Slam or bump?

[trodrig]

Hey folks! I've been having random doubles with my rifle. Usually from the bench, occasionally when shooting in a match freestyle and 2 times in a match shooting prone. At first I thought the doubles were bump fires caused by me not hooking the trigger properly. This past weekend I went out and shot again paying special attention to how I was manipulating the trigger but still had doubles on 2 separate occurrences. I was able to retrieve the brass from both occurrences. In each case, one piece of brass had a strange look to where the firing pin impacted the primer and the other piece from the double had the normal firing pin dent. Here's a pic of the two pieces of brass which I believe were the second shots from each double. The one on the left looks like the firing pin just barely dented the primer. The one on the right looks as though brass from the primer was popped back into the firing pin hole. Could it be that these occurred as the result of a slam fire and not a trigger bounce double?

The rifle is an 18" JP CTR-02 with all of the standard equipment (LMOS BCG/Buffer, JP spring, JP trigger and fire control group, etc). Gas block has been adjusted to just lock the bolt back on an empty mag with this load. Brass is getting thrown about 5 feet from the shooting position. Loads are:

1) 55gr Hornady FMJ-BT, 25.4gr TAC, WSR Primer

2) 75gr Hornady BTHP, 24.8gr TAC, WSR Primer

No pressure signs are evident on any of the rounds that were fired without the occurrence of the double. If this is the result of a slam fire, what can be done to rectify the situation?

http://www.flickr.com/photos/66863609@N08/9211768500/

Thanks for your help!

[Hi-Power Jack]

What is your velocity? Especially the brass on the right?

[trodrig]

What is your velocity? Especially the brass on the right?

10-shot average velocity of the load on the right is 2794fps. This is the 75gr Hornady BTHP. Powder charge of 24.8gr TAC is well within limits of Ramshot's published data for "Nato/Mil Specification". Here's a pic of brass from the same lot/load of ammo where a double did not occur:

http://www.flickr.com/photos/66863609@N08/9211964270/

Edited July 4, 2013 by trodrig

[AustinT]

Neither of those primers look normal. Your 75gr load is very hot, almost a full grain over Sierra's max of 24.0, but I know that people have pushed them that hard in the past.

Some folks have problems with doubles with a standard firing pin in a low mass OS. The fix is to put a titanium FP in. I bet that's what you need.

[mpeltier]

Neither of those primers look normal. Your 75gr load is very hot, almost a full grain over Sierra's max of 24.0, but I know that people have pushed them that hard in the past.

Some folks have problems with doubles with a standard firing pin in a low mass OS. The fix is to put a titanium FP in. I bet that's what you need.

Actually 25.8 is max load according to Ramshots own publications for AR15 data. He is well within a safe load for 75gr. My own loads are virtually identical to his as is my rifle set up. The two places I would be concerned with here would be the primers themselves and the disconnecter. Primers may be a little soft, what are you using? Also have you performed a function check of the disconnecter?

[jkrispies]

You're mixing your brass. LC = Lake City. The mil stuff has thicker walls, which will up the pressure if you're doing the same load as the others. The LC brass is over pressurizing.

Edited July 4, 2013 by jkrispies

[trodrig]

Sorry, I should've been more clear. All of the 75gr loads are using LC brass. All of the 55gr loads are using the FC brass. Both are using WSR primers which is what Ramshot's data calls for. Each load, with their respective brands of brass, were worked up from the starting charge listed in Ramshot's data for the respective bullet. The only time the primers look odd with either of the loads is when a double occurs. I have shot several rounds (over 50 of each) of these loads, with their respective headstamps of brass, over a chrono, and not seen pressure signs. Again, only time the issue with the primer has been observed is when the rifle doubles.

I read on another thread where Kurtm was describing an anomaly that sounds similar to the appearance of the primer on the right of my first picture. See post #3 on this thread: http://www.brianenos.com/forums/index.php?showtopic=135736

It sounds like this is what's happening in my case. Would y'all agree?

Thanks!

[MarkCO]

Typical slam fires. A little more oil in the bolt stopped this in one rifle that was running pretty dry.

Things you can do.

1. Ti firing pin.

2. Go back to a standard buffer spring.

3. Go to CCI primers (or 5.56 primers)

Those loads are fine for .223 and 5.56 is hotter still. Very few companies even publish the 5.56 data, but it is hotter and the .223 Wylde chamber can take it.

I have had two rifles that were prone to this and I pulled the JP buffer spring and went with a standard one and the slam fires stopped.

[Religious Shooter]

I think those primers you have aren't good for that load. I would back off on the charge until they don't look like that.

When they do what they are doing the primer can leave flakes (usually from the surface plating) inside the firing pin tunnel. Debris in the tunnel can cause slam fires by prohibiting the movement of the FP, etc.

Sure you are within the book data for Tac and 75's. But for that gun and the primers you have and the lot of TAC you have the loading isn't good.

Shoot the loads in another AR and see if the primers do the same thing.

And just for curiosity when did you buy the WSR primers? When were they made?

[MarkCO]

I think those primers you have aren't good for that load. I would back off on the charge until they don't look like that.

You'd have him shooting 75s at about 2000 fps then? Silly talk! Most slam fires, the primers look just like the OPs. The other primers did not. I have seen that EXACT same configuration do the EXACT same thing numerous times. Keep it from slam firing, the primers will look normal. Slam fires happen, and they happen more with the LMOS and a standard weight firing pin when benched or braced very hard.

Edited July 5, 2013 by MarkCO

[Religious Shooter]

Such a jerk.

[trodrig]

Thanks for the comments Mark and RS!

The primers were bought in either mid 2012 or late 2011. I really don't think the load is the issue. The primers only look like they do in the first picture when the rifle doubles. I had just stripped the BCG and cleaned the bolt, etc before this last shooting session and the gun doubled only about 30 rounds into the session. The way all of the other primers look, I don't think there could be that much debris built up with that few amount of rounds on a clean bolt. I'll strip it down tomorrow and see if I can identify debris in the FP hole.

Mark, do you think that the JP silent captured spring system would improve things? Does it have a weaker equivalent spring to it than the standard buffer spring? I'd run harder primers if I could find them but at the moment I've gotta work with what I have on hand. Perhaps a Ti FP will be in my future. I'll lube the snot out of the bolt next time out and see if that helps at all. I run the gun really wet, if oil doesn't splatter on my shooting glasses, I typically pour on some more FP10. But maybe I need to get more actually in the bolt?

Thanks!

[kurtm]

That IS a slam fire. That IS Exactly how they look when they slam fire.!!! I don't think you are way hot, at the upper end yes, but the strange looking primer is DEFINITELY a slam fire!

[AustinT]

Neither of those primers look normal. Your 75gr load is very hot, almost a full grain over Sierra's max of 24.0, but I know that people have pushed them that hard in the past.

Some folks have problems with doubles with a standard firing pin in a low mass OS. The fix is to put a titanium FP in. I bet that's what you need.

Actually 25.8 is max load according to Ramshots own publications for AR15 data. He is well within a safe load for 75gr. My own loads are virtually identical to his as is my rifle set up. The two places I would be concerned with here would be the primers themselves and the disconnecter. Primers may be a little soft, what are you using? Also have you performed a function check of the disconnecter?

Ramshot's max load for military brass and 5.56 chamber is 25.8 gr TAC for 75gr HDY BTHP. Ramshot's max load for commercial brass and .223 chamber is 24.1 gr TAC for 75gr HDY BTHP. OP is using mixed commercial brass in a Wylde chamber. Ramshot's 5.56 data is good for the military brass, but not so much for the commercial brass. Regardless, he will probably fine, but that is a pretty hot load.

[trodrig]

That IS a slam fire. That IS Exactly how they look when they slam fire.!!! I don't think you are way hot, at the upper end yes, but the strange looking primer is DEFINITELY a slam fire!

Kurt, both of the pieces of brass in the first picture came from doubles. They are from two separate instances. The other 2 pieces of brass that came from these separate two shot bursts looks completely normal. Are you saying that both primers in the first pic look like slams? From the other thread, it sounds like you also recommend a Ti firing pin in this instance. Is there a particular brand of Ti firing pin that is preferred here?

Ramshot's current data for 5.56x45 Nato shows WIN case and WSR primer. Not trying to be argumentative with you AustinT, just explaining my reasoning behind the load.

Thanks!

[kurtm]

I only get one picture. It is a picture of two pieces of brass. One is near your thumb nail and it has a small tit sticking out. that IS a slam fire. Nothing else looks like that. Sometimes the tit shears off and you end up with a primer that look absolutely flat but the middle has a flat discolored mark. Either way that IS a slam fire.

And while we are on this, there isn't a real difference between "commercial and military brass in .223. All you have to do is size a few pieces of each and trim them the same and weigh them. I haven't found much that are 5 grains difference in over all weight of cases with Military being usually lighter, which means it has MORE case volume than "Commercial" so all the crap being thrown around about that IS exactly that.

For a TiN pin I use what ever Brownells sells. Also be aware that there is a F.P. with a heavy collar out there that will slam fire with regularity with a light carrier.

Edited July 5, 2013 by kurtm

[trodrig]

I only get one picture. It is a picture of two pieces of brass. One is near your thumb nail and it has a small tit sticking out. that IS a slam fire. Nothing else looks like that. Sometimes the tit shears off and you end up with a primer that look absolutely flat but the middle has a flat discolored mark. Either way that IS a slam fire.

And while we are on this, there isn't a real difference between "commercial and military brass in .223. All you have to do is size a few pieces of each and trim them the same and weigh them. I haven't found much that are 5 grains difference in over all weight of cases with Military being usually lighter, which means it has MORE case volume than "Commercial" so all the crap being thrown around about that IS exactly that.

For a TiN pin I use what ever Brownells sells. Also be aware that there is a F.P. with a heavy collar out there that will slam fire with regularity with a light carrier.

Thanks Kurt! In that picture, the piece of brass that does not have the little tit sticking out was also from a double. That one was from the 55gr load. The second picture I'm talking about can be seen with the link in post #3. It's from the 75gr load where no double occurred and doesn't look over pressured to me.

Thanks,

Thomas

[MarkCO]

Well, I guess I am a jerk again for helping a guy out instead of needlessly scaring the crap out of him...so be it.

What Kurt said is certainly true.

I took the JPSCS out of a rifle that was slam firing about 1 of every 5 trigger pulls. Went with a 4 ounce buffer and stock spring and AFAIK, that one has never slam fired since.

Edited July 5, 2013 by MarkCO

[kurtm]

Third post link looks fine, warm yes, but just fine. In the first picture the one to the left is either a bump fire or double. The one on the right is a slam fire. Have enough of those and it will erode your bolt face and they will all look like that and the little tit will clog up your firing pin channel. Then you will need a new bolt.

Mark, you certainly bring a high level of expertise to these discussions. That Forensic Engineering stuff you do certainly isn't understood by some, but the advice is always sound!

[kurtm]

To be specific. In your picture the one on the left was the first round fired, that is why it looks normal. The rifle cycled and slam fired on the second round, the one on the right. You see the weight of the hammer and spring hold the firing pin in place as the rifle discharges and that gives you a nice normal dent in the primer. When it slam fires, the hammer hasn't fallen, it is still cocked and upon discharge the primer blows the "light" firing pin back and extruded into the hole for the firing pin tip.

[trodrig]

Thanks Mark and Kurt!

Kurt, your description of weight of the hammer and spring not being there during a slam fire and allowing the firing pin to get blown back makes perfect sense.

I know my posts and pictures are all confusing. I should've separated things out.

The brass on the left of the first picture was the second round that fired from the first double I had that day. No tit of primer flowing back, but it looks like a very light firing pin hit to me and has some flow around the circumference of the firing pin dent. That one is from the 55gr load running at 2979fps.

The brass on the right of the first picture was the second round that fired from the second double I had that day. Definite tit of primer flowing back and, from the discussion above, I think established as a slam fire. That one is from the 75gr load running at 2794fps.

The picture in post #3 above is from the 75gr load where no double occurred.

I'm going to assume that the case on the left in the first picture was a slam fire as well and perhaps just didn't flow the primer back to the same degree. We know from the case on the right that the rifle has a tendency to slam fire so it seems reasonable to conclude it would slam fire with any bullet/powder combination if the primers are the same.

I'll try a Ti firing pin and if that doesn't fix it I'll go to a standard spring.

Thanks so much for the help y'all!

Thomas

[kurtm]

Whatever, on the pictures. It IS slam firing and it WILL be cured by a Titanium F.P. Just so you know, my 77 grain hunting load goes 2850 out of a 20" barrel, and it has never dropped a primer , so like I say your warm on your load, by not crazy by any means. (Disclaimer...I am not using the same powder you are.)

[AustinT]

Yep, you're right. This place has a chart that says US mil brass has more case capacity than just about anything else. That's what I get for parroting things I've heard.

http://www.6mmbr.com/223rem.html

[trodrig]

Thanks all! The Ti firing pin from Brownell's is out of stock. Anyone have any experience with the ones from firingpin.net?

[kurtm]

Those pins would be fine. The only difference is the Brownells is Titanium Nitride coated, which isn't a big deal, and the price is right on those pins from firingpin.net