Ladder Test Results

[powereng]

Did my first ladder test yesterday for my 308 GAP-10 and I'm a little confused with the results.

My recipe is as follows:
Federal once fired brass (full length re-size, shoulder bumped back .002)
Federal GM215M primers (using magnum primers b/c that what I could get my hand on)
175gr SMK's (meplatted, if it makes a difference)
Varget powder (43gr, 43.5gr, 44gr, 44.5gr & 45gr)

Range: 500 METERS

Weather:
Temp: 40deg
Wind: 4mph @ 270 deg
Humid: 56
Dew: 25
Press: 30.19
Alt: 590ft

I thought I had it figured out until I shot the 45gr. I expected the 45gr it to land above the 44.5gr and out of the sine wave pattern letting me know the sweet spot was in the 43.5 to 44gr range. However, I did get my first pressure sign with a pierced primer with the 45gr.

On a side note, my rifle really craters primers. Doesn't matter if factory ammo or reloads. I have found that once the rifle pierces a primer, I'm pretty much done for the day. Once one little piece of brass gets in the firing pin area of the bolt, every round after that will have a pierced primer. Of the 6 pierced primers I had yesterday, I was able to recover 5 of them from inside the bolt.

Ladder Test (orange circle is 1.25" for reference)

FGGM factory ammo primers

Reload primers (43gr on left, 45gr on right in half grain increments.

 

[chariotdriver]

Check the firing pin protrusin. Would also say use a different batch of primers but it looks like a mess with factory stuff as well.

 

[Bear24]

I would say shoot it again with more charges in 0.3g increments after you get your pin problems taken care of.

 

[NoFail]

That is pretty crazy. I have a 308AR I assembled myself with the parts I bought. Barrel & BCG are JP Enterprises.
But anyway I've never had so much cratered primers & never ever a pierced primer. I've shot 168 AMAX with Varget powder up to 46 grains during OCW tests & my primers didn't have cratering such as what are in that photo.

Could you describe your sizing die and it's setup? How much are you head spacing? How deep are you seating bullets?
It's a GAP. Don't those run like clocks?

I'm just thinking of what would I be thinking about first if this were happening in mine. I've never had to solve this for myself. I might also reduce load more to see if this problem goes away. I certainly didn't see this at 42 gr.

Edit: Oh I didn't see at first you are using magnum primers. I've never used them in my .308 reloading. I would reduce charge if you don't find anything wrong with BCG or pin or whatever.
Have you only shot loads using the magnum primers?

 

[sharpshooterbr]

First off, I would redo your ladder test. You didn't cover nearly enough of a charge range to be conclusive of the nodes. Also, with loads less than 50 grains, I like to use .3 gr for an increment, as it is easy to skip right over a node with .5 gr increments. Next, I would definitely have someone look at your bolt. It appears that the firing pin protrusion is off, or you could need to have the firing pin bushed to keep the primer from flowing backward so bad. Doesn't appear to be a pressure issue, as I see no flattening on the primer and no ejector marks on the case head.

 

[bodywerks]

Those charges are way high for magnum primers. Get ahold of regular lg rifle primers and redo the test.

Sent from my DROID BIONIC using Tapatalk 2

 

[powereng]

Could you describe your sizing die and it's setup? How much are you head spacing? How deep are you seating bullets?

After firing about 200 rounds of new factory FGMM ammo, and using the Sinclair bump gage, I found the average head to shoulder measurement to be 1.5615". I use this dimension as my headspace measurement. From the 1.5615", I bump the shoulder back .002" to 1.5595". I am using Redding Type S FL re-sizing die with .336" neck bushing in a Forester Co-Ax press.

Using the Sinclair chamber length gage, I found my max chamber length to be 2.045". I don't have a trimmer yet, but all my once fired brass has been under the 2.045" measurement.

I found my max bullet length, bolt face to start of barrel rifling, using the wooded dowel down the barrel method, shown in the Mail Call Monday's video. I found this dimension to be 2.8725". This max length is way too long to fit in standard P-mag so I seat the bullet to an OGIVE depth of 2.1710" to just get the bullet to fit in the mag.

I did talk to Ken Ling with GAP this past week, I told him I thought I had tracked the pierced primers issue down to a bad lot of FGMM. My other two lots of FGMM have not experienced any pierced primer issues, just the cratering similar to the picture above. I asked for a new firing pin, but he said I would have the send the rifle back in for testing. Wanted to get others opinions before I shipped it off.

 

[NoFail]

1. Start using different brass. That federal brass is so soft it is not going to last long at all anyway.

2. It sucks, I can't find primers for the life of me!! I have just over 1200 Remington #9 1/2 LRP's left on hand and a mixed variety of others, including CCI large rifle magnum that I am afraid to try, don't need to anyway. I feel your pain about the primer thing, it's not fair we in this predicament. You know what? I feel like sending you some non magnum primers to try. I really feel those magnum primers are the culprit. That, and for 175 SMK's the charges you listed are quite high especially for a LR-308. Otherwise reduce your load to minimum recommended charge for you bullet/powder choice and test. If you are interested in my offer just pm me. I know I can't find any and I really feel for guys who are just getting going and are screwed by the current state of things. I suppose I'd be ok to let 50 go too you for some testing, verification. How about some Remington? How about some Hornady 1x fired out of a bolt gun .308 Match, SS media cleaned and uniformed primer pockets, deburred flash holes? I won't size it, better you do that. I have hundreds upon hundreds of those 1x fired so I can spare some samples of it for a good guy.

Edit: About your head spacing. There are those whom bump shoulders .002" for their bolt guns. That seems to be the standard recommendation there for bolt gun. For our semi autos it seems .003" to .006 is the recommendation. I try to keep the average at .0035" for my brass. You should look into that you'll find posts on it here this forum.

I use Hornady lock & load head space gauge and my sized Hornady brass comes out to 1.6185" to where gauge indexes on shoulders. Much different than yours, I guess because different gauge. The Hornady gauge sits about halfway of shoulder.

 

[Bill Larson]

check the firing pin protrusin. Would also say use a different batch of primers but it looks like a mess with factory stuff as well.

check f-pin ......... Too long...... Go to oversize f-pin & fit to hole in bolt...or send bolt to gre-tan to bush.......

 

[powereng]

Thanks for the offer NoFail, but I may have a lead on some regular primers here locally. As far as brass goes, I have a shit ton of Federal stuff I shot out of my Noveske N6 before I got my GAP. I'm not in love with it, it's just what shot over the years before I got into reloading. I start over with the little bit of Winchester and Hornady brass I have laying around.

So far I've only put 28 rounds of my reloads through the rifle, with 45gr of Varget being the max charge weight. I'll go back to 42gr and a non-magnum primer and do my ladder test over again.

I'll call GAP again and see what they say, but can someone explain to me how the bushing works?

 

[JGorski]

First off, I would redo your ladder test. You didn't cover nearly enough of a charge range to be conclusive of the nodes. Also, with loads less than 50 grains, I like to use .3 gr for an increment, as it is easy to skip right over a node with .5 gr increments. Next, I would definitely have someone look at your bolt. It appears that the firing pin protrusion is off, or you could need to have the firing pin bushed to keep the primer from flowing backward so bad. Doesn't appear to be a pressure issue, as I see no flattening on the primer and no ejector marks on the case head.

Yes, and get some CFE223, start at 46grs and work your way up. Oh, and wait for some standard primers.

 

[Deadshot2]

I did talk to Ken Ling with GAP this past week, I told him I thought I had tracked the pierced primers issue down to a bad lot of FGMM. My other two lots of FGMM have not experienced any pierced primer issues, just the cratering similar to the picture above. I asked for a new firing pin, but he said I would have the send the rifle back in for testing. Wanted to get others opinions before I shipped it off.

Look at your bolt face. Does it have a "chamfer" around the firing pin hole? I've found this to be a major cause of cratering with ordinarily mild pressured loads. I recently replaced my Remington bolt, that had a huge chamfer on the hole, to a PTG bolt with no chamfer and a nice snug fit for the firing pin. Even my "stiff" loads now show little or no cratering.

What bothers me more on your pictures is the huge "ejector horseshoe mark" on the case head. I find that occurs when either the case is short for the chamber or pressures are way too high.

For those magnum primers I'd consider a load back down around 42 grains myself.

 

[NoFail]

Yes, and get some CFE223, start at 46grs and work your way up. Oh, and wait for some standard primers.

LOL!! Yes this!!! Just read my sig hahaha!! I use CFE for my 178 Amax's and Nosler 180 Ballistic tips.
46.8 grains for the 178 AMAX. In OCW testing I went as far as 47.3 gr CFE with the AMAX. No pressure signs but it was cool out, winter. Actually that's where I stopped there and it happened to be a tight group, seemed like a accuracy node. But I don't want to push it that hard. 46.8 is a node too and 2550 from my 16".

 

[powereng]

No chamfer around the firing pin hole, but you can see how the firing pin is starting to erode due to the blow back of the pierced primers. Remind you, most of pierced primers have come from one lot of factory FGMM ammo, not my reloads. Although I do admit my reloads are not helping to diagnose the problem.

I did my best to measure the firing pin protrusion from the bolt face and found it to be 0.051". You will have to tell me if that's excessive.

Boltface

Firing pin

Firing pin protrusion

Like I said, I will start over with a new recipe using different primers and get with GAP in the morning.

 

[Deadshot2]

I did my best to measure the firing pin protrusion from the bolt face and found it to be 0.051". You will have to tell me if that's excessive.

That's pretty much standard for any rifle I've come in contact with. You need enough to make up for any extra headspace you might have due to variations in case sizing and still strike the primer.

You definitely need a new firing pin. For all my AR platform rifles I always like to keep a spare. I even have a spare Remington firing pin assembly with cocking piece, spring, and pin. Nothing ruins a day of shooting quicker than a broken or "flubbered up" firing pin.

 

[LstManOut]

As for the ladder test, German Salazar has a link to an article on Audette's Load Development that I always refer back to when I get an odd print. I've read it many times and usually learn something new each time. Maybe it will be of use to you.

http://www.desertsharpshooters.com/manuals/incredload.pdf

 

[powereng]

As for the ladder test, German Salazar has a link to an article on Audette's Load Development that I always refer back to when I get an odd print. I've read it many times and usually learn something new each time. Maybe it will be of use to you.

http://www.desertsharpshooters.com/manuals/incredload.pdf

Great link! Thanks for referencing it.