How far is too far?

[Luky]

Background:
I finally completed my LR-308 Franken-SASS after 10 months and took it to the range to break in the barrel and start working up a load for it this past Sunday. I had loaded up 50 rounds using some IMI match brass that had three firings from my Savage and used the charge my first Savage ladder test showed was promising (43.5 gr Accurate 2520/ 175 SMK, .010” from lands, Fed 210) along with three sets of 10 “ladder” loads (40.5gr-45gr) using 2520 with 175 SMK, Fed 210, jammed .010” into the lands. I also had a box of 50 175 SMK/ 43.4 gr Varget, Fed 210 primers, loaded in IMI brass for my Savage that are very similar to start breaking in with. These are not hot loads but group well in my bolt gun. Not happy with the IMI brass as the primer pockets are already pretty loose after only three firings, but I did score 500 pieces of new Win brass a couple of months ago from Midway so I do have something to move forward with... All brass was FL sized and shoulder bumped with redding type S neck bushing die (size checked with JP .308 chamber gage), and a Forester Comp seating die on a Lee turret press. Charges done one at a time with my RCBS chargemaster. Primed with RCBS hand tool.



It took me three rounds to set up the Wilson Combat adjustable gas system so the BCG would lock back on the empty magazine. I worked my way through shoot one/clean for 20, and then went to shoot three/ clean for the next 30 of the Varget loads. I noticed some flattening of the primers and some indentions from the ejector hole (almost looked a little hot, but I think the IMI brass is soft as I had similar experience in my Savage, along with some sticking issues so I stopped using it after 3 reloads). Then I moved to the 2520 loads and tried 5 shot groups. They fired OK, but would not pattern. It would take three rounds to foul the barrel and the last two would hit where I was aiming. While shooting rounds I had a failure to fire (small dimple on primer) and then I had a slam fire. WTF? I pulled the BCG and striped the bolt as I thought maybe the firing pin broke, but everything looked fine. But then I noticed some small bits of metal, like half BB’s, on the bench. I gathered up my brass and noticed several pieces had holes in the primers that corresponded with the firing pin. I had a couple that the pressure had pushed the firing pin indention flat. Apparently the pressure was blowing a bit of the primer back into the bolt through the firing pin hole. Again, WTF?











So I wiped things down and put it back together, swabbed the barrel out and fired a couple of more rounds and everything seemed fine.


I then moved to the ladder loads in the BHA brass and shot two of the same ladders at 200 yards using the 2520/175 SMK/Fed 210. Interestingly the node appears to be about 43.5 gr 2520, the same as my Savage (but they both have 24” heavy barrels). I did not have any primers blow out in the ladder test, even though the bullets were jammed into the lands, but I did use BHA match brass for these.





I talked it over with my Brother and sent him some pictures. He thinks the firing pin is punching too far into the primers and weakening the metal so the pressure is pushing it out the back when fired. I took the bolt apart tonight and snapped a couple of pics. So how far is too far for the firing pin to protrude? (Sorry it took so long to ge to the question. ) What else could be the problem? Could this be a headspace issue? I had a local shop/gunsmith assemble the upper as I needed them to time the comp, but I do not have the gages to confirm it myself. Other than the CMMG bolt catch broke after about 90 rounds (already sent them email for a new one)and the primer issue, it ran pretty well for the first time out.




Rifle specs:
Lilja .308 1:11 24” heavy barrel with JP large comp
DPMS upper
PRI Gen III carbon fiber 15” handguard
762 industries NiB BCG (I am leaning that this is a piece of shit, NiB plating is flaking off and machining marks, but that is for a different post*)
Billet lower (80%, 20% finished by me on CNC machine/Drill press).
PRS stock
DPMS LR-308 rifle buffer and spring
CMMG 2 stage trigger LPK
Vortex Viper PST 6-24x50 FFP, Mil/Mil in a NF 20 MOA unimount

*I already purchased a new RedX Arms .308 carrier+DPMS key from Brownells and sent it to WMD guns for NiB-X plating and ordered a JP .308 enhanced bolt assembly from DSG Arms today. Still debating on getting a new firing pin too.

 

[ballistic1]

Verifying the headspace and firing pin protrusion would be priority.
Replacing the BCG with quality components would also be on my list.

Did you try any factory ammo to see if you had same issues with it vs your handloads?

 

[pinsandpitons]

The firing pin or headspace could be part of the issue, BUT... the first thing I notice is blown and flat primers and HEAVY ejector and extractor marks in the first pic. Everything else aside, that's too hot and/or unlocking early from a gas system out of timing. I've never heard of anyone jamming anything on an initial load workup. I've no idea about how far is too far for the firing pin, but I don't think the firing pin is your biggest problem.

Added:
Bottom line is I think you're ignoring signs of high pressure and trying to find other explanations. Good luck.

 

[mavrick10_2000]

Your loads are too hot for a gas gun. 45gr with a 175 is a standard load for a bolt gun. Going much above 43.5 gr is probably too much pressure.

Getting some form of ejector marks on the head is pretty common with a gas .308, but those primers and the bolt gun load data are telling you to back off on the load.

 

[Luky]

Verifying the headspace and firing pin protrusion would be priority.
Replacing the BCG with quality components would also be on my list.

Did you try any factory ammo to see if you had same issues with it vs your handloads?

Did not try any factory ammo. I have a few boxes of 168 FGMM or Hornady TAP. Also have some mil surplus (south african battle packs and some M60 belts). I will try some on my next outing. How do I "verify" firing pin protrusion? I posted a picture... Is there a "spec" for how far it should protrude from the bolt face? I can measure it pretty darn close with my calipers...

The firing pin or headspace could be part of the issue, BUT... the first thing I notice is blown and flat primers and HEAVY ejector and extractor marks in the first pic. Everything else aside, that's too hot and/or unlocking early from a gas system out of timing. I've never heard of anyone jamming anything on an initial load workup. I've no idea about how far is too far for the firing pin, but I don't think the firing pin is your biggest problem.

Added:
Bottom line is I think you're ignoring signs of high pressure and trying to find other explanations. Good luck.

As for jamming into the lands, that is following the process for a ladder test outlined in the "powdering it" sticky on this very forum. I have followed this process several times and have been satisfied with my ultimate results. This is the first time I am trying it with a gas gun though.


How do I know if the gas system is "out of timing" and how do you adjust it? It is a rifle length gas system on a 24" barrel. If I turn down the gas, then the BCG will not lock open. Or do I need to go with a lighter recoil spring in conjuntion with turning down the gas? I can't wrap my mind around how to change this without moving the gas port in the barrel?

I am taking the "pressure signs" with a grain of salt. I see similar looks for these rounds in my bolt gun using 43.4 gr Varget/ 175 SMK 0.020" off the lands with this brass which should not be considered a "hot" load. I know the primer pockets are much looser than when the IMI brass was new as I can feel it when using the hand primer (requires very little squeeze to seat them, almost like they were lubed). I also thought that Fed 210 primers used a softer metal? These could account for the flatening on the lowest charge weight (40.5gr) (and assuming other things are not out of wack) so I would not expect it to get any better as charge weight moves up. Also with the ladder test rounds they are jammed 0.010" to help show the "maximum" or worst case pressure for that charge. I expect to back off the lands by 0.010"-0.015" after the second "refining" ladder which will reduce the pressure spike and primer flatening. Maybe I am just ignorant and need some help... I guess my question would be how much "flattening" is OK and how much is too much?

The Western Powders/Accurate loading manual 5th Ed calls out a charge range of 40.4 gr - 44.9 gr for 2520 using a 175 SMK with a 1:10 24" barrel so I am surprised that the lowest charge weight could be considered "hot" in a gas gun. I will probably rerun the ladder test using new Winchester brass with CCI primers after I get the new bolt and carrier (probably December as WMD has a 6 wk lead time for plating) to see how it compares to this.


The manual for 2520 says:
175 SIERRA HPBT MK 40.4 gr = 2,504fps 44.9 gr = 2,719 fps 61,881 psi 2.800" OAL

What powder charge would be considered "OK" for a gas gun or do I just need to determine that experimentally? (Not trying to be a smart ass, but I thought that's what a reloading manual was for?)

Your loads are too hot for a gas gun. 45gr with a 175 is a standard load for a bolt gun. Going much above 43.5 gr is probably too much pressure.

Getting some form of ejector marks on the head is pretty common with a gas .308, but those primers and the bolt gun load data are telling you to back off on the load.

Thanks. I am not trying for 45gr load (Just shot it as part of the laddder). As I mentioned my initial testing is pointing towards a 43.5 gr load being the center of the accuracy node for my set up. But that same powder charge was also blowing holes out of the primers in the IMI brass???

How much less than the book charge weight values should I expect to go in loading for a gas gun? As this powder is advertised for M14/Camp Perry "Service Shooters" you would think the book values would be OK for these weapon systems...

from their website:

Accurate 2520 is a medium burning, double-base, spherical rifle propellant designed around the 308 Winchester. 2520 is our “Camp Perry” powder and is extremely popular with many service shooters. 2520 also performs extremely well in 223 Remington with heavy match bullets (62 to 80 grain). This versatile powder has superb flow characteristics and is well within the threshold limit for the M14 systems. Made in Belgium.

And I do appreciate the feedback...

 

[pinsandpitons]

I would be cautious referencing data for an M14 towards a DI AR style .308. Different systems.

There are so many variables (as you know) with bore diam, chamber/throat specs, that i'm not shocked a load worked up in one gun (bolt savage) isn't peachy in another. Switching between brass makes also muddies the water due to differing case capacities etc etc. So yea, experimentally.

To the timing issue, I'm no expert, but it sounds like you have a reasonable set-up. Dwell time (time bullet remains in bore after passing vent) is a big deal in DI guns. And if it's too long it "could" cause the bcg to start moving (making a swipe on case) before pressure has dropped to a safe level. I don't see how that would cause a blown primer, but as I said I'm no expert on that stuff, certainly not with .308. It was just a thought. Buffer weight, gas block, bullet, powder speed, they all play a role. What ammo did you use to set the gas block? (the first 3 rounds?)

My feedback if you care, is test one thing at a time.

BTW that firing pin looks fine for depth.

 

[mavrick10_2000]

My standard accuracy loads for 3 different LR .308's is no more than 42.5gr of Varget with LC brass. And I get High 2495 to 2520FPS at 1400ASL with 175's. Honestly I feel H4895 has a better pressure curve for a gas gun than Varget. I can achieve those same velocities at a bit lower charge weights, and get an accuracy node with slightly higher FPS, with much less ejector marks and never primer piercing like your pics show. All brass is going to be slightly different from each manufacturer and sometimes from batch to batch. However, you should be able to find a good node and general signposts of pressure on the case head or primer. A chronograph can be really helpful in seeing impending pressure issues, and I think it's important with gas guns even more than with bolt guns.

FGMM .308 loads will get pretty good ejector marks in either 168 or 175 generally. But their .308 loads are a bit higher pressure, a few rounds of the 7.62x51 seemed to be less harsh and performed just as well for testing purposes.

 

[WildBill3/75]

Deep ejector marks, Pierced primers, your loads look to hot.

You could and most likely also have early unlocking ejector marks but early unlocking does not look like the extreme deep indentations your brass has, they look like half moon smears.

 

[JRM83]

As many others have said the pierced primers and ejector marks suggest your load is way too hot. 45gr of Varget under a 175 is a max charge in a bolt gun, I sure as hell wouldn't run that in a gas gun. The purpose of the load book is to provide data for you to start at, and a max load to work towards. Your ejector marks on the BHA brass look like they really start to show up around 44gr. Stop there and back off. Some ejector marks are normal in a gas gun, but heavy and deep ones are a sign that your load is too hot.

I would verify the headspace on your barrel using an RCBS precision mic or one of the caliper-attached tools. If your barrel has headspace issues that could cause some of the issues you are seeing. The second thing I am wondering is why you are chasing the lands in a semi? That round is getting ripped off the magazine by an accelerating bolt, slammed into the feed ramps, and then slammed into the chamber. Top that off with the rounds in the magazine getting rocked by recoil repeatedly and I wouldn't wonder if it is better to load to mag length instead. I have always had good luck loading a 175 SMK to 2.81 and the plus side is that it will still fit in the magazine.

 

[kvwpwr]

There was probably not a problem with your gun until you started firing loads way too hot for it. You cannot compare loading for a bolt gun and loading for a semiauto. And there is no need to jam those bullets into the lands. Which is creating even more pressure. Smks love jumping.

Your brass and gun are getting beat up because you're loading too hot. You need to back up and start over. Try some factory ammo. If you're going to load ammo. Start much lower and work your way up while watching for pressure signs. You should have stopped shooting those loads way before you did. The swipes alone are pretty bad plus pierced primers. And stop jamming the bullet in a semi auto.

 

[LRRPF52]

Pierced primers, brass extrusion into the ejector channel, pierced primer material wrapped around the firing pin inducing slam-fires....

I've had pierced primers in my DPMS-based .260 Rem, and the primer material was wrapped around the firing pin. I also bent my firing pin retaining pin. That was doing load development with high-energy N540.

The other issue is that the DPMS bolt has a pretty large firing pin hole that doesn't support the primer like a smaller hole would. You are obviously into pressure that is exhibiting signs that come right before you start blowing primers.

43.4gr of Varget under a 175gr is over max load in Hornady's 8th Edition....for a bolt gun, and they were using Hornady/Frontier brass.

There is one way to deal with pressure in the gas gun using the most expensive .308 brass, and that would Lapua Palma brass with small rifle primers, but I would consider working up a load using starting loads.

 

[rookie101]

Everyone has said it, but it seems pretty clear you are too hot. Load safely, it's annoying when your gun breaks and infinitely worse when someone gets hurt.

 

[JRM83]

One other thing. Your original load was in IMI brass which is military brass. Mil brass has thicker walls and less internal capacity which means that lower powder charges generate higher pressure. When you moved to bha brass, which is commercial brass with more internal capacity, the pressure decreased with the same powder charge. You were still overpressure, but not blowing primers due to the increased capacity and corresponding pressure decrease.

 

[jwb47]

One other thing. Your original load was in IMI brass which is military brass. Mil brass has thicker walls and less internal capacity which means that lower powder charges generate higher pressure. When you moved to bha brass, which is commercial brass with more internal capacity, the pressure decreased with the same powder charge. You were still overpressure, but not blowing primers due to the increased capacity and corresponding pressure decrease.

this guy hit the nail right on the head . you need to back off your loads . your firing pin has nothing to do with your issue at hand .

 

[leadbullet]

I had to drop two grain from bolt rifle load to semi auto safe with the 175 SMK.
Hope this helps.

 

[hkiller]

wow those are some scary pics.