GAP-10 Blown Primers

[oubeta]

I have a GAP-10 that was built about a year ago in 6.5CM. It has a switch block gas block and 20" barrel.
It keeps blowing primers out of factory 140 A-Max suppressed and unsuppressed. It blows 75% of the primers suppressed and 30% unsuppressed. I've tried several different lots of factory ammo. Blows primers out of all of them.
I reloaded some mild ammo for it and it helped some, but still blowing primers.
I bought this gun to shoot factory ammo with. Any ideas? Think it needs to go back? What's causing the blown primers?
It cycles great, and accuracy is decent.

Thanks

 

[leadbullet]

send it back to GAP with a sample of ammo for them to try. Let them fix it, they charge enough for that.
cheers.

 

[dcnyli]

tagged for later, curious to see how GAP fixes this. Sounds odd

 

[oubeta]

My buddies gun in the same caliber is blowing primers also.
GAP will fix it, I'm not worried about that.
Just weird it's blowing factory primers.

 

[SAPenguin]

You guys might want to take a read in the reloading section - there is a thread about the recent 6.5Creedmore match ammo being much hotter than normal. Apparently Hornady might have switched powders in the recent powder shortage, which is causing grief... i think the title of the thread is "6.5Creedmoore Old vs new"

 

[LRRPF52]

When I got into shooting .260 Remington in a gasser, I knew that I would never be firing one single factory round of ammunition, and it was a hand-loader's rifle only.

While there are plenty of top performing factory ammunition for the .260 Remington and 6.5 CM, they are really designed to work in bolt guns.

Read JP's statement on their website about this. They basically say the same thing, and that you need to keep loads ~10% lower than book max, not because the bolt and extension can't take it, but because the gas system gets hit with higher port pressures due to such slow burning powders and long bearing surface bullets.

You can address it with an extended length gas system, but that closes a lot of doors for people.

 

[Kiba]

LRRPF52 touches on some good points above regarding loads.

Another question though... does your GAP10 have a DPMS or Armalite BCG?

I had severe primer issues around last April/May with my then new 6.5CM GAP10 piercing primers. It pierced factory 140gr loads and it pierced way mild 140gr handloads. Went back to GAP twice, they finally switched it over to an Armalite BCG for the smaller .068 firing pin vs the .080 DPMS firing pin and all primer cratering & piercing issues went away. After the issue was solved George indicated that going forward all non-.308 GAP10s would ship with the Armalite BCG to prevent all the primer issues myself and others were experiencing with .260 and 6.5CM. If your rifle is about a year old it probably still has a DPMS BCG which isn't helping your primer issues.

I also found that even with the Armalite BCG 140s still caused minor issues with the rifle, mostly FTF and FTE problems; George suggested leaving the 140s for the bolt guns and running 130s or lighter in the gassers. He was right, it ran far more reliably with 130 VLDs or 123 Scenars (and was flatter to 1000Y too.) If you want to run factory loads I'd suggest trying the 123 Amax instead of the 140s but even those may be a little warm for a gas gun.

 

[81STFACP]

Kiba,

I am out of town and could not inspect the BCG on my unfired GAP 10 in 260 Remington. It was ordered with the first batch of GAP 10s. How can I tell whether the BCG is DPMS?

 

[Kiba]

Kiba,

I am out of town and could not inspect the BCG on my unfired GAP 10 in 260 Remington. It was ordered with the first batch of GAP 10s. How can I tell whether the BCG is DPMS?

Easy way to tell is that the Armalite BCG has a spring on the back of the firing pin. The Armalite BCG also uses a standard cotter key to retain the FP while the DPMS BCG uses a solid pin with the split end to retain the FP.

Another option that will hopefully be available soon is JP is releasing a new "high pressure" bolt which is DPMS pattern so it will work in current DPMS carriers but it uses a smaller .068" firing pin tip like the Armalite BCG. You shouldn't have to buy it though-- if you have primer issues and send the rifle back to GAP they'll probably fix it at no charge like they did with my rifle.

 

[oubeta]

Both of ours have the spring on the back of the firing pin so I assume they are Armalite. I haven't had any pierced any primers yet on mine.
I will try the 123's and see if that helps.
My buddy has a fully adjustable gas block on his. Would tuning it way down to where it barely cycles help?

 

[Kiba]

If you have the spring on the back of the firing pin then you have the Armalite BCG, that's probably why you are totally blowing primers instead of just piercing them. If you retrieve the blown primers are the corner radii still rounded or are they flat?

If it's still blowing primers completely out of the brass there are still a few things to check. First things I would do is clean the chamber thoroughly and make sure you aren't sizing excessively (I usually bump the shoulder back .002-.0025 for gas guns.) 6.5 & .260 in a gas gun with the typically slower burning powders like H4350 do need some caution in a gasser and the heavier bullets exacerbate the issues. The factory 140 loads do seem to have issues in many gas guns.

If the rifle is overgassed that can cause issues too; personally I'd put an SLR Sentry gas block on the rifle so you can tune it for each individual load (suppressed and unsuppressed) and adjust the gas block until the rifle *just* locks back the bolt on the last round out of the mag for the particular load & suppressor combo.

Again, I strongly suggest trying 123-130gr bullets instead of the 140s. If you call GAP they will make the same recommendation. I have both a GAP10 and JP LRP-07 in 6.5CM and they both prefer 123-130gr bullets over the 140s not only for performance but also brass condition and reliability of the rifle. With the 140s no matter how much I tweaked loads I'd always have occasional FTF/FTE issues and the brass showed some minor pressure signs whereas with 123 Scenars all the FTF/FTE issues went away, the brass looks great, and the 123 Scenar loads are actually flatter to 1000Y than the 140gr loads that showed some minor pressure signs on the brass.

 

[oubeta]

It's blowing the primers completely out of the case and I can't even find them. Not sure where they are going, I guess they are getting ejected out with the brass. The ones I remember looking at I think were nice and round, not flat. Most of the blown primers have been with factory 140's of various lots. it did still blow primers with some mild hand loads also.
My rifle has a switch block on it and it was send to GAP with my suppressor so they could 'tune' it. My buddy has a fully adjustable gas block on his and even with his cranked way down to where it barely cycles, he still has a few blown primers.

 

[LRRPF52]

I prefer the 130gr class of bullets in the .260 Rem gasser. I get excellent trajectory, wind-bucking, and am close enough to the edge that I know the 139gr/140gr/142gr don't offer enough speed to beat the 130's for me, namely the 130gr VLD.

My chamber is cut for the VLD ogives mag fed, so I get superb accuracy that out performs most bolt guns with ease for 5rd groups, and groups well at 1000yds. GAP built my .260 Rem gasser for me before they started offering the GAP-10, and I have been very pleased with the rifle.

I just wish I had started with an Armalite BCG. A buddy of mine has been able to find some very nice loads with the 142gr SMK in his stock Armalite, but he did a lot of tweaks to his bolt to take off all the edges. He's pushing the 142gr very comfortably at 2740fps from a 22", which is basically what GAP told me the limit was with that bullet back in 2009.

 

[elfster1234]

high performance factory ammo in a gasser will blow primers.... same will happen in my LMT if I use high performance factory ammo

I have a GAP-10 that was built about a year ago in 6.5CM. It has a switch block gas block and 20" barrel.
It keeps blowing primers out of factory 140 A-Max suppressed and unsuppressed. It blows 75% of the primers suppressed and 30% unsuppressed. I've tried several different lots of factory ammo. Blows primers out of all of them.
I reloaded some mild ammo for it and it helped some, but still blowing primers.
I bought this gun to shoot factory ammo with. Any ideas? Think it needs to go back? What's causing the blown primers?
It cycles great, and accuracy is decent.

Thanks

 

[pkt1199]

The author (Kiba) has already filled you in here but in case you want to read the original thread with George's input as well:

http://www.snipershide.com/shooting...vy-swipes-2-pierced-primers-factory-ammo.html

 

[Kiba]

I just wish I had started with an Armalite BCG. A buddy of mine has been able to find some very nice loads with the 142gr SMK in his stock Armalite, but he did a lot of tweaks to his bolt to take off all the edges. He's pushing the 142gr very comfortably at 2740fps from a 22", which is basically what GAP told me the limit was with that bullet back in 2009.

I'm patiently waiting for JP to release their new "high pressure" bolt that uses an .068" firing pin (Armalite-sized) but is otherwise DPMS-pattern so it drops into current DPMS carriers & extensions. My JP LRP-07 in 6.5 CM could use one to eliminate the very slight cratering I get on the primers in that rifle as it uses a DPMS-style bolt with a .080 firing pin. I check their webpage every morning to see if it's been added yet...