Tight Throat?

Nvhunter92

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FYI I posted this in the reloading forum as I wasn't sure where it belonged. So I'm having a bit of an issue and hopefully you guys can provide some help. I have a new Christenson Arms in 7mm rem mag. I am using nosler brass and 162gr hornady ELD-X's. I had trouble finding my distance to lands using the hornady oal gauge as I was getting a number well below saami max (2.619" w/ comparator). So I used Jim Wheelers stripped bolt method and a fired case with light neck tension to "jam" the bullet into the lands and both methods were very close to each other and gave me a distance to lands of 2.737" using a comparator. During my fireforming process I had the bullets seated to a depth of 2.685" using a bullet comparator and everything worked well. I even stripped the bolt and ran the unfired rounds through the chamber and they fit with no resistance. After fireforming I neck sized my brass and seated the bullets to the same depth and went shooting. I also cleaned the gun very well. The problem is that when running the bolt forward I can feel resistance as the bullet enters the throat and the bolt is stiff to lock down. When I would try to unchamber the unfired round the bolt would lift with some resistance but I had to bang on it to get it to move rearward and there is scuffing on one side of my bullet near the case mouth (see picture). The rounds shot well and showed no pressure signs and the fired cases ejected like normal. I got home and took the firing pin and ejectors out of my bolt and ran one of the now twice fired cases into the chamber and the bolt closed with little to no resistance so I think my cases are sized properly. I saved one of the problem unfired rounds and started incrementally seating the bullet deeper but was still getting scuff marks even down to a length with comparator of 2.610". It didn't matter how the case was oriented, the scuff mark was always in the same place. I bumped the shoulder back using a Redding body die and same issue. I tried seating the bullet with a rcbs gold metal match die to a depth of 2.685"...same issue. I'm really scratching my head on this one. The rounds worked well on their first firing but not on the second but the cases chamber easily.
 

J E Custom

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View attachment 90742 FYI I posted this in the reloading forum as I wasn't sure where it belonged. So I'm having a bit of an issue and hopefully you guys can provide some help. I have a new Christenson Arms in 7mm rem mag. I am using nosler brass and 162gr hornady ELD-X's. I had trouble finding my distance to lands using the hornady oal gauge as I was getting a number well below saami max (2.619" w/ comparator). So I used Jim Wheelers stripped bolt method and a fired case with light neck tension to "jam" the bullet into the lands and both methods were very close to each other and gave me a distance to lands of 2.737" using a comparator. During my fireforming process I had the bullets seated to a depth of 2.685" using a bullet comparator and everything worked well. I even stripped the bolt and ran the unfired rounds through the chamber and they fit with no resistance. After fireforming I neck sized my brass and seated the bullets to the same depth and went shooting. I also cleaned the gun very well. The problem is that when running the bolt forward I can feel resistance as the bullet enters the throat and the bolt is stiff to lock down. When I would try to unchamber the unfired round the bolt would lift with some resistance but I had to bang on it to get it to move rearward and there is scuffing on one side of my bullet near the case mouth (see picture). The rounds shot well and showed no pressure signs and the fired cases ejected like normal. I got home and took the firing pin and ejectors out of my bolt and ran one of the now twice fired cases into the chamber and the bolt closed with little to no resistance so I think my cases are sized properly. I saved one of the problem unfired rounds and started incrementally seating the bullet deeper but was still getting scuff marks even down to a length with comparator of 2.610". It didn't matter how the case was oriented, the scuff mark was always in the same place. I bumped the shoulder back using a Redding body die and same issue. I tried seating the bullet with a rcbs gold metal match die to a depth of 2.685"...same issue. I'm really scratching my head on this one. The rounds worked well on their first firing but not on the second but the cases chamber easily.


Is the scuffing all the way around or on one side ?
Also measure the fired case neck diameter and compare it to the loaded round neck diameter.

J E CUSTOM
 

Nvhunter92

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Is the scuffing all the way around or on one side ?
Also measure the fired case neck diameter and compare it to the loaded round neck diameter.

J E CUSTOM
The scuffing is only on one side. I can rotate the case 180 degrees and rechamber the round and the scuffing will stack up on top of the old scuff mark. Fired neck diameter is .314 and loaded is .3125-.313
 

L.Sherm

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May not be your problem but .0015 and .001 is not enough neck clearence in my opionion.
 

J E Custom

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So what your saying is you think the chamber is too tight in the neck region?


I would recommend that a minimum of .003 larger for the fired case in order to allow the neck to expand enough.

The other possibility is the fact that it always marks the top of the bullet
in any position, the chamber may not be concentric to the bore. this can be checked buy using a concentricity tool to check your fired brass for run out. Dies have a hard time removing all of the run out once it has been fired because of spring back.

I hope this is not your problem, but stranger things have happened.

J E CUSTOM
 

L.Sherm

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Call Christensen and ask if they used a saami reamer on your gun .314 neck dia. is not saami .316 is if they tell you they did use a saami and your only measuring .314 i would be checking for something going on with the chamber.
 

bigngreen

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Your probably getting .001+ spring back in your necks so I'm willing to bet your neck diameter is going to be good.
The scuff staying the same on the bullet means the case is going one way the bullet another. I would carefully check what measurement you have just in front of the belt on new fired and sized. Find a case that you can feel some drag on with a stripped bolt and set up a FL die and size the case back .002+ then measure the area in front of the belt and see if that let's things have enough room.
 

Nvhunter92

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I just took one of my fired cases from the problem ammo, neck sized it in my gold metal match die without the expander (I was previously using a standard rcbs neck sizer with expander), seated a bullet at 2.685" with my GMM seating die and chambered the round with the firing pin and ejectors removed. The round chambered with very little pressure and the bolt lifted and moved rearward easily (no banging on bolt to get it back). There was still very very light scratching of the bullet at roughly the same distance from the neck but it was not nearly as deep and hardly noticeable. So I think I have the problem identified...1) my old neck sizer was inducing significant runout which made chambering and extraction difficult 2) my throat is on the tighter end of normal thus the bullet is still contacting it ever soslighlty before it reaches the lands

Does this sound right?

Is there anything wrong with having a tight throated rifle?
 

300sendero

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Sep 25, 2016
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I have the same thing going on with a custom 300 win mag. Same mark on one side of the bullet. What else I find strange is 3.59 is max length but I can still see rifling marks on the bullet even when I seat them down the 3.45-3.48 range. I’ve had a hard time finding a max oal. Ive had to bang out several bullets from the barrel that have gotten hung up while experimenting with seating depth. I have never had these issues with anything before. The gun shoots 2-3 moa average no matter what I try. Sorry for a hijack of your thread but my current battle as well.
 

Nvhunter92

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Messages
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Location
Elko, NV
I have the same thing going on with a custom 300 win mag. Same mark on one side of the bullet. What else I find strange is 3.59 is max length but I can still see rifling marks on the bullet even when I seat them down the 3.45-3.48 range. I’ve had a hard time finding a max oal. Ive had to bang out several bullets from the barrel that have gotten hung up while experimenting with seating depth. I have never had these issues with anything before. The gun shoots 2-3 moa average no matter what I try. Sorry for a hijack of your thread but my current battle as well.

I had a really tough time finding my max coal with this rifle. Have you tried the stripped bolt method?
 

300sendero

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Sep 25, 2016
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No I have not tried the stripped bolt method.

I can close the bolt on that bullet at 3.59 and I think the short picture is 3.47 but I can’t remember exactly now. It is a 178 amax that’s in the pictures above but a 220 smk will do the same thing.
 
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