Blown Primers going from Fed 210M to Rem 7 1/2?

[rockchalk06]

For the last 300ish rounds (give or take), my 6.5 Creed recipe has been:
Lapua LP Brass
Shoulders Bumped .001"
Necks ran over L.E. Wilson 6.5 Mandel giving me .002" Neck Tension
COAL 2.875" giving me .057" Jump to Jam and fit in my mag with room to spare
Berger 140 Grain VLD Target (All same lot#, I have/had like 1400 of this lot#)
40.9 Grains of H4350

I made this load @90 degrees. I average 2700 FPS, SD's range between 6-7 and ES 14-17. Zero pressure signs and I'm almost full grain under what Hornady is calling for max on this load at 2.800". I've worked up all the way to 43.0 grains of H4350 at this COAL in the same temp (same day actually) before I found pressure signs. 40.9 is what I settled on due to the best #'s and best group. I also found a yuge node from 40.5 to 41.3 with my groups never going over .6" and SD/ES always sub 10. Needless to say, if the primer availability of 210M's was better, I would not have messed with this until **** went south. Round count was at 524 prior to this morning.

I gave up trying to buy and barter for 210M's, so I bought 5000 Remington 7 1/2's and 300 rounds of Lapua SP 6.5 Creed Brass. I used to use 7 1/2's on my Pdog load in 223 years ago and found they gave me the best #'s and itty bitty groups.

Hand priming, these pockets were tight. I didn't do anything to the primer pocket prior to loading. Seated below flush as I have done always. I decided to stick with the exact recipe as above as I know it works in this barrel and it's a lighter load. I loaded 5 at 2.875" and 5 at 2.865". Temp approx. 70 degrees at the time of fire.

First round sent was 2646 FPS and the primer was cratered big time

Second round was 2652 and even worse:

3rd one was blown. 2643FPS

4th was blown, but didn't register on my V3 for some reason. Shot when basically into the same hole/cluster

5th was cratered and registered at 2629 FPS.

4 shots registered, printed a sub 10 SD and a really nice group for the 1st 5 rounds of this recipe.

Group on the right

 

[rockchalk06]

The group on the left was ok, but shot 3 (the one that went low) messed that SD all up.

All 5 of these had big craters but no blown primers.

What in the bloody hell happened here? I can't think I'm so over pressure here that I'm blowing primers am I?

I did do some research before I posted this and found several folks claiming the firing pin on some rifles is too long by .020" or so and causing this. Taking some material off the pin fixed all their issues. I'm not ready to do that at all, but if I didn't run this load over a chronograph, I would immediately say it's too hot and back off. Chrono didn't lie though.

I should also add, prior to this range session, I did clean my barrel really well. I sent 3 foulers down the bore before I did these tests of my 210M LP load and had 2654/2664/2653 with no blown primers, no pressure signs and stacked them in a fairly decent group for having just cleaned my barrel. My FPS average was down from 2700, but that could be a drop in FPS due to cleaning and 20 degree temp?

Thanks in advance OSA

 

[264killer]

Measure firing pin protrusion.

 

[rockchalk06]

Measure firing pin protrusion.

I'm going to have to order a tool to measure it, but here is a picture

 

[rockchalk06]

Couple other things to note.

1. Depriming all 8 cases, primers were still super tight. Very noticeable amount of force to remove primer v's my large rifle load.

2. Priming the 8 cases felt no different than when I originally primed them. Very stiff and tight.

3. I measured headspace off a new virgin piece of brass from the same lot as these fired 8. I did not mess with headspace on the initial loading. Just adjusted the necks and loaded them. All 8 measured no more than .005" increase with 6 of 8 being .004" Only two were .005" and they were NOT the blown primer cases. Those measured .004".

 

[KurtM]

On an AR-10 this is indicative of too light a hammer spring, but in your case I would look at a couple things. First do the 7 1/2 seat deeper than the Federal? If so it could cause this. Also large pistol primers are shorter than rifle and it wouldn't be the first time the factory messed it up. Next the blown primers look right, no crown, but obviously blown. Maybe pull the bolt apart and clean the FP and spring channel real good, might have a chunk of something floating around in there causing erratic firing pin depth.

 

[rockchalk06]

On an AR-10 this is indicative of too light a hammer spring, but in your case I would look at a couple things. First do the 7 1/2 seat deeper than the Federal? If so it could cause this. Also large pistol primers are shorter than rifle and it wouldn't be the first time the factory messed it up. Next the blown primers look right, no crown, but obviously blown. Maybe pull the bolt apart and clean the FP and spring channel real good, might have a chunk of something floating around in there causing erratic firing pin depth.

The 7 1/2's seat more shallow than the Federal I have on hand which is 205 MAR's.

I'll have to do some searching on primer thickness of known 7 1/2's, but I'm getting a consistent .124" on them. I went through and randomly pulled a few from different sleeves in different boxes and all are consistently .124" My Federal 205MAR's are .120" and my Winchester #41's are .1205" to .120

I'll do that. I do know it has never been done on this rifle yet.

 

[JEVapa]

See if you can mash your protruded firing pin back into the bolt with your finger...looks like it's pushing the firing pin back into the bolt. To echo what Kurt said, check to see if those might be LPPs.

So this is small primer brass? Because 210M is LRP.

I'm thinking your firing pin spring is weak or short or like Kurt said, you have some crap in there with it.

 

[panayoti]

Primers look strange. Outer radius of primer cup usually flattens out before material extrudes out around the firing pin nose.

 

[rockchalk06]

See if you can mash your protruded firing pin back into the bolt with your finger...looks like it's pushing the firing pin back into the bolt. To echo what Kurt said, check to see if those might be LPPs.

So this is small primer brass? Because 210M is LRP.

I'm thinking your firing pin spring is weak or short or like Kurt said, you have some crap in there with it.

Previous load was 210M with Lapua Large Primer Brass. This is 7 1/2 with Lapua Small Primer Brass.

It takes a good amount of push to force the firing pin back in. Can't do it with my finger. Have to use a punch.

Removed firing pin and while it was dirty, not too terrible. Nothing chunky. Cleaned and reassembled. Looks to be about the same in terms of protrusion