Advice for an AR in 308 not firing consistently

[chutestrate]

I am chasing a problem with a build that I had done for me. It will consistently fire factory, but not my handloads. Looking at my primer seating I don't see any difference in my primer depth. The primers get light strikes. It was suggested that I reseat my primers because the firing pin might be trying to seat the primer. I'm fairly certain that isn't the issue, but after work I'm going to try that on a few of the cartridges after pulling them apart. The shells seem to be seating fully, but that did give me the thought that even though it seems to be chambering correctly maybe it isn't. Some of the light primer strikes were hard to eject. So I thought to reset the shoulder on a few of the shells and try again.

Does a free floating firing pin have difficulty setting off a raised primer? My primers aren't raised, but maybe the same principal if not chambering fully? I'm grasping at straws. Not many gunsmiths in my area. The factory stuff on hand is PMC Bronze, it goes bang all the time. Looking at my primed cases and the factory stuff I don't see a difference in the primer depth.

I'm not very good at diagnosing this stuff so any suggestions would be most welcome.

[merlin101]

It does sound like your primers are not seated all the way, perhaps they are flush but not seated to the full depth?

[chutestrate]

Now that you say that they do look flush. looking again at the factory i do see a small amount of depth to the primer.

[Winger Ed.]

I'd do some measuring.

I had a problem like that with a .30-06 one time.
My sizer die was either defective, or I'd set it down too far, the lip on my shell holder didn't fit the die's tolerances--- something.

I figured out the shoulder had been moved back too far.
My resized cases were being pushed forward into the chamber far enough the the firing pin couldn't reach the primer with enough travel left to fire it.

I found it by firing empty primed cases with the sizer die set at lower and lower adjustments down.
As the die went down, the primer was backed out farther and farther compared to a case just being neck sized,
until I reached a point where it didn't fire at all.

The problem wasn't with the primer.
It was basically my FL sized cases were too small and/or short for the chamber.

[Der Gebirgsjager]

I'm seconding Winger Ed's idea. If the factory stuff always goes bang then I'm thinking your dies are set to push your shoulders back too far when resizing. I'd try resetting the sizing die to just touch one of the factory round's shoulders. The way I'd go about it would be to remove the die from the press, remove the depriming rod and ball from the die, run the ram all the way up to the top of the stroke with the factory brass in the shell holder, gently screw the sizing die down over the brass until you just feel it touch the shoulder. Tighten the locking ring. Load a few and see if they shoot.

[chutestrate]

Well it looks like I have a list of things to try so thank you for all the suggestions. I happened to call Geissele to talk to them about my trigger. Sent some pictures so I'll see what they have to say. If that doesn't pan out then I will move on to the next set of steps.

[BK7saum]

This is the reason I use a headspace comparator. I resize my cases according to the fired headspace measurement and set the shouoder back 0.001-0.002" on bolt action rifles and 0.002-0.003" on semi-autos, levers and break actions.

My dies are set up for this amount if setback at the beginning of the reloading session and the first few sized are double checked in the chamber before the rest are FL resized.

I do full length resize every case as I want them to be consistent as they are fired and resized. I anneal every 3-5 firings depending on consistency of case neck tension.

I have never had a case shoulder setback so far that a primer wouldn't fire. Sounds like the shellholder or die are out of spec.

[country gent]

On handloads you want to bump the shoulder back .002 -.003. A tight fit can inhibit chambering enough to create a out of battery condition. THe bolt has to rotte all the way to allow firing pin to hit effectively. Ti see this remove bolt carrier group and rotate bolt open all the way forward and push on the pins head it will travel forward bt not protrude thru the bolt closed all the way It protrudes about .060.

If your chamber is cut to dead min head space your die shell holder combo may not be fully pushing the shoulder back. try different combinations of this to see if it helps or you can face a little off the bottom of the die. .010 usually does it.

A simple compactor type gauge can be made with a 7/8" nut find center on a flat and drill a .345 hole thru it and lightly chamfer it about .060 deep or so. Now set this over a few fried unsized cases to get a dimension. This isnt an actual measurement but a comparative measurement. Now Measure some off your sized brass and see how they compare the fired brass should be .001-.003 smaller than the fired.

You can also use a sharpie marker and blacken a sized case chamber it and remove the scraped removed ink will show where its tight.

[Texas Gun]

Either he’s not sizing them all the way or he’s putting to much pressure on them when he seating the bullets and cramping expanding the shoulder out just enough to where it’s not chambering right this can happen on 223 / 5.56 as well.

Only time I ever had a problem with the primers not working gun had weak firing spring That gun work with factory but not reload as well

[chutestrate]

Country gent i really don't understand how to do what you are suggesting. What do you mean by rotating the bold all the way forward and pushing on the pins head? Compactor type gauge? no clue. Is that the same as a case gauge?

[slim1836]

chutestrate,

I'd like to know what boolit and load you are using in your AR10 if you don't mind.

I have an AR10 also I want to develop a load for and this being my first semi-automatic I can use all the input I can get.

If anyone wants to share info on this, please PM me as I'm not trying to hijack the thread.

Slim

[country gent]

chutestrate. The bolt rotates in the carrier moving forward and back as it rotates, simply turn the bolt to see the forward and back length movement.. The comparator gauge is to measure from the shoulder to the case head this is the head space dimension of the round. to long and the bolt cant close completely. This dimension is a datum line on the mid point of the shoulder. The nut I described sits over the neck and down on the shoulder to compare fired and sized cases measurement. These are also available for purchase in the form of case gauges and hornady in their comparator.

[Willbird]

https://cdn-fsly.yottaa.net/53ff2f50..._1.jpg?yocs=p_

There are ways to directly measure to the .001, and it can even be done with the Wilson gauge too. Brownells lists them at $29. There are other ways to measure too but the Wilson is probably a really good way for the average person, it should pick up a shoulder bulge like another poster mentioned too.

Bill

[gnappi]

Most likely culprit the primers are not seated deep enough.

I have an LR-308 and the only time it did that (once) was when the bolt mating surfaces were dirty and the bolt had trouble closing completely.

[popper]

Slim, Hodgdon load for 31-168c, PC'd works good with harder alloy. Shoulder is set back too far. Use case gauge to set your die so your case fits.

[beshears]

Try a small base sizing die. Sounds like it is not seating fully in the chamber.

[Larry Gibson]

The key to your problem is here; "Some of the light primer strikes were hard to eject." I'll assume by "eject" you really meant extract?

That problem is usually caused by one of two things or both. First the dies are not sizing the cases enough, particularly in the expansion ring area. Thus the too larger diameter case is causing the bolt not to fully rotate closed. When the bolt almost closes the bolt jas jammed the too large case into the chamber making it hard to extract.

Second, if the case is getting sized down in the web expansion area the shoulder is pushed forward. But if the die is adjusted for proper case headspace the brass flows further forward causing the neck to lengthen. The too long cases mouth gets jammed into the front of the chamber causing the bolt not to rotate fully closed and sticking the case in the chamber making it hard to extract.

In both cases a light firing pin indent may very well be present on the unfired primer. Also, if the cases are held by the extractor that means the headspace was sufficient and the firing pin on a properly closed bolt would have fired them. You give no indication of the cartridge being stuck in the chamber and the extractor not extracting the case so that would not be the problem.

First check the OAL of the sized cases. If too long that may well solve the problem. Trim the cases to a correct OAL if too long. Measure the expansion ring at the web on several fired cases. Then measure the expansion web on several of your sized cases. They should be not larger than the fired factory case measurements. If large you are not sizing the case enough. You should have the FL dies adjusted so the shell holder bumps solidly onto the bottom of the FL die when sizing. Using any "cam over" of the press can result in cases not sufficiently sized for gas guns.

If resetting the die and or trimming solves the problem you are good to go. Having to trim the case will greatly shorten case life and incipient case head separation can happen in as little as 3 - 5 firings depending on chamber/sizing dimensions and the intensity of the load used. A SB die may also solve the problem but it sized the case more than is usually necessary leading to less case life. The use of the RCBS X-die is recommended to avoid trimming at all and to get 20 +/- firings per case.

[243winxb]

hard to eject. To much crimp bulged the case shoulder. Also keep the action from closing fully. My guess.