300-PRC Bullet Seating Weirdness (Barrett MRAD)

[rustyinbend]

Need a little advice from the gurus on this forum. Let's start with the details ...

• Rifle: Barrett MRAD with 300-PRC barrel/bolt.
• Brass: Hornady once-fired, FL sized, shoulder-bumped back 0.003 (bushing and mandrel)
• Projectile: Berger 30cal (.308) 220gr Long-Range Hybrid Target

For this issue ... including Primer/Powder/etc. isn't meaningful.

Here's my problem in a nut-shell ... in order to fit in the chamber and allow the bolt to close properly, I have to seat the bullet "WAY FAR" down in the neck ... so far that accuracy is crap (4-ish MOA). If I seat the bullet further out, it won't chamber. When I seat the bullet to the point where it chambers, accuracy is awful as a result of an over-seated bullet.

For reference ... I've done all the same things I've done successfully reloading 300-WM and 6.5-CM as I've prepared to reload 300-PRC.

• Used a modified case and bullet to calculate the proper distance off the lands (Note: This measurement gives me a much longer cartridge OAL during the measurement, but fails to chamber when I translate that depth (minus backoff) into a finished cartridge.)
• FL-sized with bushing die and mandrel
• Tested the case after shoulder bump and mandrel to make sure the empty case chambers properly (it does)
• ... and everything else that's worked just fine on my other rifles I reload very successfully

Here's the crazy part ... the factory cartridge on the left of the photo below (Hornady 225gr ELDM) chambers fine and shoots sub-MOA all day long. The cartridge on the right (my reload) chambers fine and shoots like shit because it's too deep, but if I pull the bullet out even a little bit, the cartridge won't chamber.

BTW ... the external diameter of the two seated case necks are identical, as are the rest of the case measurements. That means this is all about the "bullet" and/or how or where it's seated. I feel like there's something I'm missing, but I can't figure out what it is. Any advice is appreciated.

Why does the cartridge on the left chamber just fine, but the cartridge on the right fails if I pull that bullet out even just a little? I don't get it. This is making me crazy, and burning supplies figuring out something that makes NO sense to me.

 

[Bmghunter]

Try crimping your cartridge.

 

[FLIGHT762]

Maybe it's the lighting, but the case mouth on the 220 Hybrid looks mushroomed / not square?

I don't have the answer for you, but There's some kind of measurement you're missing between the factory and your fired / resizes case that's causing the hangup.

Do you have your seating die properly set up? Re-check it.

 

[Dave62677]

get a case gauge to check the brass

 

[rustyinbend]

Never mind ... I figured it out. Writing this out, actually germinated new thoughts, and I decided to try something.

I took off the barrel, and dropped in the factory cartridge and is popped into place just fine. Then I did the same with my reload cartridge and it "stuck" most of the way in but failed to settle and seat correctly. Out come the calipers, and I learned that the base of my reload was 0.04 to 0.06 larger in diameter. I went to my dies, and realized that as I'd decreased shell-holder size to adjust my shoulder bump, I had not "reset" my die flush against the shell-holder per the installation instructions. I reset the depth of my die to fit solidly against the shell-holder, lubed and sized the empty case that didn't seat before ... and VOILA' ... it seated just fine.

Bottom line ... this was a situation where I had a width problem on the base of my case, that I thought was a bullet seating problem where embedding the bullet into the neck gave enough chamber relieve to seat the round ... albeit improperly.

Hope that makes sense. VALUABLE lesson learned. Glad it was in a MRAD where it's easy to pop off the barrel, drop in a cartridge, and see what was actually going on. Should have thought of that WAY sooner.

 

[Dave62677]

i had the exact issue before, took me a day to figure out. Most new reloader will thought it was the case length issue.

my buddy gave 50 of the 338lm case fired from his Sako M10. I bump the shoulder back .003 of my chamber and it won't chamber in my AI. Later i realize it was the base of the case approx. 0.004 bigger than my AI chamber.

 

[rustyinbend]

Do you have your seating die properly set up? Re-check it.

That advice was spot-on. Fixed !!!

 

[rustyinbend]

i had the exact issue before, took me a day to figure out. Most new reloader will thought it was the case length issue.

my buddy gave 50 of the 338lm case fired from his Sako M10. I bump the shoulder back .003 of my chamber and it won't chamber in my AI. Later i realize it was the base of the case approx. 0.004 bigger than my AI chamber.

Yup ... exactly. It was weird how dropping the bullet deeper into the neck allowed for chambering, making me think it was a seating issue. But that was a red-herring and totally absorbed me troubleshooting in the wrong direction. Felt pretty stupid ... it's weird how you can start getting insufferably pleased with your own skills, and then something comes along that re-grounds you as a reminder that you're (I'm) a fallible human that still has so much to learn. LOL

 

[918v]

Ok so now the base fits but the shoulder is too far back.

 

[rustyinbend]

Ok so now the base fits but the shoulder is too far back.

It chambers fine now ... with the shoulder where it sized. I guess my next phase of investigation is to shoot it, and see what velocity and group size tells me after a good ladder test.

 

[918v]

S

It chambers fine now ... with the shoulder where it sized. I guess my next phase of investigation is to shoot it, and see what velocity and group size tells me after a good ladder test.

So you’re not going to measure how far you pushed the shoulder back?

 

[rustyinbend]

S

So you’re not going to measure how far you pushed the shoulder back?

OK ... answering your question took me down a totally new rat-hole, that I need some help with.

The shoulder of my recently fired cases measure 2.1975 on my comparator. As noted above, I ran the previously sized (and non-chambering) cases through my Redding FL Type-S Bushing Die, newly seated in the press, and with the 0.10 shell-holder ... and they sized to 2.1945 ... exactly the .003 should bump I'd want.

I thought ... "Victory". Then I took my recently fired and un-sized brass and started to run it through that same die with that same shell-holder. The result has me really surprised. The comparated measurement went "UP" to about 2.1995 or even a little higher. I thought, "OK, just decrease the shell-holder size, but whether I reseat the die after going downhill on shell-holder size, or not ... the result is the same. My shoulder isn't bumping ... they're "growing" in length.

WTF am I doing wrong? How do I use a Redding FL Type-S Bushing Die and Redding Competition Shellholder Set to "decrease" my shoulder, while still sizing down far enough into the body to get to the base of the case so the cartridge will chamber?

Any help is appreciated.

 

[Dave62677]

Different batch of brass or different size brass run through the same dies/press setup will always yield different measurements.

Over lube / under lube case will also yield different number

try to stay with the same shell holder and adjust the dies. I work with the competition shell plate hold before, it doesn’t work well for me.

Key point: limit the variable factors. Work with same lot of brass fried from the same rifle.

 

[rustyinbend]

Damn ... solved my own problem again. Went back to the Shellholder Set instructions, re-read, and re-installed at t he .010 foundation, including the 1/4 turn cam-over. Tested and got the desired shoulder bump on the .002 shellholder. Geez ... feeling not so bright right now. Just needed to go back to square-one, follow the instructions, and reset everything. RTFM ... should have remembered that from my Marine Corps days.

 

[918v]

Ok so the .002 shell holder is giving you what in terms of shoulder bump?

And the cases are chambering fine?

 

[rustyinbend]

Ok so the .002 shell holder is giving you what in terms of shoulder bump?

And the cases are chambering fine?

It's giving me about a .0020 shoulder bump (2.1975 to 2.1955) ... and yes, they're chambering just fine, very smoothly. Rifle is a Barrett MRAD that has a "butter bolt", so it's easy to feel when something is struggling to chamber. All good now. I'm going to load up a ladder test, and hit the range now that this problem appears to be resolved. I also used these lessons-learned to reset the other FL Sizing Dies on my Redding T-7 Turret Press. Part of what induced the back half of this problem was a week ago when I swapped over from my Redding Big-Boss 2 ... using Hornady Lock-n-Load press bushings ... to direct threads in the new T-7 Turret Press. I just wasn't meticulous about die setups. My fault ... lesson learned.

 

[Bradv86]

The specific shell holder will only allow the case to go into the die as far as contact allows, thereby giving you a consistent sizing bump at cam-over. If you had an extremely long chamber, the 1x fired brass will bump far more with that exact same shell holder because it would be much longer to start with. It is by coincidence that the .002 shell holder is giving you .002 bump, unless I am way off base here.

 

[rustyinbend]

The specific shell holder will only allow the case to go into the die as far as contact allows, thereby giving you a consistent sizing bump at cam-over. If you had an extremely long chamber, the 1x fired brass will bump far more with that exact same shell holder because it would be much longer to start with. It is by coincidence that the .002 shell holder is giving you .002 bump, unless I am way off base here.

The Competition Shellholder Set instructions say to screw the die down to contact with the .010 shell holder, back off the ram, and screw down another 1/4 turn for cam-over. Then test the shoulder bump. If you need more, start decreasing the shell holder (.008, then .006, etc.) going down as necessary to get the desired shoulder bump. Mine worked just fine when I got down to the .002 shell holder ... which you're correct ... is purely coincidental to the fact that I was looking for a .002 shoulder bump.