case acts like a shock absorber and reduces the thrust on the bolt. This is also one of the reasons why military brass is thicker or harder in the base of the case to increase the amount of pressure required to make the brass stretch/expand.

Head clearance is the air space between the rear of the case and the bolt face and this corresponds to the amount of shoulder bump. By full length resizing with minimum shoulder bump the brass tries to spring back to its "resized" shape. When neck sizing only the brass keeps getting "hammered" to the size of the chamber and the brass losses its ability to "spring back" from the chamber walls and sticks and drags on the chamber.

Below is a full length resized cartridge being fired, the firing pin will push the case forward until the shoulder of the case contacts the shoulder of the chamber. The cartridge then goes "bang" and as pressure builds the primer is forced back into contact with the bolt face. As the pressure increases it causes the brass to stretch to meet the bolt face. When the chamber pressure drops the brass springs back from the bolt face and chamber walls making primary extraction possible.

Note: I have 30-30 cases over 25 years old and the pressure generated by the 30-30 is not great enough to cause the brass to stretch to meet the bolt face. (38,000 cup or 42,000 psi) On these cases the primers always protrudes from the rear of the case when fired (headspacing on the primer) and the only "bolt thrust" on the Winchester 30-30 is delivered by the primer.

Also some of you might remember that CatShooter did a Rockwell hardness test on .223/5.56 brass less than a month ago with Lake City brass being the hardest and Remington being the softest. Meaning different manufactures of brass will exhibit different spring back rates and also start to flow at varying pressures.

At the Rifleman's Journal http://riflemansjournal.blogspot.com/p/articles-index.html you will find some very good articles on the advantages of full length resizing. Mr. Salizar also quotes the late Jim Hull of Sierra bullets and full length resizing.

"I get my best accuracy when the case fits the chamber like a rat turd in a violin case"

And a picture is worth a thousand words, and the key words are "pressure ring" "shoulder setback" (minimum shoulder bump)

Now go ahead and shoot the messenger, but remember this, you now have two people from Team Lapua USA that have given you some very good advice.