DPMS LR308T odd brass dynamic going on

cases

Sirs:
WILDALASKA and KIRBYTHEGUNSMITH:
You guys have explained the problem well, as usual and I agree with both of you!
You know, Winchester post 64 series for a while had small firing pin/large firing pin holes that I found.
WILDALASKA is certainly right to send this gun back - it's sloppy in firing pin clearance - KIRBYTHEGUNSMITH I think is right that this does happen and he didn't see anything ominous! I do think the case expansion is fine - but the cratering bothers me as WILDALASKA says it does he. I agree with him as well. Great discussion men!
Harry B.
 
That the case expanded just in front of the case head on morrison's rifle is indication of a chamber reamed oversize. This is unusual for DPMS who is noted for tight chambers, but anything can happen in a mass production situation. While I don't think it is dangerous for brass used once and discarded, it could pose a work hardening issue for brass that is repeatedly resized. Federal is also known for soft brass that would exacerbate the expansion in front of the head and also cause enlarged primer pockets after a couple reloadings. (Soft brass also caused the head to flow into the ejector hole in one of Kirby's pics, hence the circular mark on the head).

I would also send the rifle back and ask for a replacement barrel.
 
Kirby's pictures of cratered primers from the 7400 are interesting, but I wouldn't want my rifle to display that symptom. Oversize firing pin holes are a cause for primer cup failure. The cup didn't fail for that particular lot of primers in that lot of cartridges, but that doesn't mean it won't happen on the next lot. The pressure inside the cartridge creates a cookie-cutter shearing action at the firing pin hole against the thin brass primer cup. If the pressure exceeds the sear strength of the cup, the primer will be pierced and leak gas that will etch the firing pin tip and further enlarge the firing pin hole. A stiff spring behind the firing pin is probably the only reason the primers from the 7400 weren't pierced. Large firing pin hole/pierced primers is why many custom rifle makers which chamber for very high pressure cartridges use 0.062" firing pins in tight firing pin holes.

I would replace the bolt on the 7400 or install a bushing on the bolt face that has a smaller firing pin hole.
 
Details

I had a chance to get more close inspection of that Remington rifle, and here is the picture proof of the cause of the minor crater appearance around the firing pin mark.

m7400-138.jpg


m7400-144.jpg


The close fit of the firing pin is shown, so there is not a gap of the firing pin and hole causing a situation.

There is a minor chamfer on the front edge of the firing pin hole, and the tiny relief allows a small amount of primer flow into that section.

I have information forthcoming from the top man at Remington for repair and legal testimony. He is the guy that does the expert witness exams for Remington. I got lucky in finding him at Remington, and had a chance to see him at the NRA show here in St. Louis recently.

When the info. arrives, I will post the official Remington information.

More to come.

kirbythegunsmith@hotmail.com
 
In the DPMS, the chamber may have excess runout at the mouth. This can be caused by coolant failure, or a dull flute on the reamer. If the chamber mouth runs out, the chamber may be the correct size everywhere but in a localised area. a go-no go gauge will not show this. An optical comparator would. I'm not saying this is cause of the uneven expansion here, but it could be.

As WA says, send it back with some fired cases. 55,000 PSI is nothing to take chances with.

PS. I am not a gunsmith, I am a toolmaker.
 
When the info. arrives, I will post the official Remington information.
Click to expand...

Well we are the Alaska repair center for remington (going on 12 years plus) and we see a cratered primer, it goes back :)

WildthatshwytheyhavelegalcounselireckonAlaska
 
Details from Remington

Here are pictures direct from the cases that were personally sent to me from the Manager of Product Service and Law Enforcement Training at Remington Arms, Ilion NY, a 25 year veteran of Remington services.

These have been represented as having a normal primer mark for Remington 7400 Model Rifles.

3 cases fired in 3 different 7400 rifles, and all exhibit the "crater" mark from the firing pin hole chamfer present on the bolt face.

This is not something done to other rifles, but evidently just the semi-loaders, and not just at Remington.

These are the 3 cases, and the minor primer craters are very similar to the ones I previously posted from a 7400 at my shop.

fsrem-10.jpg


This is a sample case from a brand new AK74 5.45mm, and there is a crater look to that primer.
ak74-1a.jpg


This is a close look at one of the primers from the 7400 here. The tip dent is 1.2mm (about .047), and the total crater rim is 2mm, about .079. The firing pin hole is about .058". I think that what we have is a plastic-type flow of the primer cup into the chamfer, and a small amount of re-flow of the firing pin dent mark back into the firing pin hole. (Can you see that little crease in the crater between 4 and 6 o'clock?) During application of EXCESS pressure from stiff reloads, etc., that might be a place for failure, but at what level does a primer fail in such a tiny spot? 70,000? 80,000? About the same level that would cause a blow-out in a bolt-action?
7400-1a.jpg


Here is primer re-flow in shotgun primer firing pin dents that may make the principle easier to see, but just happens to occur right in the deep center section.

Taurfpbetter-1.jpg


I wanted to show another case expansion situation that is of normal appearance. These 7mm Mag. cases are from a Browning BAR, and the expansion marks just in front of the belt should not be cause for concern.
BAR7mm-1a.jpg


I noticed that nobody spotted the situation that I commented about in my 6/23 post here. Look at the first picture in that post, and see if you spot an anomaly.

I expect to have a special situation to post here for seeing extreme pressure signs, and of course with some descriptive pictures.

kirbythegunsmith@hotmail.com
 
Well we are the Alaska repair center for remington (going on 12 years plus) and we see a cratered primer, it goes back:D

Its Remingtons call to make, not ours.

And I shot a 7400 a few days ago and it exhibited no cratering of primers...none

WildsoletsgoroundandroundAlaska
 
Details

Give that man a ceegar.

One primer is backed out slightly, see?

m7400-105-1.jpg


The manager at Remington says that they have a form letter that they send to shooters, etc. that think that they have a problem with cratering of primers in their gun.
Right now, Remington is having their yearly shutdown for major machine maintenance, etc., but he is supposed to get me a copy as soon as he can.

I already believe him when he says that this is a typical condition to have a tiny chamfer on the new 7400's.

Perhaps you (WA) were shooting an older gun from prior to this minor design change.

Regardless of what I say or think, if the line personnel at Remington don't consider this minor chamfer/crater mimic to be of any concern to them (as long as we are talking MINOR, not YIKES) then I won't waste money and time on shipping in a gun with that condition.
You can avail yourself, like I did, and ask the personnel that you deal with where you could send samples of cases and/or e-mail pictures (like I have already been doing) so the response time and/or cost can be minimized.

Then, like you say (and I concur) the factory can be the one to shoulder the burden of decision and liability in questionable cases. Once they have given their decision, you can feel covered or whitewashed, as the case may be.

Here are the predecessor cases from the primers pictured in the last post showing a "re-flow" in the central part of the primer dent. These punctured primers mixed in these samples were an unpleasant discovery.

20.jpg



These were from the same time but had not punctured, but did exhibit signs of a rough firing pin tip in the center of the dents. Notice that top primer?

Why do you suppose that one shell failed to fire, and show such a minor firing pin mark, considering there were similar shells with punctured primers from the same session?



25.jpg




During the session with the .410 that made the previous examples, I had also shot another, a Stevens single shot.

Notice the re-flow on these primer dents. Now that's re-flow, ain't it?

stevsgl1.jpg



This shotgun has the rebounding hammer, so the firing pin has no pressure exerted to hold it extended for more than a micro-second. The pin hole is large enough to allow some opportunitistic reforming under pressure. There is not a large clearance between the pin and hole, as shown.

stevsgl-2.jpg


stevsgl-3.jpg


I will have more interesting pictures for the next posting.

Will anyone have any guesses of why there was a failure to fire in with the punctures?

Are there any comments about the pictures in the previous posting, such as the AK74 crater, the 7 mag. case expansion marks, or the firing pin dent measurement/commentary?

kirbythegunsmith@hotmail.com
 
Perhaps you (WA) were shooting an older gun from prior to this minor design change.
Click to expand...

No Kirby. It was "brand new". It was not extracting. We fixed that.

FOLKS...if you see cratered problems in your (STANDARD FACTORY) rifle SHOOTING FACTORY AMMO in any rifle, stop shooting. Take it to a reputable gunsmith or a service center.

Period.

WildastotherestiwillspeaktoremingtonpersonallyandyouallKNOWwhoiamasopposedtonetanonymityAlaska
 
Remington Details

I had promised to post the info. from Remington when received, but had been waiting for the Remington summer annual shutdown to complete, so sorry for the delay.
I will also post a few relevant pictures next posting.

NOTE: I was still wondering if anyone had any input on why (in the 07/08 posting) the one batch of shells that included primer dents with firing pin scarring showing also had one shell that failed to fire. Who can discern the problem that occurred that time? That cylinder load had one shell puncture a primer, and that one failure to fire, all in one batch of 5 shells. Who gets the prize this time? Pictures of the fault and cure are upcoming.

Here is the letter straight from the top man in the repair etc., the supervisor that I referenced earlier in my other posts.

FS-6-1.jpg


FS-9-1.jpg


That is the official word from Remington.

Fred said that one of his people knew WildAlaska and had a good working relationship, so no disrespect is intended in any way, shape, or form.

kirbythegunsmith@hotmail.com

I have more posts at
www.thehighroad.org
and
www.shotgunworld.com
 
Notice the word "if" in their letter.....

Folks here is the important "if"......if you have any rifle that craters primers on a factory load, stop shooting and bring same to a gunsmith right away.

Period.

Wildansomeonelsewilldetermine"if"itisnormalAlaska

Gee Kirby thanks for vouching for us :barf:
 
This thread is now so far off the original question and so confused, that I hesitate to jump in, but if I understood correctly, the original problem was what appeared to be stretched cases on one side only. If that is the situation, the most likely cause is a bolt face cut at an angle, because the bolt head was not set up correctly for end milling. That is pretty easily checked but the rifle should be sent to the factory for a fix.

Note that a rifle with an angled bolt face can show perfect headspace, since the gauges will read from the "high" point of the bolt face. If you want to check, use some Dykem blue on the bolt face and then run the gauges.

Jim
 
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