7PRC -Prone to Pressure Signs and Carbon Ring Buildup?

[donrleonard]

Someone recently said this about adopting the spanking new 7PRC: tell me your a rookie without telling me you’re a rookie.

So I’m one of those rookie hunters who jumped on the 7PRC bandwagon after salivating over those sweet ballistics tables.

At some point towards the end of my 80-round barrel break-in I got a reeeall hard bolt lift. I didn’t know at the time to check for pressure signs on the brass, but I suspect it was there. At the same time that I was struggling to get good groupings with my Hornady CX ammo, I started hearing rumblings about problems with Hornady powder. I assumed I must’ve gotten a bad round.

Now we know that the problem was with their slow powder, which is unlikely to have caused the hard bolt lift. As I order up ammo (Federal this time) and start preparing the gun for the fall hunting season, I dug deeper and found a comment by Jim on Backfire that 7PRCs are churning up a lot of pressure signs including hard bolt lifts, and that it is due to the rapid buildup of carbon near the throat of the chamber after 40 or so rounds. Now I’m feeling like a chump, pulling the trigger on a new design with tight precision tolerances that are less forgiving than other calibers like 7 Rem Mag or 280AI.

Has anyone else run into this issue? If so, what are you seeing in terms of buildup?

Was I a chump for jumping on the 7PRC bandwagon so early, or is this a common issue with magnums?

 

[PineBrook413]

This is all with factory loads or re-loads?

If reloads whats the load data and chrono data?

 

[donrleonard]

This is all with factory loads or re-loads?

If reloads whats the load data and chrono data?

Sorry, yes, factory Hornady Outfitter (CX).

 

[SDHNTR]

A pressure generating carbon ring in 40 rounds would piss me off. 400 I could deal with and would just clean out, but not 40! And no, that’s not normal. The 6.5 prc is even more overbore, and it’s not that bad.

Something tells me the carbon ring urban legend is just that, and not to blame here. But it’s easy to rule out. Let a carbon remover soaked patch sit in the throat for several hours. Then stick a .30 cal Iosso blue plastic brush just into the throat and spin it around a few dozen times. Chuck it into a drill even. Clean that throat out well at try again. You’ll know if that’s really your problem.

 

[donrleonard]

A pressure generating carbon ring in 40 rounds would piss me off. 400 I could deal with and would just clean out, but not 40! And no, that’s not normal. The 6.5 prc is even more overbore, and it’s not that bad.

Something tells me the carbon ring urban legend is just that, and not to blame here. But it’s easy to rule out. Let a carbon remover soaked patch sit in the throat for several hours. Then stick a .30 cal Iosso blue plastic brush just into the throat and spin it around a few dozen times. Chuck it into a drill even. Clean that throat out well at try again. You’ll know if that’s really your problem.

Thanks SDHNTR. I’ve got a borescope, some oversized brass brushes, and some Iosso bore paste arriving tomorrow. Will investigate and report back.

 

[SDHNTR]

Thanks SDHNTR. I’ve got a borescope, some oversized brass brushes, and some Iosso bore paste arriving tomorrow. Will investigate and report back.

Before you get that aggressive, just try a liquid carbon remover and an oversized plastic Iosso brush. I cannot imagine that big of a carbon ring after so few shots.

 

[Koda_]

I'm skeptical there is an inherent design flaw with the 7prc.
40rds seems too quick to form one, and on a new rifle. I'm also skeptical that factory ammo would run overpressure, but defective factory ammo is a possibility. And of course its summer... was it a hot barrel or ammo left in the sun?

I wouldn't use an abrasive cleaner on a new gun bore, in my experience if you run a chamber brush each cleaning it will keep the carbon ring from forming. Ive been doing this on a new gun now for a year and the chamber is perfectly clean. I learned this from a different old rifle started having flat primers with factory ammo, we never cleaned the chamber for carbon ring and it built up after years of use and was impossible to get out so I replaced the barrel recently. I brush my chambers now every cleaning.

Your borescope will tell you, I am curious what it shows please share...

Pic of carbon ring after years of use.

 

[Formidilosus]

Someone recently said this about adopting the spanking new 7PRC: tell me your a rookie without telling me you’re a rookie.

So I’m one of those rookie hunters who jumped on the 7PRC bandwagon after salivating over those sweet ballistics tables.

At some point towards the end of my 80-round barrel break-in I got a reeeall hard bolt lift. I didn’t know at the time to check for pressure signs on the brass, but I suspect it was there. At the same time that I was struggling to get good groupings with my Hornady CX ammo, I started hearing rumblings about problems with Hornady powder. I assumed I must’ve gotten a bad round.

Now we know that the problem was with their slow powder, which is unlikely to have caused the hard bolt lift. As I order up ammo (Federal this time) and start preparing the gun for the fall hunting season, I dug deeper and found a comment by Jim on Backfire that 7PRCs are churning up a lot of pressure signs including hard bolt lifts, and that it is due to the rapid buildup of carbon near the throat of the chamber after 40 or so rounds. Now I’m feeling like a chump, pulling the trigger on a new design with tight precision tolerances that are less forgiving than other calibers like 7 Rem Mag or 280AI.

Has anyone else run into this issue? If so, what are you seeing in terms of buildup?

Was I a chump for jumping on the 7PRC bandwagon so early, or is this a common issue with magnums?

It isn’t a carbon ring or any cleaning nonsense. Hornady CX beside often featuring extremely poor precision, also causes sticky bolt lift and extraction from lots of rifles.

Borescopes, drills, brushes, etc are all a waste of time. There is nothing “picky” or finicky about a 7 PRC.
At top of the firearm section there is a eval of a Browning X-Bolt 2 in 7 PRC with almost 600 rounds on it without a single thing but bullets being put in the bore. Hornady CX shots 5-6 inch groups and has very stiff bolt lift and pressure signs from the first shot out of the rifle. Get different ammo.

 

[donrleonard]

This is super helpful, folks. I’m glad to have an alternative explanation in my pocket in case I don’t see a carbon ring.

The thing that haunts me is even the Hornady folks say it’s a hot rod that needs more frequent cleaning. Which is fine if true. Gives me an excuse to play with my toys at the bench. But certainly is not ideal if true.

 

[donrleonard]

I'm skeptical there is an inherent design flaw with the 7prc.
40rds seems too quick to form one, and on a new rifle. I'm also skeptical that factory ammo would run overpressure, but defective factory ammo is a possibility. And of course its summer... was it a hot barrel or ammo left in the sun?

I wouldn't use an abrasive cleaner on a new gun bore, in my experience if you run a chamber brush each cleaning it will keep the carbon ring from forming. Ive been doing this on a new gun now for a year and the chamber is perfectly clean. I learned this from a different old rifle started having flat primers with factory ammo, we never cleaned the chamber for carbon ring and it built up after years of use and was impossible to get out so I replaced the barrel recently. I brush my chambers now every cleaning.

Your borescope will tell you, I am curious what it shows please share...

Pic of carbon ring after years of use.

View attachment 750643

What chamber brush would you use on a 7PRC? Chasing down the carbon ring rabbit, folks say to use an oversized (in my case maybe 308 or 338) bronze brush to get up in the throat. I went looking around amazon for chamber brushes and see some that look like they're for ARs.

 

[Fire_9]

When did people start talking about carbon rings? I could have missed it but I don’t remember anyone talking about it 3-4 years ago

 

[donrleonard]

It isn’t a carbon ring or any cleaning nonsense. Hornady CX beside often featuring extremely poor precision, also causes sticky bolt lift and extraction from lots of rifles.

Borescopes, drills, brushes, etc are all a waste of time. There is nothing “picky” or finicky about a 7 PRC.
At top of the firearm section there is a eval of a Browning X-Bolt 2 in 7 PRC with almost 600 rounds on it without a single thing but bullets being put in the bore. Hornady CX shots 5-6 inch groups and has very stiff bolt lift and pressure signs from the first shot out of the rifle. Get different ammo.

Thanks much for pointing me in the direction of the XBolt 2 review and the CX results. Bookmarking that thread here for those who are interested https://rokslide.com/forums/threads/browning-x-bolt-2-speed-7-prc-field-evaluation.356804/

 

[TaperPin]

Someone recently said this about adopting the spanking new 7PRC: tell me your a rookie without telling me you’re a rookie.

So I’m one of those rookie hunters who jumped on the 7PRC bandwagon after salivating over those sweet ballistics tables.

At some point towards the end of my 80-round barrel break-in I got a reeeall hard bolt lift. I didn’t know at the time to check for pressure signs on the brass, but I suspect it was there. At the same time that I was struggling to get good groupings with my Hornady CX ammo, I started hearing rumblings about problems with Hornady powder. I assumed I must’ve gotten a bad round.

Now we know that the problem was with their slow powder, which is unlikely to have caused the hard bolt lift. As I order up ammo (Federal this time) and start preparing the gun for the fall hunting season, I dug deeper and found a comment by Jim on Backfire that 7PRCs are churning up a lot of pressure signs including hard bolt lifts, and that it is due to the rapid buildup of carbon near the throat of the chamber after 40 or so rounds. Now I’m feeling like a chump, pulling the trigger on a new design with tight precision tolerances that are less forgiving than other calibers like 7 Rem Mag or 280AI.

Has anyone else run into this issue? If so, what are you seeing in terms of buildup?

Was I a chump for jumping on the 7PRC bandwagon so early, or is this a common issue with magnums?

I don’t think there’s anything wrong with the 7prc, but it’s a little bit of fluff to say it’s a lot different from a 7 Rem mag. Here’s a closeup of SAAMI specs for both the 7 prc and 7 mag - the neck and throat dimensions aren’t that much different. The tollerance for both is the stated number, or up to .002” larger on all dimensions. A rifle in either cartridge simply made with minimal throat clearance will carbon up and need cleaning sooner than one made on the looser side. Simply cleaning well with a carbon remover solvent will instantly tell if pressures are related to carbon. A borescope is the only sure fire way to tell if the carbon ring has been scrubbed out - some are so hard that normal cleaning doesn’t do much.

 

[Koda_]

What chamber brush would you use on a 7PRC? Chasing down the carbon ring rabbit, folks say to use an oversized (in my case maybe 308 or 338) bronze brush to get up in the throat. I went looking around amazon for chamber brushes and see some that look like they're for ARs.

Ive never been able to find a multi diameter chambr brush for anything other than ARs.
I cant recall the diameter/caliber of mine but 308 cal seems right. They are cheap enough to buy to find out.
FWIW i shoot a 280ai but I wont let the carbon ring build up on any rifle anymore after my experience with one. Its one of the most overlooked part of bore cleaning, everyone just focuses discussion on the bore only.

Note, after a quick scrub of the chamber I run a chamber mop to clean up any excess solvent as I understand its not good to shoot a wet chamber.

 

[Koda_]

This is super helpful, folks. I’m glad to have an alternative explanation in my pocket in case I don’t see a carbon ring.

The thing that haunts me is even the Hornady folks say it’s a hot rod that needs more frequent cleaning. Which is fine if true. Gives me an excuse to play with my toys at the bench. But certainly is not ideal if true.

That actually might be true.
My understanding is the faster velocities is what wears out a barrel sooner than later so it might make sense to clean more frequently.
A property maintained barrel should last a long time for the average hunter even a ot rod caliber, the only thing that cant be stopped is throat erosion from firecracking but even that should take a while in a hunting rifle.

 

[SDHNTR]

It isn’t a carbon ring or any cleaning nonsense. Hornady CX beside often featuring extremely poor precision, also causes sticky bolt lift and extraction from lots of rifles.

Borescopes, drills, brushes, etc are all a waste of time. There is nothing “picky” or finicky about a 7 PRC.
At top of the firearm section there is a eval of a Browning X-Bolt 2 in 7 PRC with almost 600 rounds on it without a single thing but bullets being put in the bore. Hornady CX shots 5-6 inch groups and has very stiff bolt lift and pressure signs from the first shot out of the rifle. Get different ammo.

I’ve shot Hornady Outfitter CX out of numerous factory rifles with zero such problems. Perfectly acceptable accuracy and it’s actually the preferred factory ammo out of my 7mag. Groups like a dream and no pressure issues. Every rifle is different.

 

[SDHNTR]

What chamber brush would you use on a 7PRC? Chasing down the carbon ring rabbit, folks say to use an oversized (in my case maybe 308 or 338) bronze brush to get up in the throat. I went looking around amazon for chamber brushes and see some that look like they're for ARs.

If you really want to give it a shot, use a blue plastic Iosso brush in .308. I wouldn’t use an abrasive paste. I’d soak a patch with carbon solvent, stick it just into throat until it grabs and leave it overnight. That will soften any carbon. Then spin the brush 40-50 times.

But before all that, I’d also try another type of ammo. Every barrel has its own preference. What I, or anyone else may have experienced with an ammo type in my gun, means little in yours.

 

[Formidilosus]

I’ve shot Hornady Outfitter CX out of numerous factory rifles with zero such problems. Perfectly acceptable accuracy and it’s actually the preferred factory ammo out of my 7mag. Groups like a dream and no pressure issues. Every rifle is different.

Sure, some guns shoot it fine. I’ve shot it in quite a few rifles and it’s 50/50 at best for shooting under 2.5 MOA, and it has a reputation for being either terrible or fine in rifles. The same was true of Hornady GMX factory ammo.

 

[mxgsfmdpx]

The thing that haunts me is even the Hornady folks say it’s a hot rod that needs more frequent cleaning.

Yo man. I have a 7PRC built on a Tikka action with a 22" ACE Tikka contour barrel. It's almost at 1,000 rounds now and hasn't been cleaned once.

This gun shoots the 180 ELDM's the best followed closely by the 175 ELDX's, both shooting only factory ammo now (first 200 were hand loads). I'd recommend giving either of these a try and report back.

I never shot the 160CX ammo but one of my buddies in California does due to being required to do so. He is okay with the accuracy and performance on deer so far, but his Seekins 7PRC has symptoms like your gun, very sticky bolt at least 1 out of every 5 shots.

 

[donrleonard]

If this isn't the best hunting forum on the World Wide Web, I don't know what is. Thanks everyone for sharing your experience here. Getting this kind of feedback--esp history of CX reacting poorly in some rifles-- really helps me troubleshoot.

The borescope arrived today and I was able to fumble it up the chamber to the transition area right before the bore. 3 questions:

1. Did I capture the right spot (as far as you can tell)?
2. Is that carbon buildup?
3. Should I decide I care before firing something besides Hornady CX down the barrel and seeing how it feeds/shoots/groups?

I've heard loud and clear from members that 7PRC is shooting just fine with the "ain't broke, don't fix" approach to rifle cleaning. I've got some factory loads of Federal Terminal Ascent (155gr) and their new Tipped Fusion (175gr) ready to fire if you all give me the go-ahead. (I went bonded over cup and core ELDs because out east here we tend to take em at much closer ranges).

Alternatively, if there's carbon ring maintenance to be done I can go down that road.