300 PRC rifling marks

[HEnrI]

I’m wondering what is wrong with my chamber, I’m seeing rifling marks almost back to the case with factory ammo. “212 eldx” I have tried developing a load multiple times And am getting very inconsistent results, pressure spikes and horrible accuracy. Using jam -20 to start load development the bullets are very difficult to eject -50 still sticky with the same marks.
I get the same marks on Berger 215’s

 

[HEnrI]

3 contact points leave a long mark and 2 leave a shorter square looking mark

 

[Rio Precision Gunworks]

What are you calling "jam"? The point where a bullet will get stuck in the lands? If so, you may still be in the rifling with -.020 and possible even -.050 . Nothing wrong with being in the lands, but can increase pressure.

Remove the firing pin and ejector from your bolt and find the point where the bolt falls free with the round in the chamber. That will be the touch point in the lands. Can also use something like a hornady tool as that will get you close enough.

Then you can see if the bullet is seated too deep and your chamber has too little or no freebore. You can also get some cerrosafe and make a cast of your chamber.



The quality of the pics is pretty bad. So can't really see what kind of marks you're getting.

 

[HEnrI]

What are you calling "jam"? The point where a bullet will get stuck in the lands? If so, you may still be in the rifling with -.020 and possible even -.050 . Nothing wrong with being in the lands, but can increase pressure.

Remove the firing pin and ejector from your bolt and find the point where the bolt falls free with the round in the chamber. That will be the touch point in the lands. Can also use something like a hornady tool as that will get you close enough.

Then you can see if the bullet is seated too deep and your chamber has too little or no freebore. You can also get some cerrosafe and make a cast of your chamber.



The quality of the pics is pretty bad. So can't really see what kind of marks you're getting.

I’m coming up with Jam, via - “Letting the lands seat the bullet into the casing with .0015 of neck tension” still having marks all the way seated past (min) SAAMI spec wich is “3.575”

 

[Rio Precision Gunworks]

I’m coming up with Jam, via - “Letting the lands seat the bullet into the casing with .015 of neck tension” still having marks all the way seated past (min) SAAMI spec wich is “3.575”

So, a stripped bolt won't fall free and is held up when you let it go?

Should also be easy to see with borescope if there is no freebore.

 

[Rio Precision Gunworks]

If it's a saami chamber, you should have something like .232 freebore. So, letting the rifling seat the bullet should have made your starting point noticeably shorter than normal if the rifling is that far back.

 

[HEnrI]

If it's a saami chamber, you should have something like .232 freebore. So, letting the rifling seat the bullet should have made your starting point noticeably shorter than normal if the rifling is that far back.

I’m not sure to what specs it was chambered, the bolt does not fall freely until the bullet is seated ridiculously far in.

it would make sense if the rifle would seat the bullets shorter but unfortunately that’s not the case.
it seats the 215 Berger at 3.831 coal and 3.036 bto.
It seats the 212 eldx at 3.725 coal
With .0015 neck tension in lapua brass

But it leaves 5 long marks on the bullets that look like rifling all the way around.

I can get them in and out of the chamber without trouble, but they all have the same marks, even when seating them .200 in from Jam point.

 

[Rio Precision Gunworks]

Borescope or make a cast of the chamber. Sounds like there's no freebore for some reason. Or freebore didn't completely cut out the rifling. That could be why it doesn't seat the bullet deeper when you jam....it's not full height rifling since it was partially cut.


If it doesn't, send it back to whoever chambered it and have it fixed. If that's not an option, can either have a saami reamer run into it or have it cut and rechambered.

I guess it's possible that it was cut with zero freebore with the intent to throat it for whatever bullet was going to be used. If the rest of the chamber is correct, you could also just use a throater and cut the desired freebore.

 

[Rio Precision Gunworks]

Also, if you figure out the issue and can't find anyone to fix it, or need someone to figure out the problem......let me know and you can send it to us.

We'll take a look and if it's a quick fix without a new chamber needed, it'll just cost you shipping only. We'll have it turned around in less than a week. If it needs a new chamber, we'll figure out some sort of cheap ish hide pricing.

 

[HEnrI]

Borescope or make a cast of the chamber. Sounds like there's no freebore for some reason. Or freebore didn't completely cut out the rifling. That could be why it doesn't seat the bullet deeper when you jam....it's not full height rifling since it was partially cut.


If it doesn't, send it back to whoever chambered it and have it fixed. If that's not an option, can either have a saami reamer run into it or have it cut and rechambered.

I guess it's possible that it was cut with zero freebore with the intent to throat it for whatever bullet was going to be used. If the rest of the chamber is correct, you could also just use a throater and cut the desired freebore.

This is the answer I was looking for. Thanks

 

[bax]

I’m coming up with Jam, via - “Letting the lands seat the bullet into the casing with .015 of neck tension” still having marks all the way seated past (min) SAAMI spec wich is “3.575”

Something sounds strange to me about .015 neck tension. The bullet is about .308. Are you saying that you make the case neck ID .308 minus .015 (that is, 0.293), seat the bullet long, then chamber it? Jamming a .308 bullet into a 0.293 neck would be very heavy neck tension. If I was going to try to discover where Jam is, I would make the neck ID around 305 or 306, remove the firing pin, start long and seat bullets deeper until the bolt handle drops. Finding jam by pushing against heavy neck tension will give you a number that is 15 to 20 thou too long (depends on the bullet construction, shape and metals).

3.575 is the minimum COL. Mine are about 3.62 with 230 grain Berger Hybrids because if they are longer than that they don't fit in my magazine. The Berger ogive is some mix of tangent and secant - so they are long and pointy. I don't have a good idea about the 21 ELD-X ogive shape and how it should hit the rifling. That makes it hard to evaluate the photos.

Looking at the photo where you blackened the bullet, it looks to me like the marks are on the bullet shank (the part that is .308 diameter) and the shank extends far out of the case. Am I seeing your photo correctly?

 

[HEnrI]

Something sounds strange to me about .015 neck tension. The bullet is about .308. Are you saying that you make the case neck ID .308 minus .015 (that is, 0.293), seat the bullet long, then chamber it? Jamming a .308 bullet into a 0.293 neck would be very heavy neck tension. If I was going to try to discover where Jam is, I would make the neck ID around 305 or 306, remove the firing pin, start long and seat bullets deeper until the bolt handle drops. Finding jam by pushing against heavy neck tension will give you a number that is 15 to 20 thou too long (depends on the bullet construction, shape and metals).

3.575 is the minimum COL. Mine are about 3.62 with 230 grain Berger Hybrids because if they are longer than that they don't fit in my magazine. The Berger ogive is some mix of tangent and secant - so they are long and pointy. I don't have a good idea about the 21 ELD-X ogive shape and how it should hit the rifling. That makes it hard to evaluate the photos.

Looking at the photo where you blackened the bullet, it looks to me like the marks are on the bullet shank (the part that is .308 diameter) and the shank extends far out of the case. Am I seeing your photo correctly?

it is sticking far out in this picture, but the marks don’t go away until the bullet is seated way back. 1 and a 1/2 thou (.0015) of neck tension, .3065 is the id of the case mouth.

 

[375fan]

If you are getting rifling marks on the bullets of factory 212 ammo as you stated in first post, then you need to have your chamber checked immediately by a pro. Until then quit trying to develop a load.

 

[Rio Precision Gunworks]

Something sounds strange to me about .015 neck tension. The bullet is about .308. Are you saying that you make the case neck ID .308 minus .015 (that is, 0.293), seat the bullet long, then chamber it? Jamming a .308 bullet into a 0.293 neck would be very heavy neck tension. If I was going to try to discover where Jam is, I would make the neck ID around 305 or 306, remove the firing pin, start long and seat bullets deeper until the bolt handle drops. Finding jam by pushing against heavy neck tension will give you a number that is 15 to 20 thou too long (depends on the bullet construction, shape and metals).

3.575 is the minimum COL. Mine are about 3.62 with 230 grain Berger Hybrids because if they are longer than that they don't fit in my magazine. The Berger ogive is some mix of tangent and secant - so they are long and pointy. I don't have a good idea about the 21 ELD-X ogive shape and how it should hit the rifling. That makes it hard to evaluate the photos.

Looking at the photo where you blackened the bullet, it looks to me like the marks are on the bullet shank (the part that is .308 diameter) and the shank extends far out of the case. Am I seeing your photo correctly?

You're describing finding the "touch" point. Finding the "jam" is where the bullet is as far into the rifling as possible without getting stuck (hence letting the lands push the bullet into the case with the interference fit you plan on using).

When you find touch and back off .020 the bullet is jumping. When you find jam and back off .020, the bullet is still in the lands.

 

[bax]

it is sticking far out in this picture, but the marks don’t go away until the bullet is seated way back. 15 thou (.0015) of neck tension, .3065 is the id of the case mouth.

oh yeah, the 'OTHER' 0.015 - thanks for clarifying

 

[bax]

You're describing finding the "touch" point. Finding the "jam" is where the bullet is as far into the rifling as possible without getting stuck (hence letting the lands push the bullet into the case with the interference fit you plan on using).

When you find touch and back off .020 the bullet is jumping. When you find jam and back off .020, the bullet is still in the lands.

You are right about jam, that was a careless use of words. I am really curious why he is seeing three long marks and two short marks. I have other thoughts but I will listen while you guys hash it out.

 

[Rio Precision Gunworks]

You are right about jam, that was a careless use of words. I am really curious why he is seeing three long marks and two short marks. I have other thoughts but I will listen while you guys hash it out.

Feel free to chime in. Without having the rifle in hand, I'm just guessing based on info given.

 

[Seymour Fish]

it is sticking far out in this picture, but the marks don’t go away until the bullet is seated way back. 15 thou (.0015) of neck tension, .3065 is the id of the case mouth.

0.1 = a tenth. 0.01 = a hundredth. 0.001 = one thou. Get it ?

 

[Rio Precision Gunworks]

Any updates? Curious as to what a borescope or something else may have uncovered.

 

[HEnrI]

Nothing yet. I’ll keep you updated as I learn, thanks!

 

[HEnrI]

…

 

[HEnrI]

A build up of carbon is what was creating the rifling marks. They go away after a deep clean but show up after about 18 rounds. It shoots shots 5-25 at 1/4 moa then starts opening up. At 36 rounds the group’s will open up to 2 moa and the rifle needs another deep clean. Has anyone ever seen this before?

 

[Taylorbok]

A build up of carbon is what was creating the rifling marks. They go away after a deep clean but show up after about 18 rounds. It shoots shots 5-25 at 1/4 moa then starts opening up. At 36 rounds the group’s will open up to 2 moa and the rifle needs another deep clean. Has anyone ever seen this before?

I've got a 30 Sherman mag (300 PRC improved) i've shot 150 rounds with out cleaning and didn't notice the groups open up.

 

[Ledzep]

A build up of carbon is what was creating the rifling marks. They go away after a deep clean but show up after about 18 rounds. It shoots shots 5-25 at 1/4 moa then starts opening up. At 36 rounds the group’s will open up to 2 moa and the rifle needs another deep clean. Has anyone ever seen this before?

Who's barrel and who chambered it?

We've seen a few examples of worn out reamers, or rifle builders ordering reamers AT SAAMI MIN (then getting any amount of wear on them) cutting the throat under SAAMI min (.3085") and it net results in rifles that are extremely sensitive to carbon fouling.

You should be able to shoot 75-100 rounds of PRC before seeing fouling issues crop up.