Peterson 300 WM - Std Length vs. Long - Initial Data & Impressions

The case shouldn't headspace off the belt, it doesn't need to. It should fit between the bolt face and the shoulder of the chamber like every other round. The belt is an anachronistic vestigial remnant that causes more problems (sizing, stretch) than it solves (none).
It's not going to matter, if your shoulder has .004 or .020, a belted mag will only pull the closest number either the belt headspace or shoulder but at any rate we are talking a few thou. either way will be pulled from the belt area on first firing same as a non belted case, what happens after that is where the failures are caused and if that's not addressed then regular or long will fail the same.
 
Last edited:
Great write up on this. Totally impressed with your perseverance. I have heard a lot of talk about the new brass preforming differently than the once fired. Saying that you have to redo all your testing once they have been shot once. Any truth to this or after the second shot with full fire forming. Take it easy, new to Peterson brass.
 
Great write up on this. Totally impressed with your perseverance. I have heard a lot of talk about the new brass preforming differently than the once fired. Saying that you have to redo all your testing once they have been shot once. Any truth to this or after the second shot with full fire forming. Take it easy, new to Peterson brass.
This is generally the case on all new brass shot vs more firings. That's why you develop loads on fired brass.
 
I figured you could get close then adjust for the once fired but your saying just stick something in and shoot them to get fired cases.

I wouldn't go quite that far, but Longtine is correct in that all brass will react differently to some extent between the first and subsequent firings.

It is never advisable to do what we would consider "final" load work up with virgin brass.

Your results are almost certainly guaranteed to be different between virgin brass and fire-formed brass.

Having said all of that, I would also advise not to simply throw lead downrange during fire-forming with the intent of getting nothing out of that first firing.

A tremendous amount of useful information will be collected during the fire forming process and your loads could still be exceptional, just not the finished product or final version of what your load will be.

I am currently trying to post this from my phone, so I'm probably doing a poor job of explaining it all. When I get home this evening I will try to go into better detail.

I am also sure that other skilled members will pop up here before I have a chance to respond.
 
Last edited:
I wouldn't go quite that far, but Longtine is correct in that all brass will react differently to some extent between the first and subsequent firings.

It is never advisable to do what we would consider "final" load work up with virgin brass.

Your results are almost certainly guaranteed to be different between virgin brass and fire-formed brass.

Having said all of that, I would also advise not to simply throw lead downrange during fire-forming with the intent of getting nothing out of that first firing.

A tremendous amount of useful information will be collected during the fire forming process and your loads could still be exceptional, just not the finished product or final version of what your load will be.

I am currently trying to post this from my phone, so I'm probably doing a poor job of explaining it all. When I get home this evening I will try to go into better detail.

I am also sure that other skilled members will pop up here before I have a chance to respond.
I get what your saying and I don't throw it down just to get the fired brass. I have read on here from folks that do just that. I feel like you that we can gain info from the virgin brass as well. It just hurts to use up vital primers and not get an end result. But that's why do it. Not because it's cheaper but because we love to do it.
 
I get what your saying and I don't throw it down just to get the fired brass. I have read on here from folks that do just that. I feel like you that we can gain info from the virgin brass as well. It just hurts to use up vital primers and not get an end result. But that's why do it. Not because it's cheaper but because we love to do it.
Stag, this is what i do. Build a gun, buy 200 pieces of brass virgin. Develop something that shoots with them. Load as needed the remainging brass using the load I found on virgin brass and hunt with it until they are shot up. I then take those same 200 pieces and fine tune and redevelop for fired brass. Those 200 pieces generally will out live the gun barrel.

For competition I think fired brass is the only way used.
 
Stag, this is what i do. Build a gun, buy 200 pieces of brass virgin. Develop something that shoots with them. Load as needed the remainging brass using the load I found on virgin brass and hunt with it until they are shot up. I then take those same 200 pieces and fine tune and redevelop for fired brass. Those 200 pieces generally will out live the gun barrel.

For competition I think fired brass is the only way used.
Thought of that afterwards and if I can find more quick I could probably do that but dummy me just bought 50 to try and wow I liked it. So my bad. Just trying to make the best out of it.
 
I guess I'm not seeing the reasoning behind the long brass, the issues have never been about the initial stretch on the first firing, it is the subsequent improper sizing and continual repeat of the movement on the first firing that kills the cases. The long cases will suffer the same exact or worse fate unless sizing practices are also modified.
Related to this, I have neck sized and bumped (.002") and trimmed a batch of standard length Peterson 300 WM cases five times without any issues until yesterday, when I experienced moderately stiff bolt lift (Tikka T3X) on 3 out of the 6 cases. I am shooting a pretty stiff load at 76.5 hrs. H4831SC behind 174 gr. Hammer Hunters. I haven't made a practice of tempering my brass, but was hoping to get a few more cycles on this high quality brass.

Maybe I should invest on an easy and reliable tempering device/methodology.

Your thoughts and advice would be apprectiated.

BTW I have back ordered some long 300 cases from Graf's.
 
Related to this, I have neck sized and bumped (.002") and trimmed a batch of standard length Peterson 300 WM cases five times without any issues until yesterday, when I experienced moderately stiff bolt lift (Tikka T3X) on 3 out of the 6 cases. I am shooting a pretty stiff load at 76.5 hrs. H4831SC behind 174 gr. Hammer Hunters. I haven't made a practice of tempering my brass, but was hoping to get a few more cycles on this high quality brass.

Maybe I should invest on an easy and reliable tempering device/methodology.

Your thoughts and advice would be apprectiated.

BTW I have back ordered some long 300 cases from Graf's
What's your resizing process, usually this is the area right above the belt has grown. Measure the area right in front of the belt on the sticky ones and compare to fine ones.
 
I tagged you in a recent post made by @Swamplord, as he developed info that they will be shipping some time in the next week or so.

I will be to talking to the guys at Peterson this week anyway about a different issue, so I'll try to update the members here on what I find out about their shipping schedule on the 300 Longs.

One way or another, we'll make sure you get that brass.
I just checked Graf's and the Peterson 300 WM brass is in and I got some. I really appreciate you saying I'd get some one way or the other.
Now all I have to do is wait for it to get here.
 
I just checked Graf's and the Peterson 300 WM brass is in and I got some. I really appreciate you saying I'd get some one way or the other.
Now all I have to do is wait for it to get here.
I called Peterson on Monday, but they were unable to get back to me on my questions. They are currently slammed.

I'm thrilled you had a chance to pick some up!
 
Top