Reloaded rounds wont chamber 7prc

[ActBlueDonor]

Process is important. Trim, chamfer, measure.

None of your case measurements make sense for 7prc, your measuring reference dimensions

100%.
Datum line is what it is for a reason. You cannot compare the body to another body. The shoulder and neck can grow. Datum .410"? Was that it? The standard is a standard and your measurements should be based on that.

This has been great entertainment for the night.

 

[Koda]

Process is important. Trim, chamfer, measure.


100%.
Datum line is what it is for a reason. You cannot compare the body to another body. The shoulder and neck can grow. Datum .410"? Was that it? The standard is a standard and your measurements should be based on that.

This has been great entertainment for the night.

.420dia at 1.904" per saami.
I looked up that SAC comparator and cant tell if they use the shoulder angle to measure case headspace but that doesn't make sense to me at all if they do.

View: https://youtu.be/bY8Uuux5o0g?si=ADUw41VJFkRY5KvW&t=158

 

[P7M13]

Last reply was Monday and here it is Saturday -- seems you have the problem resolved. If you still run into a jam, drop me a PM and I can stop by if you like. I consider Beaverton local to Tigard.

 

[Tgrow503]

Thanks. I got it figured out. I didn't trim the cases and didn't chamfer or debur . That was causing an edge/ deform at the end of case causing it not to chamber. After chamfering a few and loading to DTL- its chambering now.

 

[orygun]

Check the shoulders very carefully.

My first thought.

 

[P7M13]

Thanks. I got it figured out. I didn't trim the cases and didn't chamfer or debur . That was causing an edge/ deform at the end of case causing it not to chamber. After chamfering a few and loading to DTL- its chambering now.

Be aware, at a 30° shoulder, the 7 PRC shouldn't need trimming all that often.
I will say, if a burr created all this grief, your gun's chamber has a very tight throat.
I seldom chamfer or deburr if I'm doing just a shoulder bump and seating. You'll want to see exactly where you are creating this burr. Some full sizers will do it, some bullet seaters will.
Also, examine your neck bushing. I have seen some that have an inner finish chamfer on one side only, the other end being a sharp edge.

 

[Steel Head]

Thats not to saami spec and thats not the shoulder datum. I dont know how SAC comparators work but you should be checking the shoulder datum to saami spec, 1.904" -.007" if you want to assure it will fit your chamber.

saami specs are free:

https://saami.org/wp-content/uploads/2025/04/SAAMI-Z299.4-CFR-2025-Centerfire-Rifle-Approved-2-10-2025.pdf

View attachment 2071457

This.

 

[Certaindeaf]

Yea, one a them fancy measuring sticks with a dial on it comes in handy occasionally.

 

[mbailey25]

Tikka action , Proof prefit 7prc
ADG brass , eldm180gn , H4831sc

I have already sized and fired this brass once all 100 cases with 175gn eldx the first time I loaded them to 3.4 OAL and ran through them fine. Now I'm on my 2nd loading of them and using 180 eldm. I have resized all the brass and they chamber fine. I also have a hornady OAL gauge and checked with the 180s for touch to lands and came up with a 3.385 OAL . I loaded up 20 rounds for a ladder test at 3.381 and they will not chamber , not even close , bolt stops 1/4" from close. I measured my loaded neck dia at .315 spec is .317 . I have a round I loaded too deep at 3.28 same thing , bolt stops short wont close. I have measured the brass , neck, shoulder, bullet dia .284 etc and everything seems good , bolt drops on brass only. Its like I'm loading the bullets too long and there hitting the lands preventing the bolt to close , but how is this possible when the OAL gauge give me 3.385 to touch ? Hornady specs this load for a 3.32 OAl .The barrel and chamber are clean as far as I can see , the barrel has 100 rounds on it and has been scrubbed clean. I have also taken ogive measurements and everything seems good. What else could it be ? I do not have a boroscope handy . Anyone near Tualatin care to take a look ?

I have had a similarly strange issue. I had a perfected load that was shooting .27moa out of my 6.5prc browning x-bolt. I shot around 25 rounds with the same exact load/measurements on the casing and seating depth. I went into production and loaded well over 100 rounds. I stored them until the next season came around and I took 25 to go shoot, check zero, and prepare for an upcoming hunt. Only about 1 out of 5 would chamber. Some I couldn't get the bolt to close. Some I couldn't even get the round forward enough to try closing the bolt. I went home, double checked everything and my specs were right on. I tried seating the bullet a few thousandths deeper - no dice. I finally discovered that for some reason, the shoulders needed to be pushed back just a fraction more. Once I did that, everything chambered perfectly and I was back to shooting good groups. I'm not sure why the shoulders needed to be pushed back more than what they did the season prior, but that was the fix.

 

[Koda]

I'm not sure why the shoulders needed to be pushed back more than what they did the season prior, but that was the fix.

For me its production tolerances. I bump my shoulders back .003, but i can squeeze +/-.003" out of my calipers differently on any given day. So unless im going to measure each one or test each one in the chamber i adjust my target dimension to bump the shoulder back .005 or 6.
Brass thickness variations can affect sizing too.

 

[Bobbygun]

For me its production tolerances.

There are so many variables when reloading. I had some trouble just using an RCBS shell holder one time and a Lee shell holder the next with a handheld priming tool. The shell holders were not exactly alike. I think I ended up putting a tiny piece of wood under the primer seating rod when I used the Lee shell holder in order to get it to seat the primer deep enough. I wonder if there could be a variance in how far down the case the sizing die sizes if using different brands of shell holders. Unfortunately, it doesn't take much to foul things up.

 

[Koda]

There are so many variables when reloading. I had some trouble just using an RCBS shell holder one time and a Lee shell holder the next with a handheld priming tool. The shell holders were not exactly alike. I think I ended up putting a tiny piece of wood under the primer seating rod when I used the Lee shell holder in order to get it to seat the primer deep enough. I wonder if there could be a variance in how far down the case the sizing die sizes if using different brands of shell holders. Unfortunately, it doesn't take much to foul things up.

I haven't had any issues swapping shell holders, but I'm not certain how far down the case sizing dies vary.
Ive had stiff bolt closures so I kept adding to my shoulder bump target dimension till 100% pass, I test the sized cases manually right after sizing until I get 100% pass on easy bolt closures, I don't want to have to check the bolt when sizing in the future. Every component has tolerances, Ive found the shoulder bump can hold steady for several cases then suddenly grow or shrink a few thou. I attribute this to variations in case weights... its surprising how much some case brands vary in weight, since saami spec controls outside dimensions only, the case wall thickness can vary unlimited which can affect fireforming and shoulder bumping.
I bump bolt guns -.003, gas/lever guns -.005... as a general rule. But I can squeeze calipers +/-.003" depending on my mood so I typically add a couple thou to my target dim to compensate for all sizing sessions. Also, comparators are not precision gauges and the shoulder diameter can wear with use. Ive seen this bolt closure question before in other forums, someone bumping -.003 then getting stiff bolts later on wondering why. My guess is they are not averaging their fireformed shoulder dimensions over a large enough sample size and 2 or 3 fireformings, and the next time they set up they might be using a different finger pressure on the calipers. I go for no finger pressure on the calipers myself.

 

[arakboss]

I understand that your freshly resized cases chamber fine. When you seat, and crimp if you are, is it deforming the case somehow?

Of course you can measure and see, but another way is to pull the bullet and see if that case still chambers. If it does chamber, then you have a bullet length issue, if it does not chamber, the brass has been deformed out of spec while you are reloading.

I would try this.

 

[mbailey25]

I understand that your freshly resized cases chamber fine. When you seat, and crimp if you are, is it deforming the case somehow?

Of course you can measure and see, but another way is to pull the bullet and see if that case still chambers. If it does chamber, then you have a bullet length issue, if it does not chamber, the brass has been deformed out of spec while you are reloading.

That's a good idea I didn't think of.

 

[Aught Six]

Your case is too long for your chamber or you might have debris around the chamber.

Everyone should have a Hornady chamber gauge kit.
Despite what SAMMI says, some rifles are short chambered. I built my bolt gun that way.

 

[Aught Six]

View: https://youtu.be/bY8Uuux5o0g?si=ADUw41VJFkRY5KvW&t=158

Ive never seen a kit like that. The ones we use, one size fits all.
been suing these for years.

View: https://www.youtube.com/watch?v=fW6H9HJzsvQ

 

[mbailey25]

I have found that the OAL comparator has been incredibly helpful in dialing in a consistent OAL. When I started and was measuring COAL, I was getting various speeds, and some accuracy issues. Once I started measuring to the ogive using the comparator, things tightened up immediately.

 

[Steel Head]

Everyone who reloads needs some tool/tools to measure actual case headspace dimensions.

I mostly make my own from dead barrels.