Has anyone seen early signs of extractor marks when loading for a BAR. I've got a sweet little BAR in 308 with a 20" barrel. I use quickload and a chrono. My brass has about .003-.004 headspace because I share the die with another gun. So it may be a little bit on the loose side but definately not under factory headspace.
Everytime I approach about what should be 56k pressure extractor marks appear. The primer pockets don't expand and primers don't look flat. Just 2750 fps with 150 grainers and 2860 with 130 ttsx's will give the extractor marks. These loads should be approx 56k according to quickload. I'm fairly convinced my marks are showing up before I'm really on the "hot" side. Also none of my loads are "max" loads according to reload manuals...a grain or two under most all the time. Has anyone else seen this with a BAR??

kraky,
3-4 thousanths isn't much ,but it might be enough to allow the case to smack the boltblock hard enough to imprint.
i have a 6.5x.270 ackley that i was using .270 cases in and just necking down, leaving what i thought was enough original .270 neck to keep the case against the bolt. the diameter of the .270 case neck wasn't enough and it caused all sorts of problems. extractor marks, loose pockets and real flat primers... all on loads that weren't more than a grain or two over starting .270 charges. i was distgusted, upset and even started to wonder if my 'smith did a lousy job,and i never heard of anything bad from any one in 20 or so years about him. i was to the oint that i was afraid of the gun and stopped shooting itfor a long time. finally, i tried some '06 cases which gave me a bunch more secondary shoulder diameter and it all went away.

Kraky,

What speed powder are you using?

Years ago, I loaded a BAR .270 using H4831. I got markings on the case head that indicated that the slow powder was creating excessive gas port pressure and starting the action to open sooner than designed. This problem went away when I switched to a faster powder.

Could the phenomenon your are observing be a result of excessive port pressures, which can occur with an autoloader even when chamber pressures are well within the normal range?

I'm using fast enough powder...kind of have to with the 308. Using powder like tac, 748 and re12.
Some of my brass is on the 6 loading and even though some of them sport 3 extractor rings on the base of the shell the pockets are tight as can be.
Our wis deer season begins in a couple of weeks. I backed down the 130tssx load to what I think will about 2800 which will still be fine for our 100yd and less shots. Going to the range tommorrow to verify accuracy. (my 2860 fps load was getting me .75-1" groups with just a little weaver 1x3 scope). The more I think about it...even if I could get 2900-2925 it won't make a diff in this application.
I was just wondering if anyone else could chime on on BAR performance. I had two other bar's...one a 270 and one an '06...don't remember these problems with them.

Any chance that the Chamber might be a bit dirty, or even have a small amount of surface rust?

If it gets cleaned from the Muzzle, then either is a possibility. Or, do you remove the Barrel to clean it?

quote:

Originally posted by Stonecreek:
Kraky,

What speed powder are you using?

Years ago, I loaded a BAR .270 using H4831. I got markings on the case head that indicated that the slow powder was creating excessive gas port pressure and starting the action to open sooner than designed. This problem went away when I switched to a faster powder.

Could the phenomenon your are observing be a result of excessive port pressures, which can occur with an autoloader even when chamber pressures are well within the normal range?

Absolutely true. Port pressure got me for a while in mine. Moved to faster burning powder and bingo.

I have handled thousands of factory once fired cases from indoor ranges. Many of these cases had ejector marks that you could clearly tell were made by the bolt rotating while there was residual pressure in the case. None of the other indications of high pressure were exhibited. The cases that I reloaded were hand primed and I found almost no expanded primer pockets. The expanded primer pockets were primarily in 25-06 and 6mm Rem. I also found 1 in a 7X57 case. Few if any of these cases would have been fired in an autoloader.

I pushed out some primers today and see they have a tiny "ridge" on the base side. Some of the extractor marks I see are somewhat "smeared" in a rounded fashion. Also I notice some inconsistant headspace after fl sizing. Also I've notice that my hornady dies really work the brass hard...something I've noticed with other hornady dies. They really downsize far beyond what my redding body die does for my bolt .308.
So...here is some of my theory. The chamber on an auto would be pretty smooth....a manufacturer wouldn't want alot of grip from an expanding case when the bolt is violently trying to withdraw it. So..do I have enough charge to seal the chamber from blow back but not enough to make the case hang onto the walls of the chamber so it is slamming back into the bolt....which is rotating and "smearing" the extractor mark a bit??
I guess my final question is....does a gas gun have the same chamber pressure as a bolt gun or is some of it "bled off" via the operating system???

I have never owned a BAR but I have seen the brass from several. It seems that it is a common trait from how the action operates. Even with store bought ammo. So I wouldn't worry about it if I were you.

I still think that your port pressure is high.

WW-748 is the same spec powder as WC-846 and is THE powder originally formulated for the T-65 (.308) for use in the M14 IIRC. So you wouldn't think that this would cause high port pressure. However, I believe that the BAR's design is particularly sensitive to port pressures, so switching to a single-base powder like IMR-4895 which has a different pressure curve might alleviate your symptoms.

BTW, I, too, find the BAR an outstandingly accurate rifle for an autoloader. It may have quirks about port pressures, but it typically places its shots where you aim it and will rattle off five of the quickest, most accurate shots that a given shooter is capable of. I dropped three feral hogs out of a running mob at 150 yards with mine a few years ago, which is something I'd never be able to do with the bolt guns I most often hunt with.

Thanks everyone for the input. RE gas systems on BAR's....It gets me to wonder how much they have been updated over the years to handle all the new factory ammo.
It makes me wonder how the new BAR's handle all the wsm brass out there that seems loaded to the gills with what is probably a fairly slow powder. I was at the range a couple yrs ago with a buddy and his 7 wsm BAR...I can't remember what that factory stuff was clocking on my chrono any more but I remember I was somewhat astounded...I know they were matching some of my strongest 7 mag/bolt handloads!

Few weeks ago I loaded 10 300WM rounds for my BAR; it was a test with a new load. I noticed some light extractor marks on every brass, but no other trace of high pressure; since I'm VERY cautious, I lowered the charge by 1.5 grains and made another try: no more marks. The powder is very similar to the Ramshot Magnum;