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  #1  
Old 04-04-2021, 10:24 AM
whirlybird whirlybird is offline
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Default Christensen Arms BA Tactical Overpressure Questions

I have questions, I'm hoping the internet has answers.

I purchased a Christensen Arms BA Tactical chambered in 300 PRC. This is my first magnum chambered rifle. I also have a tikka T3x in 6.5 Creed that I am developing a load for. I'm also new to reloading. I'm learning a lot, I think I'm fairly savvy, but appreciate that I have knowledge gaps.

I bought the CA last summer, and finally got it to the range. I shot some factory Hornady 225 gr ELD Match. All of the casings had flattened primers - can see the tooling marks from the bolt face in the primer, a slight ring around the firing pin dimple, some had ejector marks, and the cases were difficult to extract. Bolt lift didn't seem bad. It's new and so am I.

The cases grew about 0.008" - 0.010" base to shoulder. The once fired cases do not fall within the tolerance of my Wilson case guage. They protrude at the case head side. The neck side is within tolerance. 8 to 10 thou seems excessive. My tikka in 6.5 creed doesn't have this problem - the base to shoulder measurement stays the same. I'm up to 2x fired cases on that one. I neck only size those, no shoulder bump, seems to be going well.

I sent the rifle back to CA with a spent casing. They polished the chamber, fired a round, and sent back both casings.

The casing that they fired has a flattened primer and a ring around the firing pin dimple. I can catch my finger nail on it, I'm guessing it's about a 0.005" tall ring... I haven't gone through the trouble of measuring it. I'm really having trouble imagining a gunsmith that didn't notice this condition, especially examining a rifle that was sent back to them with overpressure indications.

So here I am. I've got a $2800 rifle and I don't know if it's safe to shoot it. I've written back to CA customer service, and frankly I'm not confident they'll be any help. I've read plenty of forum threads where people complain about CA having very tight chambers dimensionally and manifesting this problem. I do not own headspace gauges for this chambering. Ultimately I want to reload for this rifle and work out a recipe for long distance recreational shooting.

What else do I need to know or have answered? Should I ask for my money back and get a different rifle? I got this one because of the carbon fiber barrel. Honestly, the rest of the fit and finish of the rifle is not impressive considering the price point. I mean really, if tikka can sell that smooth action of theirs for like $900, why does this action feel like it's lined with sand paper? Wtf? I digress... What shoould i do? will it work itself out? Should I get a proof barrel and build my own long range rig? Is it worth finding a gunsmith to fix it? What other options are there? I'm in the SF Bay Area.

I think I've attached the data that I have.

Thanks for your help.

Mike
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File Type: jpg berger data.jpg (14.3 KB, 24 views)
File Type: jpg SMK Data.jpg (18.6 KB, 19 views)
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  #2  
Old 04-04-2021, 4:34 PM
pacrat pacrat is offline
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Quote:
I purchased a Christensen Arms BA Tactical chambered in 300 PRC. This is my first magnum chambered rifle. I also have a tikka T3x in 6.5 Creed that I am developing a load for. I'm also new to reloading. I'm learning a lot, I think I'm fairly savvy, but appreciate that I have knowledge gaps.
Knowledge gaps -aka- ignorance. Is solved by asking questions, the answers to which fill in the gaps, and lessen the ignorance. So you are already on the right track.

Being new to reloading. Maybe you are unaware that everything is variable, and all variables are relevant.

Quote:
All of the casings had flattened primers - can see the tooling marks from the bolt face in the primer, a slight ring around the firing pin dimple, some had ejector marks, and the cases were difficult to extract. Bolt lift didn't seem bad. It's new and so am I.
Flattened primers is not necessarily an over pressure indicator. And often means that things are working just as intended. Same for "tool marks" in primer cup. The slight extrusion "ring" around dimple could be of concern if excessive. Bolt lift is OK, that's good thing. Extraction may have been mitigated with the chamber polish. Have you fired it since then? If chamber WAS a bit rough that would increase extraction.

Quote:
The cases grew about 0.008" - 0.010" base to shoulder. The once fired cases do not fall within the tolerance of my Wilson case guage. They protrude at the case head side. >snip< 8 to 10 thou seems excessive.
Cases growing is normal. ALL factory ammo is made slightly under SAAMI spec. To assure function in all factory rifles. Once fired, it fits the chamber. Which does not have the EXACT same HOLE as the gage. They can both be within SPEC and still not match.
Not all holes are created equal. Your actual chamber headspace. Is made to a +/- .005" tolerance. Considering that you fired slightly undersize ammo. You are within SPEC of .010" tolerance. If you size your fireformed cases. Like you do your 6.5. You have made the cases fit your gun. Throw the gage in a drawer, and forget where you left it. Since its hole doesn't match your chamber. It is useless.

Quote:
I'm really having trouble imagining a gunsmith that didn't notice this condition, especially examining a rifle that was sent back to them with overpressure indications.
What you perceived as overpressure. Most likely isn't, as you describe your after firing case condition. And bolt lift. True overpressure condition would typically include at least some "case head extrusion". And hard bolt lift.

Quote:
Ultimately I want to reload for this rifle and work out a recipe for long distance recreational shooting.
Go ahead and do so with confidence. You've already shown your rifle to be "safe". Because you shot it with no ill effects. Now that you have fireformed cases.

Quote:
Is it worth finding a gunsmith to fix it?
Fix What? Worse case scenario, as you have described. If per chance the FP dimple in primers is excessive. You can send just the bolt to a gunsmith and have the FP hole bushed. A very simple procedure.

How about posting a couple pics of fired primers, to get a proper evaluation.
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  #3  
Old 04-04-2021, 6:03 PM
whirlybird whirlybird is offline
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Thanks, pacrat! I definitely needed some guidance. Your reply is helpful.

I have not fired it since getting it back. I want to be pretty sure about lighting off 82 grains of powder next to my face. I agree the chamber polish should help. I was just super unsure about the primers. I took a couple pics and posted. I took the time to get a more accurate estimate of the ring protrusion using a feeler gauge. Pretty confident that it's smaller than 0.0025" - two and a half thousandths.

Fireformed cases - normal. Cool. I was gonna be pretty upset about having to rework a bunch of brass LOL. That $ hit is expensive.

"case head extrusion" - you mean like seeing the ejector marks? Or are we talking about thinning around the case webbing and the associated ring of death? ( which I'm totally not seeing) In the photos on this reply, the left case has ejector marks, around the "H" and "A" in "hornady". This bolt has two ejectors. I'm sure that this is the case that I sent with the rifle for warranty repair.

Lastly, forgot to mention this earlier, muzzle velocities in the velocity ladders I loaded are higher than the book suggested they would be. That alone wouldn't concern me, but combined with everything else - my perceptions and conservative judgments - is why I terminated the test 2 grains before max load per the Berger data....

Since I brought that up, and I had to call them to get data for this chambering and N570 powder... start load for 230 gr bullets is 78 grains N570, 2594 fps, max is 86.8 gr @ 2917 fps. 26" barrel. I was clocking over 3k fps at 84 grains.

Anyway. Thanks again! Looking forward to your opinions about the primer pics.
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  #4  
Old 04-04-2021, 8:12 PM
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Quote:
Originally Posted by whirlybird View Post
I have questions, I'm hoping the internet has answers.

I purchased a Christensen Arms BA Tactical chambered in 300 PRC. This is my first magnum chambered rifle. I also have a tikka T3x in 6.5 Creed that I am developing a load for. I'm also new to reloading. I'm learning a lot, I think I'm fairly savvy, but appreciate that I have knowledge gaps.

I bought the CA last summer, and finally got it to the range. I shot some factory Hornady 225 gr ELD Match. All of the casings had flattened primers - can see the tooling marks from the bolt face in the primer, a slight ring around the firing pin dimple, some had ejector marks, and the cases were difficult to extract. Bolt lift didn't seem bad. It's new and so am I.

The cases grew about 0.008" - 0.010" base to shoulder. The once fired cases do not fall within the tolerance of my Wilson case guage. They protrude at the case head side. The neck side is within tolerance. 8 to 10 thou seems excessive. My tikka in 6.5 creed doesn't have this problem - the base to shoulder measurement stays the same. I'm up to 2x fired cases on that one. I neck only size those, no shoulder bump, seems to be going well.

I sent the rifle back to CA with a spent casing. They polished the chamber, fired a round, and sent back both casings.

The casing that they fired has a flattened primer and a ring around the firing pin dimple. I can catch my finger nail on it, I'm guessing it's about a 0.005" tall ring... I haven't gone through the trouble of measuring it. I'm really having trouble imagining a gunsmith that didn't notice this condition, especially examining a rifle that was sent back to them with overpressure indications.

So here I am. I've got a $2800 rifle and I don't know if it's safe to shoot it. I've written back to CA customer service, and frankly I'm not confident they'll be any help. I've read plenty of forum threads where people complain about CA having very tight chambers dimensionally and manifesting this problem. I do not own headspace gauges for this chambering. Ultimately I want to reload for this rifle and work out a recipe for long distance recreational shooting.

What else do I need to know or have answered? Should I ask for my money back and get a different rifle? I got this one because of the carbon fiber barrel. Honestly, the rest of the fit and finish of the rifle is not impressive considering the price point. I mean really, if tikka can sell that smooth action of theirs for like $900, why does this action feel like it's lined with sand paper? Wtf? I digress... What shoould i do? will it work itself out? Should I get a proof barrel and build my own long range rig? Is it worth finding a gunsmith to fix it? What other options are there? I'm in the SF Bay Area.

I think I've attached the data that I have.

Thanks for your help.

Mike
Research the difference between SAAMI and SAAMI 2 chambers for the 300 PRC.

Short story: Some Hornady 300PRC ammo is loaded longer than SAAMI spec and requires a longer-than-SAAMI throat to be safely fired.

Ask Hornady about this.
Ask Christiansen what reamer spec they use.
Ask Hornady what reamer spec the particular load you are shooting needs to be safe.
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  #5  
Old 04-04-2021, 9:29 PM
pacrat pacrat is offline
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Well Whirly, I can sum up my own evaluation of your primers with a 3 letter acronym.

TAS.................That Ain't $h!t!

Hell they even still have round shoulders. Really overpressure primers are so flat. That there is only a slight discernable joint between the primer and case. Those aren't even close to HOT loads. Let alone overpressure.

"Case head extrusion" isn't just an ejector ding. It's when the case is so hot, and the base gets jammed so hard into the bolt face. That every little bolt face machine mark is deeply imprinted into the brass. And the brass actually flows into the ejector recess. And looks like a pimple.

Follow "aR15barrels" advice and contact CA and Hornady CS, regarding compatibility. He is a well respected gunsmith here on CG. I was unaware of the 2 differing chamber/ammo specs. With PRC. More of those pesky "RELEVANT VARIABLES".

Last edited by pacrat; 04-05-2021 at 3:20 AM..
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  #6  
Old 04-05-2021, 8:44 AM
whirlybird whirlybird is offline
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ar15 barrels and pacrat, Thanks a ton!

I'll research the chamber specs.

CA did get back to me and they were more helpful than I had anticipated, and what they're telling me tracks with what you both are saying.

pacrat, TAS made me LOL. Good to know, and good information, thank you.

I'm appreciative of you all making yourselves available as a resource, especially since I don't really have an in person mentor or anything. Without this, I'd be in the blind. And right now, I'm feeling much better about proceeding. Much gratitude.

Happy sending!

Mike
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Old 04-05-2021, 8:45 AM
whirlybird whirlybird is offline
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I'll post back about the reamer spec. Might be good info for others with CA barrels.
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Old 04-05-2021, 9:53 AM
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Quote:
Originally Posted by whirlybird View Post
I'll post back about the reamer spec. Might be good info for others with CA barrels.
See if CA will send you a cope of the reamer drawing for the tool they use. It would be a good reference to have in your records.


Quote:
I want to be pretty sure about lighting off 82 grains of powder next to my face.
Hopefully you're not going to be starting there. The only 82 gn loads I've seen were towards max (albeit with a very brief search.)

As you stated you were a new reloader, I'll post a few of my opinions:

New factory ammo may give false pressure signs due to poor fit in the chamber (namely primer signs, case head impressions) from slightly excessive space (too-small cases allow more movement than good fitting cases.)

Do not assume that all listed loads are safe in your rifle. Start low and work the loads up. There's a reason the books have the low loads listed as "Starting Loads". And every rifle is different.

If you're going to work up loads towards the higher end of the data, learn beforehand what kind of telltales offer clues that you're getting into risky territory with regard to pressure. It's better to look at, say, a, ejector imprint on a case head and a severely flattened primer and decide you might have a problem rather than to post on here asking why your rifle is now in pieces (yeah; extreme example, but it does happen.)
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Old 04-05-2021, 7:02 PM
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CA declined to identify the reamer spec, offering only that they probably use the tighter spec one in order to make rifles that meet the MOA requirement.

Thanks, divingin. If you look at the data I collected, you'll see that's exactly what I did. Started at minimum load, worked my way up, stopped when I freaked out, and asked questions. Glad I did. The max load that Berger gave me was 86.8 grains of N570 for a 230 freedom seed. It's looking like mine might have a sweet velocity node at around 82. I've got another set loaded up to try again, this time with once fired and not factory new brass, and a little help from my friends.
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Old 04-05-2021, 7:30 PM
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Quote:
Originally Posted by whirlybird View Post
CA declined to identify the reamer spec, offering only that they probably use the tighter spec one in order to make rifles that meet the MOA requirement.
Ask Hornady what freebore length is required to shoot your specific factory load that you got from them.
After they give you that length, go back to Christenson and ask them if their chamber complies with the requirement.
There's a good chance that Christenson does not even KNOW that there are two different specs and that they have guns delivered which are not safe with some factory ammo.
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Old 04-06-2021, 8:31 PM
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Quote:
Originally Posted by ar15barrels View Post
Ask Hornady what freebore length is required to shoot your specific factory load that you got from them.
After they give you that length, go back to Christenson and ask them if their chamber complies with the requirement.
There's a good chance that Christenson does not even KNOW that there are two different specs and that they have guns delivered which are not safe with some factory ammo.
I like your style. I'll report back when I find out.
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Old 04-06-2021, 9:27 PM
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Quote:
Originally Posted by ar15barrels View Post
Research the difference between SAAMI and SAAMI 2 chambers for the 300 PRC.

Short story: Some Hornady 300PRC ammo is loaded longer than SAAMI spec and requires a longer-than-SAAMI throat to be safely fired.

Ask Hornady about this.
Ask Christiansen what reamer spec they use.
Ask Hornady what reamer spec the particular load you are shooting needs to be safe.
I sent hornady the question. Then I spent about an hour trying to find anything spelling out a SAAMI vs SAAMI II spec. Came up empty. I did find the print for a 300 PRC chamber. Looks like the freebore is about 0.400 (im rounding, and tired, and not sure I did it right).

If the freebore is too short, wouldn't I be jamming the bullet into the lands?
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Old 04-06-2021, 10:08 PM
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If the freebore is too short, wouldn't I be jamming the bullet into the lands?
Yes.
That causes elevated pressures.
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Old 04-06-2021, 10:18 PM
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Quote:
Originally Posted by whirlybird View Post
Then I spent about an hour trying to find anything spelling out a SAAMI vs SAAMI II spec. Came up empty. I did find the print for a 300 PRC chamber. Looks like the freebore is about 0.400 (im rounding, and tired, and not sure I did it right).
Compare that 0.400 freebore to the SAAMI print:

https://saami.org/wp-content/uploads...troduction.pdf

And then to this print from JGS:


That JGS print is the same as the SAAMI chamber drawing in the throat lengths.
The extra 0.150" of freebore would definitely solve jamming problems.
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Old 04-06-2021, 10:49 PM
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Whirly, have you measured your magazine?

CA is not an affiliate member of SAAMI. There is no onus on them to conform to SAAMI specs.

Are you mechanically inclined, and a handy DIY guy?

A chamber cast is a painless process. And will solve the throat ?

Or you can do the neck sized case, and a Loooong seated bullet test, to determine "Base to Throat OAL".

? for ar15barrels, Since Hornady is an SAAMI affiliate. Won't their ammo have to match the SAAMI chamber/cartridge spec?
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Old 04-06-2021, 11:03 PM
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? for ar15barrels, Since Hornady is an SAAMI affiliate.
Won't their ammo have to match the SAAMI chamber/cartridge spec?
Saami compliance is purely voluntary for members or non-member companies.
Most companies like to follow the standards though so if there is ever a lawsuit, they can point to their policy of following the standards as a defense.

Funny enough, Hornady SUBMITTED the specs that some of their very own ammo does not comply with!
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Old 04-07-2021, 7:15 AM
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See attachment, hornady got back quick and simply said that their ammo is s afe in all saami spec chambers.
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Old 04-07-2021, 7:25 AM
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So, yes, I know my way around a machine shop, and have a pile of measuring tools to go with it. If the measurement in question is the freebore, haven't I already measured that when I measured the CBTO with the modified case?

I got a ---

Berger hybrid target 230 - 2.945 @ jam

Sierra Match King 230 2.956 @ jam

Factory loaded Hornady 225 ELDM measured 2.892 with that same guage. I'm guessing it's like 50 off the lands. +/-?
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Old 04-07-2021, 7:36 AM
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Let me clarify.... I know I didn't measure the actual freebore. Or any definite dimension with my cbto measurement. But it would hold relatively true, assuming the curves on those bullets aren't too dissimilar, that it woofs stand to reason that the free bore is sufficient in my chamber?
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Old 04-07-2021, 7:37 AM
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Would not woofs. Lol. My dog was typing.
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Old 04-07-2021, 7:43 AM
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And, if that's true, we circle right back around to me lacking experience on what constitutes an overpressure sign.
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Old 04-07-2021, 8:31 AM
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Quote:
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And, if that's true, we circle right back around to me lacking experience on what constitutes an overpressure sign.
To reiterate: New factory ammo; after firing, your primer was flattened and you got some cratering (the raised ring around the firing pin dimple on the primer)?

Sounds fairly normal (not ideal, but normal) for a round that is not ideally fitted to the chamber, which is why primer flattening is not the best sign to use for high pressure.

Slightly more headspace allows the primer to back out as the case comes up to pressure, then it gets flattened when the case stretches to fill the shoulder to breech area, and it get pushed back into the case head. The ring around the pin imprint likely indicates a slightly large hole in the breech for the firing pin. Again, not ideal, but fairly common.

What signs I look for in terms of pressure:

After firing, look for marks on the case head from the head being smashed against breech: You'll get brass flow into openings in the bolt at high pressure, leaving raised areas where the ejector hole is (if you have one) and the extractor cut (again if you have one.) There may be a smear of bright material if it was "wiped" as the bolt was opened.

Feel how much effort it takes to open the bolt. High pressure will usually put a little pressure between the shoulder and breech, or expand the web of the case a little, causing drag that makes the bolt feel sticky (i.e. harder to open than normal.) A long case after firing may cause "clicking", where the bolt will lift but the case sticks until you put more pressure against the primary extraction causing it to click loose.

And last, look at the primer. The reason it's last is that there are other causes of a flat primer, making it unreliable. If you do have pressure, it will likely be flattened, but a flat primer by itself is not necessarily a pressure indication.

Simple way to tell if you are dealing with a short freebore (for the cartridge in hand) is to chamber and remove it and inspect the bullet. If the cartridge is too long for the freebore, you'll engrave rifling marks at the ogive. They usually look like rectangular or football shaped scuffs, one for each land in your barrel.
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Old 04-07-2021, 12:00 PM
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That's helpful, thanks.

I think I omitted earlier from conversation with CA, they claim the ring is also pretty normal as they use a 34# firing pin spring.
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