300-PRC OCW

[rustyinbend]

After months of wrestling with my 300-PRC ... I think I've found the recipe that works. This is my second independent range session with sub-5.0 standard deviations. Time to take this out to a mile, and see if it holds up. I wanted a higher velocity, but at the end of the day, I had to let the rifle tell me what to do. Another interesting fact about this odyssey is that I had to mandrel "before" sizing to expand the neck, and then size down with a SAC .337 bushing, and leave it that way to seat the bullet. Everything else I reload prefers the mandrel "after" sizing and before seating. Weird ... but ... whatever works, right?

Discussion Question: Have any of you guys experienced a scenario where you get better results by not mandreling, or by mandreling "before" sizing instead of "after" sizing?

 

[Supersubes]

You're gonna yave to explain the process exactly, the results on both sides, and the involved dimensions. On the surface, with little information, it would appear you’re just using the wrong bushing in the sizer.

 

[rustyinbend]

You're gonna yave to explain the process exactly, the results on both sides, and the involved dimensions. On the surface, with little information, it would appear you’re just using the wrong bushing in the sizer.

Fair enough. Here ya go ...

• Rifle is a Barrett MRAD 300-PRC barrel with approximately 800 rounds downrange (combo of factory and handload)
• Lapua 1x brass
• Shoulder fired: 2.124
• Shoulder bumped: 2.121
• Mandrel: .3065
• Redding FL Type-S die w/ .337 SAC bushing
• Hornady 225 ELD-M bullets
• Seat: .80 (Acc-1 Seat Micrometer)
• Everything cleaned, lubed, annealed, etc. at the appropriate times.

Process used to be sizing with a .335 bushing, and then expanding with .3055 mandrel ... but I struggled with seating the bullets, so I went to a .3065 mandrel prior to seating. At this point, the seating was fine but about half the cartridges wouldn't chamber. I decided to reverse the process, expanding with the .3065 mandrel, and then sizing to .002 subtracted from a seated bullet outside neck which required a .338 or .337 bushing. Tried the .337 bushing first. So mandreled with .3065 to expand, and sized down with .337 bushing to shrink. Checked concentricity after sizing and before seating and got sub-1,000th of runout. Bullets seated smoothly with medium pressure on the press down-stroke ... and twice, got the sub-5.0 standard deviations I shared. Note ... I record 8 rounds instead of 10 because I always throw out the high and low in any dataset. With shots 9 and 10 included, the SD was still under 4.0.

I suppose I could try shrinking down the sizing bushing substantially, and going to a smaller mandrel to see if my chambering problem disappears ... but frankly, why would I do that if I'm now getting such smooth seating and chambering, and such tight standard deviations.

It sounds like your answer to my question is to always mandrel "last" before seating. True or False? Need more data to answer that? I got lots ... my history spreadsheets of everything I try is enormous. Doesn't make me smarter or better ... just meticulous about documenting everything. A character flaw from my prior career ...

 

[spife7980]

It sounds like your answer to my question is to always mandrel "last" before seating. True or False?

True if thats what causes it to shoot best.

Its why I get so pissed when people come on here and ask for the best whatever recipe is like there is a magic bullet. The answer is always, it depends on what your testing says is best.

 

[rustyinbend]

Agree completely ... I let others provide "insight", but testing "results" carry so much more weight in deciding what I do "next".

 

[Supersubes]

Trying my best to not write a novel. The cartridge not fitting because of a .001 larger mandrel is a red flag. What is the outside neck diameter in these two instances(both mandrels). What do you mean “struggle seating bullets”. Maybe im missing an intermediate sizing step here , but the “mandrel first” doesn't make any sense, the mandrel wouldn't touch anything but air on a fired case.

Regarding dimensions, its much more useful to measure outside neck diameters at each stage from start to finish. Trusting that the mandrels and bushings are what they say they are, plus variations in state of anneal/springback of your brass is a crapshoot at best. I have redding bushings that are marked incorrectly and are not within .003 the marking.

Havent you posted at least one thread on the conclusion of load developement for this gun already? If you're waiting on the mile shoot till some point in the future when the load is complete, dont. Youre wasting barrel and component. Guys are having great success with factory 225 ammo with its 60 fps es. Get shooting.

 

[rustyinbend]

Trying my best to not write a novel. The cartridge not fitting because of a .001 larger mandrel is a red flag. What is the outside neck diameter in these two instances(both mandrels). What do you mean “struggle seating bullets”. Maybe im missing an intermediate sizing step here , but the “mandrel first” doesn't make any sense, the mandrel wouldn't touch anything but air on a fired case.

Regarding dimensions, its much more useful to measure outside neck diameters at each stage from start to finish. Trusting that the mandrels and bushings are what they say they are, plus variations in state of anneal/springback of your brass is a crapshoot at best. I have redding bushings that are marked incorrectly and are not within .003 the marking.

Havent you posted at least one thread on the conclusion of load developement for this gun already? If you're waiting on the mile shoot till some point in the future when the load is complete, dont. Youre wasting barrel and component. Guys are having great success with factory 225 ammo with its 60 fps es. Get shooting.

All great questions ... let me take a shot at answering them.

1. Get your point about the red-flag ... need to think about that a bit.
2. "struggle seating bullets" ... means I hit a hard-stop-break when the bullet starts to seat that requires too much pressure to get past, and once past, there's no pressure. Also, the base of the bullet (if it's pulled) is scarred from the pressure seating and I actually get a tiny ring of discharge from inside the die that falls out ... seems to be part of the case mouth. Now part of my problem is that I was getting a very slight "flaring" in the mouth from the mandrel, that disappears from the case mouth when it's sized with a bushing. I was starting to believe that "this" was my problem, and it was solved when the bushing goes after the mandrel. All of this is starting to make me believe the mandrel "is" the problem. Still pondering that ... but confused by it since that's not the case on several other calibers.
3. Regarding the mandrel not hitting anything on a fired case ... I just tried that, and you're absolutely right. Thought about it and realized I had been doing my testing with cases that had already been sized, and I was actually "re-sizing" them. This is a fatal flaw in my testing process ... I now realize that. Shit !!!
4. I use SAC bushings that are machined very precisely, so I'm not worried about that issue.
5. I did post before that I had a good result, and was told I didn't have enough data points to draw the assumptions I'd drawn. Went back and tried again, and hit all the sizing and seating problems that caused me to start over.
6. Not sure what that last paragraph about the 225 ammo is saying, other than the advice to stop wasting components ... which is always good advice.

So ... Sir ... you've thrown a hell of a monkey wrench into my assumptions, and I sincerely than you for that.

I learn the most when I screw up the most. I obviously have more work to do here.

OK ... my next test will be 10 rounds that are bushing-sized ONLY with a .337 SAC bushing that gave these last results. I'm going to leave the mandrel on the shelf, and see if I can reproduce that low SD and consistency. If I can, then "that" is my process. If I can't ... then I guess I start over.

 

[Supersubes]

All great questions ... let me take a shot at answering them.

1. Get your point about the red-flag ... need to think about that a bit.
2. "struggle seating bullets" ... means I hit a hard-stop-break when the bullet starts to seat that requires too much pressure to get past, and once past, there's no pressure. Also, the base of the bullet (if it's pulled) is scarred from the pressure seating and I actually get a tiny ring of discharge from inside the die that falls out ... seems to be part of the case mouth. Now part of my problem is that I was getting a very slight "flaring" in the mouth from the mandrel, that disappears from the case mouth when it's sized with a bushing. I was starting to believe that "this" was my problem, and it was solved when the bushing goes after the mandrel. All of this is starting to make me believe the mandrel "is" the problem. Still pondering that ... but confused by it since that's not the case on several other calibers.
3. Regarding the mandrel not hitting anything on a fired case ... I just tried that, and you're absolutely right. Thought about it and realized I had been doing my testing with cases that had already been sized, and I was actually "re-sizing" them. This is a fatal flaw in my testing process ... I now realize that. Shit !!!
4. I use SAC bushings that are machined very precisely, so I'm not worried about that issue.
5. I did post before that I had a good result, and was told I didn't have enough data points to draw the assumptions I'd drawn. Went back and tried again, and hit all the sizing and seating problems that caused me to start over.
6. Not sure what that last paragraph about the 225 ammo is saying, other than the advice to stop wasting components ... which is always good advice.

So ... Sir ... you've thrown a hell of a monkey wrench into my assumptions, and I sincerely than you for that.

I learn the most when I screw up the most. I obviously have more work to do here.

OK ... my next test will be 10 rounds that are bushing-sized ONLY with a .337 SAC bushing that gave these last results. I'm going to leave the mandrel on the shelf, and see if I can reproduce that low SD and consistency. If I can, then "that" is my process. If I can't ... then I guess I start over.

Measure outside neck diameters along the way. The goal is simply to return the neck to a proper size without scoring the inside or pushing/pulling it off center or out of round.

Also, dont throw out the extremes in your velocity data. Thats just cherry picking.

 

[rustyinbend]

Got it ... already built my next test. Need a nice shooting day. Hard to imagine this hobby without being retired.

 

[TheOfficeT-Rex]

"struggle seating bullets" ... means I hit a hard-stop-break when the bullet starts to seat that requires too much pressure to get past, and once past, there's no pressure. Also, the base of the bullet (if it's pulled) is scarred from the pressure seating and I actually get a tiny ring of discharge from inside the die that falls out ... seems to be part of the case mouth. Now part of my problem is that I was getting a very slight "flaring" in the mouth from the mandrel, that disappears from the case mouth when it's sized with a bushing. I was starting to believe that "this" was my problem, and it was solved when the bushing goes after the mandrel. All of this is starting to make me believe the mandrel "is" the problem. Still pondering that ... but confused by it since that's not the case on several other calibers.

A flare on the mouth would indicate to me that you have your mandrel die too low and you're potentially ramming the case mouth into the mandrel shank. Unless it's one of those 'm' dies, or you're not actually sizing all the way onto the 'flat' of the mandrel. In any case, I'd double check that your setup hasn't drifted.

Taking a ring of brass off the mouth makes me wonder if you have enough inside chamfer on your case.

 

[rustyinbend]

A flare on the mouth would indicate to me that you have your mandrel die too low and you're potentially ramming the case mouth into the mandrel shank. Unless it's one of those 'm' dies, or you're not actually sizing all the way onto the 'flat' of the mandrel. In any case, I'd double check that your setup hasn't drifted.

Taking a ring of brass off the mouth makes me wonder if you have enough inside chamfer on your case.

I don't think that's my mandrel problem ... I two-hand the mandrel and stop after it's sized, but never let the case mouth touch the end of the path. Regarding chamfering ... I also have the feeling this is contributing. The last couple of batches of cases from earlier sizing have now been "re-chamfered" and re-burred, and the seating die is running very smoothly on brass that used to "catch" at the beginning. Probably making too many adjustments, but it seems to be working.