GAP-10 6.5 CM-- heavy cratering, heavy swipes, and 2 pierced primers with factory ammo

[Kiba]

Last Friday I finally found some time to spend at the range with my new GAP-10 in 6.5 Creedmoor. This isn't my first large frame AR so I'm used to seeing slight marks on the brass even if the loads are safe --ejector swipes, slight pressure signs on the primers, etc.

For my initial loads I purchased 500 rounds of Hornady factory 140 Amax loads to shoot through the rifle. After I shoot all those I'll reload my own with H4350, #210M, and 140 Amax as I do for my AI AE in 6.5CM. I shot 120 rounds of the Hornady factory ammo through the rifle on Friday. Considering they were factory loads the ejector swipes were heavier than I was expecting. Same with primer cratering-- it was heavier than expected and out of 120 rounds I experienced 2 pierced primers-- first time for that with any of my rifles. Brass buildup on the bolt face was also heavier than expected after only 120 rounds and being factory loads.

I suppose next trip to the range I need to bring the chronograph and chronograph this lot of factory ammo out of both the GAP10 and my AI AE. I have some chronograph data from the AI AE with a previous lot of Hornady factory 140s-- maybe this particular lot is hot.

The accuracy of the rifle is great but I'm a little worried about the pressure signs & pierced primers when using factory ammo.

To any other guys out there with GAP10s in 6.5CM that have shot factory 140s-- is this normal behavior? My next steps are to measure case growth of a fired case and compare to an unfired case to see if there might be a chamber issue (doubtful, but need to check) and also to shoot a few of this lot of factory ammo through my AIAE to compare chronograph data. Maybe I have a "hot" lot of ammo from Hornady which is being further exaggerated by running it through a gas gun?

 

[TexasMade]

I would not think it is a Gap problem. I think it might be a little Ammo picky and not like that lot. I've read some people piercing primers even on bolt guns using factory hornady. I would call GAP and see what they say

 

[powereng]

I went through this same issue with my GAP-10 308. I can already tell you what GAP is going to say. However I hope the OP can prove me wrong. In all sincerity, good luck Kiba.

Oh yeah, be sure to check your bolt for the small pieces of primer from the pierced primers. They will collect inside the firing pin area of the bolt and exacerbate the problem.

 

[Rob01]

I would not think it is a Gap problem. I think it might be a little Ammo picky and not like that lot. I've read some people piercing primers even on bolt guns using factory hornady. I would call GAP and see what they say

Maybe with the Superformance, which is not optimal in semi autos, but not with standard loads.

 

[Kiba]

I went through this same issue with my GAP-10 308. I can already tell you what GAP is going to say. However I hope the OP can prove me wrong. In all sincerity, good luck Kiba.

Oh yeah, be sure to check your bolt for the small pieces of primer from the pierced primers. They will collect inside the firing pin area of the bolt and exacerbate the problem.

I've already stripped and cleaned the bolt & firing pin; they were free of primer debris. The sides of the nose of the firing pin show a tiny bit of erosion from the 2 pierced primers but the actual tip is still domed and smooth. I must say the DPMS-style firing pin retainer is a real PITA to remove; mine required a brass punch and a small hammer to tap out and also tap back in! Nowhere near as field-friendly as the standard slip fit cotter key method that my previous Armalite AR10 used.

I'm not pointing fingers-- I want more info and data to get to the bottom of the problem. Next up will be to shoot some of this lot of factory ammo through my AIAE and look for pressure signs and also chronograph it and compare to an older lot. Beyond that I'll work up some of my own loads starting at around 39.0gr and working up-- I already have plenty of data with my AIAE with the lots of bullets/powder/primers I have on hand and know what is safe.

I with Syrac would release their 0.875 adjustable gas block-- I'd be interested in putting one of those on the rifle and shutting the gas off to see what the fired brass condition looks like.

I'll post some pictures of the fired cases tonight so show primer/brass condition.

 

[SharpsNitro]

I've seen similar issues with that ammo in an AR10. I picked up my MATEN yesterday from the barrel maker and their test shots with this ammo showed the same effects (no pierced primers though). They told me factory ammo is too hot for the gun, not just mine but all AR10s they have barreled in this caliber, and they don't know why. It's not so much a problem for me since I hand load anyway.

Is this common to see in 6.5 Creedmore gas guns?

 

[elfster1234]

if it is Superformance, then do not use it... shouldn't use any type of over charged ammo in a gas gun.. you will get blown primers... been down that road before.

Last Friday I finally found some time to spend at the range with my new GAP-10 in 6.5 Creedmoor. This isn't my first large frame AR so I'm used to seeing slight marks on the brass even if the loads are safe --ejector swipes, slight pressure signs on the primers, etc.

For my initial loads I purchased 500 rounds of Hornady factory 140 Amax loads to shoot through the rifle. After I shoot all those I'll reload my own with H4350, #210M, and 140 Amax as I do for my AI AE in 6.5CM. I shot 120 rounds of the Hornady factory ammo through the rifle on Friday. Considering they were factory loads the ejector swipes were heavier than I was expecting. Same with primer cratering-- it was heavier than expected and out of 120 rounds I experienced 2 pierced primers-- first time for that with any of my rifles. Brass buildup on the bolt face was also heavier than expected after only 120 rounds and being factory loads.

I suppose next trip to the range I need to bring the chronograph and chronograph this lot of factory ammo out of both the GAP10 and my AI AE. I have some chronograph data from the AI AE with a previous lot of Hornady factory 140s-- maybe this particular lot is hot.

The accuracy of the rifle is great but I'm a little worried about the pressure signs & pierced primers when using factory ammo.

To any other guys out there with GAP10s in 6.5CM that have shot factory 140s-- is this normal behavior? My next steps are to measure case growth of a fired case and compare to an unfired case to see if there might be a chamber issue (doubtful, but need to check) and also to shoot a few of this lot of factory ammo through my AIAE to compare chronograph data. Maybe I have a "hot" lot of ammo from Hornady which is being further exaggerated by running it through a gas gun?

 

[pby5cat]

i have a Fulton Armory 6.5 creedmoor Upper on my AR, 24 in criterion bull barrel. I have no issues with the standard 140grn or 120grn hornady ammo. Never shot superformance. I have only blown primers and had ejecter swipes on my hand loads, that is my fualt.

 

[Kiba]

Just to clarify, these are standard Hornady 140 Amax loads-- it is not Superformance.

As far as I know Hornady only makes Superformance for the 6.5 Creedmoor in 120gr and 129gr. I wouldn't use Superformance regardless-- I've seen issues with it in several calibers in friend's rifles.

I would have handloaded from day 1 with the GAP-10 had I not been given a very good deal on 500 rounds of the factory loaded stuff.

 

[Kiba]

Here's pictures of the fired brass.

Headspace measures OK using my Sinclair gauges-- the once fired brass is only .003" longer than unfired.

 

[JSF]

I have the same rifle and same caliber and mine does it as well with factory rounds. I have an adjustable gas block and it still dings the brass. I am going to work up a load for it and see if that makes a difference.

 

[dvdt]

Pierced primers would scare me and I'd definitely call GAP to get their opinion on it.

In my limited experience, usually when I see cratering on primers the entire primer is perfectly flat. The edges of the primer still look rounded to me. Even the ones with the pierced hole. Almost seems like maybe it's something with the bolt face or firing pin hole diameter ?

I'm not certain that 0.003" of headspace growth would not concern me personally. If it was 0.007", sure, but not 0.003". As long as you aren't seeing rings above the case head after the first firing (indicating a potential case head separation) you should be fine. Some guys bump their gas guns back 0.003" for loading. Personally I only go 0.0015" for either a bolt or a gas gun. I don't recall how much mine grew from factory but I'll measure when I get home.

Interested to hear what GAP says.

 

[Kiba]

I'm not worried about the datum shoulder moving forward .002 to 003" after firing compared to unfired factory rounds-- the .002 to .003 growth I'm measuring is safe IMO. I've had factory Remington 700's with far looser chambers and measured substantially more growth between unfired factory rounds and fired rounds. When I reload I typically FL size and bump the shoulders back .001-.0015 for the bolt rifles and .0015-.002 for the semis.

And yes, I do agree the primers look somewhat odd. The firing pin impact itself looks very rough with some material flow to the cratered edges and the rim on the brass shows heavier ejector swipes than I would expect for factory loads-- but as you pointed out the edges of the primers are still nice and radiused and don't appear to be flattened much, if at all, from their unfired condition.

I need to bring a couple of pin gauges home from work to measure firing pin hole clearance but it feels minimal, about .005" at most would be my guess. There isn't a substantial raised "ring" around the firing pin impact as I usually see with bolts with excessive firing pin clearance. I'll also measure firing pin protrusion.

I've got a message in with Ken-- looking forward to GAP's input on the symptoms and the pictures.

 

[Kiba]

Just thought I'd post an update...

I've been working with GAP and gathering some measurements for them-- firing pin diameter, firing pin hole diameter in bolt, firing pin protrusion, buffer weight, diameter of buffer spring & number of coils.

I finally got the GAP10 and my AIAE to the range to chrony this lot of ammo-- the AIAE averaged 2830 fps and the GAP10 2780 fps. No issues there, the lot of factory ammo I had about a year ago for the AIAE chrony'd at 2840fps. No pressure signs and perfect primers on the AIAE but lots of primer flow around the firing pin indent and 3 pierced primers out of 15 fired with the GAP10.

Since none of the trouble shooting or measurements point to an obvious problem the upper, buffer, spring, and some ammo is headed back to GAP tomorrow for inspection & testing. Thanks in advance to GAP, they saw this thread and contacted me via PM before I had a chance to call them up!

 

[dvdt]

Cool. Hope that gets resolved soon. Interested to hear what it is...

 

[SharpsNitro]

I'll be interested to see what they find. I've been continuing to work with my MATEN in 6.5 Creedmore, any advice would be appreciated.

The main thing I'm getting is ejector swipes (heavy enough to raise a burr), the bolt is unlocking too early even though the gas block is tuned to eject at 4 o'clock. So far I've been using hand loads using H4350 and 123gr SMKs, they chronograph at 2750fps (20" barrel). Not too happy with it since I can get the same velocity with this bullet without swipes in my AR15 in 6.5BR. Tomorrow I'm going to try Varget to see if a faster powder will help.

 

[smarmadu]

I too have build a METEN in 6.5 Creedmoor and are noticing overpressure signs similar to what has been discussed in this post. Been using Hornady factory ammo, but they seem too hot for my rifle. Haven't had a chance to run them through the chrono yet. Very interested in hearing what comes of this.

 

[SharpsNitro]

I had some good results at the range today, yesterday I loaded up a batch of ammo using the 123gr SMK, CCI200 primer and Varget. The powder charges started at 36.0 and went to 40.0 in 0.5gr increments, I loaded three in each charge weight. Starting with 36.0gr I got a average velocity of 2570fps and a vertical string of 1.75", no real pressure swipes, if you look hard enough you can maybe see the brass is slightly shinier at the ejector but no smear/swipe. At 37.5gr I got a triangular group just under 3/4" at an average velocity of 2639fps still no swipes. The swipes returned at 39.0gr and 2846fps, which is 0.2gr below the max listed by Hornady (Hodgdon lists a max of 39.9gr). So moving to a faster powder than H4350 did help with the pressure issues. The velocities achieved look pretty good and for accuracy it looks like I need to explore around 37.5gr. I could still try an even faster powder like H4895 or IMR8208XBR if needed.

Edit: I could also try a magnum primer to see if that would speed up the pressure event a little bit as well.

 

[troupe]

If you do not have a adjustable gas block on your rifle, I would recommend one. It may not solve the problem, but it will help decrease the gasses. May also need a stronger recoil/buffer spring. Just a thought.

 

[Kiba]

We'll see what GAP finds when they get the upper back in hand... should be there Friday.

I'd like to have an adjustable gas block on the rifle but I'm waiting for SLR or Syrac to release their .875" detent adjustable blocks. Both companies are working on them.

Looking forward to getting the upper back.

On another happy note, JP called me today to let me know the upper for my 1st SCR11 is shipping this week and my 2nd SCR11 is shipping complete next week. Now if my 2 S&B 5-25 DT H2CMR's that have been on order about 20 weeks would show up I think that about rounds up acquisitions & upgrades this year.

Should the GAP10 still be a a little hard on primers when it comes back maybe I'll finish shooting the factory stuff through my AIAE and start loading fresh stuff for the GAP10. I'm also thinking of trying different primers than the 210M.

 

[SharpsNitro]

I've now tried H4895 in my rifle, I did not get the charge weight up to max though, peak velocity was just over 2600fps at around 36gr. This powder may be too fast to get the velocity I want but the IMR4895 data suggests it might work. The next thing I tried is going back to Varget with CCI 250 magnum primers, this got me to the 2850fps range previously noted at 39.0gr but with minimal swipes so a hotter primer shortened up the pressure event. My next test is going to be the 39.0gr Varget load with CCI #34s to see if they burn even hotter. So far, I seem to have been able to dial in a maximum velocity load while avoiding the swipes with proper powder and primer selection. The next step will be to see what I can get out of the 142gr SMKs.

If I haven't noted it before, I'm running a 20" barrel.

 

[Kiba]

Just thought I'd post an update on this situation if it comes up in searches...

The upper went back to GAP where they changed the carrier and put in a new firing pin. I also sent 40 rounds of factory ammo. They shot it all and while all the primers showed cratering around the firing pin impact none of them pierced.

When I received the upper back I went to the range with factory ammo and the very first shot pierced a primer. It pierced 4 out of 10 that morning with factory ammo so I called it a day.

Fast forward to a few weeks later; I finally had time to work on some of my own loads for the GAP10 and head to the range yesterday.

I loaded 3 of each of the following loads using H4350, 210M and 140 Amax (like the factory loads): 39.0, 39.5, 40.0, 40.5, 41.0, 41.5, 42.0gr

I know from dope & chrony data with my AI AE that to duplicate the factory ammo velocity with my current jug of H4350 requires 42.4gr.

For reference, my lot of factory ammo out of the GAP10 chronographed at 2780fps.

Here's what the loads today did:
39.0 2575
39.5 2634
40.0 2640
40.5 2675
41.0 2705
41.5 2717
42.0 2739

All of the primers had a little cratering around the firing pin impact but none of them pierced the primers-- that's the first time the rifle has made it an entire day without piercing any primers. The cratering was obviously greater the higher the charge weight. Also, it was pushing 90F at 9am this morning when I was doing the testing so that's also a good sign. I ran out of ammo before the temp got to 106F at 1pm so I couldn't test for piercing at 100+F.

The 41.0gr load at 2705fps looks pretty good in terms of primer condition, the 75fps drop from the factory loads at 2780fps is a 0.6 mil difference in drop at 1000Y. While I'd like to see the velocity up around 2750 I'll take a reliable rifle that I can dial for over one I have to strip the bolt down at least once per magazine to clean out primer pieces...

Next trip to the range will involve 15 or 20 each at 41.2 / 41.6 / 42.0gr test for accuracy and also primer condition.

Also, I'd like to to try CCI #34 and Wolf LR primers if I can find another guy at the range who will let me buy about 50 of each; supposedly both of those have thicker/harder cups than the 210M and that might put an end to all the primer issues and allow me to get the velocity back up to the 2730-2750 range safely.

One thing I noticed while testing the reduced loads is that the rifle locked the bolt & carrier back on the bolt stop even with the light 39.0g loads-- so I think an adjustable gas block might help brass & primer condition since it looks like I can cut the gas down a little bit which would slow the bolt & carrier slightly. While I'm still waiting for Syrac or SLR to release their .875 gas blocks in the meantime I have a Tubb CWS sitting around somewhere so maybe I'll try putting that in the carrier and see if it helps primer condition since there's more than enough gas to run the rifle.

I'm still hoping I can get the GAP10 sorted out and running reliably. It has company due in another 8 weeks or so as I ordered a JP LRP-07 in 6.5 Creedmoor. Should be an interesting comparison.

 

[pkt1199]

Thanks for posting the followup to this - you were right in came up in a search

Also, I'd like to hear your comparison when the GAP10 is side by side the JP LRP.

 

[sch2046]

what was the out come or reasoning behing the pierced primers. I just build a 6.5 creed and mine pierced 3 out of 15 primers. Was it that the load was just too hot and needed to be backed down? Thanks for any help.

 

[Kiba]

No real outcome yet. The last round of testing showed primer flow around the FP impact even all the way down at 39.0gr. I've still be unable to find any local source for CCI 34 or Wolf LR primers to try to see if that alleviates the problem seen with the 210M's. As I mentioned in my 7/5 post I loaded up ammo from 39.0-42.0gr and while the primers were far from perfect on any of the loads none of them pierced so I loaded up about 70 rounds at 41.0gr.

2 weeks ago at the range on the first mag of the day the rifle stuck the firing pin on the 4th round out of the mag and went full auto for the last 7. These were loaded at 41.0gr which is on the light side. Luckily it didn't go off out of battery and damage itself (or me!) The rifle had 68 rounds through it at that point since the upper went back to GAP. The firing pin was OK at the start of that morning and it didn't pierce any of the first 3 rounds in the mag (I was checking each one after they ejected, they showed flow around the FP strike but nothing pierced) but it did pierce 3 of the 7 that ran away. Based on how the FP looked when I tore the bolt down after that incident, if I had to guess round #4 pierced the primer and that piece of primer bonded to the nose of the firing pin preventing it from fully retracting. I was shooting prone and had no issues holding onto the rifle-- I was anticipating a malfunction at some point but not that kind of a malfunction. Being in California you get more than a few stares when your rifle cycles that fast...

George really wanted the rifle back for a teardown and inspection after that incident so it's back at GAP right now for a checkup. GAP is just as interested in the problem as I am, when I spoke with Josh @ GAP he said they've made plenty of 6.5CM rifles that haven't had the issues mine is experiencing. I'm confident they'll make it right and I'm really hoping they'll find something definitive that explains the primer condition.

JP beat their delivery estimate on the 6.5 LRP-07 substantially (estimated 12-16 weeks, arrived at my FFL in 7 weeks) and I'm going to pick that rifle up tomorrow. I'm going to be testing the same loads in that rifle (39 to 42gr in 0.5gr increments to start) and I'll also test some of my remaining factory loaded 140's. Should be interesting to compare velocity & primer condition of the JP vs the GAP10; my GAP10 is a 24" barrel while the JP is a 22" and I'm expecting the JP to be a bit slower. I also have the option of shutting the gas off on the JP to compare the difference in primer condition with gas off vs. gas on.

If the JP shows the same kinds of primer issues with the factory 140's I think that will point to an issue with the 210M primers, factory charge weight, or the 140s when run in a gas gun-- but I won't have the info on that until next Friday when I head to the range.

Looking forward to getting to the bottom of this mystery and also getting the GAP10 back from GAP.

 

[A10XRIFLE]

Anxious to take a look and compare against a rifle we have in the shop that has shot many comps and lots of ammo without incident. Could be a bore size issue but I tend to weigh on the side of ammo primer issues as Bartlein has Impeccable inspection process.

Tom Fuller from Bushnell Tactical / Team Bushnell has a rifle identical to this one and its never had issues with factory ammo or anything else he runs through it. Ive seen him run it through 3 big comps now where over 250 rounds were shot in 1.5 days and his runs like a sewing machine.

??? when we had the rifle the first time we fired 40 rounds without any issues, we checked the headspace, Gas system and changed the BCG as well and the customer still has some issues. I then suspected lube in the chamber or a cleaning issue but the customer assures us he keeps the bore clean and the chamber dry. So we will compare it with known good ammo and and known good rifle and see what happens. Ill let you all know as we are just as eager to get to the bottom of the problem as the customer. rifle arrived Friday so We will get a good look this week..

 

[redirt78]

Interested in this thread so posting to mark it. A lot of good information regarding gas pressure. I hope both gas guns turn out to be all you expect of them or more. Good luck

 

[msalm]

The issue is too large of firing pin and firing pin hole....most likely just the bolt having too large of fp hole and too much clearance w/ the firing pin. I recently built a 6.5x47 lapua on an SPR action and had pierced primers on almost every round. I ended up bushing the bolt face and turning down the fp to .068" and that solved every problem I had. If they would use an Armalite bolt/carrier assembly instead of the DPMS type all issues would be resolved (IMO).

 

[Kiba]

George, thanks for the update.

When I sent the upper back the first time I also sent 40 rounds of my lot of factory ammo. Josh shot them all; they came back with primers that had ragged flow back around the firing pin impact but none of them pierced.

As I mentioned above, when I received the upper back from you the first time I did nothing except do a visual on the bore, spin a dry mop in the chamber, pin it on the lower and head to the range with more factory ammo from the same lot and the first round through it pierced a primer. I took it home, cleaned the bore & chamber, and loaded up my own loads from 39-42gr and headed back to the range. None of that batch pierced any primers (but all had varying degrees of primer cratering) so I loaded up a batch at 41.0gr and cleaned the chamber again before going back to the range. On the next trip back to the range with those 41.0gr loads it ran away on me part way through the first mag.

I'm with you on the opinion about the barrel; while Josh mentioned it may be possible there is a tight spot in the bore causing a pressure spike it would be *highly* unusual for Bartlein to let a barrel like that slip out the door.

You guys are awesome to work with and I'm very confident you'll find an answer; with any luck it all will boil down to a simple primer change. That's something I've been wanting to try for a while now but I've had zero luck tracking down anything in stock and none of my friends who reload have any CCI34 or Wolf LR primers that I could try; there may be other good choices but those were the two that were recommended as having tougher/thicker cups than the 210M. The only LR primers I have in my own inventory is Winchester LR and Federal 210M.

My last AR10 was an Armalite pattern in .308 that I put together myself with an Armalite AR10T barrel; I ran that rifle for about 2500 rounds of my own loads (H4895 / 175gr) without any issues except the gas port was about .004" undersized as shipped from Armalite and the rifle wouldn't cycle reliably in the early days. This isn't my first AR10 so I'm pretty confident I'm not screwing anything up with the GAP10 in regards to cleaning, maintenance, or loading... but I'm not exempting myself from mistakes either. If you find that I screwed up somewhere I'll own up to it.

I'm really anxious to compare the primer condition of the same lot of factory ammo out of the JP. I may sneak off into the orchards behind the house tomorrow and pop off 2 or 3 rounds and see what they look like before heading to the range on Friday.

The issue is too large of firing pin and firing pin hole....most likely just the bolt having too large of fp hole and too much clearance w/ the firing pin. I recently built a 6.5x47 lapua on an SPR action and had pierced primers on almost every round. I ended up bushing the bolt face and turning down the fp to .068" and that solved every problem I had. If they would use an Armalite bolt/carrier assembly instead of the DPMS type all issues would be resolved (IMO).

This was one of the first things I checked before sending the upper back the first time. Firing pin clearance was about 0.0034" on my bolt/firing pin combo and protrusion 0.054". While that isn't bushed bolt benchrest FP clearance of about .001" it was tighter than I expected; based on the amount of primer flow back around the FP impact I was expecting about double that clearance if not more.

The DPMS firing pins run about .0765" for diameter; I have 3 of them here. While I initially was considering excess FP to FP hole in bolt clearance as a contributing factor I hadn't considered just the FP diameter in playing a role-- but it's a good point now that you bring it up. I wonder how the primer condition would appear with no other changes other than say a .062" firing pin.


This has been a learning experience for sure, any more input would certainly be appreciated. Of course I'm eagerly awaiting to hear what George & gang find.

 

[SnakeDoctor27]

I have a gap 10 308 and I get about a minimum of 3 pierced primers per box of southwest run&gun 175 ammo, but copper creek gas gun runs just fine but also has ejector swipes and slight cratering... both use FC brass, I dont know what primers either company uses but it may be a primer issue. Side note I didnt realize the pierced primers were stacking up over my firing pin hole and after one mag of 20 I went to shoot a second(luckily a 10 rnd mag) mine went fully auto because the stack of pierced primer Cutouts acted as a firing pin everytime bolt went foward.

 

[msalm]

My experience (only 1 month ago) was the fp hole size/fp. Wasn't so much the overall clearance but the overall size. Bush the bolt face and turn down the the fp to .068 or so and the problem will be solved. My issue was with a SPR action (larger fp hole/fp) with lapua brass that uses a small rifle primer, but it exhibited the exact same tendencies with any and all loads. I shortened the fp protrusion and squared the fp tip first thinking that would help but same shit, perfect circular blanks cutout of every primer. I then bushed the bolt face and turned the fp tip to .068 or so and absolutely no issues since with much hotter loads than what was blanking out before. On the ar10 platform the Armalite has a smaller fp tip and hole to begin with. You can use it on the DPMS but must swap the bolt, carrier an fp assembly....not sure if headspace runs the same or not though.

Oh, and the few primers that didn't blank before showed severe cratering with no flattening around the edge of the primer..

Jmo again.

 

[sch2046]

My experience (only 1 month ago) was the fp hole size/fp. Wasn't so much the overall clearance but the overall size. Bush the bolt face and turn down the the fp to .068 or so and the problem will be solved. My issue was with a SPR action (larger fp hole/fp) with lapua brass that uses a small rifle primer, but it exhibited the exact same tendencies with any and all loads. I shortened the fp protrusion and squared the fp tip first thinking that would help but same shit, perfect circular blanks cutout of every primer. I then bushed the bolt face and turned the fp tip to .068 or so and absolutely no issues since with much hotter loads than what was blanking out before. On the ar10 platform the Armalite has a smaller fp tip and hole to begin with. You can use it on the DPMS but must swap the bolt, carrier an fp assembly....not sure if headspace runs the same or not though.
Oh, and the few primers that didn't blank before showed severe cratering with no flattening around the edge of the primer..

Jmo again.

Sorry for the question, but what is bushing the bolt face and how are you turning down your fp? I dont have access to any machines, just house hold tools. I have tried CCI BR and M210 and both pierced. Mine is also a DPMS bolt/carrier......I run a DPMS lr308 without issue. Does someone make different size FP's?

 

[sch2046]

oh yeah, this whole issue actually bent my retaining pin for my FP. I have never seen this...........

 

[msalm]

You need a lathe to do it. Basically you bore a recess in the bolt face and press/thread/soldier a blank of steel in the bolt face and then re-drill a smaller firing pin hole in the bolt face. Then you chuck up the firing pin and turn the tip down to match. This might be a problem with the chrome plated firing pins on the AR's as I've never turned those down, but when I build the 308 based AR's I always use the Armalite carrier and bolt assembly as the firing pin tip and bolt hole are a smaller diameter and you're less likely to experience these issues. I don't know off-hand the actual diameter but can check when I get home tonight and post the measurements.

 

[A10XRIFLE]

Update, shot the rifle again this morning after a good cleaning again we could not get the primers to pierce but there was some cratering, Measured the FP and FP Hole in bolt. FP is .080 Hole .082 which is standard on DPMS/CCMG/KMC, ROCK RIVER. I got to thinking that 6.5x47 LAPUA rifles have to have a smaller FP and hole due to the high pressure and smaller primer. So I measured some RD/Armalite Bolts and they measure .068 FP we changed the Barrel extention reheadspaced the Armalite bolt to this rifle and wala the Cratering is gone.

I got to thinking about the reasoning that .080 is what the standard on so many gas rifles and it comes down to a Mil Spec Primer thing. Heavier more mass to set off the Hard Military spec primers. Military primers are thicker and harder so they dont slam fire in full auto weapons. Unfortunately just about every manufacturer thinks on the side of what the Military needs as they are always after that huge market. My guess is that .068 works with most everything commercially available.

Oddly enough. BIG Joe here on the hide has a GAP-10 that we put an Armalite Bolt in and it would not set off some of the military primers and had cycling problems with Military ammo but not commercial. Indicator #1

So again the GAS GUN is always going to be ammo sensitive and there is no way to automate an on the fly solution. Find a Load/Factory offering that works well in your rifle and stick with it is the best bet. Limit the use of suppressors as they are a huge problem unless tuned to a switchblock with the ammo you plan to shoot and you keep the rifles clean.

Kiba, your rifle is good to go and another GAS Gun lesson is learned.

All GAP-10 308 caliber rifles will continue to have a .080 FP as lots of Ammo manufactures still use Mil spec Primers on this caliber.

All calibers except for 308 we will switch to the .068 FP That should be a perfect solution for 95% of the guys out there.

 

[A10XRIFLE]

its .068 and it worked!!

You need a lathe to do it. Basically you bore a recess in the bolt face and press/thread/soldier a blank of steel in the bolt face and then re-drill a smaller firing pin hole in the bolt face. Then you chuck up the firing pin and turn the tip down to match. This might be a problem with the chrome plated firing pins on the AR's as I've never turned those down, but when I build the 308 based AR's I always use the Armalite carrier and bolt assembly as the firing pin tip and bolt hole are a smaller diameter and you're less likely to experience these issues. I don't know off-hand the actual diameter but can check when I get home tonight and post the measurements.

 

[Unknown]

Quite a few years ago I had ordered a 260 Rem from DPMS, but they couldn't deliver any 6.5 bores because they had problems with cratered and pierced primers. I gave up on waiting, and eventually took a 308 rather than continue waiting for a 6.5 bore. I realize that Gap and DPMS aren't in the same league, my point was that the problem with pierced primers isn't specific to only Gap rifles.

About a year after I got my 308, they apparently solved the problem as they sell plenty of 6.5 bores now. I mention this to let the OP know that for some odd reason, other manufacturers also had problems with primers in the 6.5 bores. It would be interesting to find out what makes the 6.5 bores so prone to these problems.

 

[A10XRIFLE]

higher pressure and longer gas curve with slower powders. It could be solved with loading specific ammo for the caliber/rifle as well.

IE if you look on JP Rifles web site they warn that in 6.5 calibers you may have to hand load for your 260 as Some Factory offerings wont work in their rifles.

http://www.jprifles.com/document_pdfs/Ammunition Notice_19.pdf

Quite a few years ago I had ordered a 260 Rem from DPMS, but they couldn't deliver any 6.5 bores because they had problems with cratered and pierced primers. I gave up on waiting, and eventually took a 308 rather than continue waiting for a 6.5 bore. I realize that Gap and DPMS aren't in the same league, my point was that the problem with pierced primers isn't specific to only Gap rifles.

About a year after I got my 308, they apparently solved the problem as they sell plenty of 6.5 bores now. I mention this to let the OP know that for some odd reason, other manufacturers also had problems with primers in the 6.5 bores. It would be interesting to find out what makes the 6.5 bores so prone to these problems.

 

[Kiba]

George, you guys rock!

I was reluctant to post the latest round of trouble with the rifle fearing the blame game would start-- but now I'm glad I did for the worthwhile exchange of information. Lesson learned for everyone and a lot of good info posted regarding FP diameters, clearance, and burn rates & pressure curves with this load combo in a gas gun.

Just as another data point, I took the new JP LRP-07 6.5 out back tonight and fired 3 rounds of the Hornady factory 140gr ammo-- any more shots than that with anything bigger than my .17HMR and I risk pissing off the neighbors. The JP LRP-07 uses the larger .080 DPMS firing pin. 2 of 3 primers looked perfect and the 3rd had an almost imperceptible raised ring around the edge of the FP impact-- but the ring is only about .003-.004" high and extremely smooth with no burrs, no ragged edges, and the entire primer including the FP impact was shiny unlike the "matte" finish on the primer like I was seeing with the factory ammo out of the GAP10 early on with the .080 firing pin.

The real test will be running 75-100 rounds or so through the JP at the range on Friday and seeing how the 210M primers behave with the larger DPMS-style firing pin diameter in that rifle. I have 100 rounds of factory loaded Hornady 140s left plus another 50 of my handloads at 42.0gr.

Again, thanks for all the info and thanks George and gang for getting to the bottom of it. Looking forward to getting the rifle back! I was originally planning on selling one of them but I don't know how I'm going to be able to make up my mind between the JP and the GAP10... I have a hunch I'll end up keeping both.

 

[JL]

Friends GAP 308 was blowing factory load primers because of too tight bore. Bore was measured.

 

[msalm]

Mil spec or otherwise, it doesn't make sense a smaller tip not being able to ignite a heavier primer cup. There would be more pressure/penetration w/ the smaller fp tip. One problem is, and this is a good thing, is the Armalite doesn't have the free-floated firing pin and has a spring retraction on the bolt/ carrier....same as the M110 we have in the military....and that's about the only mil-spec I know about when it comes to the 308 AR's. those rifles need a heavier hammer strike, and some triggers will not function properly, I had problems with the Jewel trigger in one, switched to the Armalite match and all was good with the world. George, you are right about the large fp w/ small primers, it just doesn't give the support needed.

Oh, and rounding the corners on ejectors and polishing along with lightly chamfering the hole can help the ejector mark/brass wiping issue.

 

[A10XRIFLE]

Friends GAP 308 was blowing factory load primers because of too tight bore. Bore was measured.

Before Using Bartlein we used to use a lot of Obermeyer tubes, Boots uses a .298 bore but widens the groove to supside pressure, all the Mk11 Navy rifles use the Obermeyer barrels. a "tight" bore does not always spike pressure. And a lot of factory ammo is still too hot for Gas Guns.

There seems to be a misnomer that just because you buy "factory ammo" that that somehow means its 100% for sure solid perfect ammo. I could give countless stories where factory ammo is the culprit and to blame for some rifle problems.


Ill give you a couple. Large Government agency over 30 AR-10 rifles that we maintain and Re-barrel. they switched from one lot of ammo (big name factory ammo) to another and the rifles cease to function go back to the old lot back to running like champs.

A California Department was having problems with M-14 rifles we built started having erratic problems. They came out to the shop with their guns and ammo, again 2 different lots. I had a 3rd lot of the same brand. just for shits and giggles we pulled the bullets from this 3 different lots and not only was the charge all different they were 3 different types of powder. 2 of the lots worked great one would not function the rifles.

 

[dvdt]

Thanks for the replies and info, George. I'm sure this helps a ton of folks.

 

[KevinB-KAC]

Interesting stuff -- thanks for posting George and OP.

I'll second George's comments on factory ammo issues in a gas gun, and especially suppressed you see a lot of dropped primers etc as it was never designed for gas guns. Even in today's world the majority of companies make ammo for bolt guns, as they don't need to deal with chamber and port pressure relationships.

 

[Kiba]

Interesting stuff -- thanks for posting George and OP.

I'll second George's comments on factory ammo issues in a gas gun, and especially suppressed you see a lot of dropped primers etc as it was never designed for gas guns. Even in today's world the majority of companies make ammo for bolt guns, as they don't need to deal with chamber and port pressure relationships.

Excellent point Kevin and I do agree with you.

I stated early on that I don't hold the factory Hornady ammo to be the end all, be all of 6.5CM ammo (although my experience with it in my AI AE shows it to be amazingly good for factory loaded ammo.) I normally reload for everything except .22LR and .17HMR; the only reason I was running the factory Hornady ammo through the GAP10 is I was given a smoking deal on 500 rounds of the factory stuff. At the price I picked it up for it didn't make sense to buy all the components and load the first 500 myself-- I figured I'd shoot those 500 and then have brass for reloading. I just didn't expect the amount of problems I encountered with the factory ammo when the factory load is very safe if not a bit on the conservative side when run in a bolt gun.

Then again, as George mentioned the pressure curve for H4350 certainly exacerbates any problems when run through a gas gun.

While the 140s pushed by H4350 seems to be a consistent and accurate combo for 6.5CM I wouldn't mind swapping the 210M primers for something a little tougher for the gas guns just for some extra safety margin-- if only I could find some in stock!

 

[blair]

Great info George, and again - as usual - top of the line customer service from GA Precision.

 

[A10XRIFLE]

Excellent point Kevin and I do agree with you.

I stated early on that I don't hold the factory Hornady ammo to be the end all, be all of 6.5CM ammo (although my experience with it in my AI AE shows it to be amazingly good for factory loaded ammo.) I normally reload for everything except .22LR and .17HMR; the only reason I was running the factory Hornady ammo through the GAP10 is I was given a smoking deal on 500 rounds of the factory stuff. At the price I picked it up for it didn't make sense to buy all the components and load the first 500 myself-- I figured I'd shoot those 500 and then have brass for reloading. I just didn't expect the amount of problems I encountered with the factory ammo when the factory load is very safe if not a bit on the conservative side when run in a bolt gun.

Then again, as George mentioned the pressure curve for H4350 certainly exacerbates any problems when run through a gas gun.

While the 140s pushed by H4350 seems to be a consistent and accurate combo for 6.5CM I wouldn't mind swapping the 210M primers for something a little tougher for the gas guns just for some extra safety margin-- if only I could find some in stock!

I think Josh called you today, I hand loaded some 130 bergers (which I think are the cats ass in 6.5 Creed for Gas Guns.) I loaded then on top of 42.5 H4350 at 2.800 they cycled the rifle well and no Pierced or cratered primers. Primers were wolf/tula LR


Its Ready to come back for good, Im certain.

 

[sch2046]

So, will an armalite let bolt work in a dpms carrier? Is this what I am gathering?

 

[The Lawn Ranger]

It's funny, lately I have had the opposite problem with my LRP-07 in 6.5 Creedmoor.

Every 1-2 rounds out of 100 I get light primer strikes and no boom on my reloads. I checked primer seating depth and they seem to be within spec.

Factory loads of Hornady match ammo from different lots all shoot without primer issues but I did have some ejection issues due to cases being out of spec (not enough radius on the case heads).

I have always thought the weakest link to this cartridge is the brass. This, I believe is exacerbated with use in a gas gun.

 

[Kiba]

I think Josh called you today, I hand loaded some 130 bergers (which I think are the cats ass in 6.5 Creed for Gas Guns.) I loaded then on top of 42.5 H4350 at 2.800 they cycled the rifle well and no Pierced or cratered primers. Primers were wolf/tula LR


Its Ready to come back for good, Im certain.

Josh tried calling me right when I was in the middle of a *long* meeting unfortunately and I couldn't sneak out to answer it. He sent me a PM instead.

All the news so far sounds like the problem is indeed fixed for good and I'm really looking forward to getting the rifle back.

Regarding your test loads, once they're available again I'll probably switch from 210M to Wolf/Tula LR primers in the gas guns and I'll certainly give the 130 Bergers a try. I have 2800-something 140gr Amaxes on hand but I can always save them for my bolt rifle.