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JP 308 "High Pressure" bolt & primer condition pics on a 6.5CM

K

Kiba

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Minuteman
Jan 13, 2011
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Earlier last year I had horrendous primer piercing issues with my new 6.5 CM GAP-10, George's solution was to switch it from a DPMS BCG which uses a .080 firing pin to an Armalite BCG which uses a .068 firing pin and all the cratering & piercing issues went away. The .080" firing pin isn't typically a problem with .308 but it's calibers like 6.5CM and .260 with different pressure curves that usually have primer issues with the .080" firing pin.

I've been wanting to do a similar fix to my 6.5CM JP LRP-07 for almost a year now as it has always lightly cratered the primers but I didn't want to switch to a complete Armalite BCG and give up the JP low mass carrier. A couple months ago I heard JP had something in the works; Ben at JP hooked me up a couple weeks ago and sent me one of their new "high pressure" bolts before they hit their webpage. JP's new bolt is DPMS pattern so it's a drop in to rifles that currently run DPMS-pattern BCGs but it uses a smaller .068 firing pin.

Here's a pic of the new "high pressure" bolt & firing pin...

jphp1.jpg

And here's pictures of the primers. Same rifle, same load, each round fired only a couple of minutes apart-- just enough time for me to change bolts. Old bolt with .080" firing pin is on the left, new bolt with .068" firing pin is on the right. Huge improvement in primer condition is an understatement. I won't have to worry about ragged primers on hot afternoons anymore!

jphp2.jpg
 
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204 AR said:
I want one. What did it cost?
Click to expand...

JP only had limited quantities a couple of weeks ago and didn't have them on their webpage. However, I just looked on their webpage and it looks like they're available now under the "bolts and carriers" section. Comes with the firing pin obviously. When I was on the phone with Ben I also wanted to snag a spare firing pin "just in case" but he mentioned they won't have an inventory of spare firing pins for a few weeks-- right now there's only enough firing pins to cover what bolts they have on hand and not enough to sell spares yet.
 
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Thanks for the info! I wish they had one for my 300 Saum, it has the same issue with heavy bullets.
 
.308's with the longer bearing surface pills/heavier weights, will do the same thing, using slower-burning powders loaded in the upper realm of the .308 pressures (62,000psi SAAMI MAP).

A guy from the Grendel Forum sent me an experimental firing pin for the DPMS pattern bolts that is working well so far in my GAP .260 Rem AR10/DPMS pattern BCG. I'll have to give a full report later this summer/early fall. It's basically a larger pin head dia. to fill in the area where the primer likes to extrude, but I do believe a smaller pin (Eagle Arms/Armalite) is the way to go for these loads.

The larger pin hole with the KAC/DPMS is to activate hard military primers, where projectiles have typically been in the 150gr range, with faster powders, at 55ksi - 58ksi pressures.
 
LRRPF52 said:
.308's with the longer bearing surface pills/heavier weights, will do the same thing, using slower-burning powders loaded in the upper realm of the .308 pressures (62,000psi SAAMI MAP).

A guy from the Grendel Forum sent me an experimental firing pin for the DPMS pattern bolts that is working well so far in my GAP .260 Rem AR10/DPMS pattern BCG. I'll have to give a full report later this summer/early fall. It's basically a larger pin head dia. to fill in the area where the primer likes to extrude, but I do believe a smaller pin (Eagle Arms/Armalite) is the way to go for these loads.

The larger pin hole with the KAC/DPMS is to activate hard military primers, where projectiles have typically been in the 150gr range, with faster powders, at 55ksi - 58ksi pressures.
Click to expand...

This ARMALITE Kewl-Aid drinker has always appreciated the information in your posts.
 
Sorry if a dumb question but why exactly is primer cratering a bad thing? What does a cratered primer affect? Although none look as bad as the one in the pic above, I have more than a few rifles that show slightly cratered primers with mild-med loads. To me, this has always been a sign of a over sized firing pin hole but never a sign of a problem.
 
wareagle700 said:
Sorry if a dumb question but why exactly is primer cratering a bad thing? What does a cratered primer affect? Although none look as bad as the one in the pic above, I have more than a few rifles that show slightly cratered primers with mild-med loads. To me, this has always been a sign of a over sized firing pin hole but never a sign of a problem.
Click to expand...

Because cratering is getting close to a pierced primer which can cause a lot more problems and damage. The primer condition pics in the first post is from the JP and is what I would call "mild" cratering. My 6.5CM GAP10 as initially received left the primers in far worse condition. There's a difference between cratering caused by excess firing pin to bolt clearance and cratering caused by a firing pin diameter that's too large and leaves too much of the primer unsupported for the case pressure. In the case of .260 & 6.5CM in DPMS-pattern rifles it's the latter-- the .080 firing pin and hole in the bolt leaves too much of the primer area unsupported for the pressure curve of the cartridge and the primers will show cratering and stress even with very mild loads.

In addition to badly cratered primers my 6.5CM GAP10 as originally shipped with the DPMS bolt & .080 firing pin used to pierce primers with alarming regularity. It wasn't uncommon to pierce 3-5 primers out of 10 rounds fired with factory Hornady ammo. It was irritating to have to disassemble the bolt every time it pierced a primer to clear out the primer piece stuck inside the bolt... but it was far worse when it stuck the firing pin because of firing pin tip deformation from a pierced primer and then the thing ran away full auto for the remainder of the mag. Luckily none went off out of battery which could have damaged the rifle or myself!

When GAP switched the rifle to an Armalite bolt which uses a .068 firing pin all cratering and piercing issues went away. While my JP never pierced primers I wanted the same solution-- I did *not* want to pierce a primer and have a repeat of that full-auto runaway and risk of an out of battery ignition. Once was enough! Anything that gives the rifle and primers more safety margin is a big improvement and the smaller firing pin provides a LOT more safety margin when it comes to cratering & piercing primers.
 
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Thanks for the reply, that makes sense. With mine being a .308 that performs best with medium loads, I think I will be ok. However, in the event it becomes a problem, I know where to look.
 
peaceatwar said:
$249.95 plus shipping. How does that compare to other companies bolts?
Click to expand...

It's on the expensive side, but it is a well-thought out solution to a unique problem. Saved me from having to swap out the whole thing to an armalite, so worth the $$ to me.
 
You can't just swap an Armalite bolt into a DPMS type carrier or vice versa. Big no, no from what I've always been told.
 
Is there even another brand option available for a .068 FP hole in a DPMS format bolt? Anything else requires running an Armalite barrel extension and Armalite bolt/carrier, doesn't it?
 
Redmanss said:
Is there even another brand option available for a .068 FP hole in a DPMS format bolt? Anything else requires running an Armalite barrel extension and Armalite bolt/carrier, doesn't it?
Click to expand...

I ordered a Rock Creek barrel to replace the barrel on my Eagle Arms (Armalite) upper. I was told by the person that assembled that barrel that there is no difference in the .308 barrel extension across the two brands. Just what I previously stated, no swapping bolts between different carriers. IIRC, it is because the tail of the DPMS bolt is longer. Interestingly enough, I had a complete JP low mass bolt and carrier and visually could see no difference between it and my Armalite bolt, other than firing pin diameter AND I couldn't keep the port door on with it. Another member here was in contact and told me via PM that Dan Lilja has even stated that the barrel extensions are the same.

The only fly in the ointment I ran into is that the barrel I ordered (which was mid-length gas system or carbine in AR-10) was drilled with the gas port for DPMS. Armalite has a different length whereas DPMS uses AR15 mid-length gas tube for .308.

A long time ago I swapped the complete BCGs between my upper and my friends DPMS, no problem cycling but I didn't check headspace as I never intended firing it.

It's your money, but a quick check online found a vendor selling the Gen 4 complete BCG for Armalite for $225
 
It's too bad [MENTION=6412]ORD[/MENTION] always goes on hiatus in the summer. He always sorts this one out for us on the Hide!

Anyhow, I'm really contemplating whether to get one of these for a 6.5CM build I'm finishing up with. Has anyone had pressure issues with the 26" Krieger barrels and rifle length gas? Factory Hornady match ammo, not "Superperformance".
 
Redmanss said:
It's too bad @ORD always goes on hiatus in the summer. He always sorts this one out for us on the Hide!

Anyhow, I'm really contemplating whether to get one of these for a 6.5CM build I'm finishing up with. Has anyone had pressure issues with the 26" Krieger barrels and rifle length gas? Factory Hornady match ammo, not "Superperformance".
Click to expand...

I can only speak from a sample of 2 rifles, but my 24" GAP10 in 6.5 CM had horrible cratering & piercing issues with factory Hornady 140 ammo and my 22" LRP-07 had mild to moderate cratering issues with Hornady 140 ammo when using the original bolts with .080 firing pins. All primer cratering issues in both rifles went away with a swap to a smaller firing pin (Armalite BCG swap in the GAP10, new JP HP bolt in the LRP-07.) The cratering issues in both rifles was much worse with the 140s compared to 130s or 120/123s. Personally, I'd go either Armalite BCG or JP HP bolt and you'll probably never have to worry about cratered or pierced primers.

Regarding specific dimensional & design differences between the DPMS and Armalite barrel extension, carrier, and bolt, I would really like to see pictures and dimensions posted showing where exactly the differences are. I've always heard "they're not compatible, so either use a complete Armalite BCG or a complete DPMS BCG" but have never found info regarding *exactly* what the differences are and why you should or shouldn't mix and match bolts & carriers. Maybe I'll pull the Armalite BCG out of my GAP10 and compare it dimensionally to the DPMS-pattern BCG in my LRP-07...
 
I read that thread with a lot of interest when you were going through those issues, but don't the GAP-10s run on a midlength gas system? I was thinking that might induce the cratering a lot more than with an additional 3+" of barrel prior to hitting the port and another 3+" of gas tube to bleed off excessive pressures.

You're probably right though, while I have a brand spanking new JP enhanced bolt, I might as well get the high pressure version and sell the other to make up the difference. Better safe than sorry, right? The trials of semi autos...

ETA: Here's where I was referencing for the differences in the system lengths: http://www.hornady.com/ammunition/superformance-in-gas-operated-firearms
 
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No need to compare anything they are the same. If you read JP's fine print they make it pretty clear that you can use their bolt in Armalite gun. We compared bolts and extensions at my friends shop on an optical comparator. We had extensions from DPMS (Gen1), KAC , Bat Machine, Armalite. We checked bolts from KAC, LMT, JP, Armalite, LaRue and DPMS. All the bolts are have the same basic lug geometry. Only differences would be some have chamfer reliefs to allow for better unlocking on the back side of the lugs . Also the carriers have the same cam profile cuts. As for the extensions the only real differences were some had enhanced "m4" style feed ramps cut in them to match the receivers.

The issue is people trying to use a DPMS style bolt in an Armalite carrier and visa versa, the firing pins are different diameters and lengths. Also the Armalite is spring loaded. The bolts themselves have different FP channel sizes and the wrong pin might get stuck and create a slam fire condition.

This is from JP's site
With the Armalite/Rock River family of large-frame receivers, this assembly can only be used as a complete bolt carrier assembly group. Interchanging individual components will result in an unsafe configuration. DO NOT under any circumstances mix and match components between the platforms. Only use the complete JP bolt carrier assembly in the Armalite/Rock River platforms.


When it comes to barrels the reason there is Armalite vs and DPMS version for them is because of gas system length




Kiba said:
I can only speak from a sample of 2 rifles, but my 24" GAP10 in 6.5 CM had horrible cratering & piercing issues with factory Hornady 140 ammo and my 22" LRP-07 had mild to moderate cratering issues with Hornady 140 ammo when using the original bolts with .080 firing pins. All primer cratering issues in both rifles went away with a swap to a smaller firing pin (Armalite BCG swap in the GAP10, new JP HP bolt in the LRP-07.) The cratering issues in both rifles was much worse with the 140s compared to 130s or 120/123s. Personally, I'd go either Armalite BCG or JP HP bolt and you'll probably never have to worry about cratered or pierced primers.

Regarding specific dimensional & design differences between the DPMS and Armalite barrel extension, carrier, and bolt, I would really like to see pictures and dimensions posted showing where exactly the differences are. I've always heard "they're not compatible, so either use a complete Armalite BCG or a complete DPMS BCG" but have never found info regarding *exactly* what the differences are and why you should or shouldn't mix and match bolts & carriers. Maybe I'll pull the Armalite BCG out of my GAP10 and compare it dimensionally to the DPMS-pattern BCG in my LRP-07...
Click to expand...
 
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So if I have a JP bolt that headspaces correctly in my Lilja barrel with DPMS barrel extension, what are the chances a Armalite AR-10 BCG will drop in and function fine?
 
99% that it will be fine. You should always check head space no matter what alternate bolt you are using


wareagle700 said:
So if I have a JP bolt that headspaces correctly in my Lilja barrel with DPMS barrel extension, what are the chances a Armalite AR-10 BCG will drop in and function fine?
Click to expand...
 
KULT said:
No need to compare anything they are the same. If you read JP's fine print they make it pretty clear that you can use their bolt in Armalite gun. We compared bolts and extensions at my friends shop on an optical comparator. We had extensions from DPMS (Gen1), KAC , Bat Machine, Armalite. We checked bolts from KAC, LMT, JP, Armalite, LaRue and DPMS. All the bolts are have the same basic lug geometry. Only differences would be some have chamfer reliefs to allow for better unlocking on the back side of the lugs . Also the carriers have the same cam profile cuts. As for the extensions the only real differences were some had enhanced "m4" style feed ramps cut in them to match the receivers.

The issue is people trying to use a DPMS style bolt in an Armalite carrier and visa versa, the firing pins are different diameters and lengths. Also the Armalite is spring loaded. The bolts themselves have different FP channel sizes and the wrong pin might get stuck and create a slam fire condition.
Click to expand...

Thanks Kult, that's what I expected. I thought the tail of the firing pin and the cocking ramp & hammer cutout area of the carrier were probably where the differences were to accommodate the differences in firing pins between the DPMS and Armalite designs.

Redmanss said:
I read that thread with a lot of interest when you were going through those issues, but don't the GAP-10s run on a midlength gas system? I was thinking that might induce the cratering a lot more than with an additional 3+" of barrel prior to hitting the port and another 3+" of gas tube to bleed off excessive pressures.

You're probably right though, while I have a brand spanking new JP enhanced bolt, I might as well get the high pressure version and sell the other to make up the difference. Better safe than sorry, right? The trials of semi autos...

ETA: Here's where I was referencing for the differences in the system lengths: Superformance in Gas Operated Firearms - Hornady Manufacturing, Inc
Click to expand...

While the gas system has an effect on primer condition it's not as much of an influence on the primer condition as much as the firing pin diameter is. Even with the gas system shut off the GAP10 would still crater & pierce primers with the original DPMS bolt and the JP would still leave mild craters on the primers-- this was with the DPMS .080 firing pins in both. Prior to swapping to the HP bolt in the JP the change that made the largest positive improvement on primer condition was switching from 140gr to 123gr bullets-- again, even if the gas system was shut off.

wareagle700 said:
So if I have a JP bolt that headspaces correctly in my Lilja barrel with DPMS barrel extension, what are the chances a Armalite AR-10 BCG will drop in and function fine?
Click to expand...

It should be fine-- but as mentioned always check headspace.

For reference when I switched my LRP-07 from the original bolt to the new high pressure bolt the headspace changed by about 0.0005". While I don't have a full set of incremental headspace gauges I do have access to a CMM so I wrote a program and measured and compared both bolts for the dimension between the bolt face and the back surface of the lugs before swapping them. Comparing fired cases to the CMM bolt measurements confirmed the CMM measurements to within about +/- 0.0001".
 
I just got a new 22" JP 6.5 CM barrel (JPSM6.5C-22M8) and it came with this new bolt and firing pin. May 2014 date stamped on the barrel.

A welcome surprise!
 
Just put together a dpms pattern 6.5 with a krieger barrel and jp high pressure bolt and did not have a single sign of over pressure. I can post pics of the primers if you would like. 22 inch Kreiger reamed with a minimum saami reamer from Hornady and Creedmoor sports, rifle length gas system, standard dpms 308 rifle buffer and buffer spring.
 
one of the other things you don't get with switching to the Armalite stuff is the benefits of the JP low mass carrier, the superior bolt material, the enhanced JP extractor, or the JP Enhanced gas rings. All these things remove resistance from the system and give you a smoother lighter recoiling rifle as well as a longer life expectancy. You really can't compare throwing in a AR-10 bolt and carrier to a complete JP BCG with the HP bolt; just a weeee little bit of value difference and feel difference.
 
Hello and greetings from Finland - thanks for this excellent thread, I decided to register to see those primer pics in the first post.

204 AR said:
Thanks for the info! I wish they had one for my 300 Saum, it has the same issue with heavy bullets.
Click to expand...

I have an Armalite AR10(T) in 300RSAUM and the bolt broke some time ago, two lugs just didn´t like it anymore. So now I´m waiting for a new bolt from Armalite, it may happen one day - and I´m also shooting the rifle already with a new DPMS BCG and a DPMS bolt. The bolt and extractor had to be machined to the 300 specs. It works, just a minor change in headspace that I can adjust my dies to.

BUT: The primers and my ammo looked plain dangerous after firing it in this new setup with a DPMS BCG and bolt. I had no idea what was causing the insane cratering until I found this thread. We have been wondering about this thing with quite a bunch of people already , I took my powder charge down by TEN PERCENT to get normal looking primers again. I said to many people that this rifle has a wrong caliber stamp on it now because factory ammo would possibly pierce primers.

I have reloaded for a few decades, use Quick Load and chrono my ammo etc. All was good until the BCG change . Well breaking a bolt is not good but I take it as a material defect of some kind.


Gotta love The Internet sometimes.


EDIT: This means I don´t have to dump / disassemble all my old ammo. I can shoot the mild stuff for a while no probs while waiting for the original Armalite bolt, now that I know the reason for the cratering.
 
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